yet another E34 no Cold start thread! M50

[affende]

93 E34 M50, 246k, 3/4 tank fuel, no start. it has been sitting for a week.

Engine rolls over rapidly, battery is has full charge, tries to fire on a few cylinders ever few seconds but will not catch and run.

history: It has always had a little trouble starting in the colder weather but it has always started on the first or second try (cranking for 3-4 second each). The last year, when sitting for longer than a a couple of days it has started rough (but always started) and taken a few seconds to fire on all cylinders. It has ALWAYS had a stumble on takeoff and felt pretty fat. owned since 2009 and 100k.

Im thinking fuel? weak or bad pump, weak or bad injectors?

[affende]

Update. I have tried starting the car a couple hundred dozen times. still nothing.

Multimeter confirmes 12V (11.9 after straining the battery) between 30 and 87 on the fuel pump relay circuit

9V battery to the fuel pump relay itself, pins 85 and 86 does engage the solenoid (audible clicking). From what i can read, 85 and 86 are the signal / excite circuit.

starting the car with the relay removed yields the same results as with the relay in, but the relay and the relay power circuit is confirmed good .... so this to me, says the pump is bad.

heading back out to check voltage at the pump harness.

[ross1]

Fuel pressure? Spark? are the plugs wet?

[affende]

Fuel pressure? Spark? are the plugs wet?

no pressure gauge, but jumping power across the fuel relay does not run the pump. 11V confirmed at the fuel pump harness connection.

so the pump is getting power when it should.

i have suspected a weak pump for a while now. good thing im still on vacation, though! it would have sucked if it had failed one night when i had to work the next day.

[affende]

Interesting update:

I always double and triple check diagnostics if i can ...

12V directly to the pump will spin the pump. and squirt (whats left) fuel all over the garage wall.

so now im at a loss. pump seems to work with 12 V, relay checked good, voltage at the pump electrical plug checked good, jumping relay terminals 30 and 87 did not spin the pump, and the car wont start.

so could it be that the pump is just too weak with any load on it ... but spins fine when there is no load and 12V directly from a battery?

[ross1]

The ability to move fuel doesn't mean it's a good pump. Pressure should be 3 bar, ~45psi for the M50. Low pressure will result in poor fuel atomization which makes it that much harder for a super cold engine to light.
Make sure the plugs are dry, if you flood an engine in very cold temperatures you'll need to pull and dry the plugs, it'll never clear itself in very cold temps.

[affende]

also ... i am going back through and checking my diagnostics before i drop $200 on a new pump.

when i jump fuel pump relay terminals 30 and 87, i have no power at Fuse 23.

from my understanding, jumping the terminals, should power fuse 23 even with the car off.

so am i missing something?

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The ability to move fuel doesn't mean it's a good pump. Pressure should be 3 bar, ~45psi for the M50. Low pressure will result in poor fuel atomization which makes it that much harder for a super cold engine to light.
Make sure the plugs are dry, if you flood an engine in very cold temperatures you'll need to pull and dry the plugs, it'll never clear itself in very cold temps.

ill pull a plug and see what they look like.

[affende]

The ability to move fuel doesn't mean it's a good pump. Pressure should be 3 bar, ~45psi for the M50. Low pressure will result in poor fuel atomization which makes it that much harder for a super cold engine to light.
Make sure the plugs are dry, if you flood an engine in very cold temperatures you'll need to pull and dry the plugs, it'll never clear itself in very cold temps.

plugs were very slightly wet and smelled like fuel and oil (valve seals need to be replaced).

it was 15* this morning ... up to 39* now.

[ross1]

plugs were very slightly wet and smelled like fuel and oil (valve seals need to be replaced).

it was 15* this morning ... up to 39* now.

Ain't gonna start that way

[affende]

Ain't gonna start that way

i pulled all the plugs, dried them off, pulled the fuel pump relay and turned it over (without plugs) to help dry everything out. put everything back except the fuel pump relay and tried starting with starting fluid ... still nothing.

unhooked the fuel lines from the pump and plugged the pump in with it out of the tank, pump runs when i try to start the car.

im leaning toward a bad Crank position sensor.

sound right?

