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'91 740 turbo dumps boost under acceleration...weird. HELP! Usually 4000rpm. 700 1991

posted by  Dragwagon on  Fri Sep 5 07:00 CST 2003
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last visit: Thu Dec 1 16:21 CST 2011
[RELATED]

Let me elaborate a little more on it because its a weird one.

It happens around 4500 rpm when cold and 4000rpm once warm:

WHAT HAPPENS, you might be asking?

The car dumps all boost and will not regain. Also drops to about 3000rpm and stays there. It will not regain "consciousness" unless I take my foot totally off of the throttle for a few seconds and resume acceleration slowly. Get to 4k rpm again...BANG, it does it all over again. It's not the boost level. It will hold peak boost from 2200 rpm and up and then dump it around 4000rpm. If I keep my foot in it, it will just settle in and sit there at 3000rpm, barely moving along for as long as I hold my foot in it.
Replaced intercooler hoses because they were soft (old ones weren't collapsing as far as I can tell, though.) It feels like a golf cart with a governor...takes off pretty well and then drops into a no-power state. No black smoke, no red hot exhaust manifolds. Car has 179k on it, though.

I have an exhaust leak when cold but I don't think that could be related. Has anybody seen anything like this before? MAF, TPS? Wastegate? Fuel pump? Clogged converter? No codes in self-diagnostic. I'm lost. Fairly ignorant when it comes to Volvo turbos...sorry.






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