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A Mechanic's Life - Tales From Under the Hood

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  • xwesxxwesx Fairbanks, AlaskaPosts: 8,679
    So, getting back to the Fusion, I think you said that the problem your customer had was not related to the P2111 code she was convinced was the problem, but instead due to her vehicle running off battery and draining down, correct? You also mentioned that the system was charging correctly after you charged the battery.

    So, why did it drain in the first place? Was it somehow related to the 8-mile commute, since you did mention that? Or, the - nevermind. My wife is interrupting me and destroying my concentration. :mad:
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • thecardoc3thecardoc3 Posts: 1,636
    edited November 2012
    At $1,200 each, maybe I won on those deals after all?

    I have only ever sold one "used" car and that one I never really owned, or at least used. I got it because of a random stalling issue that the owner simply didn't want to deal with and once I got to figure it out and fix it a friend needed a car and asked for it. He paid for the repair and enjoyed the car for a year. Then passed it onto his son-in-law who had it for another year, who gave it to a friend who crashed it.

    Other than that one, I have given away every other car that I no longer had use for. There was never anything wrong with them as you can figure they get maintained to the max. I have a neice who will be getting her license in another year. I already know what car I will be giving her.
  • thecardoc3thecardoc3 Posts: 1,636
    So, why did it drain in the first place? Was it somehow related to the 8-mile commute, since you did mention that?

    Yes.

    So, getting back to the Fusion, I think you said that the problem your customer had was not related to the P2111 code she was convinced was the problem

    The stalling was not related to the P2111, however she does in fact have an issue with the throttle body. Keep in mind the car is not repaired unless all of the issues are dealt with.

    Now I'll give you one that will be really tough to swallow. The P2111 is basically caused by oil changes that used products that even though they were 5W20, don't actually meet the demands of the engin, or Fords specification.
  • kyfdxkyfdx Posts: 31,124
    in the past I have "loaned" family members funds

    Ah... otherwise known as a "gift".. ;)

    MODERATOR
    Prices Paid, Lease Questions, SUVs

  • roadburnerroadburner Posts: 6,859
    edited November 2012
    That doesn't seem to be an uncommon mindset, unfortunately. It's no big deal to go out and get a loan to buy a car, but $2,000 out of pocket? No can do.

    I hear that all the time; "I need a new car because__________"
    Fill in the blank:
    "I need a car that gets better gas mileage"
    "my car is old and things will start breaking"
    "I can't afford to keep my old one running"

    I once calculated that if I bought a car for $10,000(cash, no loan) plus my trade and the new car returned 16 more mpg than my old car it would take 7.5 years to break even- and that was assuming I drove 20,000 miles per year with a gas cost of $5.00 per gallon. Less annual mileage and cheaper fuel would move the break even point even further down the road...

    The lady in the Durango may not be thinking that way, but 99% of the time "I NEED a new car." can be translated: "I'm bored and want something new."

    Mine: 1995 318ti Club Sport 1975 2002A 2007 Mazdaspeed 3 1999 Wrangler 1996 Speed Triple Challenge Cup Replica Wife's: 2009 328i Son's: 2004 X3 2.5

  • steverstever Viva Las CrucesPosts: 41,942
    neither time did I ever see a penny from it. While I haven't held it against either of them, neither have they asked me for anything since then.

    If you get paid back be very careful. That just means they are going to hit you up in a few weeks for something even bigger.

    Moderator
    Minivan fan. Feel free to message or email me - stever@edmunds.com.

