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GMC Jimmy Misfiring, Backfiring, Spark Plugs

Our 1993 GMC Jimmy started building up carbon in the EGR Valve. We Seafoamed it, but that didn't seem to help. We later put a new gasket on the EGR that has a screen on it. That has seemed to fix the carbon problem.

As of right now, it keeps fouling spark plugs. It sounds like it has a huge cam in it, which I'm taking as it not running on all its cylinders. When I take the plugs out, they seem to have gas on them. Any idea on what's causing it and how to fix it?
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Comments

  • lynderaelynderae Posts: 4
    First off let me say thank you for youre help with camshaft position sensor in distributor. I have also replaced the coil, the truck ran like a champ yesterday. Today however, I didnt get out of the driveway and it started misfiring. It is rainy today, but it was wet out yesterday. I cant figure this out, any help would be appreciated.
  • repairdogrepairdog Posts: 948
    Did you change the cap/rotor to rule them out?
    Crank sensor is under the front of the motor and they can act up without a code or the connector can get wet/dirty. Any SES light and codes?
  • frschevyfrschevy Posts: 2
    I have a 04 chevy blazer 6 cyl 4 wheel drive.
    I purchased in Jan 07. (39,000 miles)
    Its been back to the dealer 4 times for stalling.
    I'm just driving down the road and its shuts off.
    I still have power but the engine quits.
    so for all that has been done is (replaced)
    the distributer cap and roater,the coil and something attached to it. They can't figure it out. I don't get any
    check engine lites. Im pritty sure the problem is electrical,but who knows. Can anyone help this is driving me crazy.
  • repairdogrepairdog Posts: 948
    Running too rich so look at the CPI and nut kit (injection and hoses) under the upper intake. Posts on that and how to look at can be found by a search in the forum. Do you smell gas also? Hows the oil consumption - if high look at clogged PCV or worn valve seals - never stated the mileage. Then air filter should be clean also and vent to other valve cover attached and good.
  • It has 175,000 miles on it. And yes, I do smell gas when I run it. I replaced all the spark plugs and it still seems like it is misfiring. Thanks for the information. I will look into it.
  • quickfoxquickfox Posts: 2
    How to change middle sparkplug on driver"s side of 1996 Jimmy with 4.3 V6- problem is steering shaft blocking acess
  • repairdogrepairdog Posts: 948
    2 ways used and 1 is short plug socket and open end wrench thru the wheel well or 2 is unbolt the steereing shaft at the flex and move the shaft - change plug and reinstall shaft.
  • jlflemmonsjlflemmons Posts: 2,240
    You can also use a 3/8 socket, an adapter from 3/8 down to 1/4, use a 1/4 extension, and come in through the wheel well. Using the adapters and thinner extention gives enough play to get around the shaft. Just barely, but enough.
  • after replacing the thermostat because of it overheating now there's a noisy lifter- could this be caused from the engine getting too hot? it also due for an oil change. :confuse:
  • repairdogrepairdog Posts: 948
    Oil and filter and hope the lower intake gasket isn't leaking into the valley. Keep a close watch on the reservior - fill it to the hot line when cold and look at each day and make sure its not dropping. No leaks either so look around. Replace the radiator cap with a new one now also. Hope you flushed the system out with that new thermostat and refilled with 50/50 Dex cool mix.
  • WELL WE CHANGED THE OIL AND THE FILTER- BUT THE LIFTER NOISE IS STILL THERE! WHAT DO I CHECK FOR NEXT? :mad: :confuse:
  • repairdogrepairdog Posts: 948
