1994 855T boost cutting in and out

azureblue · Post by **azureblue** » 18 May 2015, 10:28

1994 855T auto ---- I start it, let it warm up to normal, the drive it. After a couple of stop & starts, like backing onto the street, a traffic light or two, the boost goes away, like a switch was thrown. Up to that point, it works fine. I can drive it on the highway at say 60mph and there will be no boost, but I can feel it trying to come on, sort of like a stutter. I almost feels like a loose wire making intermittent contact..If i floor it, get the RPM's up to 4K or so a couple of times, then come to a stop, the next time I push the pedal, the boost is back. And generally, it will stay that way, working fine. I am getting a front knock sensor ODB code, but I am not sure if one has anything to do with the other. So, could it be a stuck wastegate?

Post by **matthew1** » 18 May 2015, 10:32

Sounds like a collapsing intercooler/throttle body hose. Or a half-blown off hose.

azureblue · Post by **azureblue** » 18 May 2015, 15:19

I'll look for that, but it sure acts like a bad electrical connector or stuck BOV...

Post by **scot850** » 18 May 2015, 16:06

Try replacing the TCV. Sounds like it is failing. Also check the pipes to it for cracks.

As Matthew suggested, also check the hoses and intercooler for cracks.

Neil.

azureblue · Post by **azureblue** » 18 May 2015, 17:16

TCV?

I'm going to get an OBD2 read Tuesday, too.

Post by **pkc303** » 18 May 2015, 17:39

I had a similar situation, turned out to be a collapsing intake hose. Only Volvo made that particular hose at the time, and it was priced accordingly. I suspect a hose collapse or a leak.

azureblue · Post by **azureblue** » 18 May 2015, 19:07

There is a well stocked parts yard nearby, so I'm going to get the valve and maybe hoses, and the Intercooler hoses as well. It sure acts like that valve is sticking.
The yard has 850's, 70's, 60's and maybe an 80 - are the valves all the same?

Post by **pkc303** » 18 May 2015, 21:13

I'm not sure if they are the same.

My problem was the intake hose after the intercooler. It collapsed under high suction, but not at idle. It had a lot of oil on it, and I guess got weakened.

Post by **scot850** » 18 May 2015, 22:42

TCV is Turbo Control Valve. It has 3 pipes running to it and typically mounts on the air intake box on turbo S/V70's. Having had a look at 850 parts drawings, it may be called a Pressure regulator part # 1271630. Fitted to 850 turbos from 94-97, it looks like it does the same job as the TCV. IT regulated turbo boost pressure. The valves stick or seize limiting turbo boost.

Neil.

Post by **scot850** » 18 May 2015, 22:43

Part looks like this as per FCPEuro:

https://www.fcpeuro.com/products/volvo- ... 50-1271630

Neil.