[demetk]

You can test the crank sensor for resistance while the engine is off and for ac voltage while the engine is cranking.

[affende]

You can test the crank sensor for resistance while the engine is off and for ac voltage while the engine is cranking.

how? I read a few values of 1280ohms and 540 ohms depending on the specific sensor / year. just pull it off and check between pins 1 and 2? or is there a way to check it without pulling it?

does bmw call this a timing case pulse generator?

i think i found the proper part on realoem: #12141726066 which supersedes the original number 12141726065

[demetk]

Yes, pull it off set your meter to ohms and check the resistance between pins 1 & 2. Same for ac voltage except set your meter to ac volts and check how much ac voltage the sensor produces when you crank the engine. I haven't done an ac voltage test on my e34 yet but if you're interested in doing this test I can get you the value tomorrow. My guess is the voltage should be between 2 and 3 volts ac.

[affende]

i would be very interested. Thanks!

[Mihnea"e34]

I had this problem a while back with my m50b20. When it was cold outside i had to crank it up to 20 times to fire, and when it started, i had to keep it at +1500 rpm to not die.
Turns out that the engine temperature sensor plug (underneath intake manifold) was a bit rusted (the white greenish substance that forms on old pins). After cleaning, it started like brand new no matter the temp.

Hope it helps

[demetk]

i would be very interested. Thanks!

Here's the test,

Attach your meter to pins 1&2 of the CPS connector. On my m30 it's easy since the connector is on top of the engine.




Set your meter to Ohms and read the resistance. I got .556 k ohms.



Then set your meter to ac volts and read the meter while you crank the engine. I got 3.6 volts ac.



If you're doing this yourself get yourself one of these cheap switches from harbor freight.



Attach one end to pin 11 of the diagnostic connector,



And attach the other end to 12 volts.



If you have a 5-speed make sure it's in neutral so you don't run over your foot.

[ross1]

I'm pretty sure that the only diagnostic connectors with the connection to the starter are on M20 & M30 cars, those requiring valve adjustments.
Bentley diagrams still show it but I recall hearing the late cars don't have it. I'd love to be wrong.
Curious to hear from the OP on this.

[demetk]

I'm pretty sure that the only diagnostic connectors with the connection to the starter are on M20 & M30 cars, those requiring valve adjustments.
Bentley diagrams still show it but I recall hearing the late cars don't have it. I'd love to be wrong.
Curious to hear from the OP on this.

I think you're right on that. The 93 ETM still shows pin 11 still going to the starter, but the 95 doesn't. Maybe it's an EWS thing.

[affende]

Here's the test,

Attach your meter to pins 1&2 of the CPS connector. On my m30 it's easy since the connector is on top of the engine.




Set your meter to Ohms and read the resistance. I got .556 k ohms.



Then set your meter to ac volts and read the meter while you crank the engine. I got 3.6 volts ac.



If you're doing this yourself get yourself one of these cheap switches from harbor freight.



Attach one end to pin 11 of the diagnostic connector,



And attach the other end to 12 volts.



If you have a 5-speed make sure it's in neutral so you don't run over your foot.

Thanks! i went ahead and ordered a new CPS ($14) ... so i have a spare if the old one tests bad.

The new CPS ohmed out at 578 ... well within the 540 plus or mins 10% that i had read.

Im trying like hell to get to the old CPS plug but its hidden under the M50 intake manifold in a jumble of wires. the wire retainer on top of the thermostat housing wont come off just yet and the tiny little bolt holding the CPS to the bracket is just shy of breaking / stripping so im battling.

but i do appreciate you taking the time to give me the info!

