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    85 318i issues

    Hi, forum peeps.

    I picked up an 85 318i automatic about 6 months ago as a DD/second car/project. I'm trying to figure out a couple mechanical issues before spending money on more fun things like suspension and turbo.

    The main issues are intermittent cutting out and a low pitched irregular rumbling sound, (from the rear I think).

    For the cutting out issue, it can happen at idle, low speed, or high speed. It can go weeks without doing it or it may happen several times in a day. When it cuts out, the idle acts like it wants to die, but something stops it from dying. In gear, the tach bounces between 400-900. Occasionally it will die, but usually not. So far, it's only died maybe 6-7 times and only when stopped. If it's cutting out and I put it in P or N, the revs go up to around 1500-1600, (up from normally around 1000). Also, when it's cutting out the MPG/fuel economy gauge goes to infinity, (for the duration of the cutout). The longest cutout was about 6-8 seconds on the highway, but it's normally very short and random. Obviously the car is very jerky when driving, especially at highway speeds. The cutouts usually stop on their own. The previous owner was told it was the throttle body. He bought a junkyard throttle body with attached TPS, but only installed the new TPS on the original throttle body. He thought that fixed the issue, but didn't drive it much afterwards and the problem remains.

    My research shows it could be almost anything except maybe the steering wheel.
    - Fuel tank (rust or water)
    - Fuel pumps (or bad electrical connection to in-tank pump)
    - Fuel filter (replaced by PO)
    - Fuel pressure regulator
    - Fuel pump relay or relay socket
    - One of the other 2 relays next to the fuel pump relay
    - Wiring harness/connection from the 3 relays to ICU/ECU
    - Fuel injectors
    - ICV (replaced by PO)
    - ICU (replaced by PO with a blue colored unit)
    - ECU
    - Distributor (cap/rotor/plugs/wires freshly replaced)
    - Bad ground or electrical gremlin somewhere
    - Vacuum leak (most hoses replaced by PO, recently spray tested and doesn't seem like there's a vacuum leak)
    - TPS adjustment
    - AFM
    - RTABs (just kidding)

    When changing the distributor cap, I retarded the timing a touch to bring the idle down. After doing that the car was very sluggish. I tried this for a day before changing it back, but I noticed that the cutouts were less severe/drastic. Maybe that's an important clue.

    For the rumbling sound, it's hard to describe. It's noticeable to me at 30-40mph and gets a little louder as I go faster. The sound isn't rhythmic and doesn't go faster as the car does. I took a mechanic friend for a drive and it took him a while to hear it and he didn't think it sounded like anything bad, but I can't imagine test driving it in 1985 and thinking it's normal.

    Possible issues:
    - Bad diff (checked/changed fluid recently)
    - Wheel bearings (doesn't appear likely, but I haven't ruled it out yet)
    - Bad muffler hanger (one of them is loose and causing some play, but I don't know if the sound would be a low rumble)
    - Broken cat internals (don't know if that would make a low rumble)
    - Rear suspension or bushings, (PO had some of the front end worked on, but not the rear)
    - Center support bearing and/or driveshaft (don't know if that would make a low rumble)
    - Something else I haven't thought of

    Thanks for reading this far, (unless you skipped to the end). Open to ideas to hopefully narrow this down. I've been a backyard mechanic for a couple years, which means I can follow a DIY and replace parts, but the hard part for me is figuring out what to replace.

    #2
    Bump to follow along.
    Where are you located?


    Sent from my iPhone using Tapatalk

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      #3
      Originally posted by M10Power View Post
      Bump to follow along.
      Where are you located?
      Dallas

      Comment


        #4
        - Fuel pump relay or relay socket
        - One of the other 2 relays next to the fuel pump relay
        That would be where I started. ECU relay, especially, if it's a sudden loss of power.

        For rumbling, I might start by fondling the driveshaft, especially the u joints and csb.

        hth

        t
        now, sometimes I just mess with people. It's more entertaining that way. george graves

        Comment


          #5
          Well, yesterday after work it wouldn't start. Tried to crank but couldn't turn over. Tried the diagnostic port shorting pins 11 and 14, but that didn't work and just made some sparks. Got someone to bring me a portable jump starter and that seemed to give it a little power, but still no start. It just clicks now. Initially it would try to turn over then stop like it was running out of power. Skipping work today to deal with this. Going to try the oil pan to frame rail ground strap if I can find one. Then on to the starter. Hopefully it's just a bad ground.

