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Discussion Starter · #1 ·
Hello

Some of you may have already read that I just bought a 1989 CSX-VNT from Washington state and had it delivered here. The seller says the VNT is in working order and he's a cool guy and all but I just want to make sure it's working alright as it seems a bit laggy. The seller did state the turbo was replaced with a VNT-28 rebuild from fwdperformance.com as well as some steel braided lines. When driving the car, it feels like there is lag present and I don't really feel the boost kick in until the higher RPMs. As I understand with the VNT, the boost should come on almost immediately. Maybe I'm just overthinking all of this and worrying for nothing. Also in the higher gears, such as 4th, the boost gauge reads around 10 or 12 instead of the max of 14 or 15.

Is there a way I can be sure there is a working VNT system in the car? I just want to make sure everything is as it should be.

There are 40k miles on the car, the title said 0 with an E status (most likely because of the vehicle age). Seller said that in 1991, the original owner threw a rod and the block was replaced with a mopar performance short block.
 

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On the VNT you should be able to hit max boost (12 lbs.) in 2.3 seconds from a standing start.
That was the selling point of the engine, it reduced lag time by 50%, the 89 T-2 took 4.6 seconds to reach full boost from a standing start.
90 Daytona Sales Brochure 5 VNT.jpg

Boost is totally dependent on RPM and in this case SBEC control of the VNT Solenoids and Vacuum System.

You need to be sure all basics are correct to be sure RPM is building quickly enough.
1)No Fault Codes are stored in memory

2)Ignition System Capability
If the system cannot keep up with the KV requirements needed during load and acceleration you will experience the issues that you are describing.
a)Be sure the ignition system is capable of 25 KV on all 4 cylinders.
b)Be sure the plugs are not fouled and are properly gapped.


IGNITION - Adjustable Spark Tester.jpg


3)Fuel Pressure

4)Cam/Ignition Timing

5)Vacuum Line Routing and Condition
90 VNT Solenoid Vacuum.jpg 90 VNT Vacuum.jpg VNT Solenoids 1.JPG

6)Charge Pipes/BOV are properly sealed and not leaking.
No Restrictions in the air intake system
AIR-90 T-1,T-4 Airbox-1.jpg AIR-90 T-1,T-4 Airbox-2.jpg AIR-90 T-4 Airbox-2.jpg

7)Exhaust Restrictions
Be sure there are not any exhaust restrictions.
DO NOT do anything to the exhaust that will lower the backpressure from the factory setup.
The factory exhaust system is designed to have backpressure, it is part of the "BOOST CONTROL" system, if you lower backpressure you will encounter OVERBOOST issues.
This will be the least amount of damage that will occur from prolonged overboost.
Head Gasket (A) 5-21-10.JPG
 

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Discussion Starter · #4 ·
Lots of good information here. I'm not a good mechanic but I can have all this checked out. However the Check engine light occasionally comes on and there is smoke from the tailpipe at initial startup. From what you said, these seemingly minor issues may be affecting the entire system.

Thanks so much for your reply. This will be a big help.
 

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What code(s) are stored in memory?

Smoke on startup usually indicates worn valve seals, are any plugs showing signs of "Ash" fouling or oil?

 

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1987 Shelby GLHS #0958
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Lots of good information here. I'm not a good mechanic but I can have all this checked out. However the Check engine light occasionally comes on and there is smoke from the tailpipe at initial startup. From what you said, these seemingly minor issues may be affecting the entire system.

Thanks so much for your reply. This will be a big help.
gemini, did you ever figure out what was going on? I see a lot of bologna go on in peoples car selling exploits. Have you posted any underhood pictures anywhere? I'd like to see if the PO actually sold you a VNT car. A great many cars were converted to TII over the years. Laziness one way or the other. Too lazy to diagnose a problem with the VNT system, or too lazy to experiment with alternate boost control methods when they've "gotta go fast".
 

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Discussion Starter · #7 ·
I haven't had a chance to put it in the shop. I know its throwing an engine code so I guess the first step would be to get that checked out. I need to get some money saved up so I can get my local mechanic to check a few of the above out. I'm not a very good mechanic so I have to pay someone to do my work lol I'll get a picture of the turbo when I get home. Maybe someone here cN verify if it's the vnt.

