Good crank, no spark – Anything left but ECM?

[mysocal911]

Originally Posted by AdamKaz

I can confirm the ICV is humming when the ignition is on!

@mysocal911 - I read the post you're repeatedly suggesting before ever posting here (I know the search feature exists). I do not find it helpful.

It doesn't get any simpler than that, i.e. it covers all the key troubleshooting areas. Sounds like you need to take it to a Porsche repair shop.
They'll find the problem is less than 15 minutes, or send the DME ECM for testing.

As an example of your not understanding, in post #4 you incorrectly measured the primary coil resistance, or the coil is bad. The primary resistance should be 1/10 the value you measured.
You should have resolved that before continuing!

[RobFrost]

Confirm you've checked all your fuses and your earth straps.

Priority for me would be to get a scope on the low tension lead on the coil while cranking. A multimeter set to measure frequency might work.

Sent from my SM-G988B using Tapatalk

[AdamKaz]

I do not have a spare ECU laying around, so I'll check the signal at the connector asap.

I also just ordered a new MSD Coil from our host here. Took off my black coil (to remove any test interference from the wiring/battery) and tested it off the car. Primary is still .7-.8 ohms, but the secondary is now measuring Open.

I've checked all fuses and grounds repeatedly.

I'll try the coil and check the ECU connector while cranking.

[GSixZero]

Originally Posted by AdamKaz

The Bentley manual says the crank reference sensor resistance should be >100,000 ohms, and I’m getting .96 on my 200k ohms voltmeter. But I get the same .96 when I try the speed sensor resistance, so I also think that’s user error.

I just replaced my speed sensor yesterday to fix a no start issue. Only a couple years old and gave the same resistance readings as you were getting and was no good.

[wazzz]

Originally Posted by AdamKaz

I do not have a spare ECU laying around, so I'll check the signal at the connector asap.

I also just ordered a new MSD Coil from our host here. Took off my black coil (to remove any test interference from the wiring/battery) and tested it off the car. Primary is still .7-.8 ohms, but the secondary is now measuring Open.

I've checked all fuses and grounds repeatedly.

I'll try the coil and check the ECU connector while cranking.

Here's my ohm findings on my original black coil (88 3.2):

- primary is .4 ohm. Allow for some error due to contact points and cable own resistance, so your own .7-.8 ohm is still a good measurement. In your original post you mentioned 7 ohms. It must have been a typo then.

- secondary is 5720 ohms. Again, that can vary from one coil to another, but you should not measure Open, unless you chose the wrong setting on your ohmmeter. Make sure you use a proper range for high resistance (at least 10k) or use an autorange DMM.

[AdamKaz]

Tried out a new coil from our host last night, and no change. Still no spark. Given the diagnosis so far and how the suggestions here are leaning, that comes as no big surprise. Tonight/this week I'll take out the crank sensor and bench test it. I'll also check the pins on the ECU while I crank to see if it's outputting signal (before I take out the sensor of course...).

Honest money says the crank sensor...

[ischmitz]

Adam, you are aware there are two crank sensors, right. The speed sensor signal should be readily visible with a DMV in AC mode. The reference sensor only puts out one pulse per flywheel rotation and it's a bit harder to get conclusive data. If this was me here is what I would do:

- Testing the sensor while in the car with a DVM in AC mode gives you some more information. Fine but as others mentioned this is by no means conclusive and difficult for the reference sensor

- Alternatively, get a cheap handled O-scope for real measurements. For less than 40$ you'll see plenty of offers on evil bay and while these might not be extreme precision instruments they'll be more than adequate to test the sensors in the car. Something like the DSO150 or FNIRSI-138. And it'll be a nice gadget you can use for future diagnostics.

- If you remove the sensors for bench-testing I'd say you've crossed the threshold where putting these back in doesn't make sense regardless of your findings. I say that given the costs for new replacement sensors (BMW type) and the hassle of un-installing and installing these.

- After above that it's time to focus on the DME itself. At some point you'll have to bite the bullet and test the DME or put a known good loaner to see if that is your issue

[AdamKaz]

Haven't picked up an oscilloscope, but today I played with diagnosing the ECM

All grounds have continuity to the frame

Both power supply wires show 12v

Ignition coil wire shows constant 12v at On, constant 8v while cranking. Bentley just says "pulse voltage signal" while cranking so this doesn't seem right

Continuity on both crankshaft speed sensor and reference sensor are in-tolerance at .9k. When I check the voltage on the + inputs for both sensors, I get 2.3v at On, 2.28 while cranking. Bentley says this should be variable while cranking.

So two hiccups while testing, but the last test send to point towards the sensor (at least to me). Beyond begging for a loaner ECM, a new sensor seems to be the next step.

