mcm95403

Hi Guys,

I'm posting in this section because my questions are specifically EFI related and I'm thinking those who hang out in here would have the best info.

I have a 91 with an odd problem. I recently did an ignition upgrade (cap/rotor/Taylors plugs) and had the cap break during install. Since then I've had a misfire condition. It gets worse when hot, and isn't there at all when dead cold. So far I've:

replaced the broken cap and rotor the next day, but there was an hour of drive time - this helped a lot

replaced my injectors with a set of Bosch III's from FIC - this helped a lot
also fixed some vacuum leaks at the same time

replaced the o2 sensor - not much improvement

since doing the injectors I've been able to re-add the wires - more improvement

replaced the igniton module in the distributor - again, helped more, but still missing

Today I replaced the fuel filter and did the throttle body bypass - again, it's running better, but still has the miss - although not nearly as much as before. I also pulled the AIS motor, cleaned it and the housing well - it idles much better now.

I tested the MAP sensor today and it appears to be good, but my questions concerning that and also the TPS is: can a digital VM really show an intermittent/worn contact area in these sensors? It seems that the meter doesn't respond quickly enough to show what is really going on.

I'm almost to the point where I think I should replace the MAP, TPS and IAT sensors just because they're all 20 years old. The car has no codes. I'm also wondering if it's possible that the broken cap could have let the MSD coil arc to the internal wiring and damage the computer and/or sensors. What do you guys think?

Prior to the ignition "upgrade" the car didn't show any signs of the misfire. Mileage per the dash was pretty steady at 23-24 @65 on a fairly level road. Seems like a similar cars get about 28 so I'm thinking that something electrical is still screwy.

Also, with all these fixes, the car pulls quite well at full throttle, although you can still feel a miss as the RPM's climb.

Pics of the cap damage:

mcm95403

http://forums.corvetteforum.com/c4-g...g-sensors.html

VenkmanP

What happens when you put the original parts back on? (i.e., take off the bad parts you installed)

mcm95403

It gets worse again.

jtc44

I agree that a DVOM can be to slow for a glitch. It might be worth the $ to find a shop that has a osscilloscope and have them check it out for you I got a pico scope and I am still learning it but these things are great for this. The TPS can be intermittent and a good shop can even give you a print out of this.

mcm95403

Yeah, I need to see who can do that for a reasonable price. I alreday replaced the TPS and MAP so that's 2 more down.

creekwalker

I had problem similar to yours. rough running. I changed every sensor.. still had problem..Finally checked fuel pump...a small piece of rubber fuel line at the top of fuel pump had small pin holes. Changed fuel line... ran perfect. 1984 model.

mcm95403

Thanks Cree, turned out in my case it was a bad (but brand new) spark plug. Changed it and it runs great now.