  • explorerx4explorerx4 Central CTPosts: 9,972
    Congrats, you got yourself a nice little graphic on the main Car Forums page!
  • thecardoc3thecardoc3 Posts: 1,636
    The Fusion. The main problem is all of the accessories draw some 140 amps of current, the alternator can produce 120amps as long as the engine is at or over 2000 rpm. Her communte has her "in town" for some 60% of her trip and the battery has to supplement the alternator's output when she is stopped in traffic. Over time this pulls the battery into a low state of charge because she simply doesn't drive it on the highway enough without all of the accessories on to ever allow the alternator to re-charge the battery fully, so the battery slowly sulfates and eventually dies. The car stalled because of the throttle plate sticking in the bore due to varnishes built up in it from the PCV gasses, and some reversion due to late intake valve timing under high efficiency mode. Once it stalled, the battery was simply too dead to allow it to start up and run on that morning. It had to have a new throttle body, and a software update for the PCM.

    The Lincoln. This car fired right up the moment it had fuel pressure. During cranking the first thing that I found was the battery voltage dropped to 3-4v for an instant and then the engine cranked just fine, at 7.5v. At 7.5v the voltage was too low for the PCM to be turned on and command the fuel pump to run, that could leave you crank the engine until the battery was completely dead and it would never start. Charging the battery helped but it still tested as marginal and needed replaced but that wasn't the only issue. The batteries state was aggravated by the fact that the fuel pressure would drop as soon as the car was shut off. Fuel pumps have a check valve in them to hold pressure on the fuel rail and lines and this one has to be leaking. (that or maybe the hose that connects the pump to the fuel sender is leaking) Either way the longer the car was turned off, the longer it would take to prime the fuel system and get it to deliver fuel to the engine. If your cranking it the whole time you could be cranking it for five to ten seconds. If you didn't want to do that, by cycling the key on for two seconds, off, then on for two seconds would cycle the pump and the engine would fire up normally. The shop that sent the car over is going to service the fuel pump.

    The check engine light on the Lincoln was an evaporative emissions leak and testing showed that the hoses and fittings that connect the cannisters at the rear of the car need replaced.
  • thecardoc3thecardoc3 Posts: 1,636
    That's pretty neat. It might get busier here now.
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,679
    edited December 2012
    Dang. That's an impressively complicated set of conditions for both cars, but especially so for the Lincoln! The leak aside, it seems almost counter-intuitive that the battery would be weak given its ability to crank the engine for extended periods trying to get the thing to start.

    I'm a little bummed that I didn't get a chance to respond on the Fusion's issue. I was thinking along the lines of the over-draw, but did not at all connect the throttle body issue to the no-start. I was thinking it was the charge issue that was causing the stall, which was throwing me off since you said the system was charging properly. I'm curious why the throttle body required replacement vs. cleaning if it was a varnish issue. And, what was it in the oil that would be out of spec to cause such varnish in the first place?

    Finally, how does one determine what the overall amperage load on a vehicle is? I'm having an issue with my 2010 Subaru Forester right now (over the last year) in that it doesn't fully charge it's battery. Over the course of a few months, it gets to the point where I have to hook a charger up to the battery to fully charge it in order for the vehicle to reliably start for a few more months. While running, the voltage at the terminals is 14.4-14.6. The same symptoms persist regardless of the battery in the vehicle... batteries that work fine in other rigs, including my plow truck (which demands some major current and is used infrequently, at low speeds, and for short periods of time).

    I was thinking it must be something to do with the charging system, but I cannot catch it behaving out of spec. The dealership was no help when I took it there last winter, as they simply told me the problem was due to my not having a heater on the battery for winter use. I explained to them that I don't use battery heaters on any vehicle, and have no problem with any of them (for years and years, including several other Subarus), but my request to actually investigate my concern fell on deaf ears.

    Dealerships love battery heaters here, but my experience is that they only do a great job of nursing weak batteries so when you have to start the vehicle without the luxury of electrical access nearby, you end up stranded. :sick:
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • stickguystickguy Posts: 15,661
    So, even modern cars need an "Italian tune-up" on occasion.

    I have to remember to get my Volvo out on the highway on occasion. With my daughter driving it, it will be even more short hops than before.

