Volvo RWD 700 Forum

INDEX FOR 10/2025(CURRENT) INDEX FOR 7/2006 700 INDEX

[<<]  [>>]


THREADED THREADED EXPANDED FLAT PRINT ALL
MESSAGES IN THIS THREAD




  REPLY TO THIS MESSAGE    PRINT   SAVE 

annoying intermittent boost problem 700

posted by  Rtilghman on  Sun Oct 27 05:53 CST 2002
Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS] [RELATED]

1985 745t

Brickers:

Over the past few months I've been having an internmittent problem with my turbo and car's driveability. What happens is that when the turbo enters the yellow or spools up and starts boosting, the engine seems to retard. The more boost I give it the worse the engine seems to perform, until it actually seems to kind of stumble under full boost (floored, pinned at top of yellow on boost gauge). When the car is experiencing this problem the best performance is usually found by keeping the turbo needle right at the top of the turbo gauges black area.

The problem is generally in place for an entire trip, meaning if it happens it will happen non-stop from the time I turn the car on until I turn it off for a little bit, with no let-up whether I drive easy for a bit or not. Also, when this happens I usually end up seeing a wet spot around the oil filler cap on top of the crankcase cover. Whether that wet spot is symptomatic or just coincidental I have no idea.

At first I figured the problem was just excess crankcase pressure, and replaced the oil separator, cleaned all the tubes, and replaced the plastic split. This seemed to help for a little bit but didn't solve the problem. I'm now thinking this is a faulty knock sensor issue, and that the knock sensor is incorrectly retarding the timing. However, would that cause excess crankase pressure?

Is it possible the oil return line from the turbo is getting intermittently blocked somehow, and that that is causing the engine to stumble under boost and leading to excess crankase pressure? What would cause it to happen infrequently AND to last for the duration of a trip?

Would a faulty CBV working intermittently cause the car to stumble under boost and increase crankcase pressure? Maybe the CBV is somehow getting stuck open or closed?

I'm at wits end here, and am eager for any advice folks can offer. I'm planning on replacing the knock sensor regardless because I think its dying at 220k miles and is worth swapping out, but would like to finally fix this problem once and for all.

Thanks,
rt








  •   REPLY TO THIS MESSAGE    PRINT   SAVE 

    annoying intermittent boost problem 700

    posted by  someone claiming to be Brad on  Sun Oct 27 12:11 CST 2002 [RELATED]

    I would suspect the engine coolant temp sensor also. I had the connector on mine come undone and it ran like the timing was retarded. I also had a power stage (new) that was bad and caused the timing to move around. When I replaced my knock sensor, I didn't get any improvement.
    Brad








    •   REPLY TO THIS MESSAGE    PRINT   SAVE 

      annoying intermittent boost problem 700

      posted by  Rtilghman on  Sun Oct 27 12:57 CST 2002
      Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS] [RELATED]


      john sargent mentioned that in a previous post a while back as a possible source, but I have yet to get down and dirty and really check it out.

      Why would a problem with the engine coolant temp sensor cause this intermittent problem? If the sensor is failing intermittently, does the failure to report the temp to the CPU trigger it to retard the timing? Does it respond to no signal like the engine is cold or like its hot?

      I guess I moved past the coolant sensor because I figured I would see some indication of teh problem when the boost isn't engaged as well as when it is. The fact that it only appears when I'm boosting keeps pushing me towards an electronic item associated with the turbo.

      Argh... well, I need to swap outthe radiator and the heater valve, so maybe I'll just do the coolant sensor at teh same time. Just to be sure, the sensor you are talking about is the one under the intake manifold, right? Not the one on over near the water pump?

      thanks,
      -rt








  •   REPLY TO THIS MESSAGE    PRINT   SAVE 

    annoying intermittent boost problem 700

    posted by  JohnB@MAC on  Sun Oct 27 10:07 CST 2002
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Sun Dec 9 10:15 CST 2007
    [RELATED]

    If you're pouring black smoke out the rear while this is happening you undoubtedly have an intake system leak, probabably at the cbv. There are two bolts that hold it to a bracket and on my 87 760T they backed out several times.

    I finally got them to hold with red loctite, split lock rings, and Grade 8 socket head cap screws. And a new gasket.








    •   REPLY TO THIS MESSAGE    PRINT   SAVE 

      annoying intermittent boost problem 700

      posted by  Rtilghman on  Sun Oct 27 10:20 CST 2002
      Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS] [RELATED]


      CBV connections all appear solid, so I don't think that's the problem. I'm also not blowing any smoke at all during the condition I describe, which is why I don't think it's a problem related to the turbo's operation.

      Very annoying really... except for thr symptoms I describe, there are none of the larger tell tale signs of certain problems. I do blow a little bit of white smoke/vapor at start-up in cold weather, but nothing abnormal and it disappears once the exhaust system heats up.

      thanks for the post, any further thoughts appreciated.

      -rt








      •   REPLY TO THIS MESSAGE    PRINT   SAVE 

        annoying intermittent boost problem 700

        posted by  someone claiming to be mark on  Sun Oct 27 17:13 CST 2002 [RELATED]

        Just a shot in the dark. Plugged CAT?







<< < > >>



©Jarrod Stenberg 1997-2022. All material except where indicated.


All participants agree to these terms.

Brickboard.com is not affiliated with nor sponsored by AB Volvo, Volvo Car Corporation, Volvo Cars of North America, Inc. or Ford Motor Company. Brickboard.com is a Volvo owner/enthusiast site, similar to a club, and does not intend to pose as an official Volvo site. The official Volvo site can be found here.