boost leak

[slowbubblecar]

I am sure all the bolts were put on tight. I didn't have someone look at the guage, but it really runs like crap because of it. It loses around 5 for vacuum. I don't think it probably holds any more than 5 pounds. I will have to look again late tonight.

[slowbubblecar]

It boost leak tested fine to 20pis before. My brother drove it and this happened. He said I have a boost leak.

[A//// Guy]

WEll get out the tester and get some soapy water and have at it? We cant tell you much besides this... Theres only the IM, the TB and the piping/hoses that air travels through. Watch for bubbles and wallah your leak is found. It could be the rubber seals in the TB that seals the shaft for the throttle plate too.

[john]

Peter, you make it sound so easy. You should come over and help. The boost leak tester is on the car. Car was running fine after it was all assembled again. He had a boost leak which was the TB before. I fixed and the car was boost leak tested to 20psi fine. Car made a couple pulls at 25psi and all was fine except maybe the HG (pushed coolant on the last pull). I made a BOV recirc tube by soldering some copper elbows together ( ;) ) , lowered the boost a little, and took it for a spin to see what it was at. Hoping for ~23 psi, all I could build was around 5 and the car started missing. My air compressor can build only 5psi until it stops building on the boost gauge. The last 5psi does not drain quickly from the system though. Seems as if a gasket may be blown out part way. If any of you haven't checked, it is quite hard to use soap and water on an intake manifold. That is about where the sound is coming from, cannot feel anything however. Strange how one day the car is fine, the other day it has a boost leak and runs like shit. Vaccum is around 14-15 at idle. Nothing but problems on this car...

[A//// Guy]

Well that explains alot more than what was written before. Still if you cant see any leaks on the TB then it must be the Intake manifold. Use a stethescope and try and listen where the hissing gets louder. Your vacuum should be around 18 unless that car has cams. That would have to be one giant boost leak to lower vacuum that much.

[JET]

Alright, it was pushing coolant and you can't figure out where the boost leak might be?? Think it might be the head gasket? The head gasket might be leaking out the back side of block.

[john]

The car only pushed coolant at 25 psi that one time. After it pushed coolant out the back of the block, the car drove fine. I boosted it a few times in the rain a day later (only an ass load of tire spin). All of a sudden it got a boost leak and is running like shit.

So if I turn the motor, it will close the intake vavles and eliminate the HG as a possibility right??? I never thought about the HG producing a leak in the intake path. I tried retorqing the head studs and they were fine. The car is only going to see pump gas so I planned on trying to drop the boost to around 23psi and see if the gasket holds. 23psi should be enough for most.

[Matt D.]

So you were doing a boost leak test without the intake valves being closed?

[Kracka]

This is ridiculous, more than likely your headgasket is blown since you already admitted it pushed coolant, did a few more runs, then poof, it blew out the whole way.

[john]

How would the HG produce a boost leak??? The air has to be entering the cylinderto go out the gasket. If the air is entering the cylinder, it would not produce boost leak symptoms of a poor A/F ratio correct??? The gasket is not totally blown. The car does not leak coolant. It pushed some out the back of cylinder 1 under 25psi, that is it. It didn't even loose enough coolant to justify reffilling. The system was full and there was still some left in the overflow. I am guessing that the head could be/been warped. After the 6 bolt was thrown in, compression was 140-140-130-90 (4-1). It also blew the coolant out of the #1 cylinder. It was definitly not a tuning issue as only 1.X count of knock was recorded on the first pull. I richened it a bit and the car pushed coolant getting 2.X counts of knock. I am guessing the warped head expanded enough to blow coolant by the second time after the car was heated up. Maybe we will try a comp test again and see how bad he is now...