Engine/Transmission (1998.5 - 2002) Boost 0.0 cold engine - 21.3 warm engine

[bry1216]

Anybody see a boost reading on a Scangauge II showing Boost 0.1 cold engine and 21.3 after it warms up?
While cold it drives like a slug, but when warm drives like a dragster.
Thanks for any comments.

 

[SnoKing]

Have you pulled the hose off the intake of the turbo and spun the shaft when cold? Checked for free play etc? SNOKING

 

[bry1216]

There is no variable in these 2 values it is 0.1 (runs poorly) or jumps 21.3 (runs great).

Turbo spin fine when cold with no free play.

 

[PC12Driver]

Bad MAP sensor. If the ECM sees zero boost, then fueling is limited to minimize smoke, thus no power. If it sees 20+ psi then full fueling is availabe and you get your dragster. Reported PSIs are still within range, so no codes set.

 

[bry1216]

Codes do work. I pulled MAP connector and got a P0237.
I pulled both MAP sensor and IAC. Both look really clean. Reinstalled and same problem.
I did notice the BST at 0.0 until water temperature was 170'f, then BST jumped to 22.1. Temp rose to 202'f and then cooled to 190'f and stabilized at 195'f.

Do anybody have a ScanGauge 2 that could describe the BST values they are getting?

Thank you PC12Driver for your explanation!

Dealership wants $600.00 for MAP sensor - must come with something else.

Local part store is $121.00 - $154.00.

Does this sound correct?

 

[PC12Driver]

Hoesli Diesel has them for around $75. Might want to check out Geno's also.

 

[JR]

The scan gauge reads manifold absolute pressure from the sensor via the ECU. This is an absolute reading (PSIA) not a gauge reading (PSIG)
You will not get a boost reading like you would expect from a standard gauge. Did you get a CEL prior to unplugging the MAP? It is rare for one to fail but it does happen.

 

[PC12Driver]

The boost value should vary based on engine load. If it's jumping based on how warm the engine (thus, the MAP sensor) is, then I'd put that MAP sensor at the top of my list of things to swap.
Especially if it is in fact showing 0.0 for ambient pressure, since that should be around 14 at key-on and diesels don't run with a vacuum in the manifold.

 

[JR]

The boost value should vary based on engine load. If it's jumping based on how warm the engine (thus, the MAP sensor) is, then I'd put that MAP sensor at the top of my list of things to swap.
Especially if it is in fact showing 0.0 for ambient pressure, since that should be around 14 at key-on and diesels don't run with a vacuum in the manifold.

Good catch, I didn't read the first post correctly. This may be the problem. IIRC ScanGauge allows you to choose between boost and MAP. Since the ecm receives the MAP data based on voltage from the MAP sensor you may not be getting a legitimate reading in the BST mode. Try switching it to the MAP reading and see what you get.

 

[bry1216]

MAP/Boost Sensor Solved

Replaced the original sensor with new Cummins 492147 (Geno's Garage) and problem fixed. Look at the ohm readings of new and old and the opening size.

Socket size:
Old sensor 1 1/4
New sensor 1 1/16

 

[JR]

What kind of boost readings are you seeing from the Scan Gauge now? I didn't think it could accurately read boost from both the BST mode and MAP mode, but I could be wrong.

 

[bry1216]

Seems to be reading BST very well and performance is perfect. I think the initial setup of Diesel would set up BST rather than MAP for a reading. If I floor it going up hill I almost got 21.0, but the hill ran out.