    Look for water dropping - #1 cause on 4.3 is the lower intake sprays a fine mist into the valley and the lifters make noise. You will normally NOT see any water in the oil when this occurs only the res dropping and morning lifter noise. Then if thats stable you got the engine so hot that you cooked some oil on or in a lifer or two so go buy some lifter cleaner that gets added to the oil and follow the instructions. Often takes 100 plus miles to quiet down, assuming no water getting in.
  • GOOD NEWS IS THERE ISN'T ANY WATER GETTING IN!YOU WERE RIGHT ABOUT IT BEING BETTER ONCE THE ENGINE GET WARMED UP! I'LL PUT SOME OF THAT LIFTER CLEANER IN IT TODAY & I'LL LET YOU KNOW IN A COUPLE OF DAYS OR SO THE RESULTS! I'M PRETTY CONFIDENT THAT THE RESULT'S WILL BE "GREAT"! WHEN SHOULD THE OIL BE CHANGED AGAIN (3,000 MILES)? THANKS FOR ALL OF YOUR HELPFUL INFORMATION!! :shades: :) :)
  • ONE MORE QUICK QUESTION- COULD THE SERVICE ENGINE LIGHT STAYING ON NOW BE CAUSED FROM THE STICKY LIFTER??? LAST TIME IT HAD COME ON WAS BECAUSE THE GAS CAP WASN'T ON CORRECTLY & I ALREADY TRIED THAT AGAIN. :confuse:
  • repairdogrepairdog Posts: 948
    Get the code read out at any Advance or AutoZone for free to know. Read the instructuions on the lifter bottle as some require a change sooner, some don't. I do all mine every 3000 and only use the Valoline MaxLife 10w-40 now as my 4 are all over 100k miles. Do not use the $2 oil filters either - I have used the mid grade Fram Toughguard ones for years or best is WIX or NAPA Gold - forget the ones with Teflon in them. Hope all works out noise free!
  • YOU SAID THAT 4 ALL WITH OVER 100K MILES- WHAT KIND OF VEHICLES ARE THEY?? ALSO THE BOOK THAT CAME WITH MY JIMMY SAY'S TO USE 5W-30 OIL IN IT. MY JIMMY ALSO HAS A LITTLE OVER 100K MILES NOW. AS FAR AS THE NOISE- WHEN I STARTED IT THIS A.M. (COLD) THERE WAS NO NOISE. I DIDN'T EVEN PUT THE LIFTER STUFF IN YET. I JUST DROVE IT YESTERDAY ABOUT 45 MILES AFTER THE ENGINE WARMED UP SO THE NOISE WAS GONE, BUT THE LIGHT WENT OUT FOR MOST OF THAT TIME & THEN IT CAME BACK ON. I'LL LET YOU KNOW WHAT HAPPENS THOUGH! THANKS AGAIN!!
  • repairdogrepairdog Posts: 948
    All Blazers and after 100k I switched to 10w-40 MaxLife as all the bearings and seals have worn and I'm in FL so always hot! Great if the lifters already are quiet - new oil must have flushed the sludge stuff off.
  • daylyndaylyn Posts: 12
    My Jimmy drives fine around town. I've just replaced cap and rotor, spark plugs, O2 sensors, and catalytic converter.
    The problem is every time I try to drive up a steep incline the truck will lose power, then chug and sputter like it's gonna die. If I turn around and go back down the hill, the sputtering and chugging stops and she runs fine again! What is going on? Any suggestions?
  • repairdogrepairdog Posts: 948
    Assuming no SES light on and codes present.
    Change the fuel filter and if then check the fuel pressure.
  • daylyndaylyn Posts: 12
    Previously had a 0300 code-multiple misfire, but didn't get another code during or after this incident. Fuel filter was replaced under a year ago, but will change it out, and hope that helps.
  • repairdogrepairdog Posts: 948
    Thats a hard code to clear sometimes as like 8 possible causes. Have you changed the plug wires? At night spray a fine mist on the boots and see if they arc. Then the coil could be failing so a load results in a weak spark. The crank sensor can be intermittant as it starts to go (under block and the pulses tell the PCM the crank position). Then the ign IC on the coil heat sink (not common). Or fuel pressure low so lean mixture results - again check pressure at fuel rail. Injection system problems also can cause.
  • daylyndaylyn Posts: 12
    Plugs and wires were replaced. We're wondering if maybe it's the MAF sensor.

