Overboost sensor bad?

[klefroid]

Please tell me my over-boost sensor is bad?
If so then I'm a fool not checking that sooner!

[klefroid]

I thought it cut off the fuel if that's bad? Pumps keep running when I unplug the wire.
Or does it cut off the ignition in a way? Maybe that's why I saw a weak spark before?

Edit: My car is a Euro 1977 3.3 (model 78)

[klefroid]

Never mind... ground the wire but no results... I will have a look for mechanic who can solve this... If I'll find one at least.

[mark houghton]

That overboost switch should show very little resistance, because it's intent is to provide a good ground to the wire connected to it. Only when it sees excessive boost pressure will the internal contacts open, breaking the ground connection, which feeds back to your air flow sensor relay (the yellow relay in later cars) to shut the pumps off. If your relay is working correctly, you should be able to disconnect the wire to the boost switch and ground it to the engine somewhere....and your pumps should run as normal. Your pumps should not keep running with that wired unplugged and not grounded.

[Oheggem]

Originally Posted by mark houghton

That overboost switch should show very little resistance, because it's intent is to provide a good ground to the wire connected to it. Only when it sees excessive boost pressure will the internal contacts open, breaking the ground connection, which feeds back to your air flow sensor relay (the yellow relay in later cars) to shut the pumps off. If your relay is working correctly, you should be able to disconnect the wire to the boost switch and ground it to the engine somewhere....and your pumps should run as normal. Your pumps should not keep running with that wired unplugged and not grounded.

Learned something new right there. Wow there`s so much info if you want to understand how everything works.

Hope you get fixed up very soon

[mark houghton]

Originally Posted by Oheggem

Learned something new right there. Wow there`s so much info if you want to understand how everything works.

Hope you get fixed up very soon

Well.....that's what we're all here for, to share what little we know and to learn about what we don't. The collective wisdom here is HUGE!!!

[Miguel Antonett]

^^^ Indeed...

[WERK I]

Originally Posted by klefroid

Please tell me my over-boost sensor is bad?
If so then I'm a fool not checking that sooner!

klefroid,
What symptoms are you experiencing?

I'm curious why you have the to meter set to setting shown in the pic. That particular setting is used to test a diode in reverse and standard polarity. If you set your meter to "200" ohms range you will get the actual ohms measured across the contacts of the pressure switch/sensor. The reading you will get should be very close to the reading you would get if you touch the two probes together.

[klefroid]

Originally Posted by WERK I

klefroid,
What symptoms are you experiencing?

I'm curious why you have the to meter set to setting shown in the pic. That particular setting is used to test a diode in reverse and standard polarity. If you set your meter to "200" ohms range you will get the actual ohms measured across the contacts of the pressure switch/sensor. The reading you will get should be very close to the reading you would get if you touch the two probes together.

I thought it was an open or closed contact... looks like the relay is bridged anyhow.
today I made something (tube) to bypass the inter-cooler and my afr was less then 10 and with the ic 13.3 so it looks like there is an air leak around the inter-cooler... New o-rings used after the problem. I have a few spare ones if needed.

Car does not have any power but drives good when driving slow, ones I push the throttle it stutters.

[klefroid]

Here is an update, after replacing the intercooler afr did not change.
I drove the car and it has more power (like double) +- 200hp
When it comes on boost it looses power an when I release the throttle I hear a loud tshhhhhhh, like an open blow of valve. the warmer the car get's the higher idle afr goes after driving. I have been trying to find a leak by using high flammable spray but no luck.
It's not the intercooler because I bypassed it after the run and afr stay high (15)

I'm getting closer but still not there... Still have a few hours to work on the car today...

[WERK I]

Are you using the stock intercooler? It could be a stuck or leaking recirculating valve.

[klefroid]

Originally Posted by WERK I

Are you using the stock intercooler? It could be a stuck or leaking recirculating valve.

Good one!

Inter-cooler checked multiple times.
I did a test today for a leaking recirculating valve and found this:

So I closed my muffler and oil tank vent. and removed my inter-cooler. pressurized the intake manifold and a decent amount of air came out of the turbo up pipe.
So that would mean that air is passing the piston in the recirculating valve?
I hear the piston moving when I push and release the throttle. Few parts arrived today (spark plug wires and green dizzy wire) so go to sleep early and make my hands dirty tomorrow morning. Is it possible that the piston does not close completely but still operational?

[klefroid]

a bit more additional info:
When I start the car cold and let it idle until it's warm my afr is stable (12.2)
Then I did a test drive and the car has power but still not how it should be.
After 10 min. or so the afr starts to go up as far as 15.5 on idle, so I tried to re-adjust the afr to 12.2 to see how she runs then and she was worse then before. And still making a loud shhhhhhhhh noise when coming off the gas... I'll try to upload a short video later.

EDIT: https://youtu.be/2clYanR0iUI