Help! Mysterious Turbo problem

[Peter.N.]

My bombproof, everlasting 406 Hdi has just let me down, but has now recovered. Yesterday I filled it right up with fuel, pulled out onto the Axminster bypass, put my foot down and very little happened except a lot of black smoke, I had to use 3rd to get up there, normally 5th. There was no sign of any turbo boost whatsoever although the smoke stopped, on the flat its OK.

Today I started it and had great difficulty in pulling away, stalled it twice, so I took the engine cover off, gripped the intercooler pipe and revved the engine, there was slight pressure there at high revs, I disconnected the pipe revved the engine again and suddenly got a lot of air from the pipe, connected it back up, pulled away and the front wheels spun! Drove it up to the forest went like a train.

I have had this before but with a few revs it has cleared. The only thing I noticed was a little black smoke from around the cat, could it be intermittently blocked? Its done 210k miles but the only cat failure I have previously seen is the pipe being corroded and leaking, still working OK though.

I await your comments with interest.

Peter

[Hell Razor5543]

I wonder what would happen if you were to put a blast of air down the pipe from the turbo end? If there is a blockage blowing it back the way it came might help.

[Simple76]

Probably MAF sensor

[Peter.N.]

Already changed the MAF. The performance loss is far more than a faulty MAF gives, engine down to half power or less.

James

I revved the engine a bit with the intercooler pipe disconnected and suddenly got a terrific blast of air although the performance is pretty well back to normal there is black smoke around the cat so I think its leaking and blocked. I found a new cat on ebay for about £55 so I have ordered one, it must be that, I can't think of anything else. If the free flow of the exhaust is impeded it will stop the turbo turning properly. I will have to modify the exhaust - again as it seems to be non standard so in the absence of any other suggestions I will go ahead with that. Thanks for the suggestion but as its now working there isn't much point in trying. Will report back when job done.

Peter

[white exec]

Peter, try driving without the cat attached, if you can. If power returns to normal, that would suggest a blocked or partially blocked cat. Will operate surprisingly quietly, assuming the turbo is spinning, just for a test.

[Simple76]

It would seem your correct sounds like a blockage.

[Peter.N.]

Difficult Chris. To detach the cat from the engine you need three arms about four feet long. The flexi pipe is leaking anyway so I have ordered the cat and will fit it regardless. There is no problem with the turbo air inlet side so the only other thing that can restrict it is an exhaust blockage. I have heard of the inside of the cat collapsing and blocking the pipe, I think its either that or the flexi pipe has collapsed, there is certainly smoke coming from it when revved so it needs replacing anyway. As its now going OK any further tests won't be very productive.

If it is the cat I will be pleased but also annoyed as I went to look at a very cheap 307sw with exactly the same problem but wouldn't risk it, would have been a very cheap car if that's what it was.

Peter

[white exec]

Just for interest, this was a piece of the ceramic honeycomb (diesel oxidation catalyst) from our 2003 Toyota RAV4 after about four years of use from new. It was 80% blocked with compacted soot, causing back-pressure which climbed as the revs rose, with the turbo making a chuffing noise as it vented excess pressure, and power dropping away.

? click to enlarge
Photo shows one of the clear parts. The hex 'tubes' are 1mm across, and run almost the complete length of the box (about 30cm in this case).

All this was on a 2.0L D4D running good quality fuel, dieselclean additive, and regularly doing lengthy fast motorway runs.

[Peter.N.]

Thanks for that Chris. I do drive with a very light right foot so the soot probably tends to accumulate but I never had this problem with the other two 406s. I give them an 'Italian tune up' every now and again, especially on the way to the MOT but don't get a lot of soot coming out. I have done it with this one and again not very sooty. When it wouldn't pull the other day it was chucking out loads of black smoke but even after it cleared it still wouldn't pull. We have just done 2500 miles around the country without a problem, in fact this was the first time I filled it up since Asda in Tain about 3 weeks ago with 925.5 miles covered since the previous fill up, perhaps it objects to the change from Scottish to English diesel.

Peter

[white exec]

You can't win. That is an impressive mileage on a tankful, though. You haven't lost the knack!