Misfire... another one (1 Viewer)

[3FOffroad]

Hey all, I’m chasing an engine misfire in my 97 80 series.

Misfire is coming after the truck has sat for a period of time and comes in right around 1800 rpm. Once I drive for some time, about 15 miles it goes away and doesn’t come back unless I park the truck overnight or for an extended period of time.

Problems:
- There are no codes and no check engine light. We hooked it up to a scan tool and monitored during this time and didn’t see anything.
- I have replaced EGR, Plugs, Wires, distributor, hoses.

Looking for some thoughts or ideas. At this point I’m guessing it is an injector so that is likely my next step but going to run some seafoam through it to see if I get any changes from that attempt. Thanks guys!

 

[Meckbot]

See if you can borrow a stethoscope from your local mechanic and take a listen to the injectors.

My misfire crept up and started intermittently then became permanent at cylinder 6. I went so far to replace my entire wiring harness and FP (while I was in there). Deleted my EGR as well and cleaned my MAF. Still happened.... until I took a listen and connected some other clues and realized the number 6 injector was stuck open. Was able to replace them with 4 hole injectors I had on hand and it fixed the issue.

Whats your harness look like? Have you checked the ECU? Cleaned the MAF?

 

[Rusty Marlin]

Sounds like oily plugs too. Did you notice any oil dripping down in the spark plug tubes when you changed them?

I would think seriously about changing that heater valve too. When they get that colour, they are a ticking time bomb.

 

[ppc]

I would think seriously about changing that heater valve too. When they get that colour, they are a ticking time bomb.

Agree and in addition all of those heater hoses look to be original, are swollen and need replacement.

 

[3FOffroad]

See if you can borrow a stethoscope from your local mechanic and take a listen to the injectors.

My misfire crept up and started intermittently then became permanent at cylinder 6. I went so far to replace my entire wiring harness and FP (while I was in there). Deleted my EGR as well and cleaned my MAF. Still happened.... until I took a listen and connected some other clues and realized the number 6 injector was stuck open. Was able to replace them with 4 hole injectors I had on hand and it fixed the issue.

Whats your harness look like? Have you checked the ECU? Cleaned the MAF?

Sounds like I have a lot of work to do. Thanks for the direction. I have a stethescope and will take a listen. Will also check the ECU, and the MAF.

 

[3FOffroad]

Sounds like oily plugs too. Did you notice any oil dripping down in the spark plug tubes when you changed them?

I would think seriously about changing that heater valve too. When they get that colour, they are a ticking time bomb.

View attachment 2519692

Sounds like oily plugs too. Did you notice any oil dripping down in the spark plug tubes when you changed them?

I would think seriously about changing that heater valve too. When they get that colour, they are a ticking time bomb.

View attachment 2519692

I am going to pull all the plugs and take a look. PO showed details of where they were changed just prior to my purchase but I’m finding other things that aren’t checking out. Good eye on the heater valve. I will add it to the list! Thanks!

 

[3FOffroad]

Agree and in addition all of those heater hoses look to be original, are swollen and need replacement.

I’m thinking you’re right! Thanks!