917-30

Hello all-

I have a 1994 Turbo 3.6 that only registers 0.2 bar on the boost gauge in the display in the tachometer. I have hooked up a mechanical gauge and it clearly reads that the engine is getting around 0.7-0.8 bar of boost. Does anyone have an idea of why the display in the tachometer could be so far off. Has this happened to anyone else? Thanks in advance for your help.

917-30

Also, I replaced the boost sending unit that was attached to the intercooler, it made no difference at all.....

Metal Guru

If the sender that you replaced is still functional and is receiving power, then there could be a break in the wire. Sounds like it will have to be rung out.
Do you have a multimeter?
Mine is ***** too so I ignore it and use the mechanical gauge I installed.

917-30

Aproximatly how far off is the digital gauge to the mechanical one the you instaled in the car. Is it a constant value or does is fluctuate some? Thanks in advance.

917-30

asimler

Mine would only read 0.1 yet the car was clearly boosting properly. Turned out to be bad connections on the relay. The relay sits behind the clock, there are 2 of them back there from memory and I think its blue (but I could be wrong). Anyway try taking them both out cleaning up the contacts and putting them back in (or just pull out and push back on again a number of times). Worked for me, so hope it works for you too, was 4 years ago and no problems since.

917-30

Thanks. I will try that right now. It will make a great saturday night project!

917-30

Ok, I have tried everything that has been suggested. I am starting to think that it is possible that someone put a 1.0bar wastegate spring in the car and changed the maping in the Jetronic computer. Could that explain why the stock boost display is so wrong? Also, by unhooking the wire to the boost psi sending unit, the electronic (stock) display reads 0.7 bar. So, that leads me to believe that the circuit is working, but some has "lied" to one of the computers to make it think it is not getting as much boost as it really is, hence the false reading on the digital (stock) display. Also, it would explain why I have seen close to 1.0 bar (on the analog gauge) and then a sudden fuel cut, correct??? I bought this car used, so it is hard to tell just exactaly what the three previous owners did..... Please help!

tjr

There is no mapping because Jetronic does not have a chip (or computer) so I'm afraid it can't be that. I would say that the signal is not getting through to the gauge and/or the gauge itself is broken.

917-30

Is the boost display something that is common to malfunction, or read incorrectly, on these cars? Has Porsche ever released a bulliten on how to address the problem, assuming there is one for the production run of these cars?

tjr

See this thread - it seems a similar problem:

https://rennlist.com/forums/964-turbo-forum/219544-1991-964-turbo-reading-1-bar.html

917-30

Thanks for posting that thread. it is nice to know I am not alone.

917-30

Colorado964turbo

Make sure the overboost switch is not grounded out. If it is, the boose gague will not read properly, or at least it wouldn't on my car.

Bill