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96 940 Turbo overspin

My brother-in-law has come up with another problem with his car (having sorted the oil pressure problem with a new pump, following crudy oil on purchase). I have driven it a verified the problem.

After about 10 minutes hard driving the turbo seems to overspin on application of any power and makes a loud high pitched wine combined with a loss of power. All the pipes seem in good condition, turbo is a bit oily with about 1mm of endfloat movement in the shaft (ie axially).

I don't know much about dump valves but this is where my suspicions lie. It didn't sounds right (compared to my well sorted 95 940 Turbo, although it is higher pressure/higher power). There wasn't the normal pssht after gear change and there seemed to be delay after taking the foot off for the turbo to spin down. Then if I applied power as the spin down was happening it seemed to make the dump valve stick and after that the turbo was just dumping air into the exhaust and would overspin when you put the foot down.

I don't understand is how this works. There is an electrical switch connected to the pressure line which operates the dump valve (if thats the thing connected to rigid pipes to the exhaust and inlet manifold), could this be faulty, what controls it?

Also the lamda sensor light is always on now. Is this because of the continous mixture problems?

Whats the most likely problem, dump valve, switch? Does it just need a clean or should I replace it anyway?

Reply to
Tony Stanley
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I've come to the conclusion that the thing I thought was the dump valve isn't. Where is the dump valve?

Volvo dealer parts guy thinks it is bolted to the side of the turbo.

Reply to
Tony Stanley

The valve is bolted to the side of the compressor housing on the turbo. It isn't a dump valve like the kids like to use - on that dumps the pressure out where you can hear a great whoosh - it just dumps it back into the compressor inlet. This valve is opened by vacuum in the intake manifold.

First thing I'd do is read the code, and see what that problem is.

Reply to
Mike F

I think we need to fix the turbo first before looking at the lamda light, besides thats another thing I don't know how to do, but doesn't look too difficult.

The dealer said it was just called a 'valve' and cost £150, so either I will try to clean it or we'll put in a recon turbo (£300 from ECP). The Engine has a history of sludge, blocked oil pump, oil consumption and the turbo shaft has about 1mm of axial play, so it would make sense to change the turbo anyway (if we can still get one). Also I need to check there isn't sludge in any of the control pipes.

Does the valve come off easily, needs a gasket, or should I just go for the recon turbo.

Reply to
Tony Stanley

I had a B230ET I think and had turbo /dump valve problems.The dump valve on mine was bolted to a metal bracket at the left front of the head and the hose going to the intercooler was clamped to the other side of the bracket.My problem was that the valve had come loose on the bracket and the pressure had blown the joint out.Unless you are getting a lot of oil in the intercooler or out the exhaust I would not worry too much about the end float in the turbo.Do you have a pressure gauge on the dash for the turbo?I also seem to remember that the dump valve was vacuum controlled and that there was a non return valve in the line that you had to be careful not to fit the wrong way round. This might not relate to your engine at all but if it does I have a manual somewhere. regards,Mark.

Reply to
mark

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