This is a Hobbs switch located just above the brake pedal.

Problem; When I punch my turbo hard for more than a few seconds the power falls flat in its face and I'm left with only enough power to get off the road but the engine doesn't die. The only way to clear it is to switch the engine off and restart. Then everything is fine until I punch it hard again.

No! It's not collapsed or blown or leaking hoses! I've triple checked all of that.

Apparently however there is this switch that shuts down fuel during over-boost as a protection for something.

What I really need to know is; what components get shut down? Is it one or both fuel pumps? And, is it normally necessary to restart the engine to clear the condition? That is, why not just release the gas peddle and let the system reset that way?

Thanks
--
signature

Everything I read says the overpressure switch is pressure sensitive and will cut off the fuel pump. I guess you could bypass the switch temporarily and drive and see what happens. I would be careful. You might post this question over at turbobricks.com. Bunch of smart guys/gals there.
--
Post Back. That's whats makes this forum work.

I can't figure this out, guys.

Please read original post...

The boost gauge climbs about halfway through the pressure zone and the power hits a wall. The only way to reset it is to shut down engine and restart. Kind of tricky but doable on the freeway.
--
signature

Engine: Turbo
https://www.brickboard.com/FAQ/700-900/EngineTurbo.htm


See:

Turbo Loses Performance under Boost

Maybe:

Lack of Turbo Boost

Maybe not so complex.





















At any rate:
I must reiterate, St. Louis, Missour-uh is a degenerate sh!t-hole.

A most malodorous crap-filled toilet. Pollution.

"Ain't no way!" the common refrain.
--
Give your brickboard.com a big thumbs up! Way up! - Roger Ebert.

I replaced my turbo boost-cut switch yesterday. 1986 740 LH 2.2. I found this thread researching my problem, and here’s my experience.

Symptoms: Boost would unexpectedly stop, but not abruptly. It was a mushy like stall. The turbo gauge would stop moving staying at the same point. I would let up on the gas, and then gas it again, after several tries the boost would generate as usual. It did not seem like the fuel cut off, like the few times I've had water in my gas.

I’ve had my car for nearly seven years, and I know it well. I’ve slowly but surely made it stage zero, and maintain it stage zero. For example, all of my turbo hoses are in excellent shape. This boost-cut switch is one of the few parts I have not replaced!

Between my research and a hunch, I decided the switch certainly could be worn out after 30-years of operation; most likely it was original. I’m only the third owner of car.

Bingo! The boost is back. Acceleration is snappy and tight. What an easy fix. Though, it takes some patience and headlamp to loosen the screw.

I still have problem! I cannot be sure it was the switch. The symptoms appear inconsistently, cannot re-create problem on demand.

Boost consistent, rpms hang at 3k or so. Possible it happens when engine and weather warmer.
--
I own a Volvo or Does Volvo Own Me? Try the easy to search Expanded Style FAQ Index http://40mph.com/Brickboard_700-900_FAQ_Expanded_Index_Version/

I had a conversation with the transmission shop who thought it was not the trans but a fuel problem. I thought that was possible, but I couldn't immediately figure out why.

The problem was hard to re-create, and I didn't take into the shop because I didn't want get a shrug diagnosis.

After much research and thought over the last couple months, I decided to swap out my BWD boxed FPR, new from O'Reilly 12-18 months ago, to the Bosch 0280160249 (painted black ver. of 0280160294). Problem so far seems to be fixed!

There was some gasoline smell in the vacuum line, not strong but enough. FPR is such an easy swap, I figured I couldn't lose.

I plan to make further updates to confirm problem fixed.
--
I own a Volvo or Does Volvo Own Me? Try the easy to search Expanded Style FAQ Index http://40mph.com/Brickboard_700-900_FAQ_Expanded_Index_Version/

For LH 2.2 the overboost switch shuts off the fuel injection relay. The switch is mounted near/on the EZK on 740s and 1984-87 760s. The switch is near the coolant reservoir on 1988-89 760s. The Turbo+ kits came with a switch with a higher pressure setting. You can dig out the potting over the adjustment screw and turn up the pressure setting.

It shouldn't be necessary to shut the engine off to get your car to run right. As soon as the boost level drops, the switch closes and the fuel pump relay closes the the FI works.

I've riden a Garrett T3 equipped 740T which had a broken hose to the wastegate controller. The car would generate a lot of boost. The engine would die and restart when the boost level dropped. If you left your foot on the gas, the car would really buck, as the FI would shut down, and then restart.
--
john