Too Rich

Reply Subscribe

Thread Tools

Search this Thread

Oct 18, 2003 | 07:30 PM

tfsullivan

Thread Starter

New User

Joined: Oct 2003

Posts: 8

Likes: 0

Too Rich

I'm having trouble with my EFI 302, 1986 F150 fuel to the engine. It is running extremely rich. It runs very rough at idle. I have a switch so that I can turn off the inline high pressure fuel pump. When the pump is off it runs smooth at idle but once it is loaded, like when I try to drive it, it stalls. I have replaced the fuel pressure regulator, the MAP sensor, and the TFI. Nothing has changed.
I don't understand how it can run with the fuel pump off (it never could before), and why it's running so rich. Rich to the point it's almost raw fuel coming out he pipe. I replace the spark plugs. The old ones were soaked in fuel.
In the past it would do this and I would turn off the igintion and restart it and it would be okay. The reason for the switch is that the pump would come on at will when the truck was not running and destroy the battery.
Help!

Oct 18, 2003 | 08:54 PM

f100beatertruck

Cargo Master

Joined: Apr 2003

Posts: 2,408

Likes: 5

From: Parkesburg PA

I'll assume that the ignition is up to snuff...

Two things that come to mind are the vacuum line to the fuel pressure regulator, and the return line from the regulator.

I have an '86 F150 EFI and mine was running slightly rich because of a crack in the vacuum line. After 17 years, these lines are brittle and it doesn't take much to break them (I found out the hard way...

)

Also if the return line is clogged then that would cause high fuel pressure and make it run rich. There is a test port on the drivers side of the fuel rail; it looks like a tire valve. Test the fuel pressure. It shoud be something like 38-40 psi. If it's high, then you have a bad regulator or a clogged return line.

There are a couple other things like bad O2 sensors or bad coolant temp sensors that would make the computer add fuel, but I'd start with the fuel pressure.

Hope that helps. I've been on a crash course with mine for running rich, and it was the cracked vacuum line.

Oct 18, 2003 | 09:02 PM

f100beatertruck

Cargo Master

Joined: Apr 2003

Posts: 2,408

Likes: 5

From: Parkesburg PA

Oh yeah, as for the fuel pump running on, it's the relay sticking. My Bronco used to do that. I had to tap the relay to get it to stop. I believe that Ford has an updated one that does have the same problem.

As for the truck running with the pump off, I'm guessing that you have really high fuel pressure in the rail and there is enough to keep it running for a while. See how long it runs like that. I'm sure it will die in a minute or so.

Also, I just re-read your message. Explain "the pump would come on at will"? You mean that in the middle of the night the pump would just turn on? Or did it just stay running after you shut the truck off? Could be a computer, but I'd still check the fuel pressure because that's a mechanical system that the computer has no control over (except pump on / off).

Oct 19, 2003 | 06:25 AM

tfsullivan

Thread Starter

New User

Joined: Oct 2003

Posts: 8

Likes: 0

The coolant temp sensor is bad but I don't think that is the big problem. I'm going to replace it. The pump does come on when the truck is parked. I've gone through a couple of batteries before I put in the switch. I replaced the TFI and rely but still don't trust it.
I replaced the fuel pressure regulator. The vacuum line is working. The truck does seem to have excessive fuel pressure. I haven't checked it with a pressure with a gage. Your explaination about why it runs without the pump, excessive fuel pressure, seems to be exactly what the problem is. It runs without the pump for different lengths of time, but now I think the time depends on how long I run it with the pump on.
The fuel pressure regulator doesn't have a return line so I'm guessing there is one somewhere else. Do you know where it is and where it goes?

Oct 19, 2003 | 11:04 AM

f100beatertruck

Cargo Master

Joined: Apr 2003

Posts: 2,408

Likes: 5

From: Parkesburg PA

I'm not sure where the line is on the truck, but it should go back to the tank. Maybe someone else out there can help? I'll see if I can find it on mine and tell you where it goes

One other thing that I thought of is that the fuel tank vent line may be clogged and the return fuel is pressurising the tank. Try running the truck with the gas cap off and see if it does the same thing. If it does I'd go back to the return line then the computer.

Oct 19, 2003 | 11:21 AM

f100beatertruck

Cargo Master

Joined: Apr 2003

Posts: 2,408

Likes: 5

From: Parkesburg PA

Spoke too soon on not knowing where the return line is... Here's a picture from the shop manual showing the return line. The manual is for 87-91, but 86 should be the same.

The return line should follow the main line back to the tank. It should be the smaller of the two.

Last edited by f100beatertruck; Oct 19, 2003 at 11:26 AM.

Oct 19, 2003 | 11:23 AM

tfsullivan

Thread Starter

New User

Joined: Oct 2003

Posts: 8

Likes: 0

I have two fuel tanks so I don't think the vent line is a problem. I'm going to replace the coolant sensor and check the fuel pressure and vacuum line on the regulator. I'll look for the return line. It has to be one of these things or a combination of them. The fuel pressure check should narrow it down.
Thanks for the help, I'll let you know how it turns out.