86 SE 2.8 - Misfire on 2 front cylinders (Page 2/5)
MarkS AUG 17, 11:12 AM

quote
Originally posted by willyt:


Thanks for the reply. I agree the injectors seem like the most likely cause of my problem. The weird thing is I had so many things apart, it would make more sense to me if something was just put back together wrong - Swapped wires, missing ground, something unplugged, but I can't seem to find anything like that. I'll do some more work this weekend and see what I can find.

Mark, when you say you got yourself an injector tester, what are you referring to?

Thanks,



Something I bought locally, I've used it once . I'll have to dig it out when I get home tonight, this was ~ 1997 so I'm a little sketchy on the details.
willyt AUG 17, 12:10 PM

quote
Originally posted by MarkS:


Something I bought locally, I've used it once . I'll have to dig it out when I get home tonight, this was ~ 1997 so I'm a little sketchy on the details.



I don't blame you, that was before I was born

Can't go work on it until this weekend, and want to drive it home this weekend, so I'm trying to get all of my ducks in a row before Friday...

I'm planning on picking up a set of noid lights but I'll do some more research on other ways to test tonight.
MarkS AUG 19, 08:18 AM

quote
Originally posted by MarkS:


Something I bought locally, I've used it once . I'll have to dig it out when I get home tonight, this was ~ 1997 so I'm a little sketchy on the details.



What I have is essentially an Actron fuel pressure gauge and switch cable that allows you to turn on one injector at a time noting the pressure gauge. But as I think about it, really isn't how I determined the issue. Again, it's a 25 year old memory- however I seem to remember taking off the upper plenum, pulling out the fuel rail with the injectors & fuel line still attached, briefly turning on the ignition so the pump comes on to pressurize the rail then noting that 5 of 6 injectors were leaking.
willyt AUG 19, 08:53 AM
Thanks Mark. I hadn't thought of that. I'm going to try a few things tonight but that just might come in handy.
willyt AUG 19, 07:52 PM
Okay I just tested my fuel pressure, it’s at 43 with the car off, but leaks down to 20 in a few minutes. This makes me believe that there is a leak somewhere.

I just did what Mark suggested and pulled the fuel rail/injectors to find the leak, but all of the injectors are dry.

This leads me to believe it’s the cold start injector. Could this really cause only two cylinders to misfire?
Patrick AUG 19, 08:08 PM

quote
Originally posted by willyt:

...all of the injectors are dry. This leads me to believe it’s the cold start injector.



Or the short length of flexible hose in the tank is split/leaking.
willyt AUG 19, 08:25 PM
Hmmm could be. But I wouldn’t think that would cause two specific cylinders to misfire would it?
willyt AUG 19, 10:22 PM
Okay here is where I am at:

Misfire on front right and left cylinders (not sure which numbers these are)

Fuel pressure is good but drops too quick. I checked all 6 injectors for leaks and there were none. Checked vacuum line at pressure regulator, no fuel in it. Could be CSV or hose that Patrick mentioned, but I wouldn’t think either of these would cause a consistent misfire on these two cylinders.

Double checked spark - good

Checked injector signal with noid light - good

I have the intake manifold off so tomorrow I will check timing and listen for the injector clicking.

I don’t know what else to check. I had the motor out so I am expecting something I hooked up wrong or forgot to hook up.

Could a timing issue or vacuum leak or egr valve leak/intake manifold leak cause a misfire on two specific cylinders?

Because I have the misfire at specific cylinders it seems like it would be spark or injectors, does anyone else think different?

I’m starting to run out of ideas so any advice would be greatly appreciated.

Thanks for all the help so far
Patrick AUG 20, 12:00 AM

quote
Originally posted by willyt:

Hmmm could be. But I wouldn’t think that would cause two specific cylinders to misfire would it?



No, I never suggested it would.

I mentioned checking fuel pressure and ignition timing earlier as they are both so basic (and relatively easy to do). You want to eliminate as many variables as possible.

I should also mention that a leaking fuel pressure regulator diaphragm could cause fuel pressure to rapidly drop.

If you're getting spark which is able to snap across a 1/4" gap at each cylinder (you've checked, right?), then it's probably an injector problem... but have you tested the compression of the non-firing cylinders?

[This message has been edited by Patrick (edited 08-20-2022).]

willyt AUG 20, 02:05 PM
I swapped two injectors this morning and the misfire stayed where it was. Checked spark again, this time with a spark tester, it lit up just like a good cylinder.

I blocked off the EGR valve and the car ran better, but still misfiring.

I checked timing and it looked good. Right at 10 degrees.

I haven’t checked compression, but if the car ran great before there’s almost no way compression could be my issue right?

Anyone have any ideas?