71-3.0-911

The immobilizer will prevent cranking. If the car cranks, it's not the immobilizer. Jay or Loren can confirm this as the immobilizer needs specific inputs to crank, I don't know which. This is also why many folks focus on the DME as if the car is cranking, fuel may be the next logical culprit.

jay@EZimmoblock.com

Chris -
Unmodified 993's won't crank when the immobilizer is armed - a design feature involving Relay 61 which prevents endless cranking when the immo is armed. However, some owners bypass R61 to allow cranking without depressing the clutch - a feature in 97 and 98's. Check and see if your R61 is still installed.

CosmosMoon

Oh wow - thanks so much - I will check that out when I get home (on vacation for a few days) - it would be awesome if it didn't crank when "immobilized" - it's embarrassing to have the car turn over and not start when I forget to disarm it - LOL!
I had an ECu to disable to immobilizer, but I am now back to stock.

barcobird

Asked the Porsche dealer the following question today

“If there is a problem with the ECU there must be a fault code on the diagnostic scanner?”

Their reply was
“No, there's no communication with the DME
We tried with a different machine but still no communication”

I am not particularly gifted with this subject hence me asking solutions on here but if they can’t find a fault code how can I send the ECU to be fixed?

systemsc

A common problem when the immobilizer doesn't communicate with DME ECM. Furthermore, all that's really necessary for scanning the DME ECM is a simple OBDII scanner, i.e. for no-starts.

barcobird

oh I wish it was that simple. Early 993’s have OBD2 port with OBD1 software, therefore there are no scanners other than the one Tor supplies.

systemsc

Actually, there're; The Porsche Hammer, Porsche PST2, & Porsche PIWIS I, all function perfectly on 964s & early 993s.

barcobird

when the question about scanners for my car has arisen I’ve always been lead to believe that Tor was the only sensible solution for the DIY.
I believe the hammer is in the thousands,
the other two I’ve never heard of. Being Porsche main dealers they should have the most up to date scanning equipment for their cars, so if the fault doesn’t show on their equipment I don’t think it would on anything else🤔. In saying that there’s a problem with the car so why don’t they get a fault code ?

systemsc

The '95 993 DME ECM (55 pins) is a very simple ECM to bench test, and rarely fails. I've typically fully bench tested those ECMs in about 10 to 15 minutes.
My inventory of 993 DME ECMs includes the 55 pin unit, which I use to help Porsche dealers and independents in troubleshooting.

barcobird

The dealers are sending it to a specialist to have it checked, at least then we will know if that’s the problem or something else ?
I will post on receipt of further information.

DCD

Have you had a chance to read my old thread regarding my '95 non-start issue?
https://rennlist.com/forums/993-foru...c4-solved.html

os993

Has your mechanic looked at or tested the Crankshaft Position Sensor, as several folks have brought up? Could this be the issue?

barcobird

I have now read your posts with great anticipation because it seems
to mirror exactly my problem. I have sent the resolution to the Porsche dealers (unfortunately it’s the weekend so closed) and if it is something they have overlooked they can certainly check it. I will keep everything crossed 🤞 Thank you for alerting me to your post👍

CosmosMoon

That was exactly what happened. A PO had removed and jumpered R61 - hence why it would turn over but not start if I didn't disengage the immobilizer. I had a spare relay, put it in, and it now works as expected!
It would have saved me a few gray hairs if had been working correctly when I did my engine drop and re-install and forgot to unlock the immobilizer before my first start up!
Thanks again!

NineMeister

Whilst I'm late to the party, there are (were) some simple tests that you could have done to get useful clues to the cause of the fault.

The engine cranks, so that's half the battle, so first test is for a spark whilst cranking. A spare spark plug on one of the leads would tell you.
If yes, that means that the ECU is getting power, sees the engine turning over and is sending an output to the ignition system.
If no spark we should look for other signs that the ECU is operating.
Does the fuel pump run? You might need a friend to listen in under the front of the car to hear this.
Does the rev counter register whilst cranking? Whilst I cannot recall it Motronic is the same as Motec in that it sends a 10x signal to the tacho when cranking, you should see the tacho needle flicker on crank and if so that signal is coming from the ECU.
Another simple test is with a noid light - an LED light that you insert into one of the injector plugs and which flashes if you have a pulse. You can buy a bosch noid light cheaply enough on eBay.

So with these four simple tests you know if the ECU is powered and whether you have ignition and fuel pulse and (with fuel pump running) you have fuel pressure.
If you have none of the above, likely that the engine rpm sensor has failed so the ECU is powered but does not "know" that the engine is turning over. Could be the ECU, but that's unlikely given the failure mode you experienced.
If you have fuel pulse but no spark, it's probably the ignition amplifier under the seat failed as the ECU only has a low current ignition driver and the amp does all the hard work.

Ask the question of your garage what they found as any of this information is critical to the correct diagnosis. If you're still not sure, feel free to contact me via email or WhatsApp.