Do I have a bad ECU???

[ArcticCatJay]

I need some help with my 94 Talon TSI AWD.

I can't get it to run and I found out I wasn't getting fuel. I checked the fuel pump with the fuel pump check plug next to the battery, and the fuel pump works. Checked the MPI relay and also tried a different one, and still wouldn't start. MPI relay ok

My next test was to spray fuel into the throttle body, did that and it started up for a few seconds. It ran fine for those few seconds, so I have narrowed it down to a fuel problem. If the MPI relay is ok, i'm thinking its a bad ECU? Is this correct or can it be something else???

Also, the car is a 94 Turbo AWD with an EPROM ECU. If the ECU is bad, do i have to put an EPROM ECU back in it? Can I use any ECU from a 90-94 turbo AWD? The caps in the ECU look good and the ECU looks to be in good shape in general.

Can someone please help?!?!

 

[Colt4G63 also]

Ahhh... I did no know that the starter circuit also powered the fuel side of the MPI relay. I thought it only looked at the CAS to tell it when to kick on.

Great info here...

Yeah my starter is tempermental, but when it doesn't crank, my pump always kicks on.

 

[->PrOjEcTGS<-]

Yeah my starter is tempermental, but when it doesn't crank, my pump always kicks on.

Right on... Now that I look at the schematic again it makes more sense. Damn dotted lines....

My next question is a hypothetical.

What if the starter is cranking the engine over but pin 9 of the MPI relay doesn't get a signal from the starter relay to engage the fuel pump. Looking at the schematic, if the CAS is spinning and the ECU is getting a signal from that shouldn't it pull the coil down at pin 7 of the relay and engage the fuel pump? This is of course given the fact that all the rest of the wiring from the relay to check connector is good and the relay is getting power from IG1? If this is true, then he would have power to the relay and a signal from the ecu at pin 7 to close the relay and engage the pump. But, in his case it doesn't, so what are the chances that both the coils are bad in the relay. Slim... This should indicate a problem with power to the relay or a short in the harness.

OP, to troubleshoot this ^ I would pull the cover off of the MPI relay turn the key to the "RUN" position and manually engage the fuel side to see if your getting power from the relay to your pump. Then if it doesn't kick on when manually engaged I would then start checking for power at the relay via the pinouts mentioned by steve.

 

[steve]

My next question is a hypothetical.

What if the starter is cranking the engine over but pin 9 of the MPI relay doesn't get a signal from the starter relay to engage the fuel pump.

Looking at the schematic, if the CAS is spinning and the ECU is getting a signal from that shouldn't it pull the coil down at pin 7 of the relay and engage the fuel pump?

This is of course given the fact that all the rest of the wiring from the relay to check connector is good and the relay is getting power from IG1? If this is true, then he would have power to the relay and a signal from the ecu at pin 7 to close the relay and engage the pump. But, in his case it doesn't, so what are the chances that both the coils are bad in the relay. Slim... This should indicate a problem with power to the relay or a short in the harness.

Yes, If the engine is cranking and the ECU is getting CAS signals the ECU will pull pin 7 low to run the pump. I can't remember if the ECU gates any of this by the state of the ST input to the ECU or not.

I pretty much boiled the available information down to this point already. If the contacts were bad in the relay it could also cause this. So like I said there looks to be a fault in the power side.

OP, to troubleshoot this ^ I would pull the cover off of the MPI relay turn the key to the "RUN" position and manually engage the fuel side to see if your getting power from the relay to your pump. Then if it doesn't kick on when manually engaged I would then start checking for power at the relay via the pinouts mentioned by steve.

There is no reason to pull the cover off, just test the relay. You can here it click if it activates and you don't risk damaging it.

 

[->PrOjEcTGS<-]

Steve... You know, you're the one that keeps these damn cars running. Without you we'd all be driving Evos!!

 

[steve]

, I struggle just keeping mine running the way it should.

 

[->PrOjEcTGS<-]

, I struggle just keeping mine running the way it should.

That might be because you always have someone elses broken ECU in it...

 

[ArcticCatJay]

Well I have to concur with ProjectGS...Steve does keep these DSM's running for us and I have to give a huge plug for Steve right now...he has helped me out tremendously with my problems with my car. I have emailed him ALOT outside the forum and he was always willing to help me with great info!! thanks alot Steve, I couldn't have done all this without you.

Now on to an update. I check for continuity between pin 7 on the MPI relay and pin 56 and it was good. The next thing I did was to empty the truck and pull the cover plate out of the truck floor to expose the top of the fuel pump, and what did I find!!!??? I broken/burnt wire off the top of the fuel pump. There are 4 wires going to it...a yellow (which was good), a black with white tracer, which i'm pretty sure is the fuel pump check connector wire (this was good too) and 2 others, assuming both are for operation of the fuel pump itself. One of these was broken. This is probably what shorted and caused the ignition fuse to blow.

So now i'm in search of a new fuel pump, my question is which one do i need to get? I have a 94 Talon Turbo AWD 5-spd. Do I need one from an AWD turbo 5-spd??

thanks again for everyone's help!

 

[1990AWD]

If you need a fuel pump, you might as well go out and buy a Wally 190lph. They're only like $80 and then you have some room for upgrades.

 

[steve]

On a 1G AWD you should have four wires going to the pump assembly bulkhead.

