86 Fuel issue woes
Thread Starter
|
Tuned
Joined: Mar 2004
Posts: 274
Likes: 0
From: Fountain
86 Fuel issue woes
1986 5.0. Only 90k original miles. The truck will start run a little bit and then progressively start running worse until it dies. It will crank but not start. It seems like a fuel issue. The next morning it started and then the issue returned. Starting with ther easiest, I replaced the canister fuel filter and hooked up a fuel pressure gauge at the fuel rail. The reading was right in line. After idling for close to an hour the symptoms returned and the fuel pressure dropped until it died and would not start. So I replaced the high pressure pump. Thinking that I fixed the issue I took it for a drive and the same thing happened. AI said it could be the fuel pressure relay, but I cannot find one. I have hunted high and low, under the hood and the dash. Some wiring diagrams show that there is one and others do not show it. Any ideas?Thank you so much.
Mountain Pass
Joined: Jun 2022
Posts: 195
Likes: 77
From: SW Connecticut
A shot in the dark but after it idles and then dies, crack fuel cap. If you hear suction then the tank is not venting properly and slowly starving the engine of fuel. From there you can trace the problem to the charcoal filter thingy, the fuel pump return line, etc.
Moderator
Joined: Jan 2001
Posts: 56,995
Likes: 2,741
From: Virginia
He has a 86 5.0 so he has EFI (also because he has a pump on the frame) and yes he does have a low pressure lift pump in the tank. That would be a good place to look. Check the tank, they usually are not in very good shape, especially with all that old ethanol fuel sitting around in them. Sounds like this truck was not run very much so the fuel goes bad and ruins the sending unit and the pump in the tank.
Thread Starter
|
Tuned
Joined: Mar 2004
Posts: 274
Likes: 0
From: Fountain
I have been trouble shooting and i disconnected the fuel line before the high pressure pump and then i cranked the engine rhinking that the low pressure pump in the tanks would pump. Nothing on either tank. AI told me to look at the fuel selector valve. I can't find one.
Lead Driver
Joined: Jun 2013
Posts: 5,669
Likes: 1,160
From: Tolland, CT
So you have two fuel tanks.
you should have a reservoir on the frame rail under the driver seat. It should have 6 ports. It also has a filter in it. NAPA has the replacement filter.
the fuel pump relay is near the brake booster. Outboard near the hood hinge under that black cover.
one of the experts can help if it’s a selector issue.
there is a How too up top about those reservoirs. Not sure if it will help. But the experts have lots of info on those.
Also, that gas cap idea ^ is free.
you should have a reservoir on the frame rail under the driver seat. It should have 6 ports. It also has a filter in it. NAPA has the replacement filter.
the fuel pump relay is near the brake booster. Outboard near the hood hinge under that black cover.
one of the experts can help if it’s a selector issue.
there is a How too up top about those reservoirs. Not sure if it will help. But the experts have lots of info on those.
Also, that gas cap idea ^ is free.
Last edited by Max Capacity; Yesterday at 10:10 PM.
Lead Driver
Joined: Apr 2002
Posts: 5,339
Likes: 1,248
When you have in tank fuel pumps and dual tanks I think the pump comes on in the selected tank and pushes the valve to the engine open. As max said there may be filter reservoir down stream from the valve.
You can probably figure out what you have by following the fuel line from the tanks to the valve. Should be visible along the cross frames and rails. See this site:
https://www.garysgaragemahal.com/1986-evtm.html
You can probably figure out what you have by following the fuel line from the tanks to the valve. Should be visible along the cross frames and rails. See this site:
https://www.garysgaragemahal.com/1986-evtm.html
Thread
Thread Starter
Forum
Replies
Last Post
grantpage
1994.5 - 1997 7.3L Power Stroke Diesel
7
Mar 30, 2010 07:59 PM
BW Tibbetts
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
1
Apr 28, 2004 08:47 AM
