Page 2 of 2
Re: 180 degree shutdown 1972 911T jetronic
Posted: Sun Oct 15, 2023 8:50 am
by Tom
chbaxter1 wrote: Sun Oct 15, 2023 8:41 am
This information is very much appreciated and will be applied to as quickly as possible.
When this problem began, I removed the screen filter at the bottom of the tank and flushed it with solvent. very few fine particles flushed out and the screen is clear when light is shown thru it. The tank was coated on the inside with Hirsch Sealer in 2000 and still looked good two years ago. At that time, I also replaced the fuel filter and dissected the old filter just to see what was going on. The old filter element was clean.
The injectors are Bosch MFI.
I can't wait to check out ARNE2's diagrams and let all know what I find. Thanks again Carl
Hmmm.... In that case, I'd probably just check the fuel pressure as/when the car warms up. That should tell you whether to look at fuel flow issues (dying pump?) or something else....
Re: 180 degree shutdown 1972 911T jetronic
Posted: Thu Oct 19, 2023 7:00 pm
by chbaxter1
After trying all the suggestions, I trailered it 60 miles to my Porsche dealer. They did a Primary Engine Performance Diagnosis and found the electronic Spark Control Module is losing spark when the ignition module warms up. The module is a sensor screwed into the engine's cylinder head and used to detect engine knock or detonation. The signal from the electronic spark control module is sent to the PCM/ECM and that is used to control the engine's timing.
Re: 180 degree shutdown 1972 911T jetronic
Posted: Thu Oct 19, 2023 7:15 pm
by aboyandhisdog
That is very interesting. I would have thought fuel issue for sure. Glad to hear they could get you back on the road! I had no idea that a '72 had such a "modern" electronic ignition, let alone a way to diagnose it. Do they hook up to a port such as an OBD2 or something or is it more of an old school diagnosis done with a multi-meter or similar?
Re: 180 degree shutdown 1972 911T jetronic
Posted: Thu Oct 19, 2023 7:21 pm
by Tom
chbaxter1 wrote: Thu Oct 19, 2023 7:00 pm
After trying all the suggestions, I trailered it 60 miles to my Porsche dealer. They did a Primary Engine Performance Diagnosis and found the electronic Spark Control Module is losing spark when the ignition module warms up. The module is a sensor screwed into the engine's cylinder head and used to detect engine knock or detonation. The signal from the electronic spark control module is sent to the PCM/ECM and that is used to control the engine's timing.
Well I'm glad they got to the bottom of it! Sorry we didn't point you in that direction to start. Just playing the odds with the fuel suggestions, but once you said the tank had been cleaned and coated, the odds probably favored something like this in hindsight. On the bright side, that sounds like a cheaper and easier fix!
Re: 180 degree shutdown 1972 911T jetronic
Posted: Sat Oct 21, 2023 5:54 am
by drWyreMoore
Well, who knew. That makes sense - excellent effort to connect the dots / find root cause / and fix it.
Unrelated but similar in root cause: my 87 911 cruise used to work, until the season got cold. Turns out when I put the passenger footwell heater on, the cruise would become irratic.
The cruise brain is right side under the glove box and would get very hot. Turn off the passenger footwell heat, and it would be fine (call it ok). And I’ll leave that to another story, so I don’t hijack this thread.