Another no-start thread
Thread Starter
In the Sink
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Joined: May 2003
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Another no-start thread
What happened:
Battery cables changed (both positive and negative) with a new Porsche OEM part. During the change the speed/reference sensors were unplugged and moved out of the way to access the ground connection on the back of the bellhousing.
Symptoms:
1. Car started and ran for 1-2 seconds, then died.
2. Starter cranks, solenoid engages, engine cranks but does not start.
3. The fuel pump is running. I also temporarily connected power directly to the fuel pump via the 9-pin engine harness to rule it out.
4. Connecting a test light between +12v and the #1 pin on the coil shows that the DME is providing a switched ground
5. Tach is bouncing when the key is turned to start.
6. Timing belt is not broken - rotor is turning. Does not appear to have stripped teeth or skipped timing.
7. Connecting a noid light to the fuel injectors shows that the injectors are not getting a pulse signal to open the injectors. Although this is the first time using the noid light on this car, I assume that there is no "wrong" way to use it.
8. BG sensor wiring shows some damage on the engine harness connector.
9. 10mm and 13mm grounds at the back of the engine were disconnected while removing the battery ground cable. I am using a shorter 10mm bolt to attach the bolt to the original ground point.
Questions:
1. Can one of the two sensors (BG/DG reference/speed) have gone bad to allow spark but no fuel injector pulsing?
2. The only time I heard of this failure was because of a bad solder joint for the fuel injector wiring in the engine harness. What else can cause this problem?
3. Are there any other tests that I can run?
Thanks everyone!
Battery cables changed (both positive and negative) with a new Porsche OEM part. During the change the speed/reference sensors were unplugged and moved out of the way to access the ground connection on the back of the bellhousing.
Symptoms:
1. Car started and ran for 1-2 seconds, then died.
2. Starter cranks, solenoid engages, engine cranks but does not start.
3. The fuel pump is running. I also temporarily connected power directly to the fuel pump via the 9-pin engine harness to rule it out.
4. Connecting a test light between +12v and the #1 pin on the coil shows that the DME is providing a switched ground
5. Tach is bouncing when the key is turned to start.
6. Timing belt is not broken - rotor is turning. Does not appear to have stripped teeth or skipped timing.
7. Connecting a noid light to the fuel injectors shows that the injectors are not getting a pulse signal to open the injectors. Although this is the first time using the noid light on this car, I assume that there is no "wrong" way to use it.
8. BG sensor wiring shows some damage on the engine harness connector.
9. 10mm and 13mm grounds at the back of the engine were disconnected while removing the battery ground cable. I am using a shorter 10mm bolt to attach the bolt to the original ground point.
Questions:
1. Can one of the two sensors (BG/DG reference/speed) have gone bad to allow spark but no fuel injector pulsing?
2. The only time I heard of this failure was because of a bad solder joint for the fuel injector wiring in the engine harness. What else can cause this problem?
3. Are there any other tests that I can run?
Thanks everyone!
Thread Starter
In the Sink
Rennlist Member
Rennlist Member
Joined: May 2003
Posts: 10,981
Likes: 97
Turns out that the 12V supply to the fuel injectors is interrupted somewhere after the 9 pin connector above the brake booster, but somewhere before the SP3 solder joint where the one power wire splits into 4 wires (one power wire for each injector). So there was no power to the injectors when the key was switched to the ON position.
Taking a small jumper cable and applying power from the 12V battery post to the red/blue wire on the back of on of the injectors powered all of them, and the car started right up. Now, I have to find where the wiring broke, and replace/repair the injector power wiring.
Must have been a coincidence that the battery cable wiring caused the problem, or else we caused some kind of mechanical damage to the fuel injector power wire by removing/installing the battery cables.
Taking a small jumper cable and applying power from the 12V battery post to the red/blue wire on the back of on of the injectors powered all of them, and the car started right up. Now, I have to find where the wiring broke, and replace/repair the injector power wiring.
Must have been a coincidence that the battery cable wiring caused the problem, or else we caused some kind of mechanical damage to the fuel injector power wire by removing/installing the battery cables.
1st Gear
Joined: Sep 2010
Posts: 1
Likes: 0
I have the same issues except for 9&10.
Been through all the basics :
New cap, rotor and plugs,
checked fuel at the rail.
checked for spark and injector signal with noid light
Checked tach bounce to verify the reference sensors
Checked ohms on injectors @ 2.4 across the board.
Hit is quick with starter fluid and got nothing.
Checked to see if the belt was working by marking it through the inspection window and the mark moved.
Kind of lost at this point as to where to turn next. Any help would be appreciated.
Been through all the basics :
New cap, rotor and plugs,
checked fuel at the rail.
checked for spark and injector signal with noid light
Checked tach bounce to verify the reference sensors
Checked ohms on injectors @ 2.4 across the board.
Hit is quick with starter fluid and got nothing.
Checked to see if the belt was working by marking it through the inspection window and the mark moved.
Kind of lost at this point as to where to turn next. Any help would be appreciated.
Instructor
Joined: Oct 2010
Posts: 172
Likes: 0
From: Sunny Florida
A simple check (PITA though) is to separate the injectors from the intake. Leave them connected to the fuel rail with all retaining clips in place so you don't blow an injector out of the fuel rail. If you don't see fuel spray with the engine cranking, the issue is likely reference sensor wiring. People through a lot of money (I spent my share) at an issue that is usually wiring. So far, I've cut back all injector plug boots to find bad insulation. I replace reference sensor (old one is probably good) - things were ok for a year or so, now occasional stall outs at idle. This could be reporduced on que by wiggling the engine side wiring at the reference sensor plug. Cut back the boot to find more bad insulation. Taped it up and the car stalling has gone away.
The long term solution is to rebuild DME harness. I missed a group buy this summer, but have PM's the OP to see if he'll consider doing another.
Keep in mind that tach bounce proves the speed sensor, not the reference sensor. Fuel spray proves the entire fuel system / computer.
The long term solution is to rebuild DME harness. I missed a group buy this summer, but have PM's the OP to see if he'll consider doing another.
Keep in mind that tach bounce proves the speed sensor, not the reference sensor. Fuel spray proves the entire fuel system / computer.
