993 non start

[gareth h]

Advice from the knowledgable please.
I have a 95 manual 993 C2, bought 6 months ago having been in dry storage for 10 years prior to my purchase.
I had done a few hundred miles when it cut out while driving, the symptoms are no spark and pulsing of the DME relay, which also causes the fuel pump to pulse (this has been changed for 2 new relays, and a good feed onto the pump which then works normally)
It has been recovered to a garage who look after my cars, they have checked the obvious and the ECU has been away to be checked and found to be good.
The garage is working through the wiring which is a bit labour intensive.
I wondered whether anybody had experienced similar that may short cut the fault finding?
Thanks
S

[ras62]

DME controls the fuel pump and is independent of the spark side. It needs to see a signal from the crank position sensor to close and start the fuel pump. I would suggest your ignition module is down. It feeds to two coils. Not expensive btw

[Orangecurry]

DME relays can be bad out of the box, though it is unlikely if you've tried 2 new ones. Do you know anyone nearby with a known good relay? It would be very annoying if it was simply that.

For absolute clarity - does the engine turn over on the starter?

[gareth h]

ras62 said:

DME controls the fuel pump and is independent of the spark side. It needs to see a signal from the crank position sensor to close and start the fuel pump. I would suggest your ignition module is down. It feeds to two coils. Not expensive btw

Thanks, so presumably the ignition module takes a signal from the ECU too? The garage managed to borrow another ECU but it was from a later car and wasn’t compatible so couldn’t be used to eliminate a fault.

[gareth h]

Orangecurry said:

DME relays can be bad out of the box, though it is unlikely if you've tried 2 new ones. Do you know anyone nearby with a known good relay? It would be very annoying if it was simply that.

For absolute clarity - does the engine turn over on the starter?

The garage had the same thought so ordered another from Porsche to check, I’m sure it’s possible to have 3 faulty relays, but unlikely, and doesn’t explain no spark.
Yep the engine turns over, and they’ve now also removed the immobiliser

[Orangecurry]

Pope would have the best range of solutions for this - I would drop him a PM.

[gareth h]

Orangecurry said:

Pope would have the best range of solutions for this - I would drop him a PM.

Thanks, who’s Pope?

[ras62]

gareth h said:

ras62 said:

DME controls the fuel pump and is independent of the spark side. It needs to see a signal from the crank position sensor to close and start the fuel pump. I would suggest your ignition module is down. It feeds to two coils. Not expensive btw

Thanks, so presumably the ignition module takes a signal from the ECU too? The garage managed to borrow another ECU but it was from a later car and wasn’t compatible so couldn’t be used to eliminate a fault.

Correct. The DME sends a signal to the ignition module which then triggers the two coils. If you dont see a spark from either distributor then the Ignition module is faulty

BTW the relay chatter you hear is most likely not the DME but another relay being operated by a sticky door entry switch earth

Edited by ras62 on Thursday 11th April 11:31

[Orangecurry]

gareth h said:

Orangecurry said:

Pope would have the best range of solutions for this - I would drop him a PM.

Thanks, who’s Pope?

https://www.pistonheads.com/members/directory.asp

...just 'Pope'.... scroll down....

https://www.pistonheads.com/gassing/profile.asp?me...

[avaF1]

is he still ' working ' ......................................??

Orangecurry said:

Pope would have the best range of solutions for this - I would drop him a PM.

[avaF1]

take it back le garage who sorted out your last non running 993 episode............................................?

https://www.pistonheads.com/gassing/topic.asp?h=0&...

gareth h said:

Advice from the knowledgable please.
I have a 95 manual 993 C2, bought 6 months ago having been in dry storage for 10 years prior to my purchase.
I had done a few hundred miles when it cut out while driving, the symptoms are no spark and pulsing of the DME relay, which also causes the fuel pump to pulse (this has been changed for 2 new relays, and a good feed onto the pump which then works normally)
It has been recovered to a garage who look after my cars, they have checked the obvious and the ECU has been away to be checked and found to be good.
The garage is working through the wiring which is a bit labour intensive.
I wondered whether anybody had experienced similar that may short cut the fault finding?
Thanks
S

[Pope]

Crank Sensor

The sensor has likely corroded and squashed inwards; shorting the connections. The initial pulse from the sensor sets off a response that pulses the DME CU and in turn the fuel pump relay.

