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Comments
Is there a significant difference between Amoco, Mobil and Texaco in this respect (comparing 87 octane )?
I took the truck to the dealer. They checked it out and said they heard the ping, but didn't know what to do about it, because of computer engine controls. The owners manual also states that a small amount of it is normal, that you don't have to step up to a higher grade to eliminate it. They updated my engine calibration parameters, and gave it back to me. There was no noticeable improvement after this initial eprom update.
I then modified my coolant thermostat to open at a 13 degree lower temperature. This made a noticeable improvement in drivability to me, although some stated it was in my head. I began checking fuel mileage after the thermostat mod.
When I noticed a jump in fuel mileage, I took a pause to access the possibilities. My previous best was highway 17.6 mpg, in-town city driving was averaging 14.6 mpg. The in-town mileage had improved to 17.1, with some highway speeds mixed in.
My next tank improved to 18.6, all highway, but still improving on my best highway tank before the mod.
Then my next tank was 17.2, lots of highway miles, but also hauling cargo quite a bit.
Finally brings me back to my most recent tank, 16.2 , all city, some highway speeds, empty cargo bed most of the time.
All of the tanks since the thermostat mod have been run on regular grade octane, 85 here in the altitude of Colorado.
Conclusions: My fuel mileage seems to have improved. While I cannot prove the gain came from the thermostat mod, I can't rule out some benefit either. There are other seasonal variables that could apply, and perhaps my driving habits varied, or my engine completed its break-in wear. So I'm not saying my fuel mileage improved because of the mod, but my fuel mileage does seem improved.
What about the ping? Well after the thermostat mod, the ping seemed eliminated at first, but when I reduced gasoline grades, I could notice it again slightly, intermittently, but I had to listen very carefully.
And then just this week, I became aware of another engine calibration software update from GM that stated it was to address various drivability concerns including hesitation (didn't have), and spark knock (did have). I took the truck in on Tuesday, and they re-flashed the eprom with the update. As of today, I have driven 150 miles. I thought I heard it crackle a tick driving out of the dealer lot onto the street. But I'm not sure, because I haven't heard it since.
So for whatever reason, or combination of reasons, it seems like it's gone, and I am able to run on regular 85 grade octane with good drivability, and no audible knock. My '99 Silverado truck, while delivered with a few flaws, is just about perfect now, and getting very good fuel mileage while letting me haul cargo with supreme comfort. I'm very happy with it.
By the way, the eprom update would not have been necessary if the '99 engine used a conventional camshaft driven distributor. You could just manually adjust the static spark timing. But the engine computer reads crankshaft position from a sensor, then refers to a spark map table to set the timing. So the owner cannot make any adjustments. Because my preference would have been to adjust the spark timing to cure the ping. But now you have to depend on the manufacturer to have an eprom update. Even the dealership cannot adjust otherwise.
I would not have found it necessary to begin experimenting with the thermostat, except you can't adjust the spark timing. But after I did modify the thermostat, the main thing I noticed was just a more subtle sense of calmness about the engine. Seems quieter too. Even felt like it ran slightly stronger. But to give the thermostat mod credit for reducing the ping, well I just believe the ignition timing is the variable with more influence. But I prefer the way the engine feels subjectively, at 191 degrees to the otherwise 204 degrees.
Installing a K&N air filter made the car more powerful though, if a bit noisier.
If the manufacturer recommends against a higher octane gas, that should mean that there will be no performance difference if you decide to use it.
Your car was obviously tuned to 87 octane gas. If you use a higher octane, the gasoline will not burn thoroughly, and it can quickly begin leaving harmful deposits. I would follow the owners manual, the guys who wrote it are your best guide.
That being said, if you happen to fill up with a high octane, just to test it, let us know how it feels. I've done so in 2 newer cars, and could barely tell the difference between 87 and 94 octane.
guitarzan
Community Leader/Vans Conference
I have another one for you guys. I have a 1985 F250 300ci 4.9ltr strait six that has the computer completely disabled. In fact it has a 78 distributor and coil and an 83 carb. The original carb was a feedback design and the current one is not. The exhaust system has been changed from 2in to 2 1/4in to a turbo muffler (w/o cat). The EGR and air pump is also removed.
