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View Full Version : Starter Replacement and Mystery Vacuum Hose



StoningtonXC70
08-11-2010, 04:43 AM
In the last few days, I have had more than a few incidents with my 98 V70 XC where the engine would not crank on startup, but would eventually do so after repeated attempts. When this happens, I can hear the starter relay solenoid pick up, and the lights will dim, so I believe that the stater is drawing current, and has a dead spot on the commutator, and or bad brushes. On the last incident, after several unsuccessful repeated starting attempts, it cranked immediately after giving the starter a whack with a big crescent wrench. At 185K, its probably time for a new starter.

While attempting to replace the starter last night, I came across a small diameter vaccuum line that wasn't connected to anything lying down below the throttle body. I had just removed the plastic shroud over the throttle body, and had not yet touched anything else. I could not find anything that it should be connected to within the reach of its length.

It has a single white tracer marking on it. The other end appears to be somewhere up behind the drivers side end of the head (could not trace it any further, got buried into a bunch of other hoses).

I don't think it came loose when I simply removed the TB shroud. Judging by the condition of the end of the line, which seemed pretty crusty, with the factory clamp moved up the hose about a half inch of the bitter end, it seems to have been floating loose for a long time.

After I got the turbo intercooler hose sections out of the way to get at the starter bolts, it had gotten pretty dark. It looked like getting the bolts out, and disconnecting the starter wiring was going to be a real PITA. I decided that I would bite the bullet and turn over the rest of the job to my local indie mechanic. I reinstalled all the turbo plumbing, and the car started and ran totally normal. I did not feel any vacuum suction or pressure on the end of the mystery vacuum hose with the engine running. The car has not been throwing any CEL codes either before or after I came across the mystery hose.

Any ideas what the mystery hose might be? I could not see anything about it on the small and hard to read vacuum hose diagram sticker on the underside of the hood.

StoningtonXC70
08-14-2010, 06:35 AM
It looks like the other end of the mystery hose with the white tracer terminates somewhere near the turbo wastegate. The diagram on Matthew's Volvo Site, which is an enlargement of the sticker on the inside of the hood, and does not have many color code references, shows a line from that vicinity terminating at either the throttle body or the intake manifold at the engine side of the throttle body. However, all the hose nipples at those locations are either capped or have hoses on them. I'm stumped. The length of the mystery hose end suggests that one those locations might be the intended destination.

The engine has not had any work done to it in that area since the head was replaced by an indie shop about two years ago. Suspecting that the hose was left adrift then. As I said before, no driveability issues. Will call the indie shop Monday and see if they can help with this. In the mean time, anyone else know what this line is and where it should be going? Have now plugged it for the time being, no notable change in performance.

StoningtonXC70
08-28-2010, 08:25 PM
Solved the mystery - I think. Pulled the air duct on the turbo side of the air mass meter for better access and traced the mystery hose to the bypass valve at the turbo. Read up on the turbo removal procedure in my Haynes which confirmed that the bypass valve line had a white trace on it. The vacuum diagram under the hood ( a readable copy of which is posted on MatthewsVolvoSite.com) makes no mention of a white trace line, but does show a line from what looks like the bypass valve (not labeled) to a spot on the throttle body (horribly drawn diagram). I put the loose end of the line on one of the nipples on an L shaped vacuum "tree" on the intake manifold side of the throttle body. All of the nipples there were either capped or had lines on them. The line length to go to this location seemed logical.

As soon as I took the car out for a run, I noted a big difference in the throttle response - a LOT more punch and torque when I gave the throttle the boot. It was pretty good before, but way better now! I am pretty sure now that the line was left off during the head replacement a few years back. Since all the nipples on the intake manifold were capped, I never had an actual vacuum leak that would have screwed up the idle big time. Apparently I have not been getting full boost because of the incapacitated bypass valve. Never did find a decent vacuum diagram anywhere - but did find a lot of posts from people with similar problems trying to sort out what line goes where!