SGOGT4

Anyone have experience with failing 3" boost gauges that replace the clock? I am getting really erratic readings on my gauge. Everything seems pretty normal until it climbs up to 1 B and then the thing starts going nuts. Swings back and forth between .9 and 1.3 B.

Its driving me nuts. I have tried swapping TiAL boost springs... and then even putting the stock wastegate back on. To compound things I am constantly in an overboost condition. The stock wastegate spring in my stock wastegate is allowing for 1B of boost.

Help!

nathanUK '81 930 G50

Is it plumbed in before or after the throttle body ?

911rudy

If I had to guess I would say that you have a vacuum leak somewhere in the boost gage circuit. It sounds like it is only leaking above .8 bar and then it leaks above .8 bar but recovers and then leaks again. Check the fitting behind the brake booster and if need be, add a hose clamp. Check all of the plumbing before you get into the WG stuff again. It doesn't sound like a WG problem. You can disconnect the pressure line to the WG and make sure the overboost cutout switch is operating and then see what the boost gage does. If it is still erratic, then it is in the gage or the plumbing. Have a cold one and try again!

SGOGT4

Thanks guys... can you direct me to where the brake booster is that I should be checking the fitting? I have never dealt with the gauge hook up before. Also... if I disconnect the pressure line to the WG, how will I know whether the overboost cutout is working?

Thanks again!

nathanUK '81 930 G50

Brake booster is in the luggage compartment, behind the fluid reservoir.

The overboost cutout works by cutting off the fuel pumps at high boost pressures, this will cut the engine out and will reset when the boost drops again.

PorschePhD

You can not miss it. It is a 3/4 hose going to it. Tap that line. It is the biggest line going to the intake. It runs the length of the car.

SGOGT4

Stephen are you suggesting that I re-plumb the gauge?

PorschePhD

Sorry Rob. I got your message about 5 minutes ago. I will call ya in the morning. We can chat about it then.

SGOGT4

Okay... out of desperation I had a new boost gauge and plumbing kit overnighted to where I (and the car) am. My thought was that I would hook up the new gauge real quick and use that as an indicator as to whether or not my original gauge is just shot. The problem I have is that the connector on the end of the air line does not look to mate up to the original set up.

Over the weekend (in between track sessions) I pulled out the guage and traced the line from it down and into the front trunk area. Appears to screw into a brass fitting. A similar connection as the one on the back of the gauge. The hose that I received with my gauge from Performance Products (another sign of desperation) has the brass fitting for the back of the gauge, but the other end is capped off with a plastic connector that appears to be intended to plumb into a seperate line.

If someone with some experience hooking these up could chime in it would be much appreciated. My problem is that it appears that the car is generating way too much boost and I need to try and get it diagnosed by this weekend so that my mechanic can have it corrected (assuming something is wrong) before I head to Road America next weekend.

Thanks!

nathanUK '81 930 G50

The plastic part on the end of your hose (of the new gauge) replaces the part (non return valve) pushed into your brake booster on the car.

911rudy

As Nathan said, it fits into the vacuum line behind the brake booster in the front trunk above the driver's feet. The one you have may be plumbed directly to the rear engine compartment area. If it is then you should use the new hose and connect it to the back of the brake booster. It's sorta close in the booster area so you might have to undo several pieces to get to the hose bib on the back of the booster. Just pull the black plastic fitting out of the booster and remove it from the hose, push the whit end into the hose and the big white end into the booster. This will make both gages work and it is a good source of vacuum. since there is no electrical power needed, you can just leave the gage hanging out of the clock hole and test each one on one trip by plugging each one into the hose and giving it a go. If they both read high then you have a WG problem.

SGOGT4

Well I put the new gauge in on the existing line just to see if it made a difference and it seem to remedy the twitchy needle. Boost seems very steady howver still WAY too much... like 1.3 B!

Must be a wastegate problem I guess although I may rerun the new lines just to confirm.

One thing I have noticed is that the new gauge is very noisy... sounds like it has a bit of a rattle inside under certain throttle conditions. Its really almost more of a hum than a rattle. Anyone else noticed this?

911rudy

You have a problem. It is a vacuum gage and should not make any noise. Try connecting it to the brake booster. If your overboost cutout switch is hooked up you should not reach 1.3 consistently without engine shut off.

SGOGT4

Shouldn't the wastegate be preventing the car from getting to that level of boost? Seems like the overboost cutout should be a safety net not a reliance.

As for the sound... its more of a spring like rattle... I would assume that to operate the needle there must be some spring mechanism in there...

911rudy

This will be my last post on this subject since you have now become argumentative. The vacuum gage uses a bellows which is like a balloon with a hand attached to it. As the balloon expands or contracts the hand moves proportionally. The WG does not prevent anything. It is a gate which opens when Alladin rubs his magic lamp. The lamp is called a spring. What ever the spring rate is determines when the WG opens. Once it opens the engine can blow itself completely apart and the WG will be happy. The only limiter you have on the engine is the overboost cutout switch. If this has been disconnected then you have no protection. If you will only attach the new gage to the brake booster like we have all advised you to do then you will know what is going on. I don't know what your existing gage is connected to and if you don't know then we are lost. Connect the Goddamn thing like you are supposed to and then we can go from there.