Normandy 964

Hello All,


Sorry for the wall of text, but writing this down helps me think it through…



The car started fine last weekend, and then yesterday the engine cranks but doesn’t fire.

• I do not have the immobilizer.
• Battery is new and is on a tender.
• No smell of fuel from the exhaust after cranking
• I swapped the DME relay, no difference.
• Hooked up my Durametric – no faults on any of the modules.
• I then popped open the DME relay.
  • The first contact is being closed, so the alarm is working and sending +12V to pin 86
  • The second contact isn’t closing, pin 85b should be going to ground through pin 3 of the Motronic. Since its not closing the fuel pump doesn’t run.
• I earthed 85b directly and tried starting.
  • Fuel pump runs, but no start.
  • Also no fuel smell from the exhaust, so it appears that the injectors aren’t opening either...
• I checked the continuity of the wires between DME 85b and the Motronic pin 3 = OK
• When the first contact of the DME relay closes there should be a +12V on pin 37 of the Motronic = OK
• I have checked the Motronic is being powered through pin 18 and is earthed.

• I believe that the pump should run as soon as the key is in the ignition position...it doesn't wait for the engine to start first.
• I can’t think of any dead sensor that would cause it not to run the fuel pump.
  • For example, I assume that if the Crank Position Sensor is dead the Motronic won’t activate the injectors or coils, but it should start the fuel pump as soon as the key is turned on before cranking.
  • If the oxygen sensor, temperature sensors or anything else dies then it just goes to a ‘safe’ map and the engine still runs.

Soo…

Did the Motronic just suddenly fry itself for no reason, or am I missing something really obvious?

budge96

I would suggest changing the crank sensor , just had to do this myself on my TT , probably was original ..

I f the crank sensor fails to receive and send its signal the fuel pumps will not activate and you will have no spark .

Same as if the DME relay fails , this should be changed out first to confirm if functioning or not ..Bert

Normandy 964

Thanks Bert,

I ordered a crank sensor last night, so hopefully should be back on the road in a couple of days

klokwerk

I feel your pain Norm.
I'd put money on the crank reference sensor too. Definitely if you bypassed the relay to power on your fuel pump and it worked.

There is an off chance that you're getting good signal to the DME and Crank but the coils have gone bad. Remote chance.

Another indicator the crank sensor is out is does your tach move when you try to start the car? No, then crank sensor.

r-mm

The fuel pump only runs when the motor is spinning but you can jump the relay for testing.
Check fuel pressure using the test port on rear driver side fuel rail.
You should check the injectors with a noid light. If you have a PDT type tool you can actuate the injectors with it one at a time.
I had injectors seize after cleaning - recleaning them solved a crank-no-start-no-fuel-smell.

Normandy 964

Thanks everyone,

Tried pulling the old sensor out yesterday, darn thing was completely stuck.
I really didn't want to pull the carrier out since theres not much space to reset the gap between the sensor and flywheel, so I left it to soak 24 hours.
This evening I give it a twist and.....crack.

Not a big deal, it's cheap and available and it gives me time to fix some other stuff whilst I wait for it to arrive.
Still pretty annoying though since I was trying to be carefull and I really didn't apply much force.

klokwerk

Wow, I've not seen that happen before. What year is your car again?

budge96

Damn that thing was fused solid , I think it's a reasonable assumption the sensor likely was toast as well , when I swapped mine the mount
seemed to have either a bend or a bit of wear hard to describe but got a replacement nun the less ..
your half way there got it out lol , Bert

Normandy 964

Its a 1990 C4 with a 280,000 kms
It was a German car, which I bought in Eastern France 12 years ago, so it spent 20 years of it's life with rain, snowy winters and salt.
I then daily drove it for 11 years, parking outside in all weathers.

It's amazingly rust free for what it's been through...