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Ok. 

So, I put 12 volts to the fuel pump directly. No noise of any kind. 

 

Removed and cleaned oil and metal debris from the crankshaft sensor. Can't find anything on how to test it. Bentley manual is wrong! Says remove right rear wheel to access sensor. Sensor is on left rear of motor. 

 

Changed out DME relay with starter motor relay, No change. Engine still turns over but won't start. 

 

I could change the fuel pump just for sh$ts and giggles, but I never have been just a parts changer! 

 

I don't know what to try next............So, I guess it's load it up and visit the P-dealer. It will probably be about $125 just for a scan to see if their are faults .....

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Ok. 

So, I put 12 volts to the fuel pump directly. No noise of any kind. 

 

Removed and cleaned oil and metal debris from the crankshaft sensor. Can't find anything on how to test it. Bentley manual is wrong! Says remove right rear wheel to access sensor. Sensor is on left rear of motor. 

 

Changed out DME relay with starter motor relay, No change. Engine still turns over but won't start. 

 

I could change the fuel pump just for sh$ts and giggles, but I never have been just a parts changer! 

 

I don't know what to try next............So, I guess it's load it up and visit the P-dealer. It will probably be about $125 just for a scan to see if their are faults .....

 

I think you have comprehensively proven you have a fuel problem.  You could attach a fuel pressure gauge to the fuel rail and confirm it.  Then you would need to replace the pump, which is exactly what the dealer would do for you for a lot more money.

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I could replace the pump....If the pump is not working I'm not going to have pressure at the rail or anywhere else.......But, at this point why do I not have a 12 volt signal going to the harness at the pump? I may need a pump for sure as I have supplied 12 volts to the pump with and without the connector connected. I am stumped at the point of not having a 12 volt signal at the pump!!!

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I could replace the pump....If the pump is not working I'm not going to have pressure at the rail or anywhere else.......But, at this point why do I not have a 12 volt signal going to the harness at the pump? I may need a pump for sure as I have supplied 12 volts to the pump with and without the connector connected. I am stumped at the point of not having a 12 volt signal at the pump!!!

 

The answer to that question begins by obtaining a wring diagram for the car and start tracing it until you find where the voltage stops.

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You may want to unplug the fuel pump relay and verify the following:

- 12v at pin 30 and pin 86 with key on engine off

- continuity between pin 87 on the relay socket and the pin (where the green/white wire goes into) on the fuel pump socket

- bench test the fuel pump relay

Edited by Ahsai
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I have just been out to check my car which has been standing overnight.  When I turn the ignition on, without starting the engine, after a few seconds the pump starts cycling.  It pulses at about 1 to 2 second intervals. I can hear it when sitting in the driver's seat.  I assume it is responding to pressure sensors in the system. 

 

Knowing what you know so far it looks like a faulty pump.  However, if I were you, to make sure I would crack open a fuel line so see if it is being pressurised.  I would again also run a switched and fused 12v jump to the pump.  It needs to be switched to avoid sparks, so don't wave live wires about.

 

You don't mention the quality of the fuel in all this.  Is there water in the fuel?  Is it old fuel, as fuel loses its volatility when left in an unsealed container and eventually becomes useless for its original purpose? 

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^Good points on fuse and sparks around the fuel pump. A safer way is to remove the electrical connector on the fuel pump and then ohm out the fuel pump pins (fuel pump side) that the green/white and brown cables go into. If it's open, you know for sure the pump is dead. Since you said there's no sound when you jumped it and you didn't mentioned sparks, most likely it's an open circuit.

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I could replace the pump....If the pump is not working I'm not going to have pressure at the rail or anywhere else.......But, at this point why do I not have a 12 volt signal going to the harness at the pump? I may need a pump for sure as I have supplied 12 volts to the pump with and without the connector connected. I am stumped at the point of not having a 12 volt signal at the pump!!!

 

The answer to that question begins by obtaining a wring diagram for the car and start tracing it until you find where the voltage stops.

 

Ok............ Time for an update and some questions.... AGAIN.

 

Using the Bentley manual for testing purposes. 

 

At 20-5 manual shows how to jump terminals 30 to 87. Performed this and fuel pump is running strong! That is the best way by far to test your fuel pump!

 

Performed relay tests and all checked ok.............Until 24-10 checking for ground at terminal 85!!!!

 

I started looking at all the ground locations. Un bolted the engine to chassis ground, cleaned and replaced. 