          Comment


            #6
            My car was doing nearly the same thing for a few months.

            On the driver side of the engine bay, there are the 3 relays near the AFM. The middle one controls a lot of things. I unplugged the connecter from the bottom. I popped it open, cleaned, and reseated all of the pins. The car has been driving flawlessly for months since.

            Take care to label, draw diagrams, and take pictures of where all the wires go! There are nearly no images online and when you pop the connector open they have a tendency to all go everywhere.


            Roaring that gets louder with speed is probably a wheel bearing. Replacement hubs are like $40 on rockauto.

            Comment


              #7
              Got it working yesterday. It was just the battery. Battery was only 1-2 years old, so that wasn't at the top of my list as the suspect.

              PO bought a couple odometer gears, so I thought I'd tackle that today. Took the cluster out and opened it up, but I need to order two more gears to get it working. The small main gear teeth are completely rotted and no longer grab the adjacent gear. The other has one tooth missing.

              Then I tackled the trio of relays. Carefully pried open the middle relay connector and took pictures so I knew where they went. Cleaned off some small rust and corrosion spots with a wire brush, sprayed with contact cleaner and put it back together. Then moved on to the third relay, (towards the rear). Lots more wires and several had the same color as other wires, so I used hole reinforcement stickers to label each according to the pin numbers on the plastic connector. Repeated the cleaning procedure and reassembled. Also sprayed some contact cleaner in the fuel pump relay connector and let dry. I wasn't expecting much since the rust/corrosion seemed very minor, but there was a noticeable difference when I turned the key on. There's a single click from one of the relays and a brief whir from something on the passenger side of the engine bay, (fuel pump?). It seems to spring to attention rather than slowly get out of bed. Started it up and it seems fine. It'll take a few weeks of driving to see if that fixes the cutout issue, but initial signs look good. Thanks for the tips, loki_ and TobyB.

              Here's some other background on these relays. One day, I was sitting for about 10 minutes with the key on and engine off. Then I heard some buzzing under the hood and traced it to one of the relays. Some research said a buzzing relay was probably a bad ground, so I've had my eyes on these relays since then. They haven't buzzed anymore since that I've noticed. Another time, I popped the hood while it was cutting out and all three of the relays were clicking rapidly, but I wasn't sure if that was normal.

              The rumble doesn't really have the symptoms of a wheel bearing issue. The parts aren't much, but doing the rears looks like a pain and I don't have the tools for that job. I'll probably tackle it anyway, since I don't know if they've ever been changed, but it may take me some time to get around to it. I did think of another possibility. Maybe the rear stabilizer bar is loose? I'll have to make some time to get under it and check some things. Diff bushings looked ok when I changed the fluid a few weeks ago. Didn't check the trailing arm or subframe bushings.

              Comment


                #8
                how's it going?

                Comment


                  #9
                  Well, I thought it was just the battery. Drove it to work Monday and checked the voltage with a multimeter. Only 12.4v running, so I ordered an alternator. Going home from work, it started cutting out more dramatically than usual and the battery light came on, so I left it in a parking lot for a couple days until I could try to fix it. Found a local alternator and tried a field replacement, but one of the bolts was rusted and stuck in the alternator, along with the hex nut breaking off the end of the bolt. I ran out of daylight, so had it towed home. Got the bolt out this morning with several doses of liquid wrench and an interior trim pry tool. The thick red wire to the alternator looks a little sketchy. Not sure how to address that, yet. Returned the local alternator and my Bosch one should be here Monday. Just ordered the bolt/nut and some ground straps/cables, (several are frayed). I don't know how to tell if the alternator should be 80A, 90A or 95A. All three are listed for my car on realoem and I don't see any markings on the one I removed. Also have some muffler hanging parts coming to see if that helps with the rumble.

                  Comment


                    #10
                    bump

                    kicker, you've describe my car perfectly.

                    I had that same issue with the buzzing relay. For me it was the idle stabilization relay that was buzzing uncontrollably. It would buzz if the car wasn't on but the key in the on position. Replacing the stabilization relay really helped a ton of issues I had, but it's a pricey relay ($180 from Turner).

                    Not sure if you've tried this but test your fuel pressure. Mine was hovering right around 35 psi which is low for this car. Ended up having to replace the in-tank (made no noise when the car was on) and replaced the in-line pump as well.

