89 325i Intermittent Miss

[pbc27]

Hello all and thanks in advance. I've been searching high and low all over the internet looking for a hint as to what is causing an intermittent miss in my 89 325i. Ill start with what is happening and follow it up with what I have done so far to try to fix the problem.

PROBLEM:
During normal driving occasionally the car will have some sort of fit and miss. Sometimes it is a single miss and sometimes it will be several over a few seconds. The check engine light flashes for each miss. The car feels like its bucking if I'm accelerating and this happens. Occasionally the miss will cause the car to stall. Wet/raining days as well as lower engine speeds (below 5000 rpm) seem to be when the miss happens. This could just be nothing as its winter in the northeast, however warm/dry days are not as bad and I'm not often getting the engine speed up that high.

ADDITIONAL INFO:
The car has always had a hard time starting in the cold for the several years I've owned it (I start it at 1/4 throttle back off once it will stay running) and is currently showing the code 1261 (Fuel Pump Relay Control). I've replaced the fuel pump relay and reset the computer. The code comes back once the car is started for the first time.

WHAT I'VE DONE SO FAR:
New, spark plug wires, distributor cap and rotor, fuel injectors, fuel filter and replaced the C191 plug with a new water tight connector. I have had the DME out and I checked it for any cracked soldered connections (nothing obvious). Roughly a year ago I had the engine out, all new gaskets and had the head decked before being put back on.

Once the car is at operating temperature it runs smooth and pulls hard other than this miss which at times renders the car undriveable and a hazard to be in or near on the road. I'm sure I've left out some relevant information, but i'll try my best to get it to solve this problem. Hopefully someone has the answer!

[vtechnik]

Have you checked the fuel pressure? Have you checked the CPS? My guess is fuel pump or cps.

[pbc27]

I have checked the Crank Position Sensor and measured a resistance of 512 ohms which is the best I can do and seems to be in the range of what is normal.

I'm going to try to test the fuel pump by measuring the volume it pushes, but does anyone what kind of electrical tests can be run on the pump itself (resistance, voltage)?

[MoreMayhem]

I had a bad dizzy cap right out of the box. Was one of the most frustrating problems to track down. “It can’t be that, its brand new”. Never had any of he regular signs of a bad cap. Was ready to get rid of the car.

[pbc27]

I performed the volume test on the fuel pump. As far as I can tell I should have seen 30 fluid ounces pumped by the fuel pump in thirty seconds. Only 10 or so ounces were pumped in thirty seconds. I tried this twice and got pretty similar results. I've ordered a new fuel pump and we'll see what happens.

[pbc27]

Update: I replaced the fuel pump trying to solve this intermittent miss I have been having. It did not solve the problem. It ran fine for several days and then started happening again. The car is also quite difficult to start in the cold. I'm wondering how these two things could be related if at all. I've been trying to keep an eye on the fuel gauge when this miss happens. I didn't notice any issues until I was below half a tank.

Next step: It was suggested to me to try Dry Gas and see if that helps. Possibly being that there may be moisture in the gas tank that could be causing the problem.

If anyone has any suggestions I'm all ears. Thanks

[325e '87]

Common stuff I’ve read here-

Harmonic balancer weak/bad
Fuel pressure regulator (not sure this would cause a miss)
Bad ground straps and dme ground
Bad throttle position switch
Bad coolant temp sensor, the 2 wire one for the fuel injection (may be why cold starts are tough, I don’t think you should ever need throttle at startup)
O2 sensor
Failing alternator
Clean out the idle air valve

I know, it’s not a small list

[pbc27]

Thanks for the good ideas. Since my last update I have replaced the blue coolant temp sensor (the test indicated it wasn't returning the correct resistances) and the crank position sensor (turns out it was only hanging on by a thread).

However the problem still remains. I'm going to look into testing the throttle position sensor and see if there is anything funky going on with the harmonic balance.

[rdarney]

Sorry to jack the thread, but I am having the same issues with what you could call an intermittent miss minus the check engine light flashing on miss. I recently did timing (and all to go with it), fuel pump and filters, ignition wiring, coil, plugs, distributor and cap, and a valve adjustment yesterday. The car runs significantly better in the top end of the motor just from sound alone, but there is still a small stumble. Tonight I am off to check and clean both the CPS and ICV, will update after I do so, but wanted to get some ideas going just in case those were not the culprits. I pulled plugs after running it for a week and cylinders seem to be running nice and amber brown on the plugs. I can't get the idea out of my head that airflow is the problem, I just don't know where... any ideas would be appreciated!

Again, sorry for thread-jacking, figured it was better than starting a new post on basically the same issue. :)

[TobyB]

The check engine flashing makes me think power to the ECU's getting interrupted, so
:ECU relay
:ignition switch
:grounds.

NO check engine adds AFM to the mix- the ECU seems to hate an erratic signal from the AFM.

I'm the kind of dork that will stick a meter onto the ECU supply and drive around watching it.
But then, I'm kind of a dork...

heh

t

[Old525i]

Air Flow Mass Sensor?

[ForcedFirebird]

Check coolant temp sensor resistance when warm (the blue one), should be 300-360ohm. If out of range, the ECU will choke or lean the engine during warm up.

Check the idle switch in your TPS. Two pins on the sensor should be dead short with throttle at idle, infinite open on all three when part throttle, and finally dead short on the other two pins when throttle is WOT. If the idle switch isn't working, the ECU thinks your foot is on the gas and it's fueling for it even though the throttle plate is closed.

The intermittent part of the code might be dirty relay contacts. Pull the fuel relay, clean the blades and socket. The other orange relay is for the o2 heater and are interchangeable.

What plugs did you use? The m20 isn't overly picky, but they run best on the OEM copper plugs. Check the condition of plugs, it will help diagnose the situation. While you have them out, check the resistance on the plug wires. Should be 5-7ohm.

The CPS is on the edge with resistance, specially if you measured at the sensor plug and not ECU pins. It should be 540 +/- 40. Also while in that area, check the CPS wire where it goes behind the water pump. There's a plastic channel for the wire to go in and they are old/brittle/failing, and the wire comes out of it and chafes on the pump pulley.

If all these check out, you may have a failing pump or dirty/rusty fuel system.

[MrWolf]

Having a very similar issue. Following closely.


I've got a M20B27 that I did a 200 to 885 head swap and Motronic 1.3 conversion on. After getting it running it started having the same "miss" issue listed here. While trouble shooting I found my TPS was not testing for continuity as spelled out in the Bentley manual. I swapped it for one that did - however the problem remains. Also tested/swapped AFM, CPS, and tested the idle air valve. Will look into some of the other suggestions.


I hope one of you guys finds the needle in the haystack, I've run out of hair on my head to pull out.