The dash vents on my 88 764ti stop blowing under boost (seems to go to the floor). (Background - just bought car last weekend, first 7 series and first turbo. Prior to this, I had an 88 244 for about a year.) I looked at the 700/900 faq and found a few relevant posts, as well as the archive. I used my mitivac to pull a vacuum on the motors under the dash and each held vacuum well. I've replaced various vacuum lines that looked bad. That seemed to help the situation, as it takes a little longer to bleed the vacuum and get dead vents. I was looking for a vacuum canister, but couldn't find one (does it exist on this model? I noticed a few posts point to the bumper area, I will check there tonight.). I did find what looks like a vacuum pump on my drivers side inner fender. An archive search turned up a little info, but not much. I'm guessing this pump should turn on when vacuum levels fall so the system will continue to work. How do I test? Also, there are two nipples on the bottom. Only one has a hose on it. Should the other have one too? My Haynes manual is in the mail, so if it is in there, I'll find it soon.

Also, there were three hard plastic lines coming out of the firewall near the a/c dryer. Two white, one black. One white and the black is hooked to the top of the intake with what appear to be white valves. Do these block boost from the system? If so, do they go bad? The second white line was plugged with a short piece of hose and a colored pencil. I've replaced that setup with another short piece of rubber hose and a better fitting screw. I can't find anywhere to hook this to that is obvious. Any engine bay pictures on the web that may show the routing?

Sorry for the long post. It's getting aggravating loosing air while going uphill or accelerating. All help appreciated.

Apparently, in the front bumper, there is a vacuum reserve canister. I would check this thing also. could be cracked or else.

I had the same problem with my '89 and never found any leaks anywhere. Sold the car and then I learned about that canister. Made sense that this could have been the problem as the car front end was repaired by the previous owner after an accident.

Well, I checked last night and there is no vacuum reserve canister under or around the front bumper. I'm going to the dealer today to see about getting new check valves, but I would appreciate it if somebody else with an '88 760ti check the routing of the three plastic vacuum tubes (two white, one black on mine) that come from the passenger side firewall. Also, if this same person could look for a vacuum canister, that would be great. (Maybe Volvo eliminated it in '88?) My Haynes manual still did not make it in yesterday. Hopefully today.

One other question. There is a vacuum tube running to an electical switch or sensor that is mounted in a bracket on the headlight side of the radiator overflow container. Vacuum line in, wires out. What is it?

Thanks again for all the help.

Nevermind. Not two minutes after posting, I stumbled on an explanation on the MVP site. (Overboost switch).

The vacuum pump you see is for cruise control. My '85 765T has another, larger pump mounted up high, just behind the battery. I don't thnk your's has it.

Get a vac guage, splice it into the interior system, then just keep fixing vac pipes til it always holds vac, even under boost. Also check the check valves - they may be missing.

no worries -dave