Porsche technical service bulletins

[Phantomiata]

Hello all.

My 85.5 na has been dieseling ever since I bought it over three years ago. I tried octane booster and high-test gas, but nothing seemed to work. The strange thing is that I had to replace the engine in January, and the replacement engine diesels just like the old one.

In doing a search, I found a thread from 2001 that mentioned a TSB about wiring changes to fix this problem. Something to do with the turn signal relay. I believe the TSB number is 28505, but I can't find anything beyond the number without having to pay $25 for a subscription to All Data.

Is there a website that has the technical service bulletins?

Has anyone actually seen this TSB or attempted the fix?

Thanks.

[Britwrench]

Installing the latest part number turn signal relay fixes the problem.
If you want to see the bulletins paying the $25 is the best way to go.

[SoCal Driver]

Turn signal relay causes dieseling????

Say what????

[Phantomiata]

I know, seems a little out there.

It might be my problem. When the car diesels, the needles on all the gauges jump and all the warning lights come on, so it's something electrical.

I'm going to pull the relay this weekend and see if the dieseling stops.

[Britwrench]

Yep, the relay allows a back feed which allows the engine to run on.
The original fix was a diode in the wiring at the central electric board but a better solution was the updated turn signal relay.

Strange but true.

[SoCal Driver]

Have to admit I've seen some very creative ways of logic wiring in the 944's so this does not surprise me. Lots of diodes.

[Brando]

You could just drive turn-signal-less like me... I use the universal one-finger turn signal. Then again, that's because people usually cut me off before using the standard hand signal...

[Phantomiata]

Darn. I really thought the relay was my problem.

I took the car out for a spin tonight after work and before turning it off, I popped the hood and took out the relay. I turned the car off and it dieseled pretty badly. The relay does have the new part number, but does say W. Germany. That would make it at least, what, 14 years old. I guess I'll order a new relay, but it doesn't appear this will fix it.

After three years, I'm tired of have having my car diesel like a early seventies Pinto. I don't like turning the car off in parking lots when people are around, it's so bad sometimes that the whole car shakes and makes a terrible sound. I've had strangers comment about it, asking what's wrong with the car.

[Phantomiata]

OK, the relay is not causing the dieseling. I swapped relays with my brother's 89 951 and my car still diesels.

Anybody have any other thoughts? Seems strange that a replacement engine would diesel just like the original engine. The guage needles jumping up and warning lights that come on while the engine diesels would seem to indicate an electrical issue. Could it be a faulty ignition switch? On the other hand, the engine will only diesel once it reaches normal operating temperature. If it isn't fully warm, it won't diesel. I don't think it is running hot, my mechanic checked the temperature of the engine with an infrared gun and the readings were within spec.

[adida(r 944)]

Haynes manual troubleshooting section says:

engine diesels (continues to run) after switching off.
1. Digital Engine Electronics (DEE) system fault
2. Excessive engine operation temperature

some things to check out...

1. pressure regulator
2. fuel rail
3. pressure damper
4. intake manifold
5. air flow sensor
6. throttle switch
7. engine teperature sensor
8. fuel injector

just a thought... did you use any parts from the old engine durring the swap??? AFM, throttle body switch, injectors/ fuel rail assembly???

[Phantomiata]

The only part that was carried over from the old engine was the power steering pump. The replacement engine came with the DME and DME wiring harness. The replacement engine diesels the exact same way as the old engine, so I figure it was to be something that wasn't replaced. That would mean something in the electrical sysem.

[AFJuvat]

What was the TSB number and from what year?

AFJuvat

[SoCal Driver]

Phantomiata, Please put the year and model in your signiture line.

[SoCal Driver]

"Excessive engine temp"

You didn't replace the radiator did you.

How the heck can an air flow sensor cause this when the ignition switch supposedly cuts the power.

Me thinks that the PO jacked with the wiring. Maybe a stereo install.

[SoCal Driver]

Don't let it diesel. Pull the p-brake and dump the clutch on it.

[Phantomiata]

It's TSB 28505 from August 1985.

I think SoCal right, the PO had a major stereo in the car that he removed.

[AFJuvat]

Well, FWIW, here is the TSB

AFJuvat

[ae1969]

If I were Porsche I would be embarassed to have that TSB in existence....

[AFJuvat]

Oh you should see some of the others....

Particularly funny are the TSB regarding the rubber centered clutch and all of their failure modes - which ALL equate to "owner abuse or neglect - not covered under warrenty"

AFJuvat

[Phantomiata]

Thanks AF Juvat.

Britwrench said the relay was the better fix. Is it even worth trying the TSB fix?