 

Moved to section 97-16. DME ground is running on ground point 9 or GP9. Manual says location is right front engine compartment. Looking from top or looking from bottom I cannot see a ground. I think I may have found GP10, which looking from under the car up on the right side it is just above the coolant sensor/housing. 

 

If  anyone out there could lead me to GP9 I would greatly appreciate it as I think this may be the problem. 

 

While laying UNDER the car I did notice that about three wires of one of the O2 had been sheared off, at installation I presume. I haven't looked them up, but does anyone know right away if all four are the same? Or, are their upstream and downstream? I don't think this would cause a no start problem, just an idle/check engine issue. It's nice to have two parts cars to pluck stuff off of when needed......And, if anyone needs any 996 parts just let me know. One is a 2001 C4 coupe tiptronic and the other is a 1999 Carrera coupe six speed. 

 

Thanks in advance.....

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That's some progress. I highly suspect DME grounding is an issue as the DME supplies ground to power the start interlock relay. Your car cranks so that relay is working. Have you checked the crank position sensor and it's connection? When you crank, the tach needle should bounce a little like 1/8" or so. If it doesn't move at all, most likely the DME is not getting signal from the crank position sensor.

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Ok. 

So, I put 12 volts to the fuel pump directly. No noise of any kind. 

 

Removed and cleaned oil and metal debris from the crankshaft sensor. Can't find anything on how to test it. Bentley manual is wrong! Says remove right rear wheel to access sensor. Sensor is on left rear of motor. 

 

Changed out DME relay with starter motor relay, No change. Engine still turns over but won't start. 

 

I could change the fuel pump just for sh$ts and giggles, but I never have been just a parts changer! 

 

I don't know what to try next............So, I guess it's load it up and visit the P-dealer. It will probably be about $125 just for a scan to see if their are faults .....

lakeview: I learned the same thing about the Bentley manual.....

Somewhere in this forum I did find a post about using a voltmeter to test the crankshaft sensor; sorry I don't remember where I found it. But I did pull the sensor and it was not in the range it should be. I replaced the sensor and the car then started. It took a couple of attempts, I guess the fuel system needed to prime or recharge.

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  • 2 weeks later...

That's some progress. I highly suspect DME grounding is an issue as the DME supplies ground to power the start interlock relay. Your car cranks so that relay is working. Have you checked the crank position sensor and it's connection? When you crank, the tach needle should bounce a little like 1/8" or so. If it doesn't move at all, most likely the DME is not getting signal from the crank position sensor.

 

OK time for an update quiz........ I didn't have much grey hair to start with and less now for **** sure....

 

I have found all the grounds and cleaned them. I have changed the crank sensor with one from the other running cars. Still no start. I can remove and jump the fuel pump relay and the pump runs. I know its getting fuel to the rail due to finding a leak at the (what appears to be a return line on top of the rail).....

 

Ahsai.........The tach needle would jump one time and that would be it. Occasionally when I turn the key on the fuel pump will run for about two seconds and stop. That will only happen very rarely. This is why I'm chasing a wiring problem. But, as I said it can be jumped with the relay removed and run continuously. 

 

I have spent a lot of time checking, tracing and troubleshooting. I have performed all the relay testing in the Bentley manual and the only piece of the puzzle that is not complete is section 24-10 checking for continuity to ground at terminal 85!!! This is checked with ignition on, I have no ground. I have ground with the key off.......

Manual says signal from ECM is missing????? Check wire between control module and relay............See wiring diagram. Wiring diagrams in the Bentley manual are confusing to me. Manual shows an engine speed sensor, but no crankshaft sensor? Same or different? Wire colors do not match!

 

Well, I really suck at tracing wiring diagrams. Plus, I'm partially color blind so that makes it even worse. I checked the plug going to the crank sensor with the key on and I had one wire with 12 volts, one with 5 volts and one with ground. I don't know if this is correct or not, I'm trying to rule out a broken wire in its casing or something that was done wrong at installation. 

 

A HUGE question is............Can anyone tell me what wire to check at the control module???? I don't understand why this wire at terminal 85 on the DME relay has ground with the power off but not with the power on.... Everything else checks out, relay energizes, etc. etc. 

This is a Cabriolet so everything is really close together. I could check continuity from DME to relay ground if I knew which wire at DME to check.... 

 

Also, an unrelated problem that I can't seem to resolve. The clutch pedal will stay on the floor. I bled the system and can push fluid through by pumping the pedal. No air seems to be in the system. Is it because someone pushed the pedal in with the engine out of the car? How do I get the pedal back???

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