This has been ongoing for months and slowly getting worse. I drive the car on weekends around a thousand miles. It runs perfectly after I replaced spark plugs, no misses once it runs. It used to hard start only when warm or warm weather, now it seems to be always. I thought maybe was a coolant sensor or something reporting bad. What makes this tricky is it runs PERFECT once it starts. I thought fuel pressure issues but I have cycled key and things like that without help. It takes anywhere from 3-10 seconds to start most of the time now. Fresh battery fast cranking.

Any ideas what this could be? It's gotta be some sensor; has 140k miles now so getting up there. The fact it runs so good once runs I can't think of any mechanical issues that would cause or any fuel injector or things like that. Thoughts? I need to plug into it and see what sensors are reporting for coolant temp, ambient air, MAP, etc. I think these don't have a MAF right?

Thanks!

 

My guess is the fuel pump on its last leg.

 

Wouldn’t that mean there would be power loss or hesitation while running? It never does. I was thinking maybe fuel pressure regulator. This afternoon it started flawlessly when it was colder and windy about 50F. Doesn’t make sense.

 

After extensive reading and fuel rail pressure testing, I think it could be related to a sensor like MAP, IAT, or coolant temp. I will test some more but I could not reproduce a hard start and fuel rail pressure built immediately to 52 PSI or whatever on first key cycle. Up into 60s if keep cycling so I think fuel pressure OK. But I didn't see it on a hard start so that's making an assumption.

I read also these various sensors can affect closed loop ignition timing changes, which may affect starting of course. It's never simple with me :(

 

I had the hard starting problem in my R53 also. Pulled my hair out trying to fix it. Ended up putting a gauge on the fuel rail and it was bleeding off very quickly. The problem ended up being the larger o-ring on the fuel filter housing. Fixed that it it was perfect. Hope you get it figured out pal.

 

I have done fuel pressure test and it was fine. It slowly bleeds off but will pressure back up on one key turn typically. It hard started with full 50+ psi so isn’t that.

I am planning on analyzing sensors and it could just be leaking injectors but I’ve never personally seen that. Doesn’t seem would start so hard just from that would blow out quickly. Dad made comment not if throttle body is closed and no air.

Does anyone know if it opens during starting if you floor it ? Made no difference to my starting.

I bought the training manual and have some theory of operation I will figure out eventually. It’s really annoying. I’ll try to report back here.

 

I did some scan tool readings and got 25% STFT so it’s running lean also. Not sure why maybe vacuum leak or a bad map or TMAP or off. I’m reading 864 or so mbar from the map (not sure tool reads tmap need to plug in bmw tool). This is with engine off. Is it a bit low? Like 12.5psi should be closer to 14 I’d think. Not sure tho. Wish I had another mini to compare to

 

To check for a vacuum leak while at idle, spray short bursts of starting ether around suspect