engine stalling while driving? what the?

[bpaquette]

I have a euro '89 535i (don't know engine model, but its the 3.4 220 hp v6), and the damned engine is stalling out on me while driving on the highway. It's done it from speeds varying from 20k/h to 150k/h, so I know it's not stalling b/c the tach is dipping too low. I took it to my mechanic where he replaced the o2 sensor, distributor, and gave it a tuneup. After spending all that cash, it still does it! Has anyone had this problem before? Sometimes it starts itself back up (popping the clutch style), but sometimes it just dies for a few minutes (sometimes for quite a while).

the engine only has 170k on it so it shouldn't be dying out on me like this (at least I dont' think it should!).

If anyone has any notions or ideas, please enlighten me!


BP

[Javier]

When you say dies for a few minutes, you mean engine turn off and even cranking will not start? Then suddenly, It may start back?

If so, I would suspect the fuel pump (1rst chance) then CPS. Unfortunately, either you catch it wile bad behaving, or you will not ever know for sure if you changed something unnecessarily. My fuel pump let me down a couple times before I decided not to take the car for a ride until I find the problem, when removing the pump from the gas tank, I start connecting and disconnecting it from a battery source and noticed some times it didn’t run, so changed it and the problem was gone forever (up to now I mean). My CPS also failed once, but it did positively, so was an easy catch. Got a friend though, that was let down by his 318i M42 engine several times by a bad CPS (getting worse over time).

[bpaquette]

yeah... it'll not start for a few minutes, or it'll take 5-6 turns... sometimes when i start it up in the morning (not necessarily a cold start) it'll take 5-6 turns before it starts... fuel pump I can live with , but , forgive the ignorance, what's the other thing you mentioned? anything entitled an acronym is usually expensive :P

[Tiger]

It does sound like fuel pump

[Javier]

I would keep handy a copper wire jumper to bypass the pump relay when in trouble and check it is the pump not running first. Check archives, you'll find how to. If not, just let us know.

[Tiger]

forgot about that... Crankshaft sensor is another possible reason. Here is the test... When you can't start up the engine after it shut down on you... pour cold water onto this sensor... if car start up right away, then it is the culprit.

[bpaquette]

I found the fuel pump relay but am a little vague on how to test it. bypassing is simple enough? splice in the copper wire on either side of the relay and it'l by pass, right? so that's not the problem... how does that tell me if my pumps working? i'm an electrical systems retard, as you may have noticed.

where is the crank pos. sensor? and i'm assuming the cold water cools it down? i dont' know that that's a problem b/c sometimes starting it up cold results in a very struggled start (turning it 6-7 times).... although it seems that when it is stalled for good, a few hours of sitting results in an immediate startup.

quite the enigma i've gotten myself in.

BP

[bpaquette]

I found the fuel pump relay but am a little vague on how to test it. bypassing is simple enough? splice in the copper wire on either side of the relay and it'l by pass, right? so that's not the problem... how does that tell me if my pumps working? i'm an electrical systems retard, as you may have noticed.

where is the crank pos. sensor? and i'm assuming the cold water cools it down? i dont' know that that's a problem b/c sometimes starting it up cold results in a very struggled start (turning it 6-7 times).... although it seems that when it is stalled for good, a few hours of sitting results in an immediate startup.

quite the enigma i've gotten myself in.

BP

[Javier]

Fuel pump relay K201 is a four terminals unit numbered 85, 86, 87, and 30 corresponding to socked X1515 terminals 4, 8, 2 and 6 respectively. Coil energizes with positive at 86 and ground at 85, terminal 30 gets a permanent positive, and passes it into 87 when coil is energized (energizing the pump). The problem is that the pump relay does not hold energized wile cranking if the engine does not start, so not hearing the pump wile cranking does not necessarily mean the pump is bad. The best to do in order to debug , is to bypass the pump relay so to keep the fuel pump running permanently. So, if your engine refuses to start, you can go and remove the pump relay, then connect a copper wire between its socket terminals 6 and 2 (correspond to 30 and 87 of the relay, careful not to miss them). You should immediately hear a hissing sound of the fuel flowing trough the pressure regulator in the injectors rail (just back of the thermostat housing), if not, go back near the passenger rear wheel as you should also hear the pump running. If nothing, then probably you have a bad pump (I said probably just because there is a fuse and some connections in between the pump relay and the pump, it is not probable to have a bad connection, but who knows).

If you hear the hissing, then try to start the engine, if it does, you may have a bad fuel pump relay, just test it energizing positive terminal 86 of the relay and grounding the 85 terminal, do it repeatedly, you should get a click every time you energize, also you can check continuity trough terminals 30 and 87 every time it clicks.

If the car does not start even if you have the pump running, then you should go for the CPS, it is located about 10 o clock (passenger side) over the damper pulley, it’s there to pick up the teeth in the damper pulley, and produce a pulse sequence indicating the motor electronics that engine is running, its speed, and at what stage of the turn is it. You can cool it down to see if it makes any difference or unplug its connector and get a resistance reading with an ohmmeter. Its connector is located at top of the motor between the injector rail and the head cover, jus behind the thermostat housing. The one towards the back of the car is the one. The one at the front is the cylinder identification sensor and is connected to a spark plug wire, not the CPS. To unplug, you should carefully (to avoid loosing it) remove the u shaped shiny wire spring with a tinny screwdriver. You should have about 400-600 ohms between terminal 1 and 2, no mater if not precisely, when gone, its normally an open circuit or a short circuit. You should also have an open circuit to pin three from both 1 and 2, as it is the shielding and should not connect to the sensor circuit at terminals 1 and 2.

The fact that the car sometimes take a few turns to start is normally due to a leak of pressure on the fuel system wile the car is sitting parked, then pump takes a little time to fill up the system pressure, either you have a leaking pressure regulator, a leak in the fuel system hoses (535i typically leaks gas at the short hose connecting to the back of the injectors rail, I’ve changed mine two times in 50K miles), or a fuel pump check valve leaking, of course, if the car stalled due to a bad pump, it will also take a few turns to start up as the fuel system pressure went down to zero when pump collapsed.

Good luck and happy hunting.