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Discussion Starter · #1 ·
Hi all,
My 1989 Shelby CSX seems to have an overboost issue.

I have the Snap-On computer diags system, so I immediately checked for codes
and there was a Code-67 A-side failure Boost Goal Exceeded.

The solenids pass the "function test" in the scanner, but I'm not
sure that does anything more than cycle power to them, it
doesn't actually check if the vaccum is turned on/off.

I've seen lot of overboost threads, but none for VNT that show a code 67.

Best Regards,
Philip Yanni
 

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I can give you the diagnostics tomorrow when I get home.
Curious, does the 89 CSX VNT use a SMEC or SBEC?
 

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Thanks, that means the diagnostics from my 1990 2.2L/2.5L Turbo Powertrain Diagnostics Manual will be correct and will not need to be altered to accommodate a SMEC.
 

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Right on:

Honestly, I dont know anything about VNT's

First SBEC ws a SDAC trivia question some years back.

Thanks
Randy
 
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Discussion Starter · #6 ·
Right on:

Honestly, I dont know anything about VNT's

First SBEC ws a SDAC trivia question some years back.

Thanks
Randy
I think it's fantastic that you remember the answer to an SDAC trvia question! ... I did look, it is an SBEC.

The car is extremely response, it boosts very quickly, but doesn't stop at 15... keeps right on going.

I'm hoping it's a solonoid and not the VNT...

Best Regards, Philip
 

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Out of curiosity is this something that just started happening??

Is the car all stock or modified or any new mods??

I've read some have issues with low restriction exhaust and some have not.

Is there any difference in performance after this issue??

I'm trying to figure out the result if the vanes are stuck open or closed.

They have one vacuum actuator with 2 nipples correct??

Thanks
Randy
 

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Every boost problem (lack of or overboost) I have experianced in 31 years was related to vacuum system routing/condition or the exhaust system.
The Solenoid in question is a "Universal Solenoid" and is readily available.(Mopar #5234217)

Chrysler Universal Vacuum Solenoid 5234217.jpg IMG_NEW.jpg IMG_0001_NEW.jpg IMG_0002_NEW.jpg IMG_0003_NEW.jpg
 

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Discussion Starter · #10 ·
NAJ / GLHS60,
Did not get a chance to work on this last weekend, top of the heap for later this week. Good question about, has this always been a problem. Yes and No..... I just put a new head gasket on it...I know what your thinking...probably why it needs one.

It use to run up to 15PSI, and if you held you foot in it, would ease up above that (bury the needle on the CSX), but it now it seems to just Jump to 15...and I don't think it will stop!

I'll go through the checklist that NAJ sent and see where I end up... I'm thinking it something simple like the actual solonoid leaks.

Best Regards, Philip
 

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I have replaced the headgasket on my VNT 4 times already, one was my fault, had overboost issues after the OE muffler fell apart.
The VNT requires and the factory exhaust is designed to have backpressure to prevent the turbo from overspooling.
I did not realize the issue was with the exhaust and each time I checked/changed something I took the car out and got on it, each time overboost was present and then this happened...
Head Gasket (A) 5-21-10.JPG

Luckily I was 5 minutes from my Son's house, by time I reached his house the entire car and interior where engulfed in smoke, I actually thought the engine was on fire.

The way I avoided overboost at the track was to shift earlier, I was shifting at 5500 RPM's and hitting the traps at 6100 RPM's in 3rd gear, I started shifting at 4500 RPM's and had to shift into 4th.
One day running a test and tune the day before a Mopar meet, I hit overboost shifting earlier, obviously the air was really good and the engine was reving quicker, I told my Son, thats it, I am done.

The lesson, be careful or you will be replacing the HG again.

Keep us posted on your progress and if you need/require any more assistance/info let me know.
 

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Discussion Starter · #12 ·
Naj,
thanks again for your help. I did go thorugh the checklist, and had a few questions, but there was definitely a problem wth the VNT Solenoid 1. It would turn on, but it did not let the vacuum through. I was getting 1 or 2 inches of vacuum instead of 8-10.

