Why does my Stealth keep killing ECUs?

**DK77** · 02-15-2016, 04:08 PM

I've got a 95 Stealth TT with lots of modifications which is going to make solving my problem conclusively a bit more difficult. I'll try to list any pertinent mods:

-Jester ECU w/ chrome
-Blackstealth 95>99 ECU wiring harness adapter
-Walbro 450 lph E85 compatible fuel pump
-HKS turbo timer
-Ninja performance fuel pump hotwire kit (relay triggered directly from MFI relay, stock fuel pump wiring disconnected)

What's happening is after running an ECU for a while (6 months to a year) the ECU's fuel pump circuits get destroyed and the ECU will no longer start the car. I know that is happening because I've sent my Jester ECU and a spare SL ECU to Adam and he's diagnosed (and fixed) the circuit. Once I knew that I re-did all the wiring for the fuel pump circuit and put in the Ninja kit. I also replaced the IAC since it was bad and I had assumed that the cause was either the IAC or the fuel pump circuit wiring being shorted. Well last weekend my other spare SL ECU stopped turning on the fuel pump.

Possible causes I'm already planning on looking into:
-Verify the turbo timer is wired correctly.
-Improve ECU grounding (any suggestions on how to do that?)
-Double check wiring for MFI relay and between MFI relay and ECU to ensure that nothing is allowing too much voltage into the ECU's fuel pump circuits.
-Replace MFI relay

**stealthee** · 02-15-2016, 04:58 PM

Now, I don't know if it is related but I can share a story that happened to me.

Long story as short as possible, one night out of the blue my car wouldn't start. After lots of diagnosis I found I was no longer getting power to the fuel pump, but I was getting power out of the MFI. In the end I ran a new wire from the MFI to the pump.

I'm not sure if that will help you in this situation or not. I doubt it from the sounds of your troubles, but I figured it was worth a shot.

**RealMcCoy** · 02-15-2016, 05:00 PM

Since the ECU simply grounds the relay, there's a pretty limited number of external issues that could kill that circuitry... I would pull the terminal out of the connector at the ECU, and ground it directly with an amp meter in line. Check that it isn't flowing enough current to overpower the circuitry. If no issues found there, I would use a meter with a min/max recall, and drive the car, cycle the starter etc. If nothing shows it face, I'd be pretty confident it was just bad luck with ECU's.

If Adam is confident that the failure was caused by overcurrent letting the smoke out, and you simply can't find anything, I would temporarily wire in a low current fuse, and continue to drive the car... Eventually it will pop the fuse, and hopefully give you a clue as to why.

**DK77** · 02-15-2016, 09:13 PM

Adam hasn't said that's certainly the cause, but considering I've had 3 ECUs now have the fuel pump circuit go bad, seems there must be something causing it.

I will do what you said. That all seems completely logical and more specific to my problem than me just fixing anything I can think of even if there isn't a problem (which I have done more than enough of with this car LOL).

**DK77** · 02-16-2016, 01:14 AM

Originally Posted by stealthee

Now, I don't know if it is related but I can share a story that happened to me.

Long story as short as possible, one night out of the blue my car wouldn't start. After lots of diagnosis I found I was no longer getting power to the fuel pump, but I was getting power out of the MFI. In the end I ran a new wire from the MFI to the pump.

I'm not sure if that will help you in this situation or not. I doubt it from the sounds of your troubles, but I figured it was worth a shot.

I've actually got a wire run from the MFI relay directly to the Ninja relay for the fuel pump. The mechanic that I had taken the car to when it fried one of my spare ECUs had run a wire from the MFI relay straight to the pump and with a Walbro 400lph pump that was not ideal LOL. It was only in for a couple weeks but it was melting at both ends.

I am going to try replacing the MFI relay because the car has been intermittent in whether it will start or not which is making me think I perhaps jumped the gun on my ECU having died. The reason I assumed that was the case is the only thing I changed from when it wouldn't start to when it did is swapping ECUs, but I'm starting to think something else is amiss. Perhaps my MFI relay was damaged before I rewired everything with the Ninja kit so I will replace the MFI relay (also I have a new one sitting around somewhere).

I'm still going to test out the ground for the MFI going to the ECU just to put my mind at ease.

**KeithMac** · 02-16-2016, 03:24 AM

It can only really be a fault in the MFI relay, all the transistor in the ecu does is ground the fuel pump coil inside the MFI.

You could fit a current limiting resistor in the fuel pump trigger line from the ecu to protect the circuit.

**Jesters Deadd** · 02-16-2016, 08:41 AM

Can you draw out your various forms of hot wire circuits? THis may help us figure out the issue.

**Chris@Rvengeperformance** · 02-16-2016, 10:00 AM

Originally Posted by DK77

I've actually got a wire run from the MFI relay directly to the Ninja relay for the fuel pump. The mechanic that I had taken the car to when it fried one of my spare ECUs had run a wire from the MFI relay straight to the pump and with a Walbro 400lph pump that was not ideal LOL. It was only in for a couple weeks but it was melting at both ends.

I am going to try replacing the MFI relay because the car has been intermittent in whether it will start or not which is making me think I perhaps jumped the gun on my ECU having died. The reason I assumed that was the case is the only thing I changed from when it wouldn't start to when it did is swapping ECUs, but I'm starting to think something else is amiss. Perhaps my MFI relay was damaged before I rewired everything with the Ninja kit so I will replace the MFI relay (also I have a new one sitting around somewhere).

I'm still going to test out the ground for the MFI going to the ECU just to put my mind at ease.

You completely bypassed or cut out the melted wire, right?

**DK77** · 02-16-2016, 02:02 PM

Originally Posted by Forest Gump

You completely bypassed or cut out the melted wire, right?

Replaced it. The new one is now the trigger wire for the Ninja relay that actually powers the fuel pump.

I'm going to replace the MFI relay this afternoon and I will verify how everything is wired and make sure I didn't screw something up when I installed the Ninja kit.

**futurevr4man** · 02-16-2016, 03:38 PM

If the turbo timer is wired in strange at all, they usually have adapter harnesses that are literally plug and play. You may just want to get one of those... they aren't expensive.