erratic faulty boost press reading!!

winmeister6 · 04-20-2004, 06:32 AM

On my car this morning (1991 Turbo 2) the boost reading was jumping like crazy, and I just started the engine and not moving!! Engine seem fine and drove ok. It went fro, 0.0bar, 0.7bar, 0.3bar within seconds and I was on light throttle.

Has anyone had reading like this before please??

I had been raining for last couple of days....and some said this this could cause problems because of condensation of electric wiring on the Turbo... And when dried it will be ok...

I don't believe it much.

Can anyone share some experiences on this problems??

Thanks...

hobieboy · 04-20-2004, 06:49 AM

If the 91 is similar to the older (up to 89) ones, the factory boost gauge is really not that reliable - sounds like your sender is acting up.

For real reliable reading, you should get a mechanical gauge that takes pressure reading directly from the source.

relkceb · 04-20-2004, 06:50 AM

I had the same problem with my 87 turbo. My problem was the boost pressure sensor went bad. It could also be a little dirty try taking it out and cleaning it. Im assuming it is still boosting and driving ok so its probably not a cracked hose or anything. I would check the pressure sensor first.

winmeister6 · 04-20-2004, 07:30 AM

Where about is the location of the sensor please???

My car is lowered and I can't get underneath to have a look easily..

thanks!!

mikemdd · 04-20-2004, 07:47 AM

I had the same problem on my '87 930. I had just installed a new IC and my gauge was jumping all over, especially when warm. It turned out to be bad ground. My understanding is that the intercooler, or some part of it, needs to be grounded for the signal to the gauge to work.

81 930 · 04-20-2004, 07:50 AM

Another possibility is a bad ground wire to the intercooler. I've had it happen before on my car. The needle will go nuts for a few seconds and then start working normally again. That's the first thing I'd check before replacing the sending unit.

Best of luck,

relkceb · 04-20-2004, 10:12 AM

There should be no impact on grounding the IC (ie. older models without the IC) the boost pressure sensor is on the intake. And on the newer ones it should also be on the intake. You might want to check the connection to it that was a good idea it may have some corrosion on it.

81 930 · 04-20-2004, 10:17 AM

On the C2 Turbo the pressure sending unit IS on the intercooler. I know, I installed one last year on my 930 and was getting erratic boost readings until I added a ground strap...

relkceb · 04-20-2004, 10:23 AM

Here is the picture of 930 models there is only one signal wire that goes to the sensor it is grounded by the intake not the IC. These wires get old and brittle and if you hit them right you can knock them loose. Check the host webpage at http://www.pelicanparts.com/911/911_Parts/1978-83/1-7-6.JPG for a picture.

relkceb · 04-20-2004, 10:24 AM

I thought you were talking about the 930's my bad

mikemdd · 04-20-2004, 12:45 PM

This also relates to the 930's which have replaced the stock assembly blow off valve with an updated BOV. On my '87 930, I replaced the stock intercooler and BOV with the Kokeln setup, eliminating the large (heavy) BOV assembly with a much simplier later model BOV. With this setup, the pressure sending unit is on the intercooler. The intercooler needs to be grounded for the sending unit to work, which was my problem with the erratic signal.

winmeister6 · 04-22-2004, 12:37 AM

hi guys..

I checked the car yesterday evening. There was a very small hole in the TOP of intercooler, with a small 2-3mm deep dent! I only saw the paint chipped and looked closely and there was a little hole.

Looked as if someone dropped a flat head screw driver on top of intercooler. I just had the car come back from service and probably that's when it happened!!

I can't prove it, so.... but it easy to fix.

I didn't have time last night so I put a small ammount of chewing gum on it!! Now, every thing is ok!! I will solder it later.

Thanks for your inputs!!