vacuum issue.. help!
Join Date: Feb 2006
Location: United Kingdom
1.9JTD Overboost Problem - Fixed
Car: 2004 147 1.9JTD 140bhp
Problem: At full throttle for more that 4 seconds, "Motor Control System Failure" comes up on the computer the engine light comes on and the car goes into "get you home mode" cutting power.
Solution: Variable vains in Turbo were corroded. Cleaned up.. Fixed.
Many Thanks: Medway Auto's, Rainham Kent.
Diagnostics: After being at full throttle for more that 4 or 5 seconds, so 4th gear upwards (as you couldn't be at full throttle for that long in any other gear as it would just hit the rev limiter too quickly) or I guess you could find a really steep hill. The MCSF light comes on, you could then click off the ignition (while moving) and bump her back on. The computer now reset so not to give you the "get home mode" the car felt like as there was no boost at the bottom end of the revs and bucket loads at the top .
FYI The engine light will stay on for 4 or 5 restarts without the fault occuring to turn back off, the fault code is still stored in the ECU.
So Laptop and Proscan out.. read the Fault Code. P0238 MAP Sensor Voltage too High.
MAP - Manifold Absolute Pressure, So two options... The Sensor is lying.. or it isn't.
Swapped MAP sensor for brand new Identical bosch one. Fault still occurs.
So off to the dealer They changed the VNT solinoid (Variable Nozzel Turbo). Fault still occurs.
The actuator moves freely (when vacuum removed). So the guy's at Medway Auto's looked at almost evrything in the system, All vacuum pipes for leakages, voltages going to the VNT solinoid, MAF sensors, everything.
The confusing bit was the turbo actuator (the vacuum opeated thing that moves the Variable vains in the Turbo) seems free, and moves about 10mm exactally as it should.
So with one more thing to try they stripped the turbo and found a lot of corrosion (I'm told) in and arround the vains. I'm not scientist but it can't be from water, as it's too hot, so i'm guessing it's dis-similar metal type corrosion, like on your compression fittings on your central heading, all kind of furs up.
So the guy's cleaned it at and as if by magic, it's fixed.
I think the extra couple of hundred degress when driving it hard at full throttle must have just made enough difference to seize the vains in the full boost position, hence the VNT solinoid / actuator was unable to bring them to low boost setting, i.e not directing the exhaust directly over the turbine.
I'm seen a few threads about Overbooting, and there have been some fixes, So I hope this helps someone.