    2015 Hyundai Sonata 2.4i Limited Tech (mine), 2013 Acura RDX (wife's) and 2007 Volvo S40 (daughters college car)

  • thecardoc3thecardoc3 Posts: 1,636
    Finally, how does one determine what the overall amperage load on a vehicle is? I'm having an issue with my 2010 Subaru Forester right now (over the last year) in that it doesn't fully charge it's battery. Over the course of a few months, it gets to the point where I have to hook a charger up to the battery to fully charge it in order for the vehicle to reliably start for a few more months

    The battery should be at an 80% state of charge. That's 12.5v with no loads after it's been sitting several hours to allow any surface charge to dissipate. I'm a little torn between explaining why it should not be at 100% (fully charged) and allowing some conversation to take place that would enhance the information. There are many myths out there that have stood for decades, and there are a lot of brand new strategies that are all about trying to increase the average longevity of the components as well as increase fuel economy.

    Let's do it with me waiting for a bit before I put some effort into explaining why (approximately) an 80% state of charge for the battery is preferable to fully charging it.

    When you have to hook up a battery charger to your Suby, is it because it's not cranking the engine correctly? What is the voltage at the battery terminals after it has sat all night? Has it been tested for an excessive parasitic drain? (30ma-50ma would be normal)

    How far do you drive the vehicle for it's primary use? Is this highway use, or in town similar to my Fusion customer?

    Try these numbers. (approximations, lots of variables here)
    Headlights and parking lights. 15 amps
    Ignition and computer syst. 11 amps
    Fuel pump 8 amps
    Heater Blower 20 amps
    AC compressor clutch 4 amps
    Heated Seats 8 amps (each)
    Engine cooling fan 25 amps (each)
    Entertainment / Inst Cluster 10 amps
    Rear Defogger 10 amps
    Windshield Wiper 15 amps (10 more for a rear one)

    OK that's close enough for an average car. If you are running the majority of these items on your car on a cold damp morning that pretty much guarantees that there is little if not nothing left of the alternator output to go towards charging the battery when your on the highway. Then when you have to stop the battery is now responsible for providing most of the power and not the alternator to operate these systems.

    A number of manufacturers have adopted load shedding strategies which helps explain why the BCM, HVAC, and other modules now control most of these functions. The engineers might have the HVAC controller slow the blower motor down to save power, unless the defrost setting is commanded. They may start out with the heated seats and rear defogger on fully, and then start pulsing the power to them after two to three minutes. Most of these systems only report (and possibly set a trouble code) if they have to go into a second stage of load shedding, the first stage is expected to be normal system operation. A three stage or greater load shedding condition will have the car doing things that the driver will notice.

    Now take a longer trip. Most of the systems mentioned are either turned off or cycled off and the load on the alternator is reduced. That means more power is available to recharge the battery. The load shedding strategies also have the BCM, PCM directly calculating the batteries state of charge. These modules take into account the current that the battery has had to supply and the duration of the total discharge events. They also measure how much power the alternator has been putting out. Once the modules responsible for estimating the batteries state of charge decide that it should be back at the 80%, the charging system actually gets dialed back and the correct charging system voltage could be as low as 12.9-13.1v instead of the old 14.5v.

    I was thinking it must be something to do with the charging system, but I cannot catch it behaving out of spec. The dealership was no help when I took it there last winter, as they simply told me the problem was due to my not having a heater on the battery for winter use. I explained to them that I don't use battery heaters on any vehicle, and have no problem with any of them (for years and years, including several other Subarus), but my request to actually investigate my concern fell on deaf ears.

