sgelber

I have a very annoying problem with surging with my 91 964. The car runs fantastic except for the following:

In first or second gear slowly going up a slight grade starting at around 1800 RPM’s it begins to surge and continues to get worse through 2100 RPM’s and then begins to back off and is completely gone at 2600 RPM’s.

The car is a 5 speed with a stock engine and I have done the following to try and fix this issue with no success.

I have replaced the following:
02 sensor – all fuel injectors – Reference sensor – head sensor – DME – Dist caps – rotors – dist. Belt.

I have checked – cleaned and where possible adjusted to factory specs, the following:

Throttle body plate
Spark plugs
Air flow meter and voltages
Air Filter
Fuel filter
Fuel pressure (cold – hot and driving)
C0 at idle and while driving
Checked – cleaned all grounds
Throttle switch
Smoked checked for vacuum leaks
Alternator output
Cat converter
Multiplug connectors

I have even ran the car with the 02 sensor disconnected.

Any suggestions – help you can provide would be greatly appreciated.

Stan

red911c2

Replace the coils, I'll betcha that fixes it.

Rocket Rob

Have you checked if there are any DME error codes? See https://rennlist.com/forums/964-forum/280358-964-diagnostic-tool-faq.html

sgelber

No DME codes whatsoever. BTW I had a performance chip in it and thought by going back to the stock chip, it would solve the problem but no joy!

Thanks

SG

porsche C2

ck the main/fuel pump relay (R41)

red911c2

Status?

GT9111

red911c2,


what kind of coils are you referring to?

AndrewM

Ignition Coils...
You have two, follow the primary lead from both distributor and you will see them tucked on the driver's side of the engine compartment.
Unplug one and the motor should run. Re-connect that one and un-plug the other, motor should run. My 89 C4 did the same thing and the Hammer thought it was a Hall sensor...turned out to be the coil. Car would not start when one of the coils was unplugged. 2 new coild later and the car ran great.\
Hope this helps..
Drew
89 C4 (sold)
86 930 (still at IA)

red911c2

Status?

sgelber

In reply to the gentleman who suggested I replace my ignition coils, I spoke to a master mechanic at a Porsche repair shop and he said that he is highly doubtful that this could be the cause of my problem. Could you clarify your suggestion, (did you replace - change anything else at the same time?)

Regardless, I appreciate all of the suggestions and at the present time have come to the conclusion that throwing more parts into it will not solve the problem as I am already 5k dollars poorer for this.

parsecnc4

In my opinion, the cost of replacement coils (<$200) are not really that big of a deal considering you have spent $5K already. The worst that can happen is you have a set of new coils, which you probably will need eventually if you plan on keeping it.

Hope you will find the solution to your surge and keep us posted.

red911c2

Was that master mechanic the same one that told you to replace all the "other" stuff???

mjshira

it sounds like you've been throwing parts at the problem. having made this mistake myself, I can appreciate how tough it can be to not solve the problem. I have to concur with the previous suggestion about the coils and would also suggest that you change the coil packs (drivers) that work with the coils.

AndrewM

Did you do the basics and unplug each coil one at a time to see if the engine would run?

skruggs964

And if you decide to replace the coils, and that's not the problem....you could always put the old ones on eBay. I've seen them go for around $50 bucks each.....so the worst it would cost you is a $100 gamble to see if that fixes the problem.

Good luck!