1991 LC80 3FE stalls at high speed (1 Viewer)

[drpotatoez]

Read the entire document and pay attention to item #10 on the list.

General Tech - 3FE Tune Up Info

3FE Tune Up Info

forum.ih8mud.com

Latest update.

Fixed the previous issue by
fixing wires going to the distributor, they were peeled and touching.
Changed MAF to a cardone remanufactured, this resulted in the trucking running leaner than with oem ( no more black soot everywhere)

Replaced dizzy and cap
Replaced ignition wires
Cleaned intake
Replaced fuel injectors

The truck runa great and accelerates like never before with no issues. Can actually reach 70 mph with 35s on stock gearing



NEW ISSUE:

When I go uphill for extended periods, where I’m jumping between 1st and 2nd gear alot, basically a lot of load on the truck, it will start cutting off. No check engine light or anything pops up. I press the accelerator and the truck would want to die. I have to. Keep it below 1500 rpm for it to not stall out. When this happens, even in neutral it will not accelerate past 3k rpm.

When it finally stalls, it won’t start right away. I replaced the efi main relay with the plastic one and the issue persists. It’s only after I wait around 5 minutes the truck will start right away and accelerate properly, all for it to begin the stalling again after 2-3 minutes.

The next day it will start with no issue and run without issue on flat ground. Only when I go up the mountain and really put a load on her she will start having problems.

I have attached a video of what it does. And by the way, it does the same with stock VAF and cardone remanufactured one. Also, no diagnostic codes

Could this be the ICM??

 

[jonheld]

Have you changed the pre-filter on the fuel pump?

 

[drpotatoez]

Have you changed the pre-filter on the fuel pump?

No, have not changed that yet. The mechanic did check the fuel pressure and it was high. Like a firefighter hose.

What I don’t understand is if I use the truck around town, no hill or anything where Im accelerating a lot, it will run perfectly.

Only when I go up the mountains it will start failing and when I go back on flat grounds, the issue persists unless I leave the truck off for various hours.

 

[drpotatoez]

This is a video of me with the accelerator fully pressed down after doing a short hill climb


This is a video of the truck accelerating good even hitting rev limiter AFTER resting it for 5 or so minutes. After 5 minutes it doesn’t hesitate to start or accelerate until it starts failing again down the road

 

[jonheld]

No, have not changed that yet. The mechanic did check the fuel pressure and it was high. Like a firefighter hose.

What I don’t understand is if I use the truck around town, no hill or anything where Im accelerating a lot, it will run perfectly.

Only when I go up the mountains it will start failing and when I go back on flat grounds, the issue persists unless I leave the truck off for various hours.

The pre-filter is typically a 100K mile item. When it becomes clogged, it will collapse on itself, blocking the intake of the pump. This usually happens after the fuel has warmed in the tank and under load.
What does "high like a firefighter hose" mean? There's a specification in the FSM for fuel pressure. It is given in PSI, not analogies. Please be specific.

 

[drpotatoez]

The pre-filter is typically a 100K mile item. When it becomes clogged, it will collapse on itself, blocking the intake of the pump. This usually happens after the fuel has warmed in the tank and under load.
What does "high like a firefighter hose" mean? There's a specification in the FSM for fuel pressure. It is given in PSI, not analogies. Please be specific.

 

[drpotatoez]

View attachment 3569890View attachment 3569891

Took out the fuel pump and this is how I found it. Ordered a replacement pre-filter. Will replace this pre-filter first and then the fuel filter on the frame rail when the part arrives. Hopefully this will resolve this issue

 

[jonheld]

Took out the fuel pump and this is how I found it. Ordered a replacement pre-filter. Will replace this pre-filter first and then the fuel filter on the frame rail when the part arrives. Hopefully this will resolve this issue

Yea, I would say that is way past its lifespan. New pre filters are white. You're going to want a new metal clip for the filter. Part number in the picture.

 

[drpotatoez]

Yea, I would say that is way past its lifespan. New pre filters are white. You're going to want a new metal clip for the filter. Part number in the picture.

View attachment 3570012

replaced the filter, it’s running good without any hiccup. Will tests on the mountains later tonight and update

 

[jonheld]

replaced the filter, it’s running good without any hiccup. Will tests on the mountains later tonight and update

I would replace the in line fuel filter before calling it good. It's 30 years old and doesn't owe you any more.

 

[drpotatoez]

I would replace the in line fuel filter before calling it good. It's 30 years old and doesn't owe you any more.

Yes, I’m currently waiting for the inline filter to arrive in the mail. Unfortunately here to the dominican republic does take a bit of time but thank you so much for the insight, this was driving nuts

 

[drpotatoez]

 

[drpotatoez]

I can say that changing the pre-filter has fixed this issue! Thank you Jon!