    Your Subaru is different from every other vehicle you have ever owned. I'll reserve comment about battery heaters because they are not commonly used around here, but battery temperature is very important and is measured either directly or indirectly.
  • imidazol97imidazol97 Crossroads of America: I70 & I75Posts: 18,528
    >y these numbers. (approximations, lots of variables here)
    Headlights and parking lights. 15 amps
    Ignition and computer syst. 11 amps
    Fuel pump 8 amps
    Heater Blower 20 amps
    AC compressor clutch 4 amps
    Heated Seats 8 amps (each)
    Engine cooling fan 25 amps (each)
    Entertainment / Inst Cluster 10 amps
    Rear Defogger 10 amps
    Windshield Wiper 15 amps (10 more for a rear one)

    Are engine cooling fan(s) left on when car speed reachs a nominal point where air flow is adequate for cooling through the radiator and/or condenser? Are those turned off at say 40 mph?
  • thecardoc3thecardoc3 Posts: 1,636
    Are engine cooling fan(s) left on when car speed reachs a nominal point where air flow is adequate for cooling through the radiator and/or condenser? Are those turned off at say 40 mph

    Yes, in fact the cooling fans usually turn off at speeds as low as 25mph. That's part of the variables mentioned. At highway speeds the alternator can produce more power because it's being driven faster, and then at idle when the alternator cannot produce as much power we get the load from the cooling fans.
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,679
    edited December 2012
    Thanks for that reply, Doc.

    When you have to hook up a battery charger to your Suby, is it because it's not cranking the engine correctly? What is the voltage at the battery terminals after it has sat all night? Has it been tested for an excessive parasitic drain? (30ma-50ma would be normal)

    How far do you drive the vehicle for it's primary use? Is this highway use, or in town similar to my Fusion customer?


    I tend to hook it up after noticing the starter cranking "differently" than normal. Subaru starters are, for lack of a better way to describe it, "slower" than most other cars. I've owned Dodge (one only), Ford, and Chevy vehicles as well, and they all crank significantly faster than all but my '96 Subaru. It doesn't seem to impact whether they start or not, but rather it is just a feature of the car.

    But, when the slow cranking turns to a cranking that includes a slight pause into the rhythm, then I know it's not right. Upon checking the battery voltage, it is always under 12 volts in this situation (generally about 11.95). The car still starts in the warmer months, but in the dead of winter there's enough system resistance (included the added CCA demand on the battery) to keep it from starting. Now, if I had a battery warmer, it might just start the car in those conditions, but it still wouldn't help for when my wife starts the car when leaving where ever it was she went. Personally, I'd much rather she be stranded at home than somewhere else!

    Yesterday I charged the battery (not fully, meaning the charger had not turned itself off automatically) and it tested about an hour later at 12.56 volts before I started the car, drove into town with the kids, and made three stops before driving home. The ambient temperature was -27F. We drive with the headlights, etc., on all the time. The radio was on, the interior blower fan was on full, and the driver seat heater was on its lowest setting. (The engine cooling fans generally don't run at all this time of year, as passive air flow through the front of the car and the interior blower sucks of plenty of heat.) The longest distance we drove was a little over 8 miles (a typical run for us is probably 10-15 max), with six of those being unencumbered highway miles, and the last two being mild stop/go. We had no problems with the car starting, etc., while we were on our trip over the course of three hours (drove to one store, left an hour later, etc., three times).

    Today when I checked the battery, it read 11.98. :confuse:

    We don't need the car today, so I didn't have the block heaters on and therefore I didn't try to start it.

    Your Subaru is different from every other vehicle you have ever owned.

    Why so?
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • srs_49srs_49 Posts: 1,394
    Sounds like there's a lot of room for improvement in a lot of the functions you mentioned. Looking at it from a power standpoint we get for some of the items:

    130W for the ignition and computer system
    240W for the heater blower
    300W for each fan motor
    96W for the fuel pump motor

    Back to the Fusion, sounds like the its charging system was under designed.
  • thecardoc3thecardoc3 Posts: 1,636
    Open circuit voltage that is less than 12.1 v is a dead battery.

    To fully charge it back up would take 1.5 times the reserve capacity rating at 25amps. If the reserve capacity is 120 minutes, that means you need to charge the battery for 180 at 25 amps. The problem is, the charger won't stay at 25 amps, as the batteries state of charg increases, the chargers output decreases. Here is how it works. 180/60 x 25 = 75amp/hours
    If your charger outs out 7.5 amps, then it would take ten hours to charge the battery. If it's five amps now you need fifteen hours.

