Help Me Diagnose - 2000 Cavalier -Misfire - Trac Off

[wickedude]

Im working on a 2000 Cavalier with a 2.2 automatic and Im stumped on where to go from here. It has been having a hard time idling when cold and but has not thrown any CEL codes.

When starting from a cold start last night I can feel the car misfire and the trac off light came on. When driving the car seems just fine and does not miss at all.

I have had this issue for awhile, thinking it was just needing a tune up. Car just got new coil packs, spark plugs and wires a few weeks back. No change.

I also replaced the fuel pump this weekend, pressure was good but fuel sender unit died on the module.I replaced the fuel filter and fuel regulator as well.

When looking at my scan tool I am getting misfires on random cylinders, not just one. When starting up warm the issue seems to be not there or much less noticable. Can anyone shed some light? Im lost as to where to go from here. Thanks!

[denisond3]

Im sorry I dont know any specifics, but a next step would be two things: Have a look at the plugs, to see if they are clean and white, or if one or more of them is dark, dirty, or even wet. If you had the old plugs it would be a good idea to look at them too.
Then, do a compression check. Low compression for whatever reason can lead to a plug running cold and not firing reliably when everything is cold. If the compression is good in all cylinders, my next suspect would be either poor fuel pressure in the fuel rail (hopefully there will be a fitting to check it somewhere on that fuel rail) or an injector that is partly clogged - or even not shutting off (which lets fuel leak into the cylinder it feeds, causing a too rich condition). I dont own a Cavalier, so these are the kind of things that can happen to any car with individual injectors.

[J-Ri]

There's no fuel pressure test port on the 2.2 OHV... easiest spot to check is at the filter.

Take a look inside the throttle body, especially on the back of the throttle plate. If there's lots of carbon there, it's safe to bet there's lots of carbon in the rest of the intake and probably on the valves too. The carbon will absorb some fuel which leads to the engine running lean, as the engine gets warm, two things happen. 1- The carbon gets "full" of gas and doesn't absorb as much 2- the gas that has been absorbed evaporates faster than when cold which puts more of it back into the cylinder. Take a look at your LTFT (< +/- 5-10), IAC (<25-30), and inj. pw. (<2.8mS) on your scan tool. If any or all are out of that range, there's a very good possibility that carbon buildup between the TB and valves is to blame. BG makes an "induction flush kit" that works very good for this, but you need their aparatus to use it. You could also spray a few cans of intake cleaner into it while holding the RPM at 3-4k and then add a can of good fuel injector cleaner.

[wickedude]

I drilled and added a schrader valve when I changed fuel pumps so I can test it right at the rail. Again the pump is 1 day old and I am getting 49 psi with the key on, about 47 running at idle.

I have a can of seafoam I can run through it tomarrow, I have had good luck running it throught the brake booster vac line and stalling the engine out.

[jonnyukon]

im having the same problem with my 2000 cavy and the trac light coming on but only when it starts to stumble and then it straights back out.... i stumped too...

[jonnyukon]

ok here is an update ....i found that its number 4 cylinder that is missing ....i already change coils and did wires and plugs so im thinkin possible fuel injector?? i do have a code for the up stream os sensor ...but i accidently erased it and forgot what it was...any info guys would def help...thanx

[jonnyukon]

Well i think i finally found the problem to my intermitant clyinder drop. at low engine load and cruising speed... seems to have had a small break but not a complete break in vacuum line running from the throttle body to the fuel pressure regulater ....and it seemed funny that most, if not 75 % of my misses was on the number 4 cyl....lol..well i cut the tube down since the break was closest to the regulator side (which was only at the tip just before the rubber connection end) and just used some high tack sealent on the connections ...and i checked to see if i had anymore loose vaccum connections and POOF .. the car runs so much smoother and the idle is waaaay more stable arcoss the board.... it almost feels like i took a few thousand miles off her soul that is riding the 294,000 mile mark with original motor and trans.. with only main big problems have been a head gasket and trans lines ( because of the rust )... and his mishap