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    Engine stumbles/cuts out over bumps :(

    I'm just over a year into the ongoing refurbishment of my 1985 323i (euro model) and have recently developed an issue that's got me stumped. It's got a 2.3 liter version of the M20 with LE-Jetronic Fuel Injection and a 5-speed.

    When changing lanes on the way home from work last weekend I went over one of the small reflector bumps that are attached to the dashed lines between freeway lanes where I live (Seattle area) and the car sort of hiccuped. I was in the middle of dictating a message with voice-to-text and it was such a brief interruption in power delivery that I thought I was imagining things.

    Unfortunately that proved not to be the case and a bit further down the road it happened again. This time, however, it wasn't so brief. I had struck another little reflector thing and the car simply would. not. accelerate. When I put in the clutch it would idle just fine but it wouldn't rev past ~1500 or so and would just sort of bog when in gear. After weaving through traffic over to the curb and popping the hood, I couldn't find anything leaking, out of place, or on fire. Got back in and the car started up, revved just fine, and pulled well enough to get back into traffic without causing an accident.

    This happened a couple more times on the way home, even after getting off the freeway. I got it home and starting checking electrical connections everywhere, thinking it was a grounding issue or something. Cleaned connections here and there and snugged stuff. Drove it around and thought it was fixed until I was almost home and it happened again. WTF

    Parked it for a couple of days until I had time to look at it again and check things that had helped others with similar problems according to the internet. I did find that the boots on my fuel pumps connectors were loose (probably from some testing/troubleshooting I'd been doing a few weeks before) and snugged them up. Took it for a spin and everything seemed happy. Drove it downtown for a show that night and then into work the next day and all was well.

    That is, until it happened again on the way to help my roommate check out an old Mercedes diesel he was buying. I had 50 more miles to go on that round trip and it got us there just fine. It seemed to start happening about 5 minutes into the trip and happened 4 or 5 times but then calmed itself down somewhat. It was the first rainy day we'd had in a while so I was grateful it didn't quit altogether. It made it home without a stumble.

    I made it back to work the next day (yesterday) just fine but on the way home it was particularly frequent. Any PNW member is probably aware of some rough/wavy pavement on i5 southbound in N Seattle between 145th and Northgate - that stuff kicked my car in the nuts last night several times in a row but I managed to get home with the ol' off-and-on magic cure. No idea why that would fix it.

    Anyway, it seemed worse this morning starting with the onramp to i5 and I was having trouble just getting up to speed because I was flicking it off and on so much. I just got off at the next exit and got my other car. Now here I am wondering what the hell to look at next when I get home.

    TL;DR - Basically, the car is sometimes rendered impotent upon hitting a small bump (not every small bump).
    When this happens it will sometimes be idling just fine but other times it will be roughly idling at ~500 RPM but in all cases it won't accelerate/maintain speed nor will it rev up when out of gear.
    Turning the key off and on cures it - just flicking it off/on quickly enough that the engine doesn't even miss a beat is enough in some cases, other times it takes a couple of attempts.
    It seems to happen most often at freeway speeds but does happen in city driving as well.
    '75 Honda CB400f
    '85 BMW 323i Euro
    '04 Acura TSX A-Spec

    #2
    Recently replaced:
    Spark plugs
    Nearly all vacuum lines
    Intake manifold gaskets
    Throttle body gaskets
    Fuel level sending unit

    I've recently tested my fuel pump and my throttle position switch. I've cleaned/tested my "additional air slide valve" (an old-school cold-start feature). I also adjusted the wiper arm on my AFM. The car had been relatively issue free after completing this work and had ran healthily for about two weeks before this bump-related stumbling started.
    '75 Honda CB400f
    '85 BMW 323i Euro
    '04 Acura TSX A-Spec

    Comment


      #3
      Less recently replaced (but still w/in the last 14 months):
      Other vacuum lines
      Main intake boot
      Charcoal canister filter (an emissions thing)
      Valve cover gasket
      FCAB's
      Fuel pressure regulator - replacement is used
      Fuel filter
      Some coolant hoses

      Also, I've adjusted the valve clearances and changed the oil but nothing else comes to mind.
      '75 Honda CB400f
      '85 BMW 323i Euro
      '04 Acura TSX A-Spec

      Comment


        #4
        Forgot to mention the injectors were ultrasonically cleaned and flow-tested about 3 months back.

        Nearly all the work I've done on the thing has been part of a campaign for better gas mileage. It was getting about 10-12 mpg when I first got it and it didn't really improve until this last batch of work (the gaskets etc) and I saw my first ~240 mile tank of gas the week before this bump issue started happening.