    The big battery chargers that we use will start out in the 30-40 amp range but again don't stay there very long, maybe twenty minutes. Then they drop into the 20 amp range and by the end of the first hour we are down to 10-15 amps.That means we are looking at a five to seven hour time frame to really bring a battery all the way back, and we have to do that without overheating it and/or gassing it.

    I'd be looking very closely at your Suby for a parasitic drain, and I would be testing that battery carefully. Just like keeping a battery at a low state of charge can kill it by causing sulfation, over charging it kills it by boiling off the electrolite, or by breaking the water of the electrolite down into H2 and O2. I would not be surprised to hear that your battery fails testing, but make sure that you try to find out if something about your car killed it.

    As far as your Subaru being different, it isn't as sophisticated as a lot of cars are today, but the charging system has a lot more things that it has to do very precisely today than it did just a few years ago. I'll look up some specifics when I have the chance.
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,679
    I put the charger on it today at about 11:30am. It charges at three preset outputs: 2A, 4A, 6A. I set it on the 6A output and it ran about five hours before shutting itself off. When I went out to check on it and it was off, the battery read 12.56 volts. Just now, three hours later, I took another reading and it was at 12.16 volts.

    So, it looks like this saga is just beginning. :mad:

    To start, I should probably get a manual cut off switch to eliminate parasitic draw until it can be identified, and then put the original battery back in the car so that my good batteries don't keep getting tortured by the car. I'd much rather lose the stock Panasonic battery to being chronically undercharged than the very nice (and very expensive) Optima Redtop that I put in it last winter.

    Now that I'm thinking about parasitic draws, I noticed last summer when I used my trailer that the running lights on it did not turn off when I shut off the car. Maybe the place to start looking is in the trailer wiring circuit. These cars come pre-wired for a "T-connector" 4-way trailer wiring set up, but all those wires just hang out under the flooring of the cargo area....
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • thecardoc3thecardoc3 Posts: 1,636
    I put the charger on it today at about 11:30am. It charges at three preset outputs: 2A, 4A, 6A. I set it on the 6A output and it ran about five hours before shutting itself off.

    At best you got 30 amp/hours towards the battery, which means it would really have gotten about 20 amp/hours into it. It takes 1.5 times the reserve capacity to fully recharge a battery that was dead. The problem is your charger doesn't stay at 6 amps the whole time, and it was probably down to about three amps for the last three hours. That means, and your open circuit voltage agrees, your battery is only at about a 30% state of charge.

    To start, I should probably get a manual cut off switch to eliminate parasitic draw until it can be identified, and then put the original battery back in the car so that my good batteries don't keep getting tortured by the car. I'd much rather lose the stock Panasonic battery to being chronically undercharged than the very nice (and very expensive) Optima Redtop that I put in it last winter.

    I don't expect the Subaru to be as picky as a number of cars these days, but lets take BMW for an example. When you replace a battery you need to tell the BCM exactly what battery you put into the car, that way it can correctly calculate the batteries state of charge. The car needs to also start with the battery at a full state of charge and it allows that to be dropped to the 80% range as I mentioned earlier. So why 80% and not 100%?

    A battery is a big capacitor as well as an energy storage device. By keeping it at 80% it has the ability to absorb many of voltage spikes that naturally occur on a car. Voltage spikes can disrupt communication between modules or cause false sensor readings and cause all kinds of issues. Another reason is by trying to charge a battery to 100% you will quite often overcharge it and that damages it. There is actually even more to it, but that's enough for now.

    When I went out to check on it and it was off, the battery read 12.56 volts. Just now, three hours later, I took another reading and it was at 12.16 volts.

