P 930 '78 electrical problem!!! boostgau

[klefroid]

I'm now working , trying to fix my boostgauge meter. please can somebody tell me
where i can find the white wire coming from my boost switch in the back, so i want to know where the wire is lockated in the front ? or onder my dashboard?
How can i know my boost-switch is dead? Please please

[mark houghton]

I think your question is for the boost gauge sending unit, the red rubber covered thing attached to the boost recirculation manifold. It can be seen directly beneath the intercooler in the center of the engine.

Here is some useful information for testing the sender. The internal resistance should increase as air pressure increases. Remove the sender and hook an ohm meter to it, then apply controlled air pressure and see if you get close to the following readings:

0.0 Bar 5 - 13 Ohms
0.9 Bar 117 - 129 Ohms

[klefroid]

Originally Posted by mark houghton

I think your question is for the boost gauge sending unit, the red rubber covered thing attached to the boost recirculation manifold. It can be seen directly beneath the intercooler in the center of the engine.

Here is some useful information for testing the sender. The internal resistance should increase as air pressure increases. Remove the sender and hook an ohm meter to it, then apply controlled air pressure and see if you get close to the following readings:

0.0 Bar 5 - 13 Ohms
0.9 Bar 117 - 129 Ohms

Your the man! thanks
I will try this tomorrow ... But i was thinking if i put the white wire of the sending unit to the chassis then my boost gauge must go up,no?

[mark houghton]

Originally Posted by klefroid

Your the man! thanks
I will try this tomorrow ... But i was thinking if i put the white wire of the sending unit to the chassis then my boost gauge must go up,no?

Logic would tell you that if you ground it, you affectively take all internal resistance to zero...and the gauge would stay at 0 bar. Disconnecting the wire may cause the opposite effect (resistance goes to infinite) of the gauge moving all the way to the top scale.

You know, I've done that once some time ago but damned if I can remember. Try it and see! If you get no motion either way, then that will at least point you toward a solution.

[klefroid]

Originally Posted by mark houghton

Logic would tell you that if you ground it, you affectively take all internal resistance to zero...and the gauge would stay at 0 bar. Disconnecting the wire may cause the opposite effect (resistance goes to infinite) of the gauge moving all the way to the top scale.

You know, I've done that once some time ago but damned if I can remember. Try it and see! If you get no motion either way, then that will at least point you toward a solution.

I'm getting no motion either way when i disconnect the boost sender. the sender seems to give the right valeu (ohm)
when i disconnect some wire that are connected to the boostgauge my resistance goes to infinite... so i think the problem will be in between.
Is there some relays in between or something els? i see that the colors of the wires are changing... i have a electrical manual but it's not so clear to me?
does somebody have a possible causes?
Btw : sorry for the bad explanation as i am a Dutch man...

[mark houghton]

Originally Posted by klefroid

I'm getting no motion either way when i disconnect the boost sender. the sender seems to give the right valeu (ohm)
when i disconnect some wire that are connected to the boostgauge my resistance goes to infinite... so i think the problem will be in between.
Is there some relays in between or something els? i see that the colors of the wires are changing... i have a electrical manual but it's not so clear to me?
does somebody have a possible causes?
Btw : sorry for the bad explanation as i am a Dutch man...

Sounds like your sender unit is fine and you must have a break in the wire leading up to the gauge. No relays between the sender and the gauge that I know of. I believe that the sensor functions by changing resistance to the ground connection for the gauge.

So you are certain that you have no continuity (infinite resistance) through that entire run of wire from the engine bay all the way up to the gauge? You should able to disconnect the wire from the end at the sender and from the other end at the gauge, ground one end to the chassis, and put the ohm meter on the other end and across the chassis ground (unless you have really long test leads on your meter). Do that, then try twisting and bending the wire back from the sender to see if maybe there is an internal break.

[A930Rocket]

Push comes to shove, you can always snake a new white wire in it's place. Of course, then you'll have a working guage that's inaccurate!