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Turbo System Question

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jkinsey

Probationary Member
8
0
Dec 16, 2003
Toledo, Ohio
I am having a problem with the turbo system, and don't have much experience. During light acceleration, the car feels like the engine is cutting out. At first I thought it was a transmission problem. I watched closer today, and the tach will read a constant rpm, but my boost gage (aftermarket) will drop from a couple psi to zero. It seems something is leaking somewhere, but I don't know where to start. It doesn't seem related to a certain boost number, and it doesn't always happen. Some days it is fine, others I can watch the boost fluctuating from say 5 psi to zero. Seems worse on colder days, but happens warm sometimes also. I had a Turbo XS boost controller. I think this was part of the problem because even with the controller fully closed, it would hit 20 psi boost. So I pulled it out, and it is better, but the problem is still there. I would appreciate any suggestions on what to look for.

Thanks, Jerry
 
Yeah, guess I knew that was coming. I actually did make the tester. The first time I checked, the throttle body shaft seals were leaking very bad. I replaced those, and was still getting a leak. The pressure would drop, but I couldn't hear anything or see anything with the soap bubbles. I ran out of time (and got frustrated), so I quit. Does the information above help to point to something specific I can look at closer? It confuses me that it doesn't do it all the time, and when it does, it is a severe and quick drop, like the engine died, but other days is fine.

Thanks
 
Test from three different points.

First from the turbo inlet. If you can't find any leaks move your tester to the LICP. Still can't find any leaks move it to the TB Elbow. This should help you pin-point any leaks.

Pay close attention to the bottom of your piping (if stock still) the intake manifold gasket/area, your j-pipe, and your IC.
 
ddavisaf said:
First from the turbo inlet. If you can't find any leaks move your tester to the LICP. Still can't find any leaks move it to the TB Elbow. This should help you pin-point any leaks.
The other way around :tease: , start from TB elbow and work your way back to the turbo inlet. I would also suggest doing the following.

1. Disable or turn the mbc all the way up.

2. Open the oil cap and listen for hissing.

3. Do the same at the tailpipe.

Post back with specific numbers on the boost gauge during your testing.
 
ddavisaf said:
Bah! Either way is fine. :p

Not really. If you have a leak from the TB back you will fail all 3 tests and not know where the leak is untill you have done so. If you start at the TB and work to the turbo you will know the location with the first test. Work smarter not harder.

You may be hitting compressor surge.

Where is your boost gage piped in. If it is piped before the TB it will read some weird things while cruising because you will build boost pre TB and the BOV will open because you still have a vacume post TB.

BTW compressor surge = bad juju for the turbo.
 
OK guys, started with the throttle body and it was leaking. Took off the oil cap like you suggested and could hear the hissing. Think I read somewhere else on here that could be the rings. So I ran a compression test, and I am getting 130 +/- 1 or 2 on all 4 cylinders. If I'm reading the shop manual correctly, it says OK down to 114. What do you think? I appreciate everyones help.
 
Oh, and I have the boost gage tapped into one of the vacuum fittings on the driver side firewall. Thanks
 
jkinsey said:
OK guys, started with the throttle body and it was leaking. Took off the oil cap like you suggested and could hear the hissing. Think I read somewhere else on here that could be the rings. So I ran a compression test, and I am getting 130 +/- 1 or 2 on all 4 cylinders. If I'm reading the shop manual correctly, it says OK down to 114. What do you think? I appreciate everyones help.
1. Repeat test at throttle body and record the pressure level and holding time.

2. Remove the pcv hose from the intake manifold and cap off the nipple off the manifold then retest. If oil cap hissing stops or pressure level/holding time increased, replace the pcv with an OEM one. If oil cap is still hissing but the pressure level/holding time increased, you are looking at either valve seals or blow by through the rings. Make sure you post back with specific pressure numbers on each test.
 
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