Have you made sure the factory anti theft system is not causing the issue?

Hi Scott,

sorry for not being able to talk the other day on the phone. I was traveling in Europe and roaming is killing it.....

Just so everyone is on the same page: I worked on Scott's DME. I installed a 28pin socket and matching EPROM. After testing that it worked I sent the DME back to him. While it worked perfectly on my bench tester it his car wouldn't start with it. Scott returned the DME to me one more time to check if it was bad. It could for example have suffered damage to the flywheel decoder IC. They sometimes fail.

I re-tested it and found it still worked perfectly fine. To be absolutely sure I also sent him my loaner DME along with his. Both are not working in his car. This makes it very very unlikely to be caused by a bad DME. My loaner is en-route back to me and I will check it one more time once I receive it. Assuming that it works it takes the theory of a bad DME or a DME that gets damaged in his car more or less off the table.

Moving on:

If the DME is powered it is supposed to make the ICV vibrate. That seems to be the case here. What I don't (yet) understand is why powering the DME would result in a faint spark. That is wrong.

Next, when the DME sees sensor signals from the speed and reference sensor it is supposed to generate spark, fuel and tachometer signals. Apparently that doesn't happen. To check if the sensors are reversed just put an LED test light on pin 25/26 and verify one pulse per revolution when cranking. That is the reference sensor. Then put it onto pin 8 -27 and verify pulse train from the speed sensor. When you do these measurements inside the DME connector you know you have proper sensor signals.

I can see two main reasons why this is not working.

1. Loosing power why cranking due to bad ignition switch:

One idea is a bad ignition switch. It could be possible that you loose power once the key advances to the START position. With that condition you would have the vibrating ICV when the key is in RUN but once you crank the starter is spinning but the power to the DME and the coil is cut. Try running a jumper wire from the battery to the upper portion of fuse 10-11 (TERM C). Terminal C is hot with key in RUN and START. Then crank and verify the second stage of the DME relay comes on and the fuel pump runs during cranking.


2. DME wiring harness damaged.

I wasn't aware that welding was involved and I am still not sure this is related. Reading through everything it sounds the car ran after the welding. However, the next tests should be to disconnect both the coil and all injectors and then ohm out the harness from the DME connector to the coil and injector connectors. Then, without installing injectors or coil use an LED test light and see if you can observe pulses on the injector line and the coil line. One side to +12V and the other side to the injector or coil line. Again, with power to the DME present and pulses coming to speed and reference input there need to be pulses. Also check the tachometer output for pulses.

Ingo

Factory theft.
 

I second this!!!!

http://forums.pelicanparts.com/uploa...1467233046.jpg
http://forums.pelicanparts.com/uploa...1467233607.jpg
^^^^^
The black wire to pin #86 is connected to pin#87a of the Alarm Module.

This is the 12v that pulls up the second DME relay.

No 12v to pin #86 is how the alarm module disables the car.

Good luck,

Gerry

The DME relay turns on the fuel pump when the DME senses the car is running OR the starter is engaged.

The DME has power so the DME relay control is likely receiving power from the alarm

With a test light (no LED type) you MUST have power when at the RUN or CRANK positions
of the ignition switch at pins; 1, 18, 35. All grounds MUST be checked; 5, 16, 17.
The test light can be used to simulate the ignition coil by connecting the connector end
to a constant 12 volts (fuses on left in engine compartment) while connecting other end to pin 1
of ECM (back-probe). Make sure all the injectors have power in the RUN & CRANK positions.

To totally bypass the ignition switch for Run or Crank powers to the ECM, just use 2 paper clips and
jumper the #30 to the #87, #87b pins of the DME relay. You'll still have to power the coil directly,
but the the injectors should provide a signal, i.e. if they have power which should come from the
jumpered DME relay.

Agreed - I had a 2AM brain crepitation.

Another problem some have experienced is with regard to having the proper power to the DME relay.
This results from a poor pin connection for the female #30 pin in the DME relay receptacle.
The back of the receptacle needs to be snapped open to inspect for this. The red #30 wire is
soldered into the pin and should fit tightly around the DME relay pin when connected.

Easy to check for voltage on pin #86, and ground on pin #85.

I currently have the DME connector shell open so I can back probe the connetors with everything assembled. I've checked all the terminals and there are none recessed or damaged. I've verified the integrity of the coil and injector wiring. I disconnected every injector in case there was one pulling the circuit dead and still have no pulse on a noid light.


the hot side of the coil gets battery voltage when the ignition is in run or start and it doesn't drop out

Thats what I keep coming back to but I've run end to end continuity tests and tests for short to ground and short to other wires of every wire in the harness while wiggling, moving, and jiggling them to no avail.

