Hopefully somebody can help me, I have a 95 Camaro z28 that is misfiring. The misfire is more prevelant when the engine is at operating temp, and at 2000 rpm and below. I can WOT with no problem. no matter what gear your in, or even idling. Ive spent alot of money trying to rebuild this car. The only mod on the engine is K&N Cold air intake, other than that to my knowledge, the engine is stock.
I took it to a local mechanic and they showed me the read outs that cylinder 6 and 8 were misfiring like crazy. I had a chinese piece of crap distributor in it at this point, and i bought an MSD distributor from jegs and installed it myself.
Plugs and wires are less than 20,000 miles old, I pulled #8 and #7 plugs, they werent burnt or fouled. Ignition coil was replaced about 2,000 miles ago. Map sensor about 500 miles ago. Intake gasket, valve cover gaskets, EGR valve and EGR vacuum lines about 1,000 miles ago.
If any other info is needed i will be glad to provide it! thanks

 

you may have "arc" going on at the plug boot

you say misfire is more pronounced at 2k rpm, is that in drive or higher gear if manual with engine under load?

you should look under hood at night for any signs of plug arc. It helps to mist the plug wires with some water. you may also need to look from underneath, with engine running, as the arc can be hard to see. ESPECIALLY ON ANY PLUG BOOT ENDS USING THE FACTORY HEAT SHIELDS

so with the MSD Opti you have the same symptoms as with the china made opti?

FWIW the MSD is better than offshore brands...but several have had problems with them, including me right out of the box.

 

thanks for your reply, to answer your question, when i had the china one in the car had a horrible shake to it no matter what, it even started messing with my oil pressure, when i installed the msd, it took alot of the shaking away, and my oil pressure went back to normal. i havent had a chance to put it on a scanner yet to see if the same cylinders are misfiring or if its changed, im hopefully getting to that tuesday. the only shaking that is left is around 2000 rpm, more noticable when you have a load on it, especially doing about 45-55 mph in over drive and then you try to accelerate, then the misfire ease up when it shifts down a gear, but is still there. BTW the car is automatic. ive checked for arcing , and didnt notice anything.

 

....as did I several times....and it was by chance while under the car with motor running, daylight, I saw the arc on #6. BETWEEN plug boot and inside of factory heat shield

So I would really check again as if you can not see absolutely every angle and entire plug boot end you have not looked at everything

what you describe is plug arc under the conditions you notice it most

dialectic grease is your friend on plug boot ends and if you do have any of the factory heat shields, you should remove them to see more clearly the plug & boot itself

 

I will definitely check again, I will post again once i have been able to double check it. is idle going to be good enough or should i have somebody in the driver seat revving it? also this is one of the only times that i wish i didnt have a loud exhaust so i could hear it arcing

 

you don't need anyone revving the motor. You may not even hear the arc...but if you have one you will see it. Since you can't see everything from up top...getting the front of car up on ramps or jack stands so you can see from underneath is what you need to do

scan software would show any code or what cyl is misfiring if you have access to that. But in my case the plug arc never threw any codes. Plug arc still fires that cyl so it often does not show up as a "misfire code". You could simply have a cracked porcelain of a plug bleeding spark

Do as much visual inspection as you can before throwing any more parts at it

 

Puzzled.... 95 is OBD-1, no crank sensor, and no misfire detection. How did the mechanic scan it? Or was he observing the spark pattern on a 'scope?

If oil pressure dropped, it was because the misfires and rough idle dropped the RPM. The Opti can't affect the oil pressure any other way.

Have you checked all the plugs? The misfiring may have seriously fouled a few of them.

 

i havent checked all of the plugs yet, and i do believe the mechanic used a scope, because the graph he should me looked like a heart rate monitor read out.
When my day off comes on tuesday, i plan on checking for the arcing at the plug wire boots, and ill pull the rest of the plugs to see there condition. probably just replace them while im in there.

 

Numerous previous posts have had this issue with the spark trying to find a ground and it seems the heat shield( I guess it's around the spark plug boot)sucks up the spark grounding itself.I'm no expert but maybe a plug wire change (ac delco) or better might help or remove the shield like others have done.hope this helps.Great post from Chimera96.My02.P.S.No heat shields here.

 

I found the problem it was arcing at plug wire 6, I took care of it no more misfire........ but I have another problem. If I put the car in neutral or park, the car will sit at 1000 rpm for about 5 seconds then jump up to 2500 rpm and just sit there. When I put it in drive the car won't jolt like it normally would if you were holding the accelerator down. But it will bounce up and down by about 300-400 rpm and the car will move by itself. Even fight me while I'm holding the brake to move. I have replaced the tps at the beginning of last year. I'm thinking it's the iac valve but want opinions.

 

Since nobody chimed in I'm on a roll now.I would check the connector for ground on the IAC.Next,I would check for ground to your mas(I ain't got one).Then I would check the cable connected to the engine block.If any connector is broken.I would replace them.My iac connector wire tab was broken so I replaced it.Remember these wires are over 20 years old and they don't last.Hope this helps.

 

I think I meant maf sensor,I dunno.

 

Good you looked close enough to find your arc issue...

your IAC "could" be the issue either in IAC valve itself or wiring to it. You could take TB off and remove IAC and clean it and the orifice of TB with TB cleaner. Do not push or pull on the end of the IAC...if you previously did this the IAC is dead.

high idle is often associated with a vacuum leak. As you finally did in carefully checking plug wires for arc....you need to be as diligent in checking for vacuum leaks. TB gasket or intake elbow. any vacuum hose on/around engine.

When you replaced the MAP...was the small rubber redish orange gasket on the nipple of MAP still there or torn??

having a vacuum gauge, and knowing how to use it, is helpful in diagnosing engine problems. You can get a vac gauge for a few $ at harbor Freight

 

If you remove and clean for IAC with spray cleaner, be sure to hold the connector end up so no solvent-borne crud migrates into the electrics...

 

So I checked the iac yesterday, and it has crap on the end of it, and looked oem, so since I get discounts through where I work, I just got a new one and put it in making sure to clean the part of the tb that it inserts into. That had no effect. I checked the ends of the wiring for the iac, tps, and map sensor. All are fine. The map sensor when I replaced it, the red thing was still in tact, but if I remember correctly the new sensors nipple was alittle small for it so I will check that tomorrow. As far as vacuum leaks, I've sprayed all lines I can think of with brake cleaner to see if the Rpms would fluctuate, the problem is, the car is already at high idle and the sound from the exhaust makes it near to impossible to hear it fluxuate. I've recently resealed the intake manifold and am wondering if I didn't get it good enough with rtv. The only problem is the car runs so smooth you would think it wouldnt be a vacuum leak. Is there a way to post a video on here? I have a recording of it