EFI Relay problems from hell

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Randoliof

Randoliof

10 Year
Joined
Aug 3, 2015
Threads
2
Messages
26
Location
Oregon
I'm new here, go easy on me.

I have a 91 FJ80, 3FE, yadda yadda. Starting about two weeks ago, I started having trouble with the truck starting, and staying started.

I eventually found out it was likely the EFI Relay. I replaced it, and the truck was happy for four days or so. The problem started again; truck would start, and then die like the key was being switched off. Start, drive around, truck sputters, then dies. I eventually ended up replacing the twelve gauge wires in the relay box with ten gauge, to no avail. I even jumped the hot and the ground to just continuously run power to the fuel pump, and it would occasionally start, but then it would die. Thing is, it will run fine for a day or two or a week, the give me huge issues, and I'm not sure what it could be now.
 
There is a plethora of information regarding the EFI system on a 3FE if you search a bit. You need to determine if this is an EFI issue or an ignition issue.
In a no-start situation is the CHECK ENGINE light illuminated when the key is in the ON position?
http://www.sdsysdesign.com/tlc/images/Strife/3FE EFI Diag.pdf
 
Jon, the only time a check engine light comes on is when the truck starts to sputter, or when it shuts off.

The fuel filter has been replaced. When it starts, it runs great. It's getting enough fuel
 
Randoliof said:
Jon, the only time a check engine light comes on is when the truck starts to sputter, or when it shuts off.

The fuel filter has been replaced. When it starts, it runs great. It's getting enough fuel
Click to expand...
Please read my question again. "In a no-start situation is the CHECK ENGINE light illuminated when the key is in the ON position?" That means when the engine is NOT running and you turn the key to the ON position (not START), does the CHECK ENGINE light come on?
 
Jon is trying to help you identify if it is the EFI or not. If you don't get a Check Engine Light when trying to start your truck then there is a problem with the EFI. If you get a CEL then it is somewhere else.

Nobody knows more than Jon Held about these vehicles. Listen to him and follow his guidance.
 
Jon, reading through some of the times you've helped other people with this, I've seen people mention just by passing the Relay. Can I bypass the relay with a single pole toggle switch, without burning my truck down? I would have to turn it off every time I shut the truck down, but I'm beginning to think that may be easier.
 
I wouldnt bypass the relay its there for a reason. I would start checking other parts of the system thoroughly. Like the fusable links and wiring harness. The links are connected to the battery and can give intermittent problems when they are going bad
 
While the EFI relay can cause untold grief (I have a ’91 and a ’92 and both within hours of purchase had EFI relay problems) the EFI relay is not always the guilty party. It is however one of the easiest cheapest things to throw money at and hope. Plus it never hurts to have a spare EFI relay. Rebuilding the wires and connections to the fuse block was probably a good thing too. And as you mention there are also the fusible links. Never hurts to replace them and have a set of spares, again easy and cheap.


However you have spent a lot of time messing around addressing just about everything that doesn't directly relate to your symptoms, “sputtering”. If the EFI relay dies the engine doesn’t sputter, it can’t as there is no spark. The EFI relay is basically the on/off switch for the ECU. If the ECU turns on the CEL with the key in the ON position the EFI relay is working. The sputtering is a big clue. Something is shutting down your fuel pump without shutting down the ignition or perhaps blocking fuel or airflow. Loose wire to fuel pump? Bad MAF sensor or sticky flap in the MAF (this got me just a week ago, flap locked up solid).

People listen to Jon Held and the other knowledgeable folks on the forum they will save you time and money.
 
Ok, so even with points two and 4 wired together, so the fuel pump should be getting power, the fusible links replaced, the truck won't start. With the key on, all lights are on, including CEL. Last night, it would crank, and crank, and crank, but when it would fire, the CEL would turn off, and the truck would run fine for a bit, then abruptly shut off. It has a new fuel filter. By sputtering, I meant that it would try to shut off, get fuel, start, try to shut off, etc. I'm at a total loss here.
 
OK, so you have eliminated the EFI control circuit, but that is only part of the equation. Like @SalishSea said, people will blame the EFI relay if the light in their refrigerator goes out.

What is the condition of the distributor cap and rotor?

You need to verify spark during the next no-start condition. This is either fuel delivery related or ignition related. You need to eliminate 1 possibility.

The fuel pump and the rest of the EFI circuits and sensors receive power from the EFI relay, but the fuel pump logic is controlled from the flap in the AFM which fires the second coil in the circuit opening relay which in turn powers the fuel pump. You can bypass all the fuel pump logic by shorting pins 1-8 (FP to B+) on the check connector mounted on the firewall below the wiper motor.
 
Jon, I realized that after I posted. The cap for my diagnosis port was missing, so I wasn't sure.

At any rate, I figured out that somewhere between the relay box and the fuel pump, I have a short. Tracing it now. Seems like it's shorting to the frame etc.
 
No, I'm not blowing any fuses. Maybe the connector on top of the fuel pump is loose, but I don't want to drop the tank unless I have to.

I had it towed to a friend's shop, and after bouncing around on the flat bed, I went to turn the key and show him that it cranked without starting, and of course it started right up. So after bouncing and jostling around it started. One thing I did forget to mention is that every once in a while, if I hit a speed bump, the truck would lose RPMs, act like it was shutting off, recover and go back to normal. Something somewhere must be loose, chafed, not sure.
 
did you check for integrity of the wiring harness at the EGR pipe ?
 
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