Fuel pump issue, this one is complicated - Help me pls.
05-16-2016, 10:49 PM
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Fuel pump issue, this one is complicated - Help me pls.
Ok so to start my car is running megasquirt, which may or may not be the probelm here but I wanted to preface the information I am going to share with you that the cars wiring harness, to my knowledge, is intact but I am not running a DME or KLR computer. I do have my alarm system jumpered per the factory manuals instructions, my ECU turns on(DME primary relay working) but no fuel pump power during cranking.
So my car wont start
. It will start if I jumper the fuel pump as the previous owner did and as was done when I purchased the car from him. The pump was jumpered such that as soon as the DME got power the fuel pump would kick on and stay on. It was done by jumpering switched 12V power from the headlight relay directly to the fuel pump power line underneath the central electric. This was obviously dangerous and how I got here to you now. Here is what I know to be true.
1.The pump is good - I can jumper pin 30 and 87b and voila, he pump is on, this is also how the pump was jumpered.
2.My DME relay is good - Its brand new, I bought a new one to rule this out. Both have been tested via clarks garage method.
3. I know fuel pump is not getting power during cranking, tested both at the fuel pump fuse (#34) which should have had 12v across it during cranking to prime the pump & at the turbo water pump pin 7 which is also fed off the same wire.
4. I tested my ECU's grounding circuit for the fuel pump. For MS guys out there that would be DB37 pin 37, which I have directly wired up to DME pin 20(pin 85b on DME relay).
5. I traced pin 20 on the DME relay through the firewall to the 12 pin connector in front of the firewall near the brake booster (Pin 5) and get continuity. I traced pin 5 on the 12 pin connector to Block N pin 43 of the central electric box, continuity again. Then N43 to M13, a yellow and black jumper wire in ran from M13 to M42 where I assume it goes through the central electric box to Pin 85b on the DME relay. I also tested from Pin 85b directly back to DME pin 20....All continuity.
So this leaves me scratching my head....the pump works, The relay works, the wires all trace out and I am pretty sure that my fp ground is working as well....so why am I not getting any fuel. I have a sneaking suspicion its my aftermarket ECU ground and I plan to go through it further, my hope is that someone on the forums here can tell me if I am missing something on the porsche side of things.
Some additional information, I have no turbo waterpump installed (aftermarket turbo) and an aftermarket WB02 sensor, so the other items on my fuel pumps power circuit cannot be used to troubleshoot...
Thank you all.
So my car wont start
. It will start if I jumper the fuel pump as the previous owner did and as was done when I purchased the car from him. The pump was jumpered such that as soon as the DME got power the fuel pump would kick on and stay on. It was done by jumpering switched 12V power from the headlight relay directly to the fuel pump power line underneath the central electric. This was obviously dangerous and how I got here to you now. Here is what I know to be true.1.The pump is good - I can jumper pin 30 and 87b and voila, he pump is on, this is also how the pump was jumpered.
2.My DME relay is good - Its brand new, I bought a new one to rule this out. Both have been tested via clarks garage method.
3. I know fuel pump is not getting power during cranking, tested both at the fuel pump fuse (#34) which should have had 12v across it during cranking to prime the pump & at the turbo water pump pin 7 which is also fed off the same wire.
4. I tested my ECU's grounding circuit for the fuel pump. For MS guys out there that would be DB37 pin 37, which I have directly wired up to DME pin 20(pin 85b on DME relay).
5. I traced pin 20 on the DME relay through the firewall to the 12 pin connector in front of the firewall near the brake booster (Pin 5) and get continuity. I traced pin 5 on the 12 pin connector to Block N pin 43 of the central electric box, continuity again. Then N43 to M13, a yellow and black jumper wire in ran from M13 to M42 where I assume it goes through the central electric box to Pin 85b on the DME relay. I also tested from Pin 85b directly back to DME pin 20....All continuity.
So this leaves me scratching my head....the pump works, The relay works, the wires all trace out and I am pretty sure that my fp ground is working as well....so why am I not getting any fuel. I have a sneaking suspicion its my aftermarket ECU ground and I plan to go through it further, my hope is that someone on the forums here can tell me if I am missing something on the porsche side of things.
Some additional information, I have no turbo waterpump installed (aftermarket turbo) and an aftermarket WB02 sensor, so the other items on my fuel pumps power circuit cannot be used to troubleshoot...
Thank you all.
05-16-2016, 11:00 PM
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Does your FP ground from MS (pin 37) ground out when you are cranking? That's the first place I would start. It needs to see a tach signal...possible that it's too weak during cranking. What are you using for a crank pickup? Another MS user here.
05-17-2016, 10:52 PM
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I Fixed it!
Hey Michael, nice to hear from you again. Thanks for the advice, I started exactly where you told me to and it led me to getting the car running
I tested the grounding pin (MS37) at the DME relay pin 9 (85b), no dice. So I started back testing each connection from the DME pin 20 to the DME relay pin 9. I started at the 12 pin connector pin 5, continuity. Then from DME Pin20 to N43, continuity. Then to the jumper between M13 to M42, all good. From M42 to the DME Relay Pin 9, no go. So I found the issue. The internal trace that runs from M42 to the DME Relay Pin 9 is the issue.
I soldered a wire onto Pin 9 on the DME relay and then used a wire tap onto the Jumper between M13 and M42, the pump primes and the motor starts. I even managed to street tune a bit tonight. All that being said, this means that my Central Electric box is damaged internally which stinks. It makes sense to me now why the previous owner had the DME relay jumpered to run the fuel pump.
This also may explain some of the other strange issues I have been experiencing. For example my brake lights stay on for 5-10 seconds after I let my foot off the pedal and my wipers will not return home, nor will my intermittent wipers work. I had planned to try and trace these issues individually and it may turn out that the central box is the issue here.
I tested the grounding pin (MS37) at the DME relay pin 9 (85b), no dice. So I started back testing each connection from the DME pin 20 to the DME relay pin 9. I started at the 12 pin connector pin 5, continuity. Then from DME Pin20 to N43, continuity. Then to the jumper between M13 to M42, all good. From M42 to the DME Relay Pin 9, no go. So I found the issue. The internal trace that runs from M42 to the DME Relay Pin 9 is the issue.I soldered a wire onto Pin 9 on the DME relay and then used a wire tap onto the Jumper between M13 and M42, the pump primes and the motor starts. I even managed to street tune a bit tonight. All that being said, this means that my Central Electric box is damaged internally which stinks. It makes sense to me now why the previous owner had the DME relay jumpered to run the fuel pump.
This also may explain some of the other strange issues I have been experiencing. For example my brake lights stay on for 5-10 seconds after I let my foot off the pedal and my wipers will not return home, nor will my intermittent wipers work. I had planned to try and trace these issues individually and it may turn out that the central box is the issue here.
