Page 1 of 2 12 LastLast
Results 1 to 20 of 35

Thread: HELP, engine breaks up under boost

  1. #1
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142

    HELP, engine breaks up under boost

    need some advise on what to do next............

    car starts real hard but when idling it sound good, revs good to 3k after 3.5k starts to break up.

    timed it ,new fuel filter,plugs cap, rotor, and wires.. dis gear good
    there is an adjustable fuel pressure regulator on it also

    hooked up a fuel pressure gauge, goes up to 50 then bleeds down to 20 and holds steady there.

    ordered a new fuel pump and regulator rebuild kit

    please help, thankyou, I am running out of ideas

    Bar

  2. #2
    Building Boost Robertosvo's Avatar
    Join Date
    Jan 2012
    Location
    Great White North
    Posts
    85
    Intercooler hose not sealed properly?
    do a compression check?

  3. #3
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    all hoses are tight and no vacuum leaks

    plenty of compression

    Bar

  4. #4
    Red Captain MikeFleming's Avatar
    Join Date
    Jun 2011
    Location
    Tucson, AZ. USA, Earth
    Posts
    5,081
    Compression Check
    Spark - Verify this
    Fuel - what was fuel pressure at 3500 RPM, free-revving?
    Difficult to believe that fuel would be limited when free-revving since it';s not using much fuel during that time as fuel is related to load, NOT RPM.
    hooked up a fuel pressure gauge, goes up to 50 then bleeds down to 20 and holds steady there.
    50 is kinda high, bleeding to 20 is normal. I assume thee measurements were with engine off?

    Leave the gauge on and see what FP does when free-revving to 3500.

    Air - make sure the VAM isn't sticking.

    Valve springs (aka sticking valve(s)) - related to RPM, NOT load.

    So it starts "breaking up" at 3500 RPM free-rev? Is OK at 3200? Will it get to 3800/4000? Warm engine for sure.

    Is the breaking up random or a rhythmic pattern?

  5. #5
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    fuel pressure was measured when not running
    have not started the engine yet with the gauge on

    VAM is clean and does not stick

    runs fine at 3200 rpm but breaks up above 3500 rpm and up
    break up seems to be rhythmic, when it beaks up I get off of it, do not want to do more damage

    Bar

  6. #6
    Some Boost Laredo's Avatar
    Join Date
    May 2012
    Location
    Stillwater, MN
    Posts
    410
    Borrow / rent / buy a fuel pressure gauge that you can stick under your wiper and test your fuel pressure under ACTUAL load conditions.
    This is when your highest demand for fuel occurs.
    O'reilly's will borrow a fuel pressure gauge free (with a damage deposit).

    The "breaking up" is only under hard boost, correct? What did you gap your plugs to...?

    Bad choices make great stories....!

  7. #7
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    I got a pressure gauge and have posted the results

    plugs are gaped at what is recommended for our cars cant remember what it is off hand


    Bar

    the thing that is frustrating is that I have never had any problems with the car ever since I have owned it
    and to have it start acting up all at once is mind boggling

  8. #8
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    this was a question asked by a person on another thread and my responds...............

    What do you mean by “Starts real hard”?

    Has it sat a while without being driven? Modern gas becomes crap quickly, and while a car will usually start and idle well, it will run poorly under a load. If it’s not driven often, that could be an issue, but please define your statement above better.



    ME
    engine turns over and pops once in a while, need to give it part throttle to get it to start and then the engine does start but still needs part throttle till it gets to a point where the car cleans up its idle and running through the RPM range.