    How would I find out if the coil was failing? Just replace it?

    It seems that the truck only behaves this way on one hill, which is at a high altitude. If the MAF sensor was malfunctioning, would it cause the truck to behave this way in high altitudes?

    Any way of knowing if the MAF or MAP sensors are malfunctioning before spending money to replace? I did lightly clean the MAF last nite, and made it up the hill a little further before truck crapped out......
  • repairdogrepairdog Posts: 948
    Dirty MAF does effect the mileage as runs richer so possible - clean with MAF, brake, or electronic cleaner but not carb (leaves residue).
    Have to test the primary and secondary windings and some auto stores can test for you free.
  • This 4.3 liter starts up easily like nothing is wrong , start heading down the road and after about 10 minutes of driving the engine loses power, { the more you push the gas pedal the slower you'll go } untill it then stalls , while still coasting I can put it in neutral , and restart the engine like nothing happened and go down the road , { engine runs fine } Then after a few miles it starts acting up again . And when it is acting up if you floor it it will backfire under the hood { carberator ? }
  • If General motors wonders why they are losing sales , it is because of vehicles like mine 1998 GMC Jimmy , It has been nothing but a money pit , from wheel bearings at over $150 a side tto the fuel pump at over $600 , to having to replace all four ball joints at 80,000 miles , and I haven't even mentioned the rear braking system , I go through brakes about every 5000 miles , I have replaced rotors calipers and pads up to 3 times a year . And now I can't figure out why it stalls ? It has been at the shop for over a week ! That is why I bought a Toyota ! whatever happened to buying american made automobiles that would last and be easy to fix ? If I could order a new truck and chose the year I would order a vehicle engineered in the mid 80's with no fuel injection ! no ABS , no electrical transfer case , etc ...
  • repairdogrepairdog Posts: 948
    Well lets start with the backfiring etc - what code do you get as the SES light must be ON? You have a timing problem for the backfire so has it got a new cap/rotor? Then cam sensor in distributor which effects that (starts OK then probems start) but get the code - also a crank postion sensor tells the PCM where to fire. Then if the fuel presure is bleeding down possible fuel regulator leak under the upper intake. A good GM garage can find these in an hour.
    As for the brakes the rear calipers must be replaved with rebuilts each brake job - cheap plastic piston and the slides are in the braket and must be pulled out (rubber boot pulls out) and greased or you will eat rotors. Assumes that the rotors are straight and the lines clean.

    The other repairs you did are known Blazer/Jimmy ones and soon the AC compressor will go, the alternator, water pump, and keep that cooling system changed every 3/36 or look out heater core and lower intake gasket.
  • Well my mechanic called and said that the fuel pump was drawing so many amps that when you activate the brake lights or turn signals that the fuel pump changes tone with the flash of the signals or when the brake is applied thet pump changes tone , also he said you shouldn't be able to hear the pump running over the sound of the engine , I just changed the fuel pump not even 3 years ago !! $600 . whatever happened to the $30 fuel pump change ? I'm not impressed to say the least . and yes i've changed the water pump , alternator 3 times and yes the heater core plugged up on me 2 winters ago , DEXCOOL ! what a great coolant "NOT" ! SO I flushed it out and then I caused it to leak , I then put 4 bottles of BARS stop leak into the syatem to seal that up , I couldn't afford the $400 that the dealership was going to charge to replace the heater core , P.S anyone want to buy a jimmy for cheap ?
  • repairdogrepairdog Posts: 948
    Well, only the Delco pumps seem to last at all in these vehicles and Airtex has a replacement connector for the pump top that solves many of the corroded connector problems and voltage/amperage problems and a good ground is alos a must. All of the pumps can be heard when the vehicle is running if standing by the drivers side but not while in the cab windows up. Old mech pumps ran at like 10lbs and new injection requires 60 plus.
    I have 4 of these so I know when each part dies first hand. When all is fixed they run well and handle pretty well too but as you know they are not without alot of repair and if you have to use a shop gets very expensive fast.
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