Question re "Overboost Switch"
 

My engine has been cutting out on hard right turns... and then it runs normally when I straighten the car out again. :confused:

I think I may have found the problem. After poking around with a flashlight last night, I noticed the "overboost switch" wire had vibrated loose. The wire has a rubber housing, so it was kept in loose contact with the switch. I assume right turns pulled on the wire and it broke contact... and when I went straight contact was again made.

My questions:

Will the engine die if the overboost switch is disconnected?
What does the overboost switch kill (fuel or ignition)?

I might stand to be corrected but I was having similar troubles which affected the fuel not the ignition, I had the switch replaced but the mechanic mentioned that you could just ground it to disable the switch however leaving your engine vunerable.

I think you are answering my question in a roundabout way... :)

You are saying the switch must be connected or grounded. If so, then I have found my engine cut-out problem. If the switch can be left completely disconnected and the engine still runs, I have to continue searching.

You don't want to disable the switch.

The Germans are efficient (being one of them) if you didnt need it, it wouldnt be there, my opinion. The last thing that I want or could afford is grenading my engine and having to replace it.

Off topic but how do you like your fabspeed? I just bolted up the single outlet with air intakes and a 1 bar spring...it should be on the street tonite

Answers...

Sandman,
Disconnect and disabled are two different thngs. Am I correct that if it is disabled the car will still be operational but vunerable to damage?

The car is not operational, UNLESS you have grounded the wire that once connected the switch. The fuel pumps won't run. I know this because whenever I remove my 965 intercooler, which has the overboost switch on the actual intercooler, I can't run my fuel pumps (to check fuel pressures for example) unless I ground that wire.

Gotcha, so i was correct...As Emission said I answered his questions but in a round about way.
Have patience I am new and trying to learn these cars!! Thanks

As for actually disabling the switch, I think it's set to cut the fuel pumps at 1.2 bar (from what I recall...might be wrong about this number), and I've seen a few threads where people have tripped it. So I guess it can be thought of as a good safe gaurd. However, if it really is 1.2 bar, I'm not sure if the damage is already done???!!!

running naked through a mine field...dont want to take the chance or find out.

I just had a 1bar spring installed. Pros and Cons??

I think it is 1.3 bar... and mine tripped when my wastegate diaphragm ripped open a few years back. It is an excellent safeguard that you don't want to disable.

I like it. I'll send you a PM tonight when I have more time to write... :)

- Mike

There is another thread from a couple of days ago (Name this part ....)

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/398655-name-part-its-function-win.html

that was talking about the overboost relay. Is that the same as the switch?

If not, do you have pics of the switch?

When I got my car the switch was disabled, grounded to the same connection on the intercoler as the intercooler ground. My wastegate had 1.1 bar worth of springs in it, so I am guessing that the previsous owner got tired of the fuel pumps shutting down.

I went down to .8 bar in the wastegate, and continued to have problems with the overboost. I even installed a new switch. I hate the location that it is in with regards to the 965 intercooler. I agree with teh folks that have moved their switch closer to the intake. Since I have had off and on issues with mine, I may do this as well.

Bill

I have a .80 bar spring in my Tial, and I have the mods to rock a 1.0 bar spring, but...

I am with you 100% sand_man. Not to mention when I had all the springs in the Tial, the car was REALLY fast, and I am sure I would have lost my drivers lic.

Bill

I took out my 1.0 bar spring and put the .8 bar spring back in...

Depends on what turbo, IC and fuel you are running.

Nathan,
I am running a stock IC and turbo and min 95 octane.

I should add that I dropped down to a stock spring only because California's gas sucks (only 91 octane), and I was getting predetonation. :mad: With stock boost, I don't have the issue. If you can get better gas, and your mixture is rich enough, I wouldn't worry about 1 bar.

I wouldn't run 1bar with a stock IC or a stock 3LDZ. You might be OK with a K27 or a good IC, but ideally you want both.

You can check the cut out pressure by removing it and screwing it into a tyre valve fitting, or similar and pressurising with a pressure gauge teed in. Put a multi meter (resitance) across the terminal and body and see when it triggers.
But when it is earthed - ie contact made with the housing, the fuel relays go. When it pings off this contact - no fuel. Mine is/was doing same thing - fuel now, now no fuel. The terminal in the housing was a bit loose - I can wiggle it. When I hold it left I have fuel, when I let it go, no fuel. Bit cramped inside there to hold it all the time - I'm about to order another one right now.
Alan

Hello!


Switch should trip at 1.15 bar or so. I assume trip boost will vary according to age and switch tolerances. Switch will effectivly disconnect when trip boost is reached and it will shut both fuel pumps.

I recomend to leave the switch in the loop as it's your only safeguard should wastegate pressure line or membrane develop a leak. I sure tripped mine before I found out my membrane was shot.

Also if BOV is not working correctly, switch might trip inadvertly during shifts as boost will spike when you lift off the throttle.