Other than that tho, the car runs fine.
 

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Discussion Starter · #8 ·
Actually I do still have access
gemini, did you ever figure out what was going on? I see a lot of bologna go on in peoples car selling exploits. Have you posted any underhood pictures anywhere? I'd like to see if the PO actually sold you a VNT car. A great many cars were converted to TII over the years. Laziness one way or the other. Too lazy to diagnose a problem with the VNT system, or too lazy to experiment with alternate boost control methods when they've "gotta go fast".
Actually I do still have access to the pre-sale video he sent me of the car her on his YouTube

And I screen shot of the turbo.
275256
 

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That pic shows a turbo with duel port vane control so that is a VNT.

90 VNT Solenoid Vacuum.jpg
 

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Discussion Starter · #10 ·
That pic shows a turbo with duel port vane control so that is a VNT.

View attachment 275257
Well now at least I know the vnt is there. I just need to figure out why there's a delay. I'll check that engine code and see what its all about. The seller mentioned something about an incorrect voltage reading but I can't remember exactly what he said. He seemed like a cool guy and I don't think he was trying to pull anything. Real nice guy.
 

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A delay in boost may be caused by numerous issues, not just the VNT control system.
 

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Before you guys go down the diagnosing VNT turbo rabbit hole, remember this is a larger than stock VNT25 turbo. The VNT28 has a larger than stock compressor wheel on it, so it's gonna have more lag than a stock VNT25 turbo. no question about it. I think you need more input from OP as far as driveability. Sounds like he is new to VNT's so he probably has nothing to compare it to. Turbos are compromises, bigger turbo, more push up top at the expense of more lag down low. Just don't want to see you guys chasin your tail.
 

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Discussion Starter · #13 ·
Before you guys go down the diagnosing VNT turbo rabbit hole, remember this is a larger than stock VNT25 turbo. The VNT28 has a larger than stock compressor wheel on it, so it's gonna have more lag than a stock VNT25 turbo. no question about it. I think you need more input from OP as far as driveability. Sounds like he is new to VNT's so he probably has nothing to compare it to. Turbos are compromises, bigger turbo, more push up top at the expense of more lag down low. Just don't want to see you guys chasin your tail.
Good points here. True you are that I am new to the vnt. Pretty new tk turbo in general. True this is a vnt28 from fwd performance as stated by the seller. Still something doesn't seem quite right when comparing this 89 to my 87.
 

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Discussion Starter · #14 ·
When the rain goes away and I get some nice weather I'll get some videos doing a couple 0 to 60 pulls.
 

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According to Chrysler the 89 T2 reached full boost from a standing start in 4.6 seconds.
The 90 VNT 25 reached full boost from a standing start in 2.3 seconds.
My 60' times were low 2.20s which means I hit full boost right around the 60' mark.
The VNT 28...???
 

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Discussion Starter · #16 ·
It seems like my 87 csx has more pull than this 89. Boost gauge reads 14 and 15 continuously. This 89 reads more around 12 especially in the higher gears say 3rd and 4th. With having a different size turbo, would a tune be required?
 

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They didn't mention anything about it having a socketed SBEC or anything? Yes. It's going to need different fuel maps or the engine won't run quite right. I'm not familiar with a "28" or even what it may have been installed on originally.
 

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Where does the line from the small port go? It is the pressure side and is supposed to have a connection to a reference port on the turbo outlet. The 28 you have there, doesn't appear to have a reference port.
 

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Post # 9 shows the vacuum routing for the VNT system.
 

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Discussion Starter · #20 ·
Sorry for being new to this. Not sure what you mean by reference port or or small port. Lol I'm a turbo dummy. But just to be certain I'm not crazy I just took both cars out for a comparison and the 87 does indeed pull allot stronger than the 89. 87 boosts at 15-16 steady, pulls hard and the 89 boosts at a 15 spike and then drops to a steady 11 or 12, doesn't pull as hard. I'm working on a video so you can tell me I'm imagining things lol
 
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