[ischmitz]

Adam, it sounds like you did the measurements with the DME connected? For the coil the 8V during cranking is low but as long as the engine turns over it would start if everything works. After lots of tries it’s not a bad idea to charge the car battery a bit.

The pulsing in the coil is something you need an oscilloscope for. Depending on the DVM used it might get picked up or not. So inconclusive. Use the NOID light, an LED test light or an oscilloscope.

The FW sensors seem to check out in resistance mode. Measuring DC bias while connected to the DME has little to no value. You need to disconnect the DME, set the meter to AC and measure. It will read zero with the engine stationary. While cranking the speed sensor should show a healthy AC voltage. At least 1V AC. The reference sensor it a bit more tricky and it depends on the quality of your meter what you’ll read. But you should see the meter react when cranking.

[mysocal911]

Originally Posted by AdamKaz

Haven't picked up an oscilloscope, but today I played with diagnosing the ECM

All grounds have continuity to the frame

Both power supply wires show 12v

Ignition coil wire shows constant 12v at On, constant 8v while cranking. Bentley just says "pulse voltage signal" while cranking so this doesn't seem right

Continuity on both crankshaft speed sensor and reference sensor are in-tolerance at .9k. When I check the voltage on the + inputs for both sensors, I get 2.3v at On, 2.28 while cranking. Bentley says this should be variable while cranking.

So two hiccups while testing, but the last test send to point towards the sensor (at least to me). Beyond begging for a loaner ECM, a new sensor seems to be the next step.

You need to use a test light (ice pick incandescent bulb type) to check for a spark signal (flashing bulb) at the coil while cranking.
Also, using that type of a test light provides a good way to check for a good 12V supply voltage for pins 18 & 35 on the DME ECM connector.

Furthermore, post 4 (over a week ago) provided a link; 911 3.2 No-Start Troubleshooting

That link describes the ACV (AC voltages) you should measure while checking the sensors;

"B. If neither noid nor spark then; check sensors (1k ohms, speed > 1.0VAC,
ref >.10VAC), DME ECM powers (1/18/35) & grds (5/16/17), or DME relay"

On 5/13 (post 19) you indicated that you didn't find the link "helpful". What didn't you find "helpful"?

[AdamKaz]

The FW sensors seem to check out in resistance mode. Measuring DC bias while connected to the DME has little to no value. You need to disconnect the DME, set the meter to AC and measure. It will read zero with the engine stationary. While cranking the speed sensor should show a healthy AC voltage. At least 1V AC. The reference sensor it a bit more tricky and it depends on the quality of your meter what you’ll read. But you should see the meter react when cranking.

Okay @ischmitz, that was very helpful. Just disconnected the harness and tested the speed sensor inputs (8 & 27) on the harness and got 0 voltage while cranking. So the sensor isn't outputting anything into the ECM. I'll pick up a sensor today from our host and let you all know when it arrives.

[mysocal911]

Originally Posted by AdamKaz

Okay @ischmitz, that was very helpful. Just disconnected the harness and tested the speed sensor inputs (8 & 27) on the harness and got 0 voltage while cranking. So the sensor isn't outputting anything into the ECM. I'll pick up a sensor today from our host and let you all know when it arrives.

Hopefully, you were on volts AC and not volts DC, right? Did you check for a reference sensor signal on pins 25 &26, again AC volts?
You are aware that the DME ECM needs both signals to start?

Again, this was posted over a week ago in post 4.

Also, if you need to replace one sensor, better to replace both, as minimal additional effort required.

[AdamKaz]

Left on a vacation, but just came back and got a result I did not want to see:
Tested the new FW / Speed sensor and got no change. Still no start. Tried the new sensor in both positions to see if it was reference or speed, but no love either way. This looks like it might be the ECU after all.

So now I need to rustle up a loaner ECU to swap and try.

[ischmitz]

If you trust your data and findings then the answer is probably "no" to your question in the title and your ECU needs help

[AdamKaz]

***Solved***

It's the ECM. Tried my ECM in a working car - no start. Used that proven ECM in my car and it fired right up. Something in my computer went.

So now it's off to service.

Thank you everyone for your suggestions, patience, and help with this problem. There's finally light at the end of the tunnel!

[AdamKaz]

Got the ECM back from repair and the car started right up! Thank you to all who helped on this thread, especially @ischmitz!

Already did a canyon day, so happy to have the car back!

[GH85Carrera]

Originally Posted by AdamKaz

Got the ECM back from repair and the car started right up! Thank you to all who helped on this thread, especially @ischmitz!

Already did a canyon day, so happy to have the car back!

After fighting problems, it is a really sweet sound to hear the engine fire up!

BTDT, I know the feeling. The best part, is your DME is all freshly fixed, and ready to go.