        Okay, that's finally all I can think of. Any insight would be appreciated!
        '75 Honda CB400f
        '85 BMW 323i Euro
        '04 Acura TSX A-Spec

        Comment


          #5
          This has been happening to me to, I'm about to replace a vacuum hose, tps, coolant temperature sensor. I'm almost thinking its a loose ground or electrical short or something. It's been happening to me ever since its been raining for the last month.

          Also I did clean my engine bay about 2 weeks ago and it's almost like it aggravated the problem and has been happening a couple of times a week.

          Comment


            #6
            Ah, that reminds me. I have installed a new coolant temp sensor for the ECU and a new coolant temp sending unit for the dash. And a new thermostat.
            '75 Honda CB400f
            '85 BMW 323i Euro
            '04 Acura TSX A-Spec

            Comment


              #7
              Maybe it's the ignition coil or something getting bumped. Or maybe there's water in the CPS. This issue has been pissing me off lately too. If I pull over and stop, then continue driving it seems to be okay until I hit another pothole at a weird angle. It doesn't happen after every bump, it only happens on some.

              Comment


                #8
                CPS meaning crank position sensor in the front driver's side of the engine bay aimed at the pulley? I did think that perhaps it was somehow "losing position" and screwing everything up until being rebooted. Does anyone else think it might be related?

                I did check that it wasn't loose or anything. Seems like a sealed unit so I'm not sure how water would get into it. Is there any way to test it short of outright replacement?
                '75 Honda CB400f
                '85 BMW 323i Euro
                '04 Acura TSX A-Spec

                Comment


                  #9
                  the Bently repair manual has a test procedure to check the resistance of the CPS however to fully test it you need to use an oscilloscope to look at the pattern. if the cps signal is lost the fuel pump wont run, but im not sure that would act as you describe. if you do want to replace it though use an OEM replacement as the aftermarket ones are hit or miss right out of the box.

                  I had a problem with my car cutting out over bumps and it was the fuel pump relay wiggleing loose and loosing conection.
                  Shawn @ Bimmerbuddies
                  Bimmerbuddies LLC
                  717-388-1256
                  2971a Roundtop Rd, Middletown PA 17057
                  bimmerbuddiesllc@gmail.com

                  Comment


                    #10
                    Thanks, I'll take a look at the relay. It's new - perhaps I didn't install it tight enough and it slowly worked itself loose over the two weeks or so of reliable driving I did get out of it.

                    I do have a spare crank position sensor lying around somewhere. The only reason I didn't install it right away after this happened was that it's wired to a big diagnostic connector that sits right above my distributor on the driver's side of the engine bay. They're crimped up into the connector somehow along with 20ish other wires and wouldn't come out with some semi-firm tugging. Might need to revisit that.

                    In either case - FPR or CPS - I'm skeptical that bumping the connection to temporarily short it or w/e would cause this behavior. Namely, how could either of them render the car in such an impotent state that's handily fixed by just cycling the ignition?

                    I do appreciate the input. And either way, it's best to remove possible culprits from the list. Does anybody have any other ideas/applicable experience?
                    Last edited by bloodsnot; 06-23-2013, 05:17 PM. Reason: type-o
                    '75 Honda CB400f
                    '85 BMW 323i Euro
                    '04 Acura TSX A-Spec

                    Comment


                      #11
                      maybe check the inline fuse link in the trunk?? that could have a bad connection.. i read through this fast so sorry if you mentioned that already..

                      R.I.P. 87 White 325is, Sold 85 Black 325e

                      Comment


                        #12
                        Thanks for your response. I haven't checked that yet; in fact, I'm not even sure what/where that is. What is it connected to in the trunk?
                        '75 Honda CB400f
                        '85 BMW 323i Euro
                        '04 Acura TSX A-Spec

                        Comment


                          #13
                          could be CPS wire rubbing raw on water pump pulley. check that shit.

                          Edit: oh yeah just ignore that. missed that it was early model...
                          Originally posted by Andy.B
                          Whenever I am about to make a particularly questionable decision regarding a worryingly cheap diy solution, I just ask myself, "What would Ether-D do?"
                          1987 325iS m30b34 Muscle car (Engine electrical phase)
                          ~~~~~~~~~~
                          I was born on 3/25…
                          ~~~~~~~~~~

                          Comment


                            #14
                            Originally posted by bloodsnot View Post
                            Thanks for your response. I haven't checked that yet; in fact, I'm not even sure what/where that is. What is it connected to in the trunk?
                            its the small wire next to the large cable to the battery on the right side



                            found a decent pic online..

                            R.I.P. 87 White 325is, Sold 85 Black 325e

                            Comment


                              #15
                              Check the relays on the driver fender, they pop out at times.

                              Also as stated the fusible link in trunk, follow it from the small cable coming off the positive lead. Mine was broken in a way that it would sometimes cut out.

                              Sent from my Galaxy Nexus using Tapatalk 2
                              -Build http://www.r3vlimited.com/board/showthread.php?t=295277

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