Here's the problem;
I have bought new intake/exhaust manifolds and have blued them to the head and to each other. No
problems there, great fit up. I have followed the
required torque specs and procedures. All new
bolts, nuts, washers and gaskets. Loose fit up on
the hotbox bolts torqued the head bolts in three
stages to 11-13 ftlbs and followed up with the
hotbox bolts to 22 ftlbs. Warmed up the engine to
operating temps and retorqued to specs. The
gaskets on the hotbox will last for one or two weeks and start to leak on the side with one bolt. It has a three bolt patern (triangle design basically). I have tried different gasket designs with no real difference in the problem.
I suspect three areas,
1. Unable to automaticly adjust the timing to compensate for cold engine operation during warmup. (timing advance/retard)
2. Excessive backpressure caused by a two pass muffler combined with the timings inability to compensate for cold engine operation.
3. Uneven heat distribution to and in the hotbox. This maybe (along with #1 & #2 above) causing the cast iron manifolds to heat unevenly allowing the gasket to leak (flame from ignition is carried into the intake/exhaust (hotbox) area).
I put this here because of the discussions posted earlier about knock sensors and the effects of advancing and retarding the timing to compensate for engine knocks and pings. I currently experience pinging at speeds in excess of 65 mph. I contribute the to the inability of the engine to advance the timing any further due its current settings. I have found the engine operates best with the points set at 44-48 degrees and the distributor set at 6 degrees before TDC.
HoHo
guitarzan
Community Leader/Vans Conference
BTW gas tank at 3/4, report to follow.
Although there was no clear place to submit a question to them I did send an Email to the webmaster asking for the link to ask such a question. In the mean time here is two addy's for Summit Racing an Professor Overdrive.
Thanks Gman, Good info, Cool site.
Professor Overdrive;
http://www.summitracing.com/techzone/profov15.htm
Summit Racing home page;
http://www.summitracing.com/index.htm
HoHo
The catalogs are where Professor Overdrive answers tech questions. I also have a pile of those answers, and periodically go through them for knowledge. I recall many a people specifying specific setups, and asking what they did wrong. He many times will pinpoint the problem. Of course, many of the setups are race setups, which may be most familiar to him. However, this column of the catalog, like Edmund's, is a great way to slowly pick up good quality car smarts
guitarzan
Community Leader/Vans Conference
I kinda have the same thing with posters of dragsters from yesteryear along with the guy required ball caps. My wife insists that I keep them out there. Too dirty with all the red dust so I got them in ziplock bags. (kinda defeats the purpose though) I have been thinking about giving them to a couple of parts stores around here b/c they have helped me help others for a long time now.
LSC
cooling system "power flush". I am hesitant of taking their advice because I just "power flushed" the coolant a year ago, and I regularly add fuel system additive (TL3 or STP). Any thoughts or advice are greatly appreciated. In addition, this car has always been taken car of well while in my possession (3 yrs)with regular basic maintenance (oil, trans fluid, coolant, etc) and it has only 68k miles. Don't know if that helps. Thanks.
My next question is: Do the fuel system cleaners you use keep the valvetrain clean? Also, is carbon-buildup in the cylinder common for this engine? Is your travel mostly city or highway? A lifetime of stop-and-go traffic can leave deposits everywhere, no matter what cleaners you use, because only the heat that a good long drive causes can keep the engine clean.
Most obviously, can the computerized timing of this car be adjusted? Since high octane seems to cure the problem, I would think that altering the timing could do the same.
guitarzan
Community Leader/Vans Conference
The car doesn't get enough highway miles, so I will start driving it a little more on extended drives. The TL3 says it cleans intake valves.
I am going to go ahead and flush it one more time with Prestone Super Radiator Cleaner to see if that helps. Any other thoughts? Thanks.
I tried both 89 and 92 octane in the Concorde and the results are that it runs the same except for the 92 octane. It seemed to ping and knock a little on heavy acceleration. It was enough to make me decide to stick with the 87 octane the manufacturer reccommends.
