Mystery cold hard start issue – 89 525i M20

[RonnieB]

If I had hair to pull out! I would!
So here is the situation , car has 70,000 miles on it. Had been sitting with little driving so over the last month or so I have been sorting out the issues and fixing as I go. Many service items needed attention and I have completed the following
1. all fluids and filters including fuel filter
2. valves lashed to spec (X2)
3. R/R O2 sensor
4. Eliminated all vacuum leaks
5. R/R Engine temp sensor ( blue top)
6. R/R plugs
7. R/R rotor/cap
8. R/R injectors

she has gone from a rough , low power , gas eating car to a smooth as silk engine, with plenty of power , and much better gas mileage. Once warm or for that fact any time after the first ( cold start) of the day she runs well…..perfect
Here is the scenario
• Come out after a cold night , 40 or so in the garage. Car cranks and cranks , them will fire , but I really got to work on it. This will sometimes take a full minute or so of cranking.
• The exhaust once started smells pretty rich to me
• I not 100% sure it is the cold temp , or just sitting that is the issue
• Once it does fire the next 60 seconds or so , perhaps two minutes , if I press on the gas she wants to die, like cars of old that had choke stuck open

After this - she runs perfect. Idle is rock steady at 800, no vibrations, sounds great . I can start and stop it all day long

I am at a loss, I have searched but most items that were thought of as culprits I have addressed.

Any ideas or things I should check ???

[Mordan]

R/R?

-replace/clean ignition wiring
-replace/clean ignition coil

I might also say fuel pressure regulator. Maybe test residual pressure / or wait 30 secs with ignition on before starting to crank.

battery with no corroded connections.

just thoughts.

[RonnieB]

thanks , battery is new, I am going to check coil tonight ,

the wires are clean, connections are good as well, all checked with cap and rotor replacement ,I did not check coil but will per bently manual. What about crank posisiton sensor , can they be intermitantly bad??
I will check pressures as well, but that may have to wait till I get more time. thanks

[DDK's 525]

I am in a similar boat but have a theory. With my '90 M20 when I start in the morning, most times it will fire fine, it is typically at lunch on a cold day that I have the problem. This morning though it happened right off. Here's what mine is doing:

If will usually fire immediately first try then die right away. It will then take me cranking for long periods of time with my foot to the floor during which the engine will have little fires but nothing enough to start the car. Then it will get enough fire to start at which time I have to pump the throttle to get it to "clean out" and keep it running (5-10 sec). then all is good and running smooth. It would do this randomly for the last year no matter the temp, maybe every 4-6 weeks but now that it's cold out it does it quite often. Sometimes I have to crank till the battery is almost dead (the battery is new).

My theory:

My fuel pump has been making noise for some time and is getting louder. I think the fuel pump is going and not putting out the pressure it is supposed to.

Does this make sense?

[Ross]

If throttle opening causes it to stumble chances are it's lean rather than rich. Double check the temp sensor.

[tim eh?]

I've been having similar issues with my m20 and am pretty close to giving up also :( I know one thing that often is a reported cause of trouble is the connector to the fuel injector wiring... the big round one that is on the ds of the engine. If you ever had a coolant leak from the throttle body warmer then the coolant might have run into the connector and caused some corrosion there.

In my situation if I do a computer reset then the problem goes away for a little bit but comes back fairly quickly. I still have to check the wiring to the oxygen sensor heater... not sure if that could lead to this kind of trouble but I will check that in the spring. My fuel pump is also noisy but I have replaced the pump and it didn't change anything... have to check to see if there is any resistance in that circuit anywhere... I suppose the place to check that would be between the fuel pump relay and the connector in the trunk (which could itself be a problem)

Frustrating, isn't it. Mine runs very well also once it has started. Good luck with it and please let us know!

[RonnieB]

doubt O2 would cause this, but may be a contributor, check your fuel pressures , system and rest to rule them out, like I did. Mine were fine. I will check the injector connection, but last time I was there is was good.
How does one "reset the computer"
I am still leaning to electrical:) CPS is on order

[Ross]

Cranks forever to start and falls on it's face on throttle opening when cold, right? It's lean, no cold enrichment.
Spray some fuel (carb cleaner) into the intake next cold start to richen the mixture and watch it pop right over.
Not the crank sensor, they work or they don't albeit sometimes intermittantly. Put the CPS in the glovebox as it's one of the more common causes of a no spark condition.

[RonnieB]

so what do you suggest is the problem?

