Hello.


This is an odd one and I would welcome any advice.

OM606. Running it on a blend of Diesel and clean new SVO, although I don't think that has anything to do with this issue, especially as I put it back on 100% diesel and it's made no difference. Also runs a Steinbauer performace box and an EGR delete modification.

During a Long motorway journey, I randomly lost turbo boost. This was obvious, as even at full-accelerator, there was no turbo whistle. Car still ran and drove fine, just at what felt like massively reduced power. Still got to my destination. Parked the car up overnight and ignored it. Next morning, all back to normal, car is boosting just fine. At least it did for about 15 minutes, then I lost boost again.

This was very repeatable. Park up for 20 minutes, and you get full power back, but only for about 10 minutes. The time that you have boost for has gotten less and less and less, and now I have no boost at all even from a cold start. If you caught the car just as the boost was going to fail, it would be hesitant, giving you a couple of seconds of boost, then none, then boost again, then none. It felt like a loose connection.

None of the vacuum pipes to the turbo or EGR are perished, the solenoid for the turbo is working fine. Tried running the car with the exhaust disconnected to prove it wasn't a part-blocked catalyst, and no difference. The turbo is spinning freely and I can find nothing really wrong. The pipe to the MAP is clear and in good condition.

What I have discovered, however, is that if the MAP sensor is disconnected, I go from having about 2psi boost available (IE basically nothing) to about 5psi boost. (I fitted a mechanical inlet pressure gauge) and the ECU is clearly making use of this additional boost, as the car has more power. Which it clearly wouldn't if the turbo was just spinning up and no additional fuel was being supplied.

Clearly this is something electronic. I've checked the MAP sensor, and it shows 1.45v at atmospheric, (I'm assuming it's scaled at 0.1v/1psi absolute) and rises if you apply pressure to it, so I don't think that's at fault.

Other than that, I am somewhat at a loss. Any ideas?