    You should have put the charger back on overnight. That might have gotten the battery back to about 50%. About 12.3v

    To start, I should probably get a manual cut off switch to eliminate parasitic draw until it can be identified

    Nope, that's the wrong idea today. Depowering the car can cause it to lose a number of trained functions (auto power windows for one), trouble codes, adaptive strategies such as fuel trim and transmission shift compensations. You need to measure the system's draw and if it's excessive go find it, and that does not mean off the wall guesses like :

    Now that I'm thinking about parasitic draws, I noticed last summer when I used my trailer that the running lights on it did not turn off when I shut off the car. Maybe the place to start looking is in the trailer wiring circuit. These cars come pre-wired for a "T-connector" 4-way trailer wiring set up, but all those wires just hang out under the flooring of the cargo area

    Sometimes a guess like that can be correct, and that's fine because a proper testing routine will lead you right to it anyway. However most of the time they guesses are simply a waste of time and cause lots of frustration. We teach techs electronics and voltage drop testing based on ohms law. With that they then understand that if there is any current flowing in a circuit, then the voltage applied to it will have a drop as it flows arcross a resistance. A fuse is a resistor, so any parasitic drain will cause a small voltage to be measurable across the fuses terminals. Do you have a voltmeter that is accurate into the 10,000ths of a volt or smaller? (.000XX) That is how you go about locating what circuit the drain is on. A low amps probe allows a technician to measure the drain on the car without opening the electrical system and clearing out all of the memories as well. Some of those are accurate down to about 5ma (.005 amps).

    On a side note, last week I got a call from a lady who has been to Autozone several times in the last few weeks. They already replaced her battery, twice, and have done electrical tests on the car and can't find anything wrong. Her battery keeps going dead, usually over a weekend, but after a couple times then its dead every day and has to be jumped.

    The call was on the shops answering machine, you see I was out teaching that day as I do that to subsidize our income from the shop. The tools and equipment that we need to have in order to do everything required of us today are so expensive that the shop cannot support them and have us earn a living too. The last two years the shop accounted for about 30K net profit for the 50-60 hours each week that we put in there. We made our living essentially from the teaching income.

    Had we of been her first call and especially if we had gotten the easy work too, we could have made a reasonabe return for the effort required to be "Service Ready" for her vehicles problem. Plus we also would have solved it on the first visit and it would have been a non-event from our perspective. Now it's a nightmare for her because for all the times the parts stores get away with those battery sales (and a lot of the other things they are doing) the loss of oppertunity to us eventually has made enough of a difference that we weren't there when she needed us.

    The tough part here is should we take her in and fix her car or not? I haven't called her back yet, first of all we have been booked solid, that's the advantage of shutting down two days in the middle of the week, I get to be much more productive the rest of the time that we are in the shop instead of having a lot of idle time. Even if I bring her on and fix this for her history has shown that she is not likely to be come a permanent customer. She started out at the parts store with this problem because everything the consumers have ever been taught is how the cheapest price is all that really matters, right up until that routine fails. Then in some ways it doesn't matter what we charge, "it's too much" so the only way we ever see them again is in five or six years when they have another nightmare that no one else seems to be able to solve. :sick:
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,679
    I certainly see your point regarding the problems associated with "taking" a call like that. While I like to try to solve my vehicles' issues, I also don't have a problem with taking it to a shop for repair when I can't figure out the problem. For me, though, I want the problem solved if I do take it in, and my past experiences are that with electrical issues, shops tend not to solve the problem. That, of course, creates a negative feedback loop in which I am more reluctant to take it in and instead become more stubborn about figuring it out. :blush:

    I should note that the last time I took a car in for such an issue, the shop did solve it. Of course, it turned out to be plug wires, and I'm still kicking myself over that one, but I didn't even check them because they were only a couple years old. Since I already convinced myself that it was something else, I looked at everything else I could think of and couldn't find a problem.

    I guess I should have fallen back to the mantra of my profession: Trust, but verify. :D

    ----

    Okay, so back to my car. Good point about the system memory. I should remember that this is a "new" car. Part of the issue with testing right now is that the temps are at -30F and lower (no garage here!), so I'd like to push things off to warmer weather so I don't risk breaking plastic things (or getting frostbite).

