Hi,
I have been troubleshooting the D jetronic on my 914-4 1975, 2 liter engine for quite a while now.

Here is what I have done so far:

-Overhauled fuel tank.
-Installed new fuel pump, lines and filter.
-Checked fuel pressure at the regulator (2 bar)
-Changed all vacuum hoses (no leaks)
-Adjusted valves
-Installed new trigger contacts
-Checked dwell angle (46 deg.) and replaced breaker points
-Adjusted timing
-Adjusted throttle switch
-Compression test showed 121 Psi on all cylinders
-Installed new pressure sensor after the old one failed during vacuum test (membrane cracked)
-checked electric system with Bosch tester
-checked electric system manually
-Injectors checked

I have found an old Bosch mechanic and had all adjustments checked. Everything was ok. I am experiencing trouble in the rev range of 300-3500 rpm that
one cylinder is not firing causing bucking. He also mentioned that the Californian D-Jetronic setup is very strange to him. He couldn´t find any information from BOSCH or PORSCHE. I told him that the Californian cars were fitted with a speed limiter. Has anybody experienced trouble with the speed limiter or had similar problems?

Cheers

You don't mention ignition condensor, or injectors, or plugs and wires, or head temp sensor, or ts1. One cylinder not responding points towards a plug, a wire, an injector, or maybe a diz cap. With engine at idle, remove one plug wire at a time till one cylinder does not change the idle. That's the dead cylinder.

Give us some more detailed description of the symptoms. Is it different when cold or hot ?

The engine is fine when the engine is cold and even at idle when warm. The distributor has a new condenser, cap, points and trigger contacts. I also replaced the TS1 and head temp. sensor. Checked wiring and connectors as the ECU. The trouble starts when I accelerate up to 3000-3500 rpm.

The engine is fine when the engine is cold and even at idle when warm. The distributor has a new condenser, cap, points and trigger contacts. I also replaced the TS1 and head temp. sensor. Checked wiring and connectors as the ECU. The trouble starts when I accelerate up to 3000-3500 rpm.

The engine is fine when the engine is cold and even at idle when warm. The distributor has a new condenser, cap, points and trigger contacts. I also replaced the TS1 and head temp. sensor. Checked wiring and connectors as the ECU. The trouble starts when I accelerate up to 3000-3500 rpm.

All the information you need on D-Jet is here:

D-Jet Trouble Shooting

Do you have a 052 ECU matched to a 043 MPS? If it's fine cold then bucking when warm it's running too lean .
If you have the speed limiter just unplug the module.

I agree, its lean.

Each Injector has a rubber seal on the tip.
If those are old, missing, or not installed properly, you get a large vacuum leak in one cylinder, and sometimes way to much air for that cylinder to fire properly.

The rubber seals are very old, brittle, and break.....

replacing them is cheap and quick...

rich

The first thing I did was I verified all parts for matching numbers.

I replaced all the injector seals when I fitted the injectors.

Thanks for all the replies

That silver box by the battery is the speed limiter circuitry, just unplug it if you even still have it. It cuts off the fuel flow at certain revs, perhaps it has gone bad. It is an emission device, not necessary for function. It receives a signal from the trigger points and the fact that the TP are new is interesting. Can you use the Bosch tester to verify that the trigger points are putting out the correct signal at the rev range of the issue? You may need a O-scope and or a breakout box to see the pattern, its a simple alternating on-off signal from the middle contact to either side. Or maybe easiest to just swap in another set of trigger points.

Beyond that, has the TPS functionality been verified?

Have you identified what the issue is on the dead cyl...is it ignition related (spark) or fuel injector related. Could be an intermittent wiring issue that just pops up at that rev range. Very hard to diagnose.

Hi Jeff,

it is quite funny because my mechanic started working for BOSCH as an apprentice
when the D-jetronic was introduced. There are only a couple of master craftsmen left in Germany that can actually do all the adjustments (pressure sensor...etc.). I told him that the Californian cars had an external speed limiter. He only new about the speed limiter in the rotor and could not believe that the car had an external speed limiter because he could not find any documentation off BOSCH or PORSCHE. He has all the BOSCH testing equipment and tested the trigger contacts and adjusted the TPS. The trouble only starts during acceleration and is hard to detect. It would be different if we had the testing equipment with us while driving. You are correct with wiring. After all them years the possibility is high that there is an issue which is just hard to detect. Cheers Mate

Still sounds like a TPS issue.
Have him remove the cover and look at the grooves in the board.


Does your guy have the Bosch Djet Electronic tester? That can be used while driving, but you might need someone to read along to watch it when the bucking starts.

I had a weird bucking, random, but harsh in my 911.
Turned out to be the ignition switch was wiggling and could basically shut dow the car and turn it back on again... Took me a long time to figure that out.

I have got the BOSCH EFAW 193 tester and tried to trouble shoot the problem.
Using an oscilloscope while driving would be interesting to analyse the signal pattern. The BOSCH guy is actually quite interesting even the legend Walther Röhrl is one of his customers.

Let me know if/when you get it resolved.
I have been fighting this same issue for 3+ years.
Exactly the same symptoms.

Maybe he does not have access to the FWSM or the Service and Training Manuals.

I had a similar issue, showed to be the TPS, not the board but the pickup points.
TPS points

Lars S

i tried a replacement board but still had issues. a completely new tps unit cured my ills. no more bucky!!! none. 100% smooth acceleration.

Phil

Yes Phil I think the pickup points often are overlooked but easy to identify it by listning for the 20 clean clicks.

Lars S

Where did you get a new TPS? I have replaced the board, but no difference.

Bruce Stone. It was slightly used but very clean, no wear on the board or contacts. Also it has to set correctly too.