                    As for the hum when driving down the road I haven't narrowed it down yet, but my thoughts were leaning towards wheel bearings or the diff. I haven't been under the car yet to verify the condition of the diff fluid, but I'd imagine mine is quite old.

                    Good luck with the troubleshooting, I'll be reading up on your success.

                    Comment


                      #11
                      Well, installed the new alternator and put it back together, but I'm planning to redo the charging system wiring. It's back up and running, anyway.

                      I'm not sure which relay is which, but I traced the buzzing to the rearmost of the three.

                      The high pressure pump has a constant buzz while running and the cutouts seem consistent with a bad pump. I'm leaning towards replacing the tank, which is most likely rusty, pumps, filter and having injectors rebuilt. I'll probably consult my trusty Bentley manual for some troubleshooting first, though.

                      I can hear some diff whine, but my rumble is different. After driving it yesterday on a stretch of new smooth road, I'm leaning towards the muffler hangers. I'll find out soon enough when I put my new parts on.

                      There's also a new clunk when coming to a stop. Maybe motor or trans mounts? My daily driver has officially turned into a restoration project. It'll be worth it, though.

                      Pavane, what issues did the relay fix?

                      Comment


                        #12
                        Originally posted by kicker View Post
                        Pavane, what issues did the relay fix?
                        For me, it fixed my car from dying at idle. Ever since I changed it the car no longer cut out at a stop. It still had a bucking issue at highway speeds but I was sure happy I didn't have to worry about the car dying every time I approached a stop sign or light.

                        And the rapid clicking noise stopped too when the key is in the ON position.

                        These two threads helped me as far as identifying the problem:


                        Comment


                          #13
                          Pavane, did the new fuel pumps fix the bucking issue you had?

                          On mine, the cutouts are most severe at highway speeds, but it will cut out at any speed or while idling. It's had 2 long road trips in the past 2 years and on both of them it was fine for a few hours and then cut out almost constantly the rest of the way.

                          Parts will be slowly trickling in over the next month. I'll replace them as they come in if it makes sense to do so. The relay is 3 weeks out. Found a pretty good deal on a new green ICU. New alternator power cable from bavrest.

                          Comment


                            #14
                            The only thing that fixed the bucking issue was the AFM.

                            My AFM was tampered (the vane had no spring tension, the idle mixture screw was all the way in) and the only way i could get the bucking to a minimum was adjusting the tension on the vane. Now, the bucking is limited only when the engine is not up to temperature.

                            Comment


                              #15
                              Well, the relay came early and I installed it 4 days ago. No sign of cutouts since then and it's running smoothly, but too early to claim victory yet. Installed the new green ICU later the same day, but I didn't notice any change from my existing blue one. I intended to replace only one part at a time, but I needed to see if the new ICU worked. I'll give it another week or two before I consider it solved. If there's interest, I can swap the blue ICU back in for testing to figure out which of the two solved it. The old relay has a week and year date stamp on it and it was original from 1985. The other large (middle) relay is also original. The adjacent fuel pump relay appears newer than the other two. I've seen some discussion about the number of pins on the relay I changed. My original one is black with a large white circle on top and has 9 pins while the new one is green and has 10 pins. Same part number and only 9 wires go into the connector. My theory is that Siemens had another application for this relay that required 10 pins, designed a revision that still worked on 9 pin applications and didn't want to produce two different relays. While the relay isn't exactly cheap, it's a lot easier than changing out the fuel tank and pumps, so I figured it was worth a try.

                              As for the alternator...since I changed it the battery light on the dash doesn't go out until it's revved to about 1200 and it stays out once it does. When I tensioned the geared bolt, my torque wrench didn't click and the geared bolt was maxed out on the geared bracket. I was looking into that and found that there are two versions of the alternator pulley size, two versions of the fan pulley size and two versions of the belt width. Talked to the dealer parts counter guy and even he was confused and said he'd never seen that before. I think I just need to adjust the bracket angle to allow for more travel. Beyond that, maybe the exciter wire or exciter circuitry in the alternator.

                              Wanted to get under it and fix the exhaust hangers yesterday, but the weather didn't cooperate. Hopefully this coming weekend.

                              I'm getting ready to look at upgrading the suspension. Bilstein sport with H&R seems to be the consensus pick, but most of the discussion is for the later model 6 cylinders. Thought I'd check to see if you M10 readers have any other wisdom on winning combinations for the lighter E30.

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