Hi, This is a tough one. I just bought an '88 535i 5-speed and it has these intermittent problems that I'm about pulling my hair out over. I listed the issues below, along with what I've tried so far. I've tried to be methodical. If anyone is willing, please read this through and offer some suggestions. Also, if you will, notice what I've already done before suggesting ideas. I think I've hit most of the biggies. I need some methodical way of debugging this rather than a "replace the _____ I did this and mine worked" approach, if you know what I mean. Thanks a bunch, everyone! Problem(s): Engine cuts out intermittently - When it does this, there is an immediate, sudden drop in engine power (the car bucks), the MPG gauge on the dash swings to the far left and sometimes the tack jumps to the left. This happens randomly, sometimes as few as 5 times a day, but most often within the first 20 minutes of running the car. It lasts about ¼ second then the car runs normally. It can happen any time during the day. When it's doing this, I can feel the Fuel Pump relay clicking if I put my fingers on it. So it's like the ECU is telling the thing to drop out. Along with this, when the car is started from dead cold in the morning, it runs fine (except for a few cut-outs described above), then at about 4 minutes 20 seconds the car begins misfiring badly and loosing power. After about 1-2 minutes of this it evens out and is fine for the rest of the day. Note: After exhibiting the problem in the morning, the car will often run fine the rest of the day even after sitting 9 hours on a work day. I talked with the previous owner and confirmed it's been doing this for years. (This seems to not be moisture related because I drove home from work after the car sat in the pouring rain all day and never had a problem.) When running normally, I think the car is running rich, but other than that the engine is smooth and quiet and has good power. Revs up nicely, sounds solid and smooth. When it runs, it runs very nicely. What I've tried with no effect to the problems: - bypassed the main relay with jumper. - bypassed fuel pump relay with jumper. - run with O2 sensor unplugged. - run with Throttle Position Sensor disconnected. - bypassed CODE relay (in OBC relay box). - cleaned and re-seated every connector on the fuel injection wire harness (inside engine bay and under dash near ECU). - cleaned every ground connection in engine bay and under dash (not in trunk, though) and applied contact cleaner, then electrical grease. - wiggled every wire I could find under the dash, wiggled every wire and connector I could find under the hood. Parts replaced or tried with no effect: - crank position sensor and speed sensor on the flywheel - new - fuel filter - new - fuel pump relay - new - coolant temp sensor - new - spark plugs - new - plug wires, rotor and cap - new - thermo time switch - swapped with used - Air Flow Meter - swapped with used - Motronic unit - swapped with used - Vacuum hoses (small ones) - new - Intake boot - replaced with known good used - Ignition coil - previous owner swapped with used I thought next I'd try ohming out the fuel injection wire harness. The other thing would be to bypass both the Fuel Pump and Main relays. I've bypassed each individually so I know it's not the relays OR control to the relays that's causing these issues. Other more "shot-gun" things are to swap the ICV, sap instrument cluster and a different AFM. As an asside -- does anyone have a known good fuel injection wire harness they'd sell REALLy cheap? Or maybe let me try out, or be willing to trade for something? Thanks! Mark.
I had a very, very similar problem in my E30 a while back, and reading through your description of the problem and what you did to try to rectify it, there might be a possible cause for your problem that is similar to mine. Mine used to run normally and then just buck and keep revving down (despite me flooring it) until the engine died out. Is that what you're having? The cause was partially weather related. You say your problem isn't, but it could be partially related as I had. What happened was that I have a leak into the car somewhere, and every time it rains, the rear carpets are wet. I don't know where else the water gets in, but I took it to my mechanic and he said the wires to the fuel pump were corroded by the water that kept getting in. The corroded wires caused intermittent operation to the fuel pump. When the fuel pump was tested, it was operating fine, but that was because the wires were also operating fine at that particular moment. Once the wires were replaced, the car never bucked and died again, though it does have a rather annoying side effect of the engine idling rough in the morning [I have to keep the revs up for about a minute so it won't stall]. Before it I got it fixed though, one day it just stopped and the car wouldn't start at all, and this random engine cutting out would happen randomly, even in completely dry and sunny weather. I understand that this post might fall into the "try this it worked for me" category, but it makes sense; technically, you haven't done much with the fuel pump or related wiring/electronics other than the relay. Besides, checking the wires costs nothing and it won't hurt to check, as I'm assuming you haven't done this yet.
I had the same problem in the 2002 and it turned out to be the fuel pump, same with with my friend that has an Audi 80 Quattro.
Yes, when it's doing this even if I floor it it can rev completely down. Thanks for the input. It's funny should mention that. One thing I started wondering about was the fuel pump(s). I will certainly get into the trunk this weekend and check out the wiring. Mark.
If you use it as a daily driver, then look at it ASAP. One day it could just die on you and not start up again. When it happened to me, I just picked the car up from the shop I took it to for a timing belt/tensioner, distributor cap/rotor, water pump job. When it was ready, I pulled out and I literally went up the street and it just died. I literally ROLLED back down (it is a hilly street) to the shop and backed right into the yard where I drove it out of, got out, and pointed at the car saying "NO WORK!" Seriously though, I had another shop look at it previously and they inspected the spark plugs [I had the wrong plugs installed - auto store gave me the wrong plugs for my car!] and the fuel pump pressures and the fuel pump checked out OK, so it could just be wiring that causes your grief and not the fuel pump. Hope it's not the fuel pump at least because those can get expensive.
Yah, it will become my daily driver in late November when I put the 635 away for the winter, so it is somewhat urgent that I get it running right. Mark.
I vote possible fuel pump problem as well. Put at fuel pressure gauge on the car and drive it around with the gauge visible (I clip it under the wiper so I can see.) When it dies out, see if the pressure drops below the 3bar (approx 42psi) as it is dying out. If so, it is not getting fuel. If the fuel pressure is in range when the car dies out and only drops after the car dies, you have ruled out a fuel delivery issue and can put that possibility to bed.
Thanks. I'm going to have to find a pressure gauge somewhere. Maybe I can scare one up this week. Any suggestions as to where to find an inespensive one would help. Mark.
Bavarian autosport, www.bavauto.com, has a fuel pressure tester for about 90 bucks hope that helps, and good luck with your car.
Mark - there are two wires connected near the lower portion of the transmission housing which feed up into the engine compartment (they connect to a brace on the back side of the valve cover gasket). I had similar issues you have experienced and they were resolved by replacing these wires. I can't remember what they are called, but they are identical (you have to make sure the connect the same wire on both sides and not interchange them). Hope that helps. Dave
Year-and-a-half old thread, Dave. Mark got the car running. I know this because I followed him in it last year. In fact, I think he even sold it since.