Unplug the sensor and crank the engine - if the symptoms disappear that's a quick check #thumbup

Edited by Pope on Thursday 11th April 12:41

[Orangecurry]

avaF1 said:

is he still ' working ' ......................................??

Orangecurry said:

Pope would have the best range of solutions for this - I would drop him a PM.

Pope transcends reality. He was here before, he is here now, and he'll still be here after.

He's also a top bloke.

[gareth h]

avaF1 said:

take it back le garage who sorted out your last non running 993 episode............................................?

https://www.pistonheads.com/gassing/topic.asp?h=0&...

gareth h said:

Advice from the knowledgable please.
I have a 95 manual 993 C2, bought 6 months ago having been in dry storage for 10 years prior to my purchase.
I had done a few hundred miles when it cut out while driving, the symptoms are no spark and pulsing of the DME relay, which also causes the fuel pump to pulse (this has been changed for 2 new relays, and a good feed onto the pump which then works normally)
It has been recovered to a garage who look after my cars, they have checked the obvious and the ECU has been away to be checked and found to be good.
The garage is working through the wiring which is a bit labour intensive.
I wondered whether anybody had experienced similar that may short cut the fault finding?
Thanks
S

It’s the same problem not yet sorted, it’s been on hold over winter as the car wasn’t in use, trying to sort it now for the summer

[gareth h]

ras62 said:

Correct. The DME sends a signal to the ignition module which then triggers the two coils. If you dont see a spark from either distributor then the Ignition module is faulty

BTW the relay chatter you hear is most likely not the DME but another relay being operated by a sticky door entry switch earth

Edited by ras62 on Thursday 11th April 11:31

Thanks, it’s definitely the DME relay chattering and causing the fuel pump to cycle

[gareth h]

Pope said:

Crank Sensor

The sensor has likely corroded and squashed inwards; shorting the connections. The initial pulse from the sensor sets off a response that pulses the DME CU and in turn the fuel pump relay.

Unplug the sensor and crank the engine - if the symptoms disappear that's a quick check #thumbup

Edited by Pope on Thursday 11th April 12:41

Thanks, I think the sensor has been tested, but I’ll get it checked again

[Pope]

There is an outside chance the sensor wiring could have been trapped/squashed to give the same result if the sensor was indeed found to be good.

[ras62]

A crank sensor problem will not cause loss of spark...

[Pope]

ras62 said:

A crank sensor problem will not cause loss of spark...

The DME relay controls the switching on of the fuel pump and ignition circuits. The DME control unit controls the relay. Certain parts of the DME control unit are switched on by the input signal received from the crank sensor. If the crank sensor signal is shorted, the DME is not activated correctly and does not switch fuelling or ignition on; therefore, a crank sensor fault can indeed cause loss of spark - however indirectly.

In the cases I have seen (I am only going by physically seeing the fault personally and associating the similar symptoms experienced by the OP with my own) as soon as the engine is cranked, the relay - and anything controlled by it - pulses indefinitely (or until the relay or crank sensor connector is disconnected; opening the circuit). I assumed a situation is created by the damaged sensor/wiring; when the sensor was disconnected the pulsing didn't occur.









Ignition module could fail - but there are two separate outputs (pin 1 and pin 6) one to each coil - they would both have to fail to cause a total non-spark situation. That said, I have had a case where one coil and one module had failed - on different circuits!! Swapping the good module output to the good coil resulted in start there - but key to this/that was the no 'pulsing electrics' scenario. In that case the owner reported a 'flat' performance for a time before it eventually just didnt start (I had never really concerned myself with why it happened but definitely make sure now to check in the same situation! It had been through a few hands first!)

Edited by Pope on Saturday 13th April 19:24

[gareth h]

Thanks Jon, the cars with Ray West, I’ve passed him the info, he says hello