924Board.org

[Joao_Portugal]

Hello everyone,

I’m reaching out for some help with my 1981 Porsche 924 Turbo (July build), which I own here in Portugal.

I’ve been facing persistent fuel injection problems and have already replaced:

Spark plugs

Ignition wires

Fuel tank

Fuel lines between the tank and the engine


However, a new issue has developed:

The car has trouble starting both when cold and hot.

When cold, it idles but at very low RPM.

In both situations, once it starts, pressing the accelerator at low revs results in no response from the engine.


I would be very grateful if someone knowledgeable could help me diagnose this. Unfortunately, in Portugal it’s quite difficult to find mechanics who are truly familiar with this model and its CIS (K-Jetronic) injection system.

Thank you in advance!

João
Portugal

[morghen]

Hey, have a look on my website.
I make EFI kits for the 924 that look very close to the original k-jet.
There are quite a few 924s running my kits all over the world.
_________________
Supercharger and EFI kits
https://www.the924.com

[924RACR]

For sure, the first point will be to check the control pressure of the system; this requires a slightly unusual/less common fuel pressure gauge than used for EFI systems, due to the way it hooks up. So you need one that has a valve in it, plumbing designed for CIS systems.

Not sure what the best source for you over there will be, but this is the type I have and am talking about:
https://www.fcpeuro.com/products/fuel-injection-pressure-tester-cta-manufacturing-3850

You can see it not only has a number of adapters to match the fuel system, more importantly it has a valve to stop the fuel flow allowing testing of both pressures...

But I'm sure there's a closer source than the link I posted above, since that's in the US...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Cedric]

I really recommend reading through the manuals, if you have them, its not that complicated if you read up.on it first, and it makes it easier to diagnos in the correct order.

Any workshop working with older Mercedes, vw, audi, saab, Volvo, Ferrari Porsche etc etc should be able to diagnose the fuelling, its pretty much a similar system in all of them.

Fuel pressure test kit as mentioned above is a key tool for diagnosis.
_________________
1980 924 Turbo
www.instagram.com/garagecedric/

[Raize]

Buy a wideband gauge and sensor.
Buy or make a k-jetronic pressure test kit.
Then you will have all the information you need to diagnose.

K-jet is really easy once you have this stuff but if you rely on just randomly replacing parts that’s why people end up saying they hate k-jet and how k-jet is so terrible etc etc.

[Beartooth]

I'll just chime in to agree with what others are saying here: the right tools and enough know-how are critical. My 931 sat for around a decade with fuel lines open, so the fuel in the system evaporated and left a lovely coating of gunk in the system. Despite that, a new fuel pump and filter were the only parts I actually needed to get it running as well as a motor with three out of four cylinders in bad shape could. I rebuilt the fuel distributor, but I think that was only necessary because I sprayed brake cleaner in it trying to get the plunger free (not good for the soft parts in it). The two big hang-ups I had getting mine to run right were that the frequency valve wasn't working, and I had to clean out the warm-up regulator a couple times because the gunk in the system plugged it up until it all got worked out. The book on Bosch fuel injection from Bentley publishing was the most helpful thing; the Haynes manual is also helpful, but (understandably) limited in its explanation of the function of the system.
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1980 931 diamond in the rough

[Mclaren924]

[DCM]

My '82 931 runs and drives... However, when you rev it to 5000 RPM, it just quits and doesn't rev higher, doesn't die