The large black with white stripe is the power for the pump. (Pin 1)
The yellow wire is the fuel level signal. (Pin 2)
The large black wire is the ground for the pump and senders. (Pin 3)
The yellow with blue stripe is the low fuel warning light. (Pin 4)

 

[ArcticCatJay]

Steve, the one that is broken/burnt is the large black one (ground). I thought it would be the power wire that shorted out.

Would this wire being broekn cause my problem??, but yet still allow the pump to turn on at the fuel pump check connector??

One other question, do I have to drop the fuel tank to changed the fuel pump? Or will it come out through the hole in the trunk?

 

[donniekak]

On a 1 g awd the fuel pump comes out of the tank through the hole in the trunk.

 

[steve]

If you never have done a 1G AWD pump before, your in for a ride.

Don't try and disconnect the rubber fuel hose from the metal line to the pump. The nut on the fitting doesn't turn and the line is likely rusted to the point where any torque will twist it. Disconnect the other end under the car from the hard line running forward. Soak the mounting nuts with PB Blaster and try to remove as much rust as you can from them and the studs before attempting to loosen them.

I can't say if the ground being broken would act this way. If the pump wasn't getting any ground it wouldn't work at all. I'm guessing that it's grounding through the tank mounting right now. If you can find any unrusted part of the bolts holding the cover to reattach the wire and see if that helps.

I'm really expecting to hear that even after connecting it you still have the problem. I think there were several other checks I suggested to help diagnose this.

 

[ArcticCatJay]

I'm going to confirm which wire(s) are messed up on the pump. I remember one was broken off and another was loose.

I confirmed the resistance between pin 7 on the MPI and 56 on the ECU connector. And also these pins to ground. I have switched MPI relays and had the same results. I have also tested the MPI relay according to the tests in the service manuel and everything checks out.

Either way i have to replace the fuel pump because the connectors are loose and or broken. Everything is pretty rusty on the car since it has been sitting.

Steve, I received the ECU today. Everything looks great. Thanks again

 

[steve]

I confirmed the resistance between pin 7 on the MPI and 56 on the ECU connector.

I saw that.

And also these pins to ground.

Don't know what this means. If it means you grounded the pin and the relay activated and you saw voltage on pin 2, the check connector, and back by the fuel pump that would be good.

I have switched MPI relays and had the same results. I have also tested the MPI relay according to the tests in the service manual and everything checks out.

I really don't see many real failures of the MPI relay. I see lots of posts where people changed them and spent days messing with them but usually the problem is somewhere else.

Anyway as long as you have an assistant you should be able to test the whole thing now. I'd do that before you start messing with taking the pump out because there is a high risk your next post will be where can you get a replacement fuel pump assembly. Depending on what you find you may not need to touch it.

 

[->PrOjEcTGS<-]

there is a high risk your next post will be where can you get a replacement fuel pump assembly.

That or he'll be making a High $ purchase of AN fittings and SS hose to one of our various site supporting vendors.

 

[viprez586]

If you don't want to deal with the headache later... Just drop the tank. Run AN fittings with hose barb ends so you can still utilize the OEM lines by using pushlock hose + fittings.

That's what my latest project is anyway. Damn you rust! I'm only up to $66.70 for all the fittings so far (Feed and return).

 

[ArcticCatJay]

Ok so here is the update! It took me awhile, but with some help from my Dad and a little patience, my problem is fixed!!! The car is back up and running!

I needed to get the fuel pump out very carefully without breaking any nuts or studs. The car had been sitting for a few years so needless to say everything was pretty rusted. I cleaned off the top of the fuel pump as best I could, and began by spraying PB blaster and any other loosening juice we had in the garage on everything. We sprayed everything everyday for about 3-4 days before we even tried to get the nuts and the hose fitting off. We were able to get the fuel out with out screwing up anything!!

So now we had a broken power and ground wire and a broken neck out of the top where the fuel comes out. After searching the junkyards and finding that they were all worse then mine, my dad decided to fix it. I'm going to have to post pictures later so everyone can see this fix job!!

Anyway, we got everything fixed, put the fuel pump back in, and the car fired right up!!! It sat there are idled for about 30 minutes. Don't forget, the car hasn't run in about 4 years!! It was such a sweet sound!!

Thanks to everyone that helped me with all my questions, especially Steve. I couldn't have gotten through this problem without him!

 

[GooeyGus]

Sweet!!!

Dont you love that feeling? When you've been working on something forever, trying to get it figured out, and it fires up and runs fine??

Best feeling in the world, IMO.

 

[Red Alert]

Glad you got it fixed, lot's of good info in this thread

And I hope to have my Talon up and running in the next few days, can't wait to hear it run again!

 

[ArcticCatJay]

It was such a great feeling to hear it run again! My next project is working on the brakes. Everything is rusted from sitting so long. I worked on them a little bit so far, but I might have some seized calipers. I'm going to get the insurance put on it today and get the title transfered tomorrow!! I can't wait!!

 

[viprez586]

It was such a great feeling to hear it run again! My next project is working on the brakes. Everything is rusted from sitting so long. I worked on them a little bit so far, but I might have some seized calipers. I'm going to get the insurance put on it today and get the title transfered tomorrow!! I can't wait!!

Ha, you and me both. My car sat for 6 months while i got funding to rebuild my motor. Now that I'm driving it, warped rotors and poopy pads make stopping a scary experience.
I'm going with:
Hawk HPS pads ($87shipped from extreme psi)
Centric 2-piston semi-loaded calipers($50 each)
Centric premium rotors ($39 each)
Maybe SS lines as well.

I'm going to cut my rear rotors and sand the pads and hopefully i can save the rears. The fronts however are toast!