I have an 86 with a 2.8 that I recently removed the engine and transmission to replace the clutch and fix a few oil leaks. I have everything back together now, and it drives/shifts fine, but I believe I have a constant misfire on two of the front cylinders.

I verified this by pulling the plug wires off of the dist. with the engine running, and the engine sound didn't change.

It looks like I am getting spark to the cylinders - I verified the plug end of the wires are sparking, and I swapped a plug wire and spark plug with one that was firing with no change.

This leads me to believe that it may be a problem with an injector? I did have the injectors off to replace valve cover gaskets, but there definitely isn't an external leak, I double checked that.

I did have a bunch of wiring etc unplugged when I took the engine out - is it possible something could be unplugged? I verified that the injector connections are all plugged in and clean.

Could it be a ground missing?

What is the best way to check if an injector is working? Should I take two off and swap them to see if the misfire moves with the injector? Any ideas or troubleshooting advice would be greatly appreciated.

Thanks!!!

quote Originally posted by willyt: I verified this by pulling the plug wires off of the dist. with the engine running...

I hope you didn't do exactly what you posted... as that spark has to go somewhere... and can damage ignition components in the process.

For testing purposes, always ground a disconnected spark plug lead... rather than doing what you posted.

quote Originally posted by willyt: What is the best way to check if an injector is working?

I don't know if it's the "best" way, but you can use a mechanics stethoscope with the rod attached and touch/listen to each injector to make sure it's clicking.

[This message has been edited by Patrick (edited 08-15-2022).]

Haha I indeed did exactly what I posted. I read that I shouldn't a few minutes after posting the initial message.... oops.

I don't think I initially damaged anything by doing this, because the issue is still localized on two cylinders. However something may now fail prematurely because of damage caused - oh well.

The stethoscope is a good idea Patrick. I need to do some more reading on how to test/fix injectors if that is my issue.

Is there anything else I should be checking into besides spark plugs/wires (spark is definitely good @ dist.) and injectors?

Thanks

If it was three cylinders that appeared to not be firing, I'd suggest checking to make sure that one of the two injector fuses hadn't blown.

[This message has been edited by Patrick (edited 08-15-2022).]

It appeared to be only 2, but I did have the same thought. Both fuses were good.

If you haven't got one... get one!

Thanks Patrick for your responses. Here is my current plan, if anyone has a better order to narrow this down, feel free to chime in.

1. Listen with stethoscope to see if injectors are clicking.
2. Hook up noid light to check wiring at injectors
3. Double check spark with spark tester
4. Test injectors with 9v to listen for clicking
5. Check injectors with ohm meter
6. Swap 2 injectors and see if misfire moves

If none of these find my issue:
1. Check fuel pressure
2. Check timing
3. Roll the car outside and set it on fire

quote Originally posted by willyt: If none of these find my issue: 1. Check fuel pressure 2. Check timing 3. Roll the car outside and set it on fire

Maybe hold off on #3 ... but the first two are so easy that they'd be among the first of my basic tuneup/troubleshooting procedures.

FWIW, my experience with exactly the same problem on my 86 2.8 was the injectors. Messed and messed around with ignition- no joy. The mechanic in town went and disconnected the injectors one by one while running and found the injector with the problem. Here's the thing, I got myself an injector tester and found that the problem injector was the only one NOT leaking under pressure. I replaced all the injectors, problem solved; this was way before I knew injector cleaning was an option.

quote Originally posted by MarkS: FWIW, my experience with exactly the same problem on my 86 2.8 was the injectors. Messed and messed around with ignition- no joy. The mechanic in town went and disconnected the injectors one by one while running and found the injector with the problem. Here's the thing, I got myself an injector tester and found that the problem injector was the only one NOT leaking under pressure. I replaced all the injectors, problem solved; this was way before I knew injector cleaning was an option.

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,

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.

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.

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.

Thanks Mark. I hadn't thought of that. I'm going to try a few things tonight but that just might come in handy.

