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?

If it is really a boost issue you should be getting a check engine light? Do you have one? What are the codes? You should not normally hear the turbo unless you have an exhaust leak or something so you can't really go by that. How long have you been running it on VO?>

^x2

How is vacuum supply to wastegate solenoid?

__________________
Jim

I have had a couple of "EPC Engine Electronics" errors, but no check engine lamp.



absolutely no idea. I have (currently) no way of reading them. I'm looking for a cheap system off ebay at the moment to connect to the 38-pin mercedes connector.


I can always hear the turbo spool up. I suspect it may be a little tired and hence a bit noisy, but there's a definite noise. Remember also that this is a RHD vehicle, so the Turbo is directly in front of me, rather than on the other side of the car for most of the world



On and off for a couple of years. Changed a few seals, but that's about it. I only run it on a blend, never 100%


Looking in various other threads, I'm beginning to suspect the MAF sensor. it's definitely something electronic, not mechanical.

Appears in good order. Vacuum is available and the solenoid appears to be doing it's job.


That said, does this system apply vacuum to open the wastegate or to close it? IE if I remove the vacuum line to the wastegate, should I get an overpressure, or sod all?

You will get sod all, and the egr valve will not operate either with its supply taken off.

It is just a guessing game until you pull the codes.

Follow up to this, as it's always nice to put a conclusion to a fault thread.

It was indeed the MAF. I had a very helpful independent read the codes, but the only ones stored were issues I was well aware of, and wouldn't affect the running of the engine or turbo. He cleared them anyway, and it made no difference. So on a whim we swapped out the MAF for one which appeared identical (although the BOSCH part number was not quite the same). Result: Car is back to full turbo pressure available, runs better than it has in my ownership, and the full-power smoke is massively reduced. I think the economy is improved a bit too, as usually I get just over 600 miles on a tank when driving gently. This last tank I've enjoyed all the performance available to me on quite a regular basis, and I've still gotten well over 600 miles on a tank, so driven sensibly I would expect 650 or so. Which equates to about about 35mpg. Seems fairly good for a near-two-tonne, 23-year old, indirect-injection 3.0-litre engine through a non-lock-up autobox with an estate (IE less aerodynamic) body.

Total cost from the indy? £20, including the second-hand MAF. Blimmin' brilliant they are!