    I did two things last night: 1, I disconnected the T-connector from the factory trailer wiring plug just because it was on my mind. 2., I put the charger back on it last night and let it charge over night (~12 hours) on the "slow" (4A) setting. At 0730 when I checked it, the charger had shut itself off again saying the charge was complete, and the battery read 13.06V.

    I'll check the voltage again when I go home at noon to pick up my daughter for school. I have the car plugged in (block/oil pan heaters) right now, though, and expect (based on its prior behavior) it will start for my wife at 3pm this afternoon.

    As for my tester, I think it goes that small. it switches between a mV reading and V reading automatically, and displays tenths in the mV setting, so theoretically it will. It's only a $35 Innova unit, though, so I'm not sure how accurate it'll be.
    2010 Subaru Forester, 2011 Ford Fiesta, 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup, 1974 Ford Pinto Wagon
  • thecardoc3thecardoc3 Posts: 1,636
    As for my tester, I think it goes that small. it switches between a mV reading and V reading automatically, and displays tenths in the mV setting, so theoretically it will. It's only a $35 Innova unit, though, so I'm not sure how accurate it'll be.

    You should be using a meter with an accuracy of .1% +1
  • srs_49srs_49 Posts: 1,394
    On measuring parasitic current draws-

    You said to measure the voltage drop across the fuse, then calculate the current from that and the resistance of the fuse.

    Question - how do you measure the resistance of the fuse without removing it from the circuit? Do you just measure a fuse in the parts bin, and assume it's close enough to the one in the vehicle?

    If you have to remove the fuse from the vehicle, then aren't you right back at the issues you raised with opening up the circuit to insert a current meter? Unless you jumper around the fuse before pulling it out to measure it's resistance.

    Could use a non-invasive current (Hall Effect) probe, providing you can clamp it around the wire of interest.

    Just thinking out loud...
  • obyoneobyone Posts: 8,065
    Even if I bring her on and fix this for her history has shown that she is not likely to be come a permanent customer. She started out at the parts store with this problem because everything the consumers have ever been taught is how the cheapest price is all that really matters, right up until that routine fails. Then in some ways it doesn't matter what we charge, "it's too much" so the only way we ever see them again is in five or six years when they have another nightmare that no one else seems to be able to solve.

    I think you've answered your own question though you won't know for sure unless you go ahead and repair it. On then will you be certain whether she will be a loyal customer or not as we never judge a book by its cover.

    In this case, I'd agree and unless it's real slow I'd pass on it.
  • thecardoc3thecardoc3 Posts: 1,636
    Question - how do you measure the resistance of the fuse without removing it from the circuit? Do you just measure a fuse in the parts bin, and assume it's close enough to the one in the vehicle?


    Actually what I said was.

    A fuse is a resistor, so any parasitic drain will cause a small voltage to be measurable across the fuses terminals. Do you have a voltmeter that is accurate into the 10,000ths of a volt or smaller? (.000XX) That is how you go about locating what circuit the drain is on. A low amps probe allows a technician to measure the drain on the car without opening the electrical system and clearing out all of the memories as well. Some of those are accurate down to about 5ma (.005 amps).

    Could use a non-invasive current (Hall Effect) probe, providing you can clamp it around the wire of interest.

    So the answer is yes, measure the current draw, and if it's excessive use can use the voltage drop technique to identify the circuit.

    Question - how do you measure the resistance of the fuse without removing it from the circuit? Do you just measure a fuse in the parts bin, and assume it's close enough to the one in the vehicle?

    It is possible to measure the resistance of a fuse with the correct tools but a regular ohmmeter isn't the correct tool. Besides, it's easy to calculate the fuse's resistance by measuring the current through it, and the voltage drop across it. The fun part about this is the fuses resistance isn't fixed. Like anything else the temperature of the fuse makes quite a difference in it's resistance, which of course explains exactly how they work when you think about it for a few moments.
  • I read this entire thread and wanted to say thanks for all the great info.

    And insight. I'm a backyard hack, but a stubborn one, so I only use a garage occasionally. But when I do I'll look at it a little differently now.

    The only thing I have to add is, don't buy the cheap rotors!! Even if you're lucky enough to not get the ones that shatter, I was buying $13 fronts for my old 97 Grand Marquis and had to replace them more often than the pads! Also, while the rotors on my 03 are hatless, because they are so much bigger than the 'hatted' rotors on my 85 Town Car they seem to weigh about the same.

    Bartbarter
  • stickguystickguy Posts: 15,661
    good point about the parts, and I will bet that "doc" will agree. Not worth buying cheap parts, unless you like to replace them and do your own work. and have lots of spare time.

    but when you are paying to have a job done, usually (or at least often) the labor is the biggest part of the job. So saving a few dollars on an inferior part seems counter-intuitive to me.

    2015 Hyundai Sonata 2.4i Limited Tech (mine), 2013 Acura RDX (wife's) and 2007 Volvo S40 (daughters college car)

  • Where I live, the past few times I've replaced the tires on my vehicles, I've had to take the car back 3 - 4 times for a re-balance for the shop to get them properly balanced. I've had this problem with local independents and national chain tire dealers as well. My most recent experience - I recently replaced all 4 tires on my Honda CRV. I've had the car back to the shop 3 times for a re-balance and they still didn't get it right. Monday I took the car into my local Honda dealer for a brake job, and, had them balance all 4 wheels as well. The Honda techs got the wheel balance right on the money. Is there a shortage of folks who know how to mount and balance tires correctly? Around here the only places that I currently know that will get it right the first time are my local Honda and Mercedes Benz dealers. I'm tired of sitting in waiting rooms for hours while they make multiple attempts to balance the tires correctly.

    Regards:
    Oldbearcat
  • stickguystickguy Posts: 15,661
    My guess, a combination of poorly trained low paid techs, the need to get them done quick, and the ever increasing size and weight of the wheels/tires all come into play.

    2015 Hyundai Sonata 2.4i Limited Tech (mine), 2013 Acura RDX (wife's) and 2007 Volvo S40 (daughters college car)

  • thecardoc3thecardoc3 Posts: 1,636
    edited December 2012
    My guess, a combination of poorly trained low paid techs, the need to get them done quick, and the ever increasing size and weight of the wheels/tires all come into play.

    Many of the chain stores pay their techs an hourly wage, plus a bonus based on productivity. Then they turn around and exclude some items from the list from which they accumulate productivity. Guess what one of those items is?

    In essence, the techs are "punished" for doing tires, unless they upsell other services from the tire replacement. Then in the case like bearcat, since techs are not paid for a "comeback", they are in effect punished again. The only recourse is for the techs to minimize the personal financial hit by not being paid for installing tires and that happens with speed. When everything goes correctly, nobody else cares what actually happened inside the shop.

    Now as far as balancing the tires, there are problems with some wheels on some balancing machines. The wheels have to center correctly in order for the machine to be accurate and many manufacturers have an uncanny ability to make sure their wheels don't mount up without specific adapters. My machine (Snap-On) doesn't do a lot of the 3/4ton truck wheels as easily as it does any car steel wheel. Some of the Jeep mag wheels force me to be very creative in double, and triple checking the wheel/tire assembly which often means that I have to spin it to measure it out, add the weights to balance the assembly and re-spin it to check it. The I have to break it loose, turn it on the spindle and then tighten it up and re-check it again. There have been a number of times that I have found that I have to use different adapters between individual wheels from one car. If the wheel is balanced correctly, I should be able to take it loose, reposition it, and tighten it back up and end up with "0's" again.

    The advantage for me is that I don't have to rush through a job like this. I'll take whatever time I need to and in some cases I have had to buy additional adapters for my machine.
  • obyoneobyone Posts: 8,065
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