Carpokes Porsche Forum

I drive my 79 Targa weekly at a minimum.
Took my normal weekly Friday drive and the car was running good but back firing during down shifts. Not one back fire but 'popping' after down shifts. Has never done this?
Parked the car after my 30 mile cruise.
The next week it will not start...sounds like it is trying but will not 'catch".
Battery is new and fully charged, the car is turning over rapidly as normal but will not start.
What can I check before scheduling with my mechanic $$$$$?

New plugs, fuel filter...?

Do you have a spark ?

I checked one plug and getting spark.
I can hear a partial fire during cranking, sort of sputter like it wants to start but fails.
Tks

I'd be inclined to look closely for obvious vacuum leaks and/or see if it will catch with starter fluid. If not, probably safest to tow it to someone who can properly diagnose the issue. Hard to say from symptoms alone if it is an engine management issue (vacuum leaks, WUR, etc.) or a more mechanical issue like timing chain or head studs. Did you hear any engine rattling sounds when it ran or while cranking?

Thanks for the feedback.
Will look for vacuum leaks, again...WUR was replaced a year or so ago.
Worried about timing chain and head stud...fingers crossed. I did not hear any rattling but planning on another attempted start this afternoon, will listen closely.
Do like the idea of a little starter fluid as part of the trial.
Many thanks for the thoughts, this old ladies can be a challenge.
DW

'79 SC is CIS. Not much in the way of engine management. I'd say it is possibly a vacuum leak, or maybe insufficient fuel pressure.

Arne2 wrote: Sun Apr 27, 2025 11:48 am '79 SC is CIS. Not much in the way of engine management. I'd say it is possibly a vacuum leak, or maybe insufficient fuel pressure.

I have a '79 450SL with a very similar CIS system. I might give it too much credit calling it an 'engine management system.' I was trying to distinguish between basic fuel and spark issues on the one hand --vacuum leaks, bad fuel pressures, spark timing or strength, etc. -- and more mechanical engine issues --e.g., timing chain, head studs-- on the other hand. Hopefully its something simple in the first category...

Many thanks to all.

After an over night battery charge the start sounded promising. It sounded like low fuel, would turn over and fire a few times and die.
Charging over night again, buying starter fluid, thought I had that..., changing fuel filter and giving it another go.
Have a fresh set of plugs, will try that if starter fluid and fuel filter do not solve the prob.
Always an adventure, fingers still crossed that this is something simple. Have a good mechanic if all else fails.
DW