Alright, I recently have acquired an intermittent mis under low throttle/low rpm under load. At least that is where it is most noticeable. Anyway, I ohmed out all the spark plug wires (MSD 8.5mm) and they all checked good but one. Number 8 ohmed at about 5K ohms and the rest were 105 ohms or under depending on length. Great I thought...got a single wire and ohmed it before installing and put it on...same issue. I have also replaced the coil with a Delco replacement and spaced the coil/ICM off the head about 1/4"-1/2". The spark plugs are all new since the header install which was about a month or so ago and under 500 miles..Delcos/OEM replacements as well.

I guess my question is this. How likely is it to be the ICM itself. I haven't replaced it yet and I only replaced the coil because I had the assembly off anyway to space it out from the head and figured why not for $60 as it was 15 years old and had 115K miles or so. I know everyone loved blaming opti's too, but it seems like it would either be more noticeable if it was the opti and more consistent or would just have stopped altogether one day out of nowhere...not just kick up an intermittent mis under load at low rpms. Anything else it could be aside from ignition?

I have replaced the fuel pump...fuel pressures test good at idle...after letting it sit...at WOT. Maybe leaking injectors...but I was probably going to clean them and replace them eventually anyway...but an intermittent mis due to an injector? MAP sensor maybe?

By the way this is a '93...so no MAF. Aside from vacuum leaks, I have checked most of the obvious stuff. I will check for a vacuum leak next anyway as I haven't seriously pursued that avenue yet...I did eliminate the EGR/AIR and could have a slight gap where the cover/elimination plate went to the intake...but I did use a gasket and put some silicon/gasket goop on all of those pieces. I guess I will check for vacuum leaks next, but wanted to see if anyone had any other ideas or similar problems that were fixed by something I may be missing or haven't thought to check yet.

 

You can't rule out anything, including the opti.
I doubt it's your ICM, but as I said, can't rule out anything.
Checking for vacuum leaks would be a good idea.
O2's can cause bad symptoms like this as well...
You can unplug them and drive the car and see if it drives any better.
Testing for leaky injectors is easy, just pull up the rail and injectors and prime the system.

 

The O2's have been a concern of mine since the headers as the pass. side O2 is now way down line from where it was on the factory manifold...probably like a foot and half or more further down stream past the collector now. Since they are not heated and it is down further I have wondered if that is my problem. Also, they are Bosch's which is all they had at the time, but I am not thrilled about them being there none the less. I will try disconnecting them and seeing what that does...didn't think about that. Will it run rich if I do that? Speed density...will it matter if both are disconnected? One at a time? What is the best method for this test?

Rich concerns me anyway as I think I have a slight exhaust leak somewhere upstream as when i let off the gas I tend to get a "pop" in the pipe from time to time...sometimes worse than other times.

 

I have also just installed a PCM For Less piggy back chip. Should have accounted for the long tubes, EGR/AIR being gone, etc. I pretty much gave them my setup and they were supposed to do what they could from there. I know mail order isn't the best, but it was better than nothing I figured.

 

Unplug both o2's and take it for a drive. It might run a little rich, but it's no biggie, just temporary. I get the popping as well, I have an exhaust leak somewhere. Mail order tune is fine for bolt-ons.

 

Last question then for now :-p If it does end up running better with the O2s out does that mean I need to buy Delco's? Put them further upstream in the headers on the pass side? Burn the car with gasoline to the ground? :-p

 

I would say all of the above.

Ok ok, just the first two.

 

Alright...I have to check out the vacuum and unplug the O2's and test still...going to do that in a few here, but I had a thought. What would it take to put heated O2s inline? I am pretty sure I have seen a thread on it before, but I can never find anything using the search. Can anyone link me to that thread or remember who started it and I can search by user name? Also, would a heated O2 help in this case you think being down line the way it is or would I have the same issue (if it is O2 of course) due to it being down line? I am thinking that if it is the O2 here, it is because of brand (Bosch instead of GM) and distance down line not getting enough/the right amount of heat. Any thoughts?

I will be back later after I check for vacuum leaks and unplug the O2s and take her for a drive. Just thought I would throw that out there and see what others thought.

 

http://shbox.com/1/heatedsensor2.jpg