Good power, no crank - A real head scratcher

[Marshall Webber]

About me because I'm new: Been wrenching on vehicles for 40 years, including adapting OBD2 engines into vintage cars. I work with engineers who build robots, and I build my my own stuff with microcontrollers. I'm a Fluke guy. 

I'm hesitant to write this up, because I've seen stock answers lead people astray. All of the details of the current state of affairs are here. Please read before commenting.

Diagnostic statement: 2003 986 Base w/Tiptronic. 45k miles, always garaged. New battery in June 2022. Always garaged. Never even been rained on: no joke. Pulled it into my shop when the weather got weird 6 weeks ago, and left it on trickle. Went out to move it yesterday. Battery at 12.8v. Turn key to run, fuel pump primes, turn key, idiot lights don't dim, starter doesn't even click. Nothing. All other functions work normally.
 

Change keys. Same thing, both keys. Not handshake problem between the CLU and keys.
Vehicle has never failed to start, nor the starter switch misbehave.
Did someone dump a soda under driver's seat. Nope: Dry as a bone.
Disassembled the cover on the CLU, and the board is so clean, you could perform surgery on it.
Checked every fuse at the front and the rear with meter, not just visually. Continuity on all.
Bench tested starter relay. Works, and I have continuity on the load side when the control side is closed. Not the relay.

When I hook up OBD2 (Using the Torque Pro app) I get all of the data that basic OBD2 provides. Nice chat with the ECU.

Tested start with Tiptronic in Park, Neutral, and switching back and forth between them to test for NPS failure. No change.

Therefore: Immobilizer failure unlikely. Starter switch failure unlikely. 2 Keys transponder failures unlikely.

Before I tear in to the engine compartment or invest in a PIWIS, any suggestions? What have I missed?
 

Marshall

[Loren]

 

Brake microswitch?

Any codes like crank sensor?

Does the transmission show in Park position?

[Marshall Webber]

Loren,

Good questions. I didn't have any codes until I disconnected the battery to bleed down the caps for the airbags before removing the driver's seat. After that, I got the code for a power failure because, yes, I'd had one.

But I'll re-query the ECU to see if any other code is up. I'll check the Park position indicator. It occurred to me that I should also close the load side of the starter circuit at the relay socket (rear relay bank. position 7) to see if the starter will crank at all. If it does crank there, the problem is somewhere on the control side of the circuit. If it doesn't, then it sounds more likely the problem is between the relay and the guts of the starter.

Great to get advice from someone who reads the whole problem statement. Thank you. 👍

[Loren]

I would also inspect the high current cable to the starter as they have been known to fail over time.

[Marshall Webber]

Here's the latest update:

 

Reconnected CLU, reconnected battery. 12.8v

Key to RUN, turn to START. No change.

Tested brake pedal: Brake lights come on.

Tested gear shifter: PRND all light up in the instrument cluster correctly while changing gears with key at RUN and brake ON.

With key to RUN, removed starter relay from position 7, rear relay carrier, and measured voltage between pin 30 and GP8: 0 volts. That's not good.

With key to RUN, shorted relay socket pin 30 to pin 87. No change. 

 

To recap, no change at all. Apparently, no power at pin 30, where there should be.

 

However!

My ELM327 Bluetooth to OBD2 adapter seems to have some squirrelly behavior at the OBD2 socket. Not broken, just...wrong, like not all of the pins are connecting. Torque Pro reports BT connectivity, handshake, and even connection with the ECU. But everything comes up "NO DATA". (I usually look at the coolant temp as a good check. Nada.)

When I moved the ELM327 to my Subaru powered VW Bus (OBD2 compatible ECU from 1997) I got the adapter handshake, and the handshake to my Subaru ECU, and it DID report data.

This may be a wild goose chase, if the pins aren't perfectly aligned in that socket on the Boxster, sometime it won't 'Sprechen Sie Porsche.'

 

Unless the room diagrees, or has other suggestions, I think I'm going to have to go into the engine bay.

 

Marshall

[Marshall Webber]

UPDATE:

I've decided to ship the DME & CLU off to ECUDoctors in FL for diagnostics. I've truly never had so much grief out of a car's starter. I'm not sure what I'm hoping for. If they find something wrong with the ECU or CLU...well, God knows I'd never have been able to diagnose it, so as expensive as repair or replacement would be, I'll be back on the road.
However, if they DON'T find anything wrong, I pay $149 for the analysis (which is fair for this kind of specialty work) but I'm right back where I started: or rather, no-started. I never thought I'd HOPE for the computer to be the problem.

 

M

[Stephen Benson]

Hi Marshall. I'm having the same issue with my 1999 Boxster except that the non-starting began as a very random thing but over the last year it's now the norm. Have you figured your issue out?

[Loren]

1 hour ago, Stephen Benson said:

Hi Marshall. I'm having the same issue with my 1999 Boxster except that the non-starting began as a very random thing but over the last year it's now the norm. Have you figured your issue out?

 

Any fault codes (current or pending)? 

[Stephen Benson]

No fault codes. Immobilizer replaced a little over a year ago due to water damage, and ignition replaced more recently. Car last started about a month ago and I took it for a drive (didn't dare turn off motor though). After I parked in my garage, I tried starting and no crank and hasn't since then. I bought an ignition switch and replaced it myself. Still nothing.

[Loren]

Clutch switch?

An intermittent Crankshaft Position Sensor?