1994 855T boost cutting in and out

[azureblue]

Thanks - I found a picture of it. I gather that this is the only one for the 850, as the design was changed, but the way it works wasn't changed.

[azureblue]

I found a replacement (they had a C70 with some beautiful wheels on it at the yard - not the right time for me) , and put it in, but I think the real problem is the hose that runs from the center nipple to the intake pipe was loose and rotted. The "white" hose will have to be replaced, too, but the red hose that leads to the wastegate was fine. No more time until Saturday to work on it.... I may put the original TCV back on, too.

[scot850]

Yup, not having the hoses on there won't allow the pressure to build and hold in the valve. 2 pipes are pressure, 1 is vacuum. Can't remember which just now, but you can look on IPDUSA web-site, they have an aftermarket HD TCV for P80 models, but there is a set of install instructions with pipe routing. I suspect it will be similar for 850's.

http://www.ipdusa.com/products/8901/120 ... 70-v70-c70

Near the bottom of the page there is a set of install instructions on a pdf file. Read this first.

They actually list this as an option for the 94 850 turbo also.

If you decide to go this route and try the IPD HD TCV, don NOT turn the front elbow in any more than 4 turns max. If you do it jams the valve from operating. Ask me how I know......!

Neil.

[azureblue]

Yup, not having the hoses on there won't allow the pressure to build and hold in the valve. 2 pipes are pressure, 1 is vacuum. Can't remember which just now, but you can look on IPDUSA web-site, they have an aftermarket HD TCV for P80 models, but there is a set of install instructions with pipe routing. I suspect it will be similar for 850's.

http://www.ipdusa.com/products/8901/120 ... 70-v70-c70

Near the bottom of the page there is a set of install instructions on a pdf file. Read this first.

They actually list this as an option for the 94 850 turbo also.

If you decide to go this route and try the IPD HD TCV, don NOT turn the front elbow in any more than 4 turns max. If you do it jams the valve from operating. Ask me how I know......!

Neil.

thanks _ wish I had taken the time to research interchange - I didn't know the 60 and 70 series TCV would swap. But I got a used one from an 850. I will assume that all the Volvo TCV valves for 850, 60 70 and 80 function the same way.. IOW, I could go get a newer one, if it would improve the performance over the stock one. Considering parts yard wants $5.00 for it, it's worth a try..

The original one looked to be in good condition, so I may try to clean it out and put it back in. I still have to replace that TCV to turbo hose. I will bet it is leaking, too, and the two were probably the problem, not the TCV.. That's on the Saturday greasy cuss word to do list..

Thanks for the advice -always spot on..

[azureblue]

Something is hanging up in there! I thought replacing the TCV and hoses solved it, because it worked great for a while, but the problem returned. Ideas? I don't know much about the OBD1 but can that be used to track down the problem?

[azureblue]

As the cow said, if it ain't one thing it's an udder...

When I pulled out the airbox, It found a hose under there that was keeping it from locking into place. It's about an inch in diameter and seems to run from an idle speed control motor above the starter, under the airbox, then back towards the firewall. It's in good shape, but I can't figure out how to correctly route it. I also found an intercooler hose and a radiator hose touching each other with this 1" hose running under both of them. Does anyone have a picture (or link to pix) of that area, so I can route all of them them correctly? My Haynes manual pictures are too low rez to make anything out.The 1"hose has a couple of cuts in it from rubbing on the mounting brackets for the airbox, too and it has a junction connector under the airbox, too. The car had the drive train replaced before I got it, and I keep finding things like this every time I get under the hood..

I'm going to try the whack on the waste gate "fix" next. I'm running out of ideas....

[hausmeister]

Pretty sure that is the vacuum line to the brake booster. I think you can find some pictures of it in the PNP removal threads - as it needs to come out during fixing that. I think there is also a video from Robert.
If it is damaged I would replace it. Best would be to replace all vacuum lines with silicon, especially if you are having boost issues and they are still original.

[azureblue]

This cuttign out problem is getting aggravating. I think I fix it and it comes back. What is happening is that it will go into boost sometimes, then sometimes not. If it does not boost, I try a couple of full throttle accelerations on a slight incline from both standing start and at maybe 25mph, to see if something is stuck. Sometimes, that will get the boost back, but not always. If it does not, when I am on the highway at maybe 60mph, level ground I feel it cutting it and out. Then, for not reason I can find, it comes back and everything works great. Sometimes it will come back, but not boost to factory spec, just sort of halfway, but then on next cycle of take foot of acc. pedal then accelerate, it works fine. And sometimes, if it does not boost, I can shut the car off, and it works perfect after a restart. All hoses look good I can't find anything disconnected - It acts like a stuck valve or bad electrical connector.

Is there a way to ID with an OBD2 test?

Anyone have any ideas, before I give up and send it off to a mechanic or exorcist?

[matthew1]

https://www.matthewsvolvosite.com/forums ... 27#p366727

[erikv11]

What Matt said. First thing that must be completely exorcised is vacuum leaks. So that includes all PCV lines, brake booster line, TCV lines, and especially the intercooler hoses, and their connectors in every case. If you car has still any of the original rubber lines then any one of these could be rotting and bad.