Miss fire help

[Danny G]

I might have to walk it back, it may have been the misfire sound I was hearing after listening to some audio.

[Gary Lewis]

There are several sounds, like misfire, backfire, pinging, and detonation that one might hear. But a misfire is when the wrong cylinder fires, and that usually causes a bang in the intake as the intake valve is frequently open then.

A ping, which is a mild form of, or the precursor to, detonation is a mild tinny sound. And it’s big brother detonation is a clatter. But neither will be a one-time occurrence.  Instead, they usually continue as long as you keep the throttle at the same position or shift gears.

[Danny G]

Gary Lewis wrote

There are several sounds, like misfire, backfire, pinging, and detonation that one might hear. But a misfire is when the wrong cylinder fires, and that usually causes a bang in the intake as the intake valve is frequently open then.

A ping, which is a mild form of, or the precursor to, detonation is a mild tinny sound. And it’s big brother detonation is a clatter. But neither will be a one-time occurrence.  Instead, they usually continue as long as you keep the throttle at the same position or shift gears.

I really love this site, getting more educated on the mechanical stuff every day. That also gives me some insight to my sister in laws issues after throwing a random misfire code. I think she may have some valve lash(clearance?) issues typical for her 99 CR-V. I did a quick compression test and got 170-155-155-170 across the cylinders, need to drive it a bit and try again. I wish I had a leak down test set to play with and learn how to use, my understanding is this is a more accurate tool for diagnosing issues. But her engine is making a good bit of noise, combination of a rattle can and a knock like it wants to be a little diesel.

Back to the 4.9l if it is not throwing the code for a misfire but sounds like it I was told you could ground the spark plug wire to ground cylinder by cylinder and listen to for that cylinder to misfire, if it doesn't that is the suspect cylinder. Not 100% sure how to ground it out, at the distributor? Moving on to using a spark plug tester to look for good spark, then fuel, then compression.

[Gary Lewis]

Glad you like the site!  

On pulling a plug wire, I wouldn’t truly ground it. Instead I’d pull the plug wire and slip a plug in it, and then ground the side of the plug to the block. That way the ignition system isn’t working into a dead short, but is jumping across a plug just like it should.

[Danny G]

Ok got the van today and it's home. On the drive home it felt like it was jerking here and there. Losts of pulsing in the brakes and abs light came on. The parking brake seems a bit funky and may have been partially engaged.

Didnt lack power had no problem speeding off when needed.


Took a picture of the door tag. H9? I think that is a limited slip rear end with 3.55 gears. If so that's another bonus as mine does not have a limited slip rear.

[Danny G]

[ArdWrknTrk]

Vans have a different track width and spring perch/frame width than trucks.
If it's the same type of rear, you might be able to swap the R&P, and carrier over, but I don't know if your axles have the same spline.

[Danny G]

ArdWrknTrk wrote

Vans have a different track width and spring perch/frame width than trucks.
If it's the same type of rear, you might be able to swap the R&P, and carrier over, but I don't know if your axles have the same spline.

Well shoot, ok, ill be saving the tires then at least has 235/75-r15s just like the truck. I guess the only way to tell when I get to that point is to tear open that 8.8 and see whats there. Feels like it may be missing. Also looked like a spot of oil under the trans, need to get under it to make sure it isn't leaking anywhere. It has been sitting for a good while the 30 mile trip home is the farthest it has run in years. I'll probably start digging into it this weekend when I have some free time and see if I can get  the misfire sorted. Still waiting on parts from RA to fix my sister in laws misfire issue (found some plug boots with what looks like cracking in them after I adjusted the valves).

[ArdWrknTrk]

The tag on the pumpkin will have a L between the ratio numbers if it's limited slip.

i.e.:. 3L55
lots less messy than opening it up.

[Danny G]

ArdWrknTrk wrote

The tag on the pumpkin will have a L between the ratio numbers if it's limited slip.

i.e.:. 3L55
lots less messy than opening it up.

Very True, may not even be worth bothering looks like if only the gear set may be interchangeable, seeing as I cant swap the axles as they are too long. Especially since it has over 300k on the odometer, 400k (OD issue?) per the PO.

Gary, did you happen to find that EVTM for the vans?

[Gary Lewis]

TheScatch wrote

Gary, did you happen to find that EVTM for the vans?

Unfortunately I don't have an EVTM that covers the vans.  Sorry.

It is possible that the wiring is the same but just the length of the wires and the placement of the parts is different.  So if you want to look at some of the pages let me know.  I could post some and you could see.

[Danny G]

I appreciate it, picked up a haynes manual, I know it will have some schematics in it. I would think the wiring should be the same with the trucks, just length and ground wire locations different.

[Gary Lewis]

What "system" would be most helpful?

[Danny G]

Ignition/vacuum if you have it should help me hammer a few things out.

The misfire does not seem to be constant so, thinking about making a smoker to check for vac leaks.

Will do a KOER test/cylinder balance test today to see if it gives me any codes that the KOEO didn't.

After that planning on checking plugs first to see if there is any indication of whats going on, do a compression test at the same time. Leak down test kit comes in today as well. Wires, ignition coil and TFI are on that list as well. Between this and my sister in laws 99 Honda I'm getting some good misfire troubleshooting practice.

[Gary Lewis]

Well, I'm not sure I can help you.  The EVTM I have is a '96 and the only wiring diagrams it has for anything smaller than a 460 is for EEC-V with MAF and sequential injection.  Yours should be speed density and bank fire.  So, do you still want the diagrams?

[85lebaront2]

Gary, who has a 1986 EVTM?

[Gary Lewis]

Bill - We do on the site, thanks to you.  But the 300 six wasn't EEC-IV then.  Are you suggesting he use the 5.0L wiring for EEC in the '86 EVTM?

[Danny G]

It's ok Gary thanks for looking. Ill wait for the manual to get in and pull schematics from it.

[Danny G]

Gary Lewis wrote

Bill - We do on the site, thanks to you.  But the 300 six wasn't EEC-IV then.  Are you suggesting he use the 5.0L wiring for EEC in the '86 EVTM?

What computer is in a 86 with 300?

[85lebaront2]

Gary, the FBC 300 in 1986 was EEC-IV, earlier models used an MCU, look at the pinout pages.