89 CSX Overboost Shutdown

All,

I have posted elsewhere in here my cars issue, but I thought it better served in here.

I have a 89 CSX that I bought in Sept from the original owner. The car had sat for 9 years in his garage prior to my purchase. I have done all the usual maintenance to make it safe to drive and it drives well, except the engine hits 23lbs of boost and goes into and overboots (OB) shutdown. The car is basically stock exhaust with the exception of an aftermarket catalytic converter. All boost reading have been confirmed using two different boost gauges. Car idles just fine and has 21" of vacuum at idle. Car drives perfect except the OB shut down. So yeah, basically I have never been able to really enjoy a WOT run except in 1-3 gear as it builds so fast and the load is not on the engine as bad as high gears. I should also add there are no strange noises for either the engine or turbo.

As for troubleshooting my OB condition, here is what I have done to date to find a cause:

1. Put a smoke machine on the vacuum line off the intake manifold to make sure no vac leaks.
2. Bought a OTC 4000e test set and actuated all solenoid and all work. Also actuated them using the 4000e and smoke machine hooked up verifying correct operation.
3. Traced and retraced vacuum lines about 5 times confirming proper routing.
4. Replaced most hard plastic vac lines with silicone hoses.
5. Put new MAP in as it was cheap and no change (now have a spare MAP on hand if I need one).
6. Hooked air compressor up to VNT actuator open port and confirmed actuator moves and lever arm hits full open stop pin
7. Confirmed base timing is spot on
8. Ran two boost gauges with one on the actuator can open signal line and one on the closed line confirming closed is vac and goes to "0" as it starts to boost. Open reads "0" until it starts to boost and then reads the 23lbs of boost.
9. No exhaust leaks
10. Ran a boost gauge on the map sensor line and it sees 23lbs of boost
11. Ran a line from compressor scroll directly to open port on actuator can
12. Inspected compressor for damage (none) and no perceptible axial or radial shaft movement
13. Using my air compressor applied air to the actuator can open port, got under car confirmed lever arm is against full open pin and safety wired the lever arm in full open position
14. Put a 2" to 1.5" exhaust reducer on the muffler tip and it slowed down the boost build rate, but still OB shut down.


I am sure I am missing more troubleshooting, but basically I have gone through everything I can think that would cause the OB shutdown and everything work like it should and nothing changing my OB. My feeble mind says if I safety wired the lever arm open with no change that ruled out any controls issue (ECU or solenoids). And since I added the exhaust reducer that tells me it is not a lack of exhaust back pressure. With that being said, the only thing I can think of would be something like just because the vane lever arms was wide open, it does not mean all the vanes are opening.

So I sourced a NOS VNT-25 setup and plan to install that in hopes its the turbo (which I feel it has to be). I also need to replace the OEM clutch so will pull the engine/trans as one and separate while out.

Anyone in here have any suggestions for me to try before I dig into this later this spring?

Thanks in advance for any help anyone may be able to provide!

Ended up being the turbo. A couple vanes would not open all the way op by hand. Installed new VNT and works perfectly now.

I'm glad you figured it out. Was that the CSX that was for sale in Pinellas a while ago?

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Originally Posted by EaZyE426

I'm glad you figured it out. Was that the CSX that was for sale in Pinellas a while ago?

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No sir. To my knowledge this car was never up for sale. The original owner approached me at a Cars n Coffee that I took my GLHS to and asked if I would like to own another Shelby.

BTW it was in Valrico