A bit of a weird issue ive encountered with my 93 FD. Whenever I turn the ignition on, all 4 injectors open up 100% and just dump fuel into the motor, you can audibly hear it and I can watch the fuel pressure guage drop very fast. They arent firing/cycling like normal they are just wide open. I tested the injectors and none of them are stuck open, all resistance values are within spec, I completely rewired and ran a dedicated harness from the Power FC to the injectors assuming there was a short to ground, that didnt work, I tried putting a known good Power FC in on the off chance the computer was bad and that still didnt fix the issue. The tune that is on there right now was running normally before this. Im having trouble finding anything that might be useful in the OEM wiring daigrams. To my knowledge the injectors are ground switch activated through the Power FC. Im really not too sure where to go from here, any help would be greatly appreciated.

 

Is the TPS signalling WOT?

 

Based on what you described, an internal short is the only explanation but that doesn't work unless the injector body is somehow continuous with ground..... but that would be crazy.

The injector circuit doesn't go anywhere but the ecu. Building that separate harness was genius troubleshooting. It not working is the clue to a solution but I'm not sure exactly what. The ecu pulses the ground to fire the injector. The only way an injector can fire is if it's getting a ground from somewhere since one pin is constant 12v.

I would suggest chasing the ground side of the circuit. See if you have continuity from the injector pin to ground. It would be SUPER strange if you did but to me, it's the only thing that makes sense since you tried a different ecu AND built a sub harness. Excellent approach so far, you're doing great.

 

Was you injector harness the whole way from injector to ECU? It sounds like a rub through on something.

 

Thats something i havent thought about but even if the TPS is at WOT, it still shouldnt spray fuel with KOEO right?

 

Yeah thats where my brain is having trouble with this issue. Ill go test the injector pins to ground thats a good thought but based on how they are acting it kinda seems like the only logical thing, especially after putting a whole other Power FC in and rewiring. I appreciate the help I love this community thank you!

 

Yes, I depinned the ecu connector and ran a seperate harness all the way to the injectors to completely remove any possibility of rub through or shorts.

 

Swap in a different TPS?

 

What about the tps has you connecting it with the injectors staying on?

 

If the TPS is stuck in the full open throttle position what is the ecu telling the injectors to do?

 

Reading the TPS position on the Power FC commander is a fairly easy step. If for some reason the TPS is always sending a full open signal, it should show up on the commander.

 

The power fc does not have a flood clear mode

regardless of tps position, there is no KEY ON circumstance that tells the injectors to lock OPEN

If the power fc did have a flood clear mode then it would keep the injectors CLOSED, not open

Im not sure what you're asking.....

 

Redbul mentioned the TPS I didn’t quote his post correctly though

 

Yes I agree with you the TPS should have no buisness in the injector issue. I did test the injector pins for continuity to ground and there is no issue there, I’m going to go over the tune and make sure I didn’t make a dumb mistake somewhere by accident

 

The entire problem with the injectors is with the key on, engine OFF, they are spraying wide open

 

Well maybe not full WOT, a la flood clearing, but pretty much WOT.

1. OP ran a wire direct to the injectors, they stayed open
2. OP put in another ecu, injectors stayed open

So what is telling the ecu to tell the injectors to stay open?

I have not heard of this happening with a TPS. But failing TPS are quite common. The insides of the TPS looks very fragile and the TPS is in a vulnerable position to getting knocked about, say when people are repeatedly removing the UIM.

Just a simple thing to check , if nothing else seems to be explaiing what is happening.

I guess you have ruled out the injector o-rings are leaking badly?

Is the FPR working? If the FPR is closed, say for lack of vacuum, it would increase back pressure to the injectors, making leaking o-rings worse.

 

Just a shot in the dark but unplug the injectors and see if they still spray. Maybe the issue is the o rings INSIDE the rail. Fuel will flow past a side feed and go directly into the motor if the o ring(s) on the injector go bad. Never seen it but you have a weird circumstance. The issue may be mechanical and not electrical.

 

Does the ecu start to prime the injectors, i.e. run the fuel pump, once the key is turned, immediately prior to firing?

Normally the fuel would flow back to the gas tank. But if the FPR is closed, that route is shut off.

While you are in there check your fuel pulsation damper. Is the little rubber plug intact? Likely good to replace the FPD with new.

 

What I have read just now is the ecu sets up a base injection amount based on maybe three inputs. It then adjusts the injection amount from inputs from other sensors, etc., including the TPS.

 

the injectors are not commanded to do anything prior to an rpm signal. The pump does prime with key on but that circuit is in no way related to injectors operating.

 

When the pump primes would leaky injectors leak at that stage.

 

At the pintle for both top and side feed and for side feed only, the lower o ring. They can fail and fuel will bypass the injector entirely and just leak out between the rail and the injector body. Typically a drip causing random misfires but with a full blown failure it can drain the rail.

 

So would such leak mimic the "injectors spraying wide open"?

 

This is something we suspected for my car, because it seemed to reflood after a deflood, before we could restart the car.

 

If this is a PowerFC, I've had one fail and do the same thing. See if you can borrow an ECU stock or another PowerFC before you start chasing something that may be a bad board in the computer