[Mr._Graybeard]

I'm with Ross. It's likely the coolant temperature sensor. IIRC, it's supposed to measure 2.5K ohms at 60 degrees,and resistance will fall as the temperature rises. So if the ohms are way low, it's bad.
Here's what the sensor for an M20 engine looks like: http://www.rmeuropean.com/Part-Number/Temperature-Sensor-(Coolant-Temp-Sensor)-20-deg-C--2500-OHM-2-Prong-FI-Type-Connector-with-Blue-Insulator-__13621709966_BOS_94E6B777.aspx

[RonnieB]

I have replaced that and it is within specs, thanks.
In my first post you will see all that has been done, recently I checked fuel pressure for system and rest and is within spec. TPS is within limits
the only other areas of concern are the CPS, possible bad spark plug wires ( unlikely ) or a ICU/ECU issue.
This is a tough one

[tim eh?]

doubt O2 would cause this, but may be a contributor, check your fuel pressures , system and rest to rule them out, like I did. Mine were fine. I will check the injector connection, but last time I was there is was good.
How does one "reset the computer"
I am still leaning to electrical:) CPS is on order

Ronnie my symptoms are exactly the same as yours and I have been chasing this forever! My suspicion is there is some kind of short/grounding problem that really kills the system voltage and is only really evident immediately after the starter has been going. I do not suspect the O2 sensor itself, more that there is either a short in the sensor heater or something like that. I know it seems far-fetched.... definitely following your progress... wishing you the best!

Here is a good site... reset procedure is under 'fixes' / 'control systems' http://twrite.org/shogunnew/topmenu.html

[RonnieB]

with 296km on your car , you are doing something right!! I will promise to keep you posted . The last 4 days I have put the key to on, ( radio ect active) counted to 5 and then cranked, has not reoccured . That would make me think fuel pressure but since i ruled that out I am still thinking voltage/electrical like you are. Coil - no tested that , ecu - dunno, would that pause impact the cps - dunno - plug wires =- dunno. Gotta love it lol :) I am sure more to follow

[Mr._Graybeard]

Sorry, I read right over that.

[RonnieB]

NP, i do it all the time!

[tintrx]

Do you have any oil in the intake? I've been having the same type of problem on mine.

[RonnieB]

no I do not , very clean, why do you ask

[Mordan]

check for spark cold. Anyways if you plan to keep the car, I would invest in new wires and new coil.. they help improve spark quality. at worst, you have piece of equipment to further test the car in the future.

[RonnieB]

I did ohm the coil and wires - all within specs, new plugs , gapped correctly , good color as well. I am looking for a coil , as you say , cant hurt
Thanks for the advice
PS also have all three small relays on the way ( new) and a used ECU - that I am goign to take apart and resolder :)

[Tiger]

Ronnie, I am sorry people didn't mention CPS... crank position sensor... these thing do go bad on BMW all the time. The other thing that goes bad on BMWs are the fuel pump.

Put a fuel pressuge gauge on the system and check for the spec. If this is good, then go for the CPS. stick with factory BMW style... that that troublesome pin type CPS that lots of places sells.

[DDK's 525]

I am in a similar boat but have a theory. With my '90 M20 when I start in the morning, most times it will fire fine, it is typically at lunch on a cold day that I have the problem. This morning though it happened right off. Here's what mine is doing:

If will usually fire immediately first try then die right away. It will then take me cranking for long periods of time with my foot to the floor during which the engine will have little fires but nothing enough to start the car. Then it will get enough fire to start at which time I have to pump the throttle to get it to "clean out" and keep it running (5-10 sec). then all is good and running smooth. It would do this randomly for the last year no matter the temp, maybe every 4-6 weeks but now that it's cold out it does it quite often. Sometimes I have to crank till the battery is almost dead (the battery is new).

My theory:

My fuel pump has been making noise for some time and is getting louder. I think the fuel pump is going and not putting out the pressure it is supposed to.

Does this make sense?

So I went to start the car yesterday morning and she would not go. she cranks, and fires but will not start. I was finally able to get her to run last night after probably 30 min of cranking, and at that it took a lot of throttle work to keep her running. after 30 sec or so she cleaned up and ran great. I replaced the temp sensor (blue top) before trying to start last night and it did not seem to fix it as she did the same thing this morning. So maybe fuel pump? Where is the best place to check the pressure? I know its easy access at the trunk but will that give me an accurate reading? Any other ideas what could be causing my problems?

Thanks in advance.

[RonnieB]

yes, mine ended up being the ECU and the relay to the ECU unit