    Bar

  9. #9
    Some Boost Under Pressure's Avatar
    Join Date
    Jul 2014
    Location
    newnan, ga.
    Posts
    371
    I'm having that same problem. I just ordered a new rebuilt distributor. From what I've read about the symptoms I have I think my p.i.p. is bad and probably smoked my TFI all due to heat.
    Your Best Bet, Hire a Vet!
    To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

  10. #10
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    Quote Originally Posted by Under Pressure View Post
    I'm having that same problem. I just ordered a new rebuilt distributor. From what I've read about the symptoms I have I think my p.i.p. is bad and probably smoked my TFI all due to heat.
    let me know want happens,
    I am leaning to fuel on mine
    need a good day where it is not raining to do a pressure check when running

    Bar

  11. #11
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    Well I am going claim a small victory.........................

    change to a different distributor and it seemed to start better but still breaking up out 3500rpm (going to regap plugs and change pip in the original dist. and see what happens then)

    fuel pressure is set at 40 at idle and vacuum unplugged
    pressure goes up and down with the change in RPM's


    Bar

  12. #12
    Some Boost Laredo's Avatar
    Join Date
    May 2012
    Location
    Stillwater, MN
    Posts
    410
    Excellent!!
    Bad choices make great stories....!

  13. #13
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    Quote Originally Posted by Laredo View Post
    Excellent!!
    Not yet.........

    as I said I claim a SMALL victory


    Bar

  14. #14
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    Well thought I had the problem figured out but went to start it last week end aqnd no start

    hear fuel pump
    turn the key to start, engine cranks pops once or twice but that is it
    tach does bounce while cranking

    replaced ignition switch, pip,and TFI(ignition module )

    I am at my wits end PLEASE HELP!!!!!!!!

    Bar

  15. #15
    Red Captain MikeFleming's Avatar
    Join Date
    Jun 2011
    Location
    Tucson, AZ. USA, Earth
    Posts
    5,081
    Quote Originally Posted by svopony View Post
    tach does bounce while cranking

    replaced ignition switch, pip,and TFI(ignition module )
    Sure sign of primary ignition issues: Coil, TFI, PIP, wiring harness to TFI, etc.
    Helping SVO owners & racers since 1984

    Poll Finds 30% Of Americans Still Undecided Whether To Vote Out Of Fear Or Spite

  16. #16
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    coil has been replaced also

    will be doing a computer swap(with a known working unit) today to rule that out.

    Bar

  17. #17
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    The saga continues.....................

    Swapped computers and that did not change anything

    ordered a TFI connector that should be in later today (more fun for tomorrow)

    Bar

  18. #18
    Some Boost
    Join Date
    Jun 2012
    Location
    Acworth, GA
    Posts
    221
    Did you verify your timing and pull codes? Popping while cranking sounds like a timing issue. Maybe it jumped a tooth?

    Weak valve springs will also cause the car to stumble (break up). My Norcal car does it above 3800 RPMs. Haven't had the time to swap the head yet. Can you accelerate or rev slowly past 3500 rpm without issue? If so, my bet is on weak or broken valve spring.

  19. #19
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    Oufda, take a look at these pics,

    thought that might be the problem but after replacing the connector...............

    still have the same symptoms..

    I am at my wits end.

    Bar
    Attached Images Attached Images

  20. #20
    Some Boost
    Join Date
    Jun 2012
    Location
    Back home Whitewater Wi.
    Posts
    142
    Quote Originally Posted by Mike S View Post
    Did you verify your timing and pull codes? Popping while cranking sounds like a timing issue. Maybe it jumped a tooth?

    Weak valve springs will also cause the car to stumble (break up). My Norcal car does it above 3800 RPMs. Haven't had the time to swap the head yet. Can you accelerate or rev slowly past 3500 rpm without issue? If so, my bet is on weak or broken valve spring.
    timing was just reset.

    I think the breaking up was that I did not have the plugs gapped right after the tune up, but now they are at .030

    car has ran a couple of times since all this has happened.

    the car ran great last year up until last fall it sat for 2 months and then I had trouble starting it then got it started and put it into storage for the winter and then you know the rest of the story from the posts.................

    time to call in the certified mechanics................(the big guns ........... my last ditch effort..........)

    Bar

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •