NEOS97SS

hey everybody i finally have my car all put together and running, no exhaust leaks no nothing only one problem and no one can figure it out. first off the plugs and wires are brand new and good they have already been checked along with the distributor and the coil. heres the problem with a set of bad o2's in it, she runs really rich, premanantly in warm up cycle it never goes open loop it just runs off a set program you know. and like that it has a slight miss or studder everyso often. but when i put the new o2's in it runs fine in warm up cycle but as soon as it switches to open loop and starts to read and adjust off the o2;s reading it starts to get a random misfire. not enough to throw a code but enough to notice and make you not wanna drive it. and it is primaily in sylinders 1 4 7 8 but just random. the lead tech at my store thinks its running too lean but i dont think thats it. ive never had any tuning and the ipw is identical to every other camaro we have tested. my car has the following mods if this helps...jethot longtubes, taylor 8mm wires, plat plugs, its a 97 ss so it has ram air with a k&n filter descreened the maf, 1le intake elbow, no egr no AIR, lt4 km, tb bypass, rear o2 sims, no programing, a 3" cutout (closed on the street), a custom 2 1/2 to 3" ypipe, and a 3" flowmaster catback. i think thats it but please help cause i cant figure out the miss. thank you in advance joe

NEOS97SS

ttt

slopokrodrigez

First of all let's get something strait. The engine runs in OPEN loop while it's warming up. Once the engine reaches I think 140 degrees it then goes to CLOSED loop. So prior to closed loop it ignores the 02's. You say that 1 4 7 & 8 misfire. How do you know these are misfiring? Are you looking at the plug wire signals with an O-scope to see this? If you do see an electrical misfire than he shouldn't be suspecting a lean condition. If it's only 1 4 7 8 and not 2 3 5 6 then it aint random. What are the plug gaps?


The O2's your using, are they OEM or some cheap aftermarket? Has anyone checked fuel pressure during this problem? What are the IAC counts during all this? What is knock retard during this problem? Have you done a leak down or compression test lately?

Remember what goes on with fuel and spark once the engine is running in closed loop. Based on feed back of a few sensors, the PCM will vary the pulse width of the injectors. As far as ignition, it can only advance or retard the firing of plugs. It can't randomly (the PCM) shut off plugs from firing.

More answers will help us diagnose the problem.

NEOS97SS

sorry about the open closed loop thing i got it backwards, oops
i know its 1 4 7 8 misfiring b/c i work at firestone and we have several machines to hookup to the car like sunscopes, CAS, and hand held versions that monitor everything and show it graphically. yes i was looking at the plug wires with an oscope. and it wasnt only on those cylinders it was just jappening on those four the most. ocassionally it would happen on the others but rarely.

the o2s im using are new acdelco's so they are about as good as they come. i cant remember the iac count and i havent done a leakdown test on compression lately but the knock retard is zero.

the ipw in warm up starts at like 3.2 i think and works its way down to 2.8-2.9 after that. and timing is pretty normal through the whole process.

i hope this helps a little thanks

slopokrodrigez

Sounds to me like your coil is a problem. Did you install it with heat-sink compound available at any Radio Shack? Your ignition misfiring is from either the coil, the opti, wires or plugs. Just a matter of figuring that part out. Since it is when the engine heats up, I'm putting my money on the coil. Could be the optical sensors in the distributor though. Good choice on O2's by the way. Glad to see you agree about electical parts.

NEOS97SS

well i checked the coil compression and the iac and they were all good. so i guess ill be checking the crankshaft position sensor next. any other ideas. still cant figure this thing out and its starting to get pretty frustrating you know.

jer4251

i get the same problem from my car. 97 SS, just put jet hot long tubes, 8mm spyro pro's, bosche plats, !AIR, !EGR, !CATS, my car will run great for a little while but it doesnt perform after it heats up to 180+, i get a little backfire pop every once in a while, I'm running 3" side exhaust with bullet mufflers. i havent programmed my PCM yet but im going to really soon. and im going to get a y-pipe made and remoce the side exhaust. also planning on getting the lt4 Km. My car runs really rich, i get less than 10 mpg. i really need to get it fixed, i dont drive it anymore because it cost too much

slopokrodrigez

How did you check the dist. and coil? Particularly when you have a random miss fire. If you did indeed see a misfire when you were hooked up to the scope, you have to be seeing something in the ignition system. I would suggest changing plugs and check the gap. Double check the wires connected TIGHT. Check the wires for black spots indicating leakage to ground. Check them for burned spots. Also run the car at night with the hood up and look for fireworks if the problem pursists. Check the connectors to the opti for bent pins or corrosion. Check the grounds at the engine, the PCM etc.