Good that you posted the result. It might help out someone else in the future. Apparently the power from the coil was not able to be discharged to that damaged wire, so it was looking for another place to go.

 

Road test indicates I still have the miss after 1/2 hour of driving and the black spots on the top of the bumper. I am seeing opti and o2 sensors in my future.

 

With the relative low miles you mentioned earlier, I advise only changing the cap and rotor. Particularly if you have no other issues at the front of the engine like leaks etc.....

I've seen too many others get into all types of problems by changing the entire unit when they only needed a cap and rotor.

One other point. You had back firing and poor running issues. So now the plugs are not in the best of shape. You didn't mention them being changed but they should be.

 

speedygonzales-

I did swap out the plugs and coil and two bad wires as I was trouble shooting. My poor running issues now ONLY show up after running for 1/2 hour. I was not aware that a cap/rotor replacement would fix this, I thought sure I was in for a whole opti.

I was thinking the black spots on the bumper were due to fouled o2 sensors after ceramic coated lt header install.

Hope this helps fill the gaps in my story.

 

O2s can and usually are shot after running extremely rich. Not to mention they are tune up items anyway. A good start for sure. However if they were the only problem, they would show the problem as soon as it got to operating temperature and not take 1/2 hour to show up. But then a cap and rotor wouldn't solve the dreaded 1/2 hour problem either.

Your problem sounds more like a heat soak issue. So there is the slight chance the feedback section of the opti is the problem and would require the entire portion to be replaced. However you can do some experimentation to find out first.

If the engine is dead cold and when started for merely a second runs good, shut er down right away. Then heat up the opti with a hair dryer to point of just not being able to touch it. You can find a way to support the dryer to warm it up while you do something else. Then fire it up and see what it does.

Of course the other way to do it is after the problem shows up, put a scope on it like a Vantage and see if the wave forms from the opti are changing.

 

So are the o2's to blame for the spots?

 

If your talking about soot on your bumper, they may be. If your talking about the rough running after 1/2 hour it's iffy.

All these questions can be answered with real time monitoring of the PCM.

 

Yep - I was thinking o2s for the soot spots and opti for the 1/2 hour fail. I have a datamaster read on the car from when the plug wires were failing. I was going to take another ready after trying your "warm up the opti" idea.

I also spaced the icm off the head while I was doing the coil, I figured it could not hurt.

 

I took a datamaster capture on the car today driving to and from work. I am definately running rich at times - up to 953mv on the o2s. They seem to fluctuate from 100-900, leading me to think they may be ok.

I did get the car to backfire under wot, but not codes thrown (thanks obd1), leading me to think I may have a plug or wire issue when heated.

Gotta love the multi-faceted issues.

I have a datamaster capture if anyone is interested in checking it out.

 

1) Does a bad plug wire always take the plug down with it?

2) What would cause the timing to retard at idle in closed loop for 15 minutes, then stop?

3) Would a GM Tech 1 give me more help than Datamaster?

 

If you suspect your O2's are the issue you can do a few things to check them. First, disconnect one and see how it runs when warmed up.

While it's disconnected, see that the signal has gone to around 450.

If when they are plugged in they don't swing like they should, try shorting the signal wire to the ground wire and be sure they went to near 0.

 

speedy-

Sent you my datamaster file of most recent run. Idle timing retard is gone. Car still misses at wot after warmup.

 

Tried the best I could to view the file but only got suggestions to fix the file error. Sorry. Did send you a PM for something to start with.

 

Speedy-

would it help if I changed it to excel format and resent? What I sent you has the car cold right up to where the miss starts.

I am still thinking opti, but for $600 for the right part, I have to be sure.

I appreciate the assistance. I just checked my PMs and don't see anything yet.

Paul

 

how does it start when the engine is hot? When my opti was going bad, it would miss occasionally when it was warm(1/2 hr of run time). Sometimes it would throw a code but not all of the time. When it was cold it would start right up but when it was hot it would crank for a long time before it started.........Good luck with whatever you find, Mike