The connection to the speed sensor has been replaced. The picture Scott posted was before. I found that and thought it was going to be the solution.. no dice.

I thought the same about a melted wire inside the harness but I can't find anywhere the harness looks even slightly damaged. Also the electrical testing points to there not being an issue there. I'm almost to the point of pulling the entire harness and opening it up to physically inspect every wire

Thats been done... twice now. The second go round I was more vigorous with the shaking flexing and jiggling to try and find an issue.

I currently have the DME connector shell open so I can back probe the connetors with everything assembled. I've checked all the terminals and there are none recessed or damaged. I've verified the integrity of the coil and injector wiring. I disconnected every injector in case there was one pulling the circuit dead and still have no pulse on a noid light.


the hot side of the coil gets battery voltage when the ignition is in run or start and it doesn't drop out

Thats what I keep coming back to but I've run end to end continuity tests and tests for short to ground and short to other wires of every wire in the harness while wiggling, moving, and jiggling them to no avail.

The connection to the speed sensor has been replaced. The picture Scott posted was before. I found that and thought it was going to be the solution.. no dice.

I thought the same about a melted wire inside the harness but I can't find anywhere the harness looks even slightly damaged. Also the electrical testing points to there not being an issue there. I'm almost to the point of pulling the entire harness and opening it up to physically inspect every wire

Thats been done... twice now. The second go round I was more vigorous with the shaking flexing and jiggling to try and find an issue.

Ingo,


I Honestly do not think the problem is the DME. While it does seem like a reasonable part to suspect you've tested it twice and its been changed out with your loaner and does exactly the same thing.


the faint spark is a single pulse, as soon as the DME is powered up. Only once and not again unless the power is shut off first. It seems to be a built in test or simply a function of DME initialization.

The ignition switch is working properly. I put an old sealed beam headlight at the starter solenoid end of the harness to simulate the solenoids load and then turned the ignition switch to start and checked all the voltages. Nothing is dropping out and the fuel pump does run during an ignition switch start event

I'm absolutely positive the reference and speed sensors are connected properly, but I've switched them around just to be sure.

We've also tried a combination of five different sensors in different locations just to rule absolutely out the possibility of a failed one.

I've disconnected the injectors and the coil and tested for outputs as you've suggested and there are no outputs from the DME to either set of injector wiring or to the ignition coil. There is also no output on the tachometer wiring but I have verified its integrity


There is no alarm playing into the situation and I've jumpered the main/fuel pump relay and its not the problem.


I'm going to try new wiring from the speed and reference sensors to the DME. I keep coming back to the DME not seeing the inputs for some odd reason. The shielding isnt' shorted to ground but the comment about an isolated scope seeing a perfect waveform even though the car wouldn't is troubling me.

Moderator
 

Moderator - My mechanic friend Alex created an account (al525i) and he is now blocked from posting without moderator first vetting the post?

http://forums.pelicanparts.com/uploa...1467286398.jpg

Another 911 3.2 simple no-start diagnosis becomes overly complex. At most, the diagnosis should
have taken less than 15 minutes. Maybe it's time to take it to a qualified Porsche shop!

????

Hmmmm, with all due respect Dave if this was "another 3.2 simple no start diagnosis becomes overly complex" I think that the collective expertise of the board and an electrical engineer is at least as competent/qualified as any local talent that we have here in S. Florida?

I'm from S. Cal btw and we have far fewer qualified shops here (alarmingly so) besides, IMHO, the point of the forum is to solve "simple no start" situations.

Scott

Many in this thread have suggested simple diagnostic steps which seem to have been overlooked.

Such as???

No spark tried everything - Ingo even loaned me his DME??
 

Scott, did you use an o-sope to verify the speed sensor signal on the DME connector on pins 8/27 ? Maybe something went wrong when replacing the connector on the DME harness. Same for reference signal on pins 25/26 ?

Pins 8/27 & 25/26
 

Morning Ingo,

Alex's outgoing posts are being held because he's newly registered, might be why it appears we aren't responding to the forums suggestions.

I know he's receiving posts and will make certain that he sees yours, thanks.

Scott

Sounds good. Maybe have him give me a call when he is at it. I'm mostly available today