Results 1 to 8 of 8

Thread: 1999 GMC Sonoma BADLY misfiring; 2.2 liter 4 cyl

  1. #1
    Registered Blaine B.'s Avatar
    Join Date
    Nov 2005
    Location
    Northwest Indiana
    Posts
    1,876

    Default 1999 GMC Sonoma BADLY misfiring; 2.2 liter 4 cyl

    A friend of mine recently purchased a 1999 GMC Sonoma (2 wheel drive and 2.2 liter 4 banger with automatic transmission) from a local auction. Advertised as driving and running, although we later found out that is a bit deceptive as it says it does not have to be road safe or road legal to be considered as driving and running. Anyway besides all that and nothing to do except keep it now, the original idea was to fix a few small things, add a radio, and resell it for profit...bla bla bla

    Anyway the truck was misfiring badly when he first started it at the auction location. Suspected the cat was clogged, so cut it off....no change, just 10x louder. So he had it towed back to my place. I pulled all of the plugs. They turned out to be Bosch Platinum +2's. Cylinder 1 and 2's plugs appeared to be in a lean environment. The plugs from cylinder's 3 and 4 appared to be in a rich environment and covered with soot. So I cleaned the 4 plugs with a wire brush and reinstalled. Also made sure the "gap" of the two grounds on each plug were even, as some appered to be slightly closer to the electrode than others. The metal on these grounds seems to be softer and thinner compared to any other spark plug I've seen.....

    Anyway I ran a resistance check on the 4 plug wires too. Three gave readings, one gave absoultely NO reading at all. Thought there was an internal brake in the wire. So we installed a new set of plug wires without any change.

    Tonight I welded the cat back onto the rest of the exhaust and he replaced both of the coil packs with new units. No change.

    Motor appears to be misfiring really badly. The motor is moving around inches in each direction. It has no power at all. Also if you turn the lights on, they fluctuate in brightness. Just to show how bad the "misfire" is (if it is truly a misfire or not) if it is causing the alternator to charge at an inconsistent rate.

    There does not appear to be any coolant in the oil or vise versa either.

    Actually today after the new coil plugs were installed, it would not start without putting the accelerator pedal to the floor (so that the injectors are disabled during starting)

    Also you can smell A LOT of gas when starting the vehicle or when it is running.

    Perhaps the injectors are screwed up? If this were the case it is probably more than 1. I think the intake manifold would have to come off to get to these. This small 4 banger is really packed in there......nasty!

    Whoever had (or worked on) this truck prior was really a dumbass. The wire that is supposed to hook up to the A/C compressor clutch was left dangling and got chewed up by the radiator fan while the plug which was intended to plug into the intake air temp sensor (in the air intake tube) was jammed into the A/C plug. They are clearly different plugs too, not even identicle!

    The "service engine soon" light is also on. We are working on getting a code reader to read the codes. I am guessing it will show a bunch of misfire codes and that is it.

    Does anybody have any GM experience or any suggestions relating to these problems?

    Thanks in advance!

  2. #2
    Forum Leader
    Join Date
    Aug 2000
    Location
    Parker, CO
    Posts
    9,067

    Default

    Get the codes and go from there. You will get more than simple "misfire" codes. You will get sensor specific codes. That's why we pull codes, to know where to start.

  3. #3
    Registered Blaine B.'s Avatar
    Join Date
    Nov 2005
    Location
    Northwest Indiana
    Posts
    1,876

    Default

    Got another buddy to come by today with his code reader. Only code it was throwing was an "injector circuit open" code or something to that effect.

    Ohmed the injectors themselves. Two of them were reading 2.1 ohms and two of them were reading 2.2 ohms.

    Also checked the plugs to each injector. 3 of them were reading .1 volts while one of them was reading .8 volts (WHILE CRANKING THE MOTOR OVER)

    What voltage are the injectors supposed to be receiving? I am thinking that .1 volts is way too low....

  4. #4

    Default Same problem with 2000 GMC Sonoma

    Did you ever figure out what was wrong with your truck? We have a 2000 GMC Sonoma, and it has been running great for over the year that we have owned it, but just today the exact same problem that you originally explained is happening to us. We took it to get a diagnostic and it says that Cylinder 2 is misfiring, and some of the different problems is spark plugs and/or wires, igiition coil, pressure leak, high or low fuel pressure, and I forget maybe something else too. But anyways, did you ever figure it out? It seems weird the exact same thing is happening. Also, we can smell fuel too.

  5. #5

    Default

    Check fuel psi.might have a bad fuel pump.
    1998 5.9 Limited Slate

  6. #6
    Registered Blaine B.'s Avatar
    Join Date
    Nov 2005
    Location
    Northwest Indiana
    Posts
    1,876

    Default

    The shop my friend brought it to diagnosed and repaired as a bad engine computer and fuel injection wiring harness.

    After the cost of that, I think that will be the first and last auction car he ever purchases :/

  7. #7
    Registered 54cj3b's Avatar
    Join Date
    Apr 2011
    Location
    Colorado
    Posts
    70

    Default

    He could have bought the comp and harness on Ebay for $100.

    HA HA YOU MISSED

  8. #8
    Registered Blaine B.'s Avatar
    Join Date
    Nov 2005
    Location
    Northwest Indiana
    Posts
    1,876

    Default

    Very true, he had purchased the engine computer for $100 at a salvage yard, it would run but die after a few seconds. He didn't know it needed to be reflashed...

    So live and learn, too late now, he sold it long ago for a big loss, like I said probably the last auction car he buys. His first was a major financial lemon unfortuantely. Scarred for life if you will.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Jeep Parts | Jeep Accessories | Trektop NX | Jeep Seat Covers | Jeep Wrangler | Jeep Wrangler Parts | Jeep Wrangler Accessories | Bestop | Jeep Tires | Jeep Stuff | Jeep Wrangler Tires | Jeep Wheels