- - - Updated - - -

I had this problem a while back with my m50b20. When it was cold outside i had to crank it up to 20 times to fire, and when it started, i had to keep it at +1500 rpm to not die.
Turns out that the engine temperature sensor plug (underneath intake manifold) was a bit rusted (the white greenish substance that forms on old pins). After cleaning, it started like brand new no matter the temp.

Hope it helps

ill keep that in mind for sure. any time i work on or replace an electrical component i always take time to clean up the contacts and put some dielectric grease on the boots to seal out moisture.

[demetk]

Im trying like hell to get to the old CPS plug but its hidden under the M50 intake manifold in a jumble of wires. the wire retainer on top of the thermostat housing wont come off just yet and the tiny little bolt holding the CPS to the bracket is just shy of breaking / stripping so im battling.

I figured the CPS on the M50 was harder to get to. Hope you fix it.

[affende]

I figured the CPS on the M50 was harder to get to. Hope you fix it.

so do i. Its been down for a week now, and im very close to solving this issue with a can of gasoline and a box of matches.

[affende]

So, the BMW is still dead. No start whatsoever. Starter spins the engine just fine, but it wont fire.

So far here is where i am.

1) I have suspected the fuel pump was on its way out for the last year. New fuel pump installed.
2) Fuel Pump Relay tests good. Adding voltage to 85/86 pins closes the solenoid and i get continuity though 87/30 pins.
3) power into the fuel pump relay socket is good from the DME relay and when i crank the engine, i do get power to the fuel pump fuse 23 and to the fuel pump wiring harness on the fuel tank.
4) Plugs are wet when pulled so fuel is not the issue.
5) I suspected the Crank position sensor was faulty or near faulty. Old sensor testes 490 ohms (Spec was 540 ± 10%) and 2.8 AC (demetk had 3.6 while cranking) volts while cranking. CPS replaced.
6) Spark tester confirms spark.
7) starter cranks and engine turns over ... will not run on starting fluid either.

still no start. Im out of ideas.

[fo3]

Is it flooding somehow (leaky injectors or could a maf or tps be putting too much fuel in?)
How about a bad ground for injectors, pump or sensors.
Are you getting 'a spark', or 'a real good spark at the right timing'?

Other than that, seems like timing (valve timing, spark timing) or compression issue.

I would be really pulling my hair out if I was in your place too, because fuel, spark, timing/compression = running engine usually

E: What does the cam position sensor do in the m50?

[Mihnea"e34]

will not run on starting fluid either.

Well..al least you can exclude the entire fuel sistem now. Don`t you have a friend with a m50 around that can borrow a sensor from? Would be a major help

[affende]

Is it flooding somehow (leaky injectors or could a maf or tps be putting too much fuel in?)
How about a bad ground for injectors, pump or sensors.
Are you getting 'a spark', or 'a real good spark at the right timing'?

Other than that, seems like timing (valve timing, spark timing) or compression issue.

I would be really pulling my hair out if I was in your place too, because fuel, spark, timing/compression = running engine usually

E: What does the cam position sensor do in the m50?

I think i can rule out a bad ground for injectors and pump. a bad ground would render them non operational and we are getting fuel.

I get a good strong spark ... but im leaning toward timing as the issue. Its got to be a spark timing problem.

Cam postiion sensor, from my research, would cause a hard start or rough running condition ... but not a no start / no run condition.

TPS sensor was new in 2015, and again, it caused a rough running condition not a no start condition.

compression is low (it has just shy of 250k on it but it does have equal compression on all cylinders).

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Well..al least you can exclude the entire fuel sistem now. Don`t you have a friend with a m50 around that can borrow a sensor from? Would be a major help

no one that i know of locally. Im about done with it.

Im already looking for a new ride ...

- - - Updated - - -

I'm pretty sure that the only diagnostic connectors with the connection to the starter are on M20 & M30 cars, those requiring valve adjustments.
Bentley diagrams still show it but I recall hearing the late cars don't have it. I'd love to be wrong.
Curious to hear from the OP on this.

ill check and see if it has a pin 11 and what happens if i give it power.