88 Town Car random misfire

[drhill]

Got a new daily driver 1988 Town Car, it had been sitting for a few years but was running when I got it, just not well. I did some work to it but still seem to have a random misfire. It's easiest to feel when I put the car in gear and give it a bit of throttle, miss is not consistent, it's random, a miss here or there and then smooth for a while then a another miss or three. Once I'm driving at speed or even just normally I hardly notice it, if it even misses at all. It runs terrible when cold missing badly under load and it takes a few tries to start it when it's cold. Starts right up when it's warm and most of the noticeable missing goes away.

I replaced spark plugs, cap and rotor, bench tested and cleaned the injectors, replaced the fuel filter and checked for vacuum leaks: fixed some broken plastic lines for the smog pump/egr control and a couple hoses under the intake. Currently it idles at about 19" of vacuum. I pulled codes and there were none, I checked it a couple times to make sure.

Any thoughts on what to check next? I thought I knew these motors pretty well but it's been a decade since I've had stock one to work on!

[gadget73]

What sort of shape are the plug wires in? Are they routed properly? Coil terminal isn't a crusty mess is it?

Maybe check it for codes, and measure the voltage or resistance on the air and coolant temp sensors to make sure one hasn't gone stupid.

http://www.grandmarq.net/oldfuelinjection/page10.html

[drhill]

What sort of shape are the plug wires in? Are they routed properly? Coil terminal isn't a crusty mess is it?

Maybe check it for codes, and measure the voltage or resistance on the air and coolant temp sensors to make sure one hasn't gone stupid.

http://www.grandmarq.net/oldfuelinjection/page10.html

wires look good, routing is not the best but I checked them all for possible ground paths etc, I will do that again at night in the dark. cleaned the coil terminal - no change. No codes at all, I did check that. I will also look at the Temp sensors and test them thx! Where is air charge temp sensor - I don't remember where that one is. i went back out to test it again, seemed a bit worse with some heat soak if that means anything? still cleans up and runs good with higher rpm and load

[gadget73]

ACT is in the lower intake just behind #5 injector

by no codes at all do you mean no codes at all, or no faults and you got an 11 ?

[drhill]

ACT is in the lower intake just behind #5 injector

by no codes at all do you mean no codes at all, or no faults and you got an 11 ?

Ah yes, I remember now. No faults, I got 11 for KOEO and KOER

[drhill]

https://youtu.be/IFlQxkp9iac

No sparks visible tonight from the plug wires, I also checked the fuel pressure and it appears to be normal a little over 30 at idle with FPR connected and about 42 or 43 psi with it disconnected and plugged. see attached video for what the miss feels like in gear

[sly]

Double check that all the spark wires are fully seated. I know I've had issues when changing out wires that the boots sometimes slip off and need to be reseated and will stay put then.

[gadget73]

random thought, pull the green vac line off the EGR and see if anything changes. I had issues with a sticky EGR reg once causing the valve to open full just off-idle and it did odd things.

[drhill]

random thought, pull the green vac line off the EGR and see if anything changes. I had issues with a sticky EGR reg once causing the valve to open full just off-idle and it did odd things.

Damn, the guru strikes again! I installed new plug wires and routed them as best as I could and it helped a bit. I unplugged the green vacuum line from the egr and problem is solved. So given that worked, what needs to be fixed/replaced since the green egr line fixed my issue?

BTW, you and Sly have been around forever on this site, I bought my first panther in like 2011 and you guys were well established way back then, how long have you guys been on here? Nevermind - I forgot I can see your join dates!

[DerekTheGreat]

Damn, the guru strikes again! I installed new plug wires and routed them as best as I could and it helped a bit. I unplugged the green vacuum line from the egr and problem is solved. So given that worked, what needs to be fixed/replaced since the green egr line fixed my issue?

BTW, you and Sly have been around forever on this site, I bought my first panther in like 2011 and you guys were well established way back then, how long have you guys been on here?

Hah, I'm going to try investigating EGR as an issue with the 5.8 in my truck as well.

I remember lurking around this site before I was a member and noticing sly and gadget73 were top posters who gave solid advice & tips. Then I remember that giddy feeling the first time either of them replied to my post or comment: "Yes! The gurus have spoken!" Very similar to, "Oooh! The Claw! It moved!"

[gadget73]

Its probably something goofy with the EVR. The solenoid on the fender that the other end of that green line goes to. Canned answer is a new one, but I fixed mine by taking the cap off, cleaning all the dust out from the disintegrated foam filter that used to live in there, and shooting some WD40 in each of the ports to flush it out. Worth a shot, otherwise it probably just needs to be replaced. Mine wasn't regulating, it was just going full open just off-idle which is what it sounds like yours is doing.

[drhill]

yeah, that makes sense. I'll clean it out first before getting a new one. Gotta get it through a smog test next week. Weird that it didn't throw a fault code

[gadget73]

it won't for this specific problem. Its not quite smart enough to verify that if it commanded say 20% open that the position sensor actually opened 20%. It just knows that it opened when told to and shut when told to and the position sensor was somewhere in the range that it was happy with.

[drhill]

So - bought a new EVR and installed it, car still misfires with it hooked up. not as badly as the original EVR but still missing. With it disconnected from EGR, runs perfectly no issues. Any thoughts?

[gadget73]

hm, sounds like the evr is passing vacuum to the egr when it shouldn't be.

the other thing I found that causes that is no VSS input for some completely baffling reason but that will set a code. If the cruise works its definitely got good VSS.