must find boost leak (pix)

254 Views 8 Replies 6 Participants Last post by Trevor, Oct 24, 2001

kalla

Discussion Starter · Oct 23, 2001 (Edited)

The VR-4 has been showing knock on the logger every now and then at low boost. I will shift to second and get on the gas and the logger will start to show knock and I can feel the car lose power as the timing is retarded. This is under low boost (6-7 psi), so I'm trying to find the cause. I suspect either a boost leak (the y-pipe gasket was suspect #1) or the fuel filter. Those are being taken care of this week. Of course, the first thing I have to do is take everything apart ... Hey Rob, bring me some more beer .....

Oh, and that EGR flange that connects to the rear of the plenum ... damn me if that stupid gasket didn't fall down behind the engine somewhere ...

I bet mitsu charges $5 for it ...

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DodgeStealthGuy

· #2 · Oct 23, 2001

Check the clamps connecting the turbo hoses to the y-pipe. I had a friend with the same problem. They looked fine...
Hope it helps!

Brian Snowden, Member #760

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maTT

· #3 · Oct 23, 2001

I think I found your boost leak. There is suppose to be a plenum connected to the throttle body and lower intake manifold. I am surprized your car even starts!!

j/k

I am not sure that a boost leak would cause knock. Make sure all your injectors are working properly.

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kalla

Discussion Starter · #4 · Oct 23, 2001

matt92vr4 said:
I am not sure that a boost leak would cause knock. Make sure all your injectors are working properly.

I don't think it would either. I'm probably going to remove the injectors and take them to a friend for cleaning. I need a new fuel filter too. I dunno if the one in it has *ever* been changed .. and the car has 99k on it .....

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Trevor

· #5 · Oct 23, 2001

Damn EGR gasket!

I've gotten better at lining it up as the years go by...

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Roger G.

· #6 · Oct 23, 2001

Carefully loosen and properly retourque all bolts of the knock sensor plate and the sensor plate itselfs.

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Jeff Lucius

· #7 · Oct 23, 2001

A boost leak will make your fuel mixture richer and tend to reduce knock. You can make a cheap pressure tester using ideas on my web page below.

http://www.geocities.com/lutransys/jlucius3/j3-2-pressuretester.htm

However, a problem with fuel supply - pumps, injectors, filter - may make the mixture leaner and exacerbate knock. Definitely be sure you are getting enough fuel. 6-7 psi (you are measuring this with an aftermarket gauge right?) usually is not high enough to cause knock with good gasoline and basic timing set correctly.

At low boost and low RPM, the knock sensor may not be responding to cylinder detonation as this usually happens at higher cylinder pressure (assuming octane and timing are OK). Knock also can occur after you let up on the gas (shifting, etc.).

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kalla

Discussion Starter · #8 · Oct 23, 2001

Jeff Lucius said:
However, a problem with fuel supply - pumps, injectors, filter - may make the mixture leaner and exacerbate knock. Definitely be sure you are getting enough fuel. 6-7 psi (you are measuring this with an aftermarket gauge right?) usually is not high enough to cause knock with good gasoline and basic timing set correctly.

I have two aftermarket boost gauges, the Greddy electronic gauge and the gauge on the blitz dsbc. I think this is probably a fuel related issue. BTW, the rear turbo has been passing a fair amount of oil ; The rear intercooler hoses have oil residue inside them, and it's been collecting in the y-pipe. Something to worry about?

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Trevor

· #9 · Oct 24, 2001

Oh yeah, that's definitely something to worry about. That oil will cause premature knock.

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