Having a VNT Solenoid 1 handy, I installed it assuming all was good, but I still have overboost. While doing my test drive I did get a code 34 S/C Servo ckt-open or short. I'll check that out next.

I really thought the VNT Solenoid 1 issue was going to solve it.

Is there a check sheet for Code 34? Seems odd, I thought that was Speed/Control but there is no cruise control.

Also, one more question, should I be doing basic vacuum test in on the VNT servos? I know you can't "see" the vanes move, but should they hold vacuum?

Thanks Again, Philip
 

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Is there a Code 45 stored in memory? (Boost Limit Exceeded)

90 Code 45 VNT 1.jpg 90 Code 45 VNT 2.jpg 90 Code 45 VNT 3.jpg

Other possible causes of overboost on a VNT...
1)Exhaust System, the VNT requires backpressure to prevent the turbo from overspooling, the original exhaust was designed to have the proper backpressure.
a)Is the exhaust original.
b)Is the exhaust in good condition, no leaks before the muffler, no baffles down in the muffler?
2)Is Map Sensor calibration correct?
3)Vacuum System
a)Lines are routed correctly
b)No lines are cracked/disconnected/loose fitting/collapsed
90 VNT Vacuum.jpg 90 VNT Solenoid Vacuum.jpg
 

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Discussion Starter · #15 ·
NAJ,
There was no code 45, just the 34. I was not pushing it, but I could tell it was not going to stop at 15PSI Boost.

There is a Cat and Muffler on the car, but I don't think either are stock. I doubt you can buy the OEM parts for
this car, if I need to change them, what should I put on the car?

Best Regards,
Philip Yanni
 

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Discussion Starter · #16 ·
Forgot to add, now the MAP sensor has Not been calibrated, it looks the stock OEM unit. I presume there is a calibration routine out there?
 

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You want to verify the Map Sensor calibration is correct, you cannot physically calibrate it.
You need to verify that the voltage readings are correct for atmosphere/vacuum/pressure and that the proper vacuum/pressure is actually reaching the Map Sensor.
If the controller is seeing wrong info, fuel/spark advance/boost control will all be incorrect for the conditions you are actually driving under.

Run the Code 45 diagnostics and see where they lead, if they do not lead to a conclusive end that corrects the issue then you will need to think about the exhaust system.

That was exactly my issue when the OE muffler fell apart and I had to replace it with a Walker Dynomax muffler.
The OE used an intricate chambered design to create backpressure and was designed as part of the boost control package for the VNT.
The Dynomax was a high flow, less restrictive design, due to that the turbo spooled quicker than the engine controller could react or control.
Eventually my cure was to stop racing and stop pushing the RPM/Boost limits.

The Dynomax eventually rotted out and is no longer available.
The only exhaust I could find and which I am currently using is for an N/A 2.5L, the only thing I had to modify was the intermediate pipe, I had to cut to the proper length and use reducers so it would fit at the Cat.
Does this 2.5L N/A muffler provide enough backpressure to gain back boost control, we will never know since I no longer race.

If it turns out that the exhaust is the cause of your issue, these are the parts I used.
Here are the other pipes.

These exhaust parts are listed for an 89 Shadow 2.2L N/A

 

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A little bit of info: A good friend of mine(v8sr4u) examined the calibrations to compare the CSX VNT and production SBECs. Besides slightly different spark and boost curves, the CSX version completely lacks the vane cleaning cycle that the Lebaron, Daytona, and Shadow CS had that would run the vanes every time the vehicle is started.
 

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Now that's a fascinating historical tidbit of info!

I'm electronics dumb but really like to learn things.

It makes perfect sense to cycle the vanes periodically.

Thanks
Randy



A little bit of info: A good friend of mine(v8sr4u) examined the calibrations to compare the CSX VNT and production SBECs. Besides slightly different spark and boost curves, the CSX version completely lacks the vane cleaning cycle that the Lebaron, Daytona, and Shadow CS had that would run the vanes every time the vehicle is started.
 

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Discussion Starter · #20 ·
Interesting background, I would think the Boost, Spark, and Cleaning routine is in the ECU? Can you use an ECU from a Daytona in a CSX VNT? I would thnk the first time you step on the throttle the vanes would open and close?
 
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