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.

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

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).]

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?

quote Originally posted by willyt: I checked timing and it looked good. Right at 10 degrees.

With ALDL jumper in place?

Yes sir

Man, at this point I’d look at the dist.. specifically the magnet, could be giving false or erratic trigger.

I just replaced the cap and rotor, what do you mean by the magnet? Any good way to check?

Just curious... but if you connect your timing light to the spark plug leads of cylinders that appear to be firing properly, and to the spark plug leads of cylinders that don't appear to be firing properly... do you see a steady flash in both situations... or do you see some irregularity in flashes with the "bad" cylinders?

I definitely saw irregularity in the cylinders that are firing correctly, let me check one that isn’t. Give me about 5 minutes here.

quote Originally posted by willyt: I definitely saw irregularity in the cylinders that are firing correctly...

That's weird. I would've thought those cylinders should've been rock steady.

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

Patrick, it’s hard to tell but it seems like there are more irregularities with cylinder 1. When I tile cylinder 1, it bounces around a bit but it averages around 10 degrees.

When I time cylinder 6(one of the bad ones) I see two timing marks, but they appear more steady. One around 0 one around 10.

Any thoughts?

I wasn't even concerned with the timing, I was more interested in simply how regular and/or steady the flash pulses were.

I don't understand why the flash pulses are all over the place... unless it's due to the idle speed fluctuating. I wonder if the flash pulses would be steadier on the "good" cylinders if you held the throttle open at say 2000 RPM. If so, then repeat with the "bad" cylinders and see if there's any difference. I'm trying to determine if you can "see" when the suspect cylinders aren't firing.

[EDIT] I was going with the "all or nothing" theory in regards to spark in the "bad" cylinders... but yes, I suppose it could also be a situation where for whatever reason the spark could still be occurring in all of the cylinders, albeit with very erratic timing... as PhatMax was suggesting.

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

Interesting, it probably is due to idle speed. Give me 5 I’ll see what I see

quote Originally posted by willyt: The other thing I just thought of was when I rev the motor, the mark moves, like spark is advancing. Shouldn’t it hold steady if the ALDL is jumped?

I'm not 100% sure.

Just to cover all bases, is your jumper connecting the Diagnostic and Ground terminals? Keep in mind that your ALDL port could be flipped over.

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

Yes sir it is. Does the flashing at half speed mean anything to you? Wouldn’t this cause my misfire?

quote Originally posted by willyt: Cylinder 6 appears to be flashing at 1/2 or 1/4 speed. The flashes are easily distinguishable. Any thoughts?

That's what I was suspecting would be the case, but maybe an ignition expert could chime in now!

Do you know anyone local you can borrow known good ignition components from?

Oh boy, if Patrick doesn’t know what to do then I’m really out of luck

I don’t know anyone I can borrow from, but I am miles ahead of where I was. I appreciate the help, I’ll do some research and see what I can find

quote Originally posted by willyt: Oh boy, if Patrick doesn’t know what to do then I’m really out of luck

Oh man, I'm no expert with these cars. I know a little bit about a lot of things. There are plenty of members here who know a heckuva lot more than I do on specific issues.

The magnet is just above the pickup coil. It’s sandwiched between two plates. If it’s cracked it will cause a miss. I know for a fact as I had a friend with an 86 that ran like crap…they changed, exhaust….thought it was a clogged cat, cap, rotor, wires, plugs.a bunch of sensors…..finally on a whim bought a new dist….and it ran like new. The one that Cardone now has is updated and should alleviate the problem.
As the magnet spins it will cause a break in the voltage present in the pickup coil…..that is what causes the ICM to fire. If the magnet is all cracked you will have all kinds of false triggers …or no trigger at all.

Okay I played around with the timing light a little more and it looks like when I wiggle the pickup around it changes the frequency at which it flashes. I don’t think the misfiring cylinders are actually doing anything different.

Got a code 34, working on that now.