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SOLVED: Half-power, bucking, 500rpm idle, won't rev past ~5K

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    SOLVED: Half-power, bucking, 500rpm idle, won't rev past ~5K

    PROBLEM SOLVED: Failed keyway/woodruff key on crank and crank end gear, to which the harmonic balancer bolts. Timing was therefore WAY off (both cam and spark). See page 3.

    Power is now normal - torque is great, idle is dead steady at 650. She's a runner!!!

    [Original post below]

    Well, damn it.

    Just picked up a cheap '88 cabrio over the weekend - great interior, manual transmission smooth as butter, suspension, brakes, top works nicely, looks decent... has heated seats that work! Neat.

    But runs like a dog. Like, if this thing makes 80 HP, I will eat it. See:


    I've had many e30s, currently have another 325is I can drive back to back, and it's SO SLOW. I drove it about 1,000 miles to get it home, and it got progressively worse - from just slow and unresponsive, to bucking and barely idling.

    Symptoms:
    • Idle is low. 500 RPM.
    • Just cracking the throttle is worse - stumbles and wants to die.
    • No torque under 2K RPM.
    • 2K-3K, pulls smoothly, but very very slowly, at any throttle, including WOT.
    • Above 3K, to about 5K, it sputters at part throttle, very slow at WOT.
    • backpops (burbles) on lift throttle (actually sounds awesome, but it's bad)


    Details of what's been tested/observations:
    • For sure a 2.5 head. Likely a 2.5 block too.
    • TPS tests fine
    • FPR seems good - tested pressure at the rail and it looks great
    • Cap and rotor were swapped for known good - no change
    • C191 looks great
    • Plugs ended up being fouled. New plugs have been swapped in (bosch copper supers)
    • Pulling each plug wire makes the idle worse - seems each plug is firing
    • Grounds look good (hood, strut tower, oil pan)
    • Oil is nice and clean - seems like no blow-by, very little consumption in 1K miles
    • No fuel smell in FPR vacuum line
    • AFM has been swapped with known good - no change
    • Coil swapped with known good - no change
    • Swapped 153 ECU with known good 173 - no change
    • Disconnected O2 sensor - no change
    • CPS replaced
    • CTS replaced
    • Toothed wheel torqued to spec and not separated.
    • Timing belt marks are spot on
    • Valves adjusted to spec - smoother and better top end, no change on part throttle bucking


    I feel like the timing could be way off. Could be a fueling issue, but the car never pings, under any load, and burbles on lift, so maybe too rich?

    Since all the plugs look the same, I don't think any single injector is leaking.

    I'm stumped. I plan on just plowing forward with a timing belt change (don't know when it was last done) and a valve adjust, just to know those aren't the problem... But what could this be?

    Hoping it's something someone else has experienced and fixed.
    Last edited by hwy84; 06-30-2016, 08:27 AM.
    Current:
    1991 325i Sedan - S50 Swap
    1988 325i Cabrio

    Past:
    1991 M3
    1991 318is
    1985 325e

    #2
    You said maybe too rich? Does it smell like it's running rich? If so, it could be timing...as in timing belt jumped a tooth.
    sigpic

    92 325iC Diamantschwarz factory M-Technic appearance
    99 M Roadster Dakar Yellow II
    97 318ti Active Bostongrun DD
    01 Z3 3.0i Coupe Black Sapphire
    93 325iC Schwarz II. Sold, but not forgotten.

    Comment


      #3
      Originally posted by e30topdown View Post
      You said maybe too rich? Does it smell like it's running rich? If so, it could be timing...as in timing belt jumped a tooth.
      It certainly doesn't smell WAY rich, but it doesn't smell stoich-y either.

      I am thinking timing belt as well (have a new tensioner and belt on order - since I don't know when that job was last done anyhow) but I read conflicting reports about that:

      Some say "I was one tooth off, and the car ran smooth! I never knew!" and some say "One tooth off, and you're toast."

      Have you had experience with running one tooth off?

      Thanks for your help - I am totally looking for data/recommendations at this point... Keep 'em coming!
      Current:
      1991 325i Sedan - S50 Swap
      1988 325i Cabrio

      Past:
      1991 M3
      1991 318is
      1985 325e

      Comment


        #4
        Check the crank position sensor off your list.

        1991 325iS turbo

        Comment


          #5
          Originally posted by ak- View Post
          Check the crank position sensor off your list.
          I have a known good CPS - I'll swap that in tomorrow night and see if it makes a difference. Thanks!

          I have had CPS failure before - usually the car just won't start at all. Guess there are multiple kinds of failures...