LSC
I used to fill 92 octane in my 98 concorde lxi.
Once i just decided to try 87 octane and found that the car drove better. Have been using 87 octance since.
Moreover .. I have noticed that Amoco works better for me than any other brand. I just get the feeling that the engine is a bit smoother.
LSC
Thank you,
James
Now I use only 93 or 92 octane for my brand new Civic - engine runs quieter (19,000 miles)than of those of my friends.
Sign me up for that eXXon clean stuff.
Andrey2
Your Civic requires '87, right? Try a tank of '87. You probably won't notice any difference in power or smoothness. That should tell you that '87 is fine to use, and there is no benefit of higher octane. (I've owned an Integra and an Acura CL, which has an Accord engine.) When your Civic has 80k+ miles, it may start pinging, and necessitate the high octane.
To reduce carbon buildup throughout the life of the engine, try to do extended highway drives of 30+ miles on a weekly basis. That darn stop-and-go does the most long term dirtying of the cylinders.
Maxim, see if you can get an explanation of this. I've never heard it, nor read it in Acura materials. Also, try asking another dealer about this.
guitarzan
Community Leader/Vans Conference
If you own a euro car, chances are the compression ratio is higher than 8.5 and will require something a little higher. Volvos for instance require premium due to the 9.5 compression ratio. Although if you live in a cold climate, the carbon build-up within the engine will be less and one could use a lower octane for a while.
The HONDA line should only require regular gasoline but you may want to put a bottle of Chevron Techron about every oil change interval, say 3000 to 5000 miles. This should keep the Honda running very nice. Your engine will thank you.
Also using 93 octane is waste of money because your car's computer is not adjusted to differentiate or see the difference between 87 octane and 93 octane. even though you use 93, your car thinks that you are using 87. Plus higher octane will cause carbon built up in combustion chamber in long run.
Octane creep-up is common in old cars, gitarzan is correct. A booster additive like Techron will often help. Beware, some aftermarket additives are crap...just mineral spirits with a bit of old-technology cleaners maybe.
"EPA minimum" gasoline only has enough additive to keep injectors clean...you can get combustion chamber buildups with these Polybuteneamine based products added to the gas. Major oil co's. (Chevron, Texaco, Shell, Amoco are some) likely use Polybuteneamine chemisty additives that do not permit carbon build-up/octane creep. Engine sensitivity to carbon build-up is also big factor...insensitive engines might be fine with cheap gas. Even some "big" gas brands at retail do not use good detergents in my opinion. Price is a good clue, not marketing.
I'd almost bet a day's pay the Caravan discussed above used cheap gas a lot...
Octane/supreme fuel use is commonly misunderstood.
Life has no free lunch...cheap gas
can have problems.
Disclaimer: I have a Chemical Engineering background & work for major oil co. The informed opinions above is my own and is correct. Be careful in Edmund's Townhalls, these are *great* & fun forums, but some opinions are not at all informed but are offered authoritatively anyway. Caveat emptor.
"... At least 89 AKI or 95 RON. Because these engines are equipped with predetonation detectors (knock sensors) they automatically adapt for operation with fuels of various specifications etc.... The higher-octane fuels will provide increased performance and fuel economy, while the use of gasoline with a lower octane rating will have an inverse effect".
So, they're saying it's up to you, you don't have to buy premium, but if you want 100% output from your car - you better use premium.
Any ideas on that. Maybe it's true for any car.
but have second thoughts when it comes to
gasoline.
Does anyone have any facts supporting brand name
fuels, such as Chevron, being better than generic
brand fuel? I live in Northern California where
gas
prices are unreasonably high, $1.60 for brand name
87 octane.
I've heard ethanol and some other "fillers" can
leave valve deposits. Is this true? I've also
heard
MTBE (added to Ca. gas) has harmful effects. Any
thoughts?
Can this be so?
Thanks
ps: I have been using 91 oct and getting 25mpg (40mile commute 50/50 city/Hwy).