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87 325es: Hesitation and near stall after warmed up

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    87 325es: Hesitation and near stall after warmed up

    Hello everyone.

    I'm having an issue with my 1987 325es with an M20B27. After the car gets warmed up, it will lose almost all power and seem to stutter. When this happens, the revs stay up but the econometer goes to zero, even off throttle. If I'm at a stop, the engine will not make enough torque to move and it will have a lot of hesitation to bring revs up. I captured a video of the behavior while stopped:



    Sorry for the shoddy camera work, but you can hear the rough sound of the engine while at a stop sign. After a while, the behavior resolves and I'm able to take off. The rest of the video is on the downhill, but you can see the econometer is pegged at zero in the beginning phase when the car is moving, briefly even when i'm off the gas.

    My research suggests that it's the injector pulses or fuel system delivery but where do I begin diagnosing that? Most of the threads that feature this issue dead end. I'll do my best to bring it to completion.

    Thanks in advance for the help.

    #2
    Lets start by looking at the current shape of the engine. Have you replaced any parts? Was the car running well before? Did you just get the car running after sitting for a while?

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      #3
      Originally posted by jbontke View Post
      Lets start by looking at the current shape of the engine. Have you replaced any parts? Was the car running well before? Did you just get the car running after sitting for a while?
      No parts replaced yet. If possible I want to put extra effort into testing because I plan to take this engine out next spring for an LS swap. Doesn't make sense to be replacing a bunch of parts trying to fix and issue.

      The history of the car looks like this:

      -The previous owner drove the car some but I suspect it was not driven often. He reported that the car suffered from some surge on the highway and had a new regulator that he gave me to hopefully address the issue. However most of what I've read does not point to a bad regulator causing my issue

      -Purchased in December and drove it about 60 miles home. It drove fine for about the first half of the trip but in the second half I would get this type of hesitation and bucking behavior. It seemed to occur if I was driving at relatively low speed (~40mph) at a steady state (unchanging throttle position) for a mile or more. It went away relatively quickly after it started but came back a few times on the remainder of the trip. I filled up about halfway through the trip with 93 octane.

      -I chose not to register or drive the vehicle over the winter to protect it from salt. It sat in an unheated but covered carport. The car was kept protected from vermin but not winterized in any other way.

      -I took the car for a drive for the first time on Friday to get a VIN check performed. It started up real easy, first couple cranks. It drove fine on the way to the station (6 miles) but started exhibiting the issue on the second half of the return trip. It seems to be related to the car being fully warmed up for a while.

      -One more piece of info. I looked at the battery voltage when the vehicle is on and it only reads 13.2V. I'm wondering if a bad alt could cause this issue.

      Thanks for any info you can provide. Personally, I think my next move should be to plumb the fuel line and get a voltage readout in the cabin so I can see what changes when the issue occurs.

      Comment


        #4
        Lets try a few things. Pull the fuel filter and see if rust/junk comes out of the input side. When its running rough, use a pair of pliers and pinch the return fuel line from the fuel pressure regulator. See if it wake back up with more pressure. Lastly, the ECU coolant temp sensor tells the ECU what fuel/timing maps to use as the engine warms up. Test it so see if it within specified range.

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          #5
          Originally posted by jbontke View Post
          Lets try a few things. Pull the fuel filter and see if rust/junk comes out of the input side. When its running rough, use a pair of pliers and pinch the return fuel line from the fuel pressure regulator. See if it wake back up with more pressure. Lastly, the ECU coolant temp sensor tells the ECU what fuel/timing maps to use as the engine warms up. Test it so see if it within specified range.
          These are all very easy to check. Will do and will report back.

          Comment


            #6
            If only when warm, need to check systems that affect fuel and/or spark at said temps.

            Sounds like a bad TPS or CTS for ECU. Simple multi-meter test will do. Check for short on idle switch and resistance on coolant sensor. "Might" be bad AIT in AFM, also easy check with DMM.
            john@m20guru.com
            Links:
            Transaction feedback: Here, here and here. Thanks :D

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              #7
              Okay, I replaced the coolant sensors, checked the fuel pump (everything is good there), also cleaned the MAF and TB. I noticed that if I crimp the vac line from the ICV, the idle is fixed. My next task is to test what's actually causing the ICV to be open when it shouldn't me. Does anyone know the proper voltage that's supposed to be sent to that solenoid when it's closed/open?

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                #8
                You can clean up carbon deposits form the ICV and help it's operation. It maybe gummed up with carbon deposits. I cleaned mine with some electronics parts cleaner (I heave read to not use too harsh of a solvent when cleaning). See if that helps the idle out.

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                  #9
                  Might be the notorious injector harness connection under the intake manifold.

                  Try cleaning it first.

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                    #10
                    ^^^ c191 isn't on eta cars.
                    john@m20guru.com
                    Links:
                    Transaction feedback: Here, here and here. Thanks :D

                    Comment


                      #11
                      Sorry i know nothing about etas

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