          Keep the thoughts coming - and thanks again!
          Current:
          1991 325i Sedan - S50 Swap
          1988 325i Cabrio

          Past:
          1991 M3
          1991 318is
          1985 325e

          Comment


            #6
            Originally posted by hwy84 View Post
            I have a known good CPS - I'll swap that in tomorrow night and see if it makes a difference. Thanks!

            I have had CPS failure before - usually the car just won't start at all. Guess there are multiple kinds of failures...

            Keep the thoughts coming - and thanks again!
            No worries. My issue was my CPS was positioned too far from the gear when assembling the engine so I had a brick wall at an RPM with some hesitation prior.

            1991 325iS turbo

            Comment


              #7
              Added a video above to show how slow it's running.

              Note:
              • No pinging at WOT (so not lean)
              • Starts bucking at 5K or so, eventually made it to 6K, after I stopped the vid
              • This is actually it doing well - it's often worse than this/more pronounced
              Current:
              1991 325i Sedan - S50 Swap
              1988 325i Cabrio

              Past:
              1991 M3
              1991 318is
              1985 325e

              Comment


                #8
                Originally posted by ak- View Post
                No worries. My issue was my CPS was positioned too far from the gear when assembling the engine so I had a brick wall at an RPM with some hesitation prior.
                Well, I quickly removed and cleaned the CPS (not the good one yet, but the one on the car all this time). It was very dirty with road grime.

                Idle is now up to 750 or so, instead of 500, but that may be coincidence - the car was also stone cold, and the problems usually worsen when it's warm.

                But maybe it's a positive sign! If cleaning helps, maybe replacing will really help... maybe. Heh.
                Current:
                1991 325i Sedan - S50 Swap
                1988 325i Cabrio

                Past:
                1991 M3
                1991 318is
                1985 325e

                Comment


                  #9
                  Holy moly that is slow. You sure your throttle cable isn't miss-adjusted or super stretched? Haha.
                  I'd be looking at fuel next, pressure, injectors, pump considering your hesitations.

                  1991 325iS turbo

                  Comment


                    #10
                    Originally posted by ak- View Post
                    Holy moly that is slow. You sure your throttle cable isn't miss-adjusted or super stretched? Haha.
                    I'd be looking at fuel next, pressure, injectors, pump considering your hesitations.
                    Seriously! Throttle cable stretch was the first thing I checked - I just couldn't believe it was all the way open. ...But it is.

                    I'll check fueling, though I feel like if it was lean, it's be pinging all over the place. Maybe not... worth looking into for sure.

                    Thanks!
                    Current:
                    1991 325i Sedan - S50 Swap
                    1988 325i Cabrio

                    Past:
                    1991 M3
                    1991 318is
                    1985 325e

                    Comment


                      #11
                      Fuel Pressure is good - Teed in a gauge and it looks perfect. So, not the FPR...
                      Current:
                      1991 325i Sedan - S50 Swap
                      1988 325i Cabrio

                      Past:
                      1991 M3
                      1991 318is
                      1985 325e

                      Comment


                        #12
                        Sound similar to my issue last summer

                        Crank position sensor.

                        And keep the injectors clean. (Lubricant)

                        Comment


                          #13
                          Thanks for the reply - lots of things pointing to CPS, or other timing-related problem. I have a new CPS arriving tomorrow, so we'll see!

                          I also noticed that the toothed wheel on the harmonic balancer is a little wobbly at idle - maybe moves 3mm as it spins. I'm starting to wonder if in fact it has come loose from it's backing, and is totally out of whack, like in this thread: http://www.r3vlimited.com/board/show...=147102&page=2

                          I'll investigate more over the next couple of days.

                          Keep the ideas coming, and thanks all!
                          Current:
                          1991 325i Sedan - S50 Swap
                          1988 325i Cabrio

                          Past:
                          1991 M3
                          1991 318is
                          1985 325e

                          Comment


                            #14
                            Having similar issues, gonna keep an eye on this thread.
                            Dean
                            Instagram
                            1987 325isA
                            1987 325i - 383k

                            Comment


                              #15
                              How little play should the vibration dampener have when bolted to the crank?

                              I pulled the belts from the pulleys, and if I work at it, I can make the vibration dampener clunk around a little bit.

                              When I watch it spin with the car idling - It appears to be pretty out of round, maybe by about 3mm.

                              Replace it? Is it fine?
                              Current:
                              1991 325i Sedan - S50 Swap
                              1988 325i Cabrio

                              Past:
                              1991 M3
                              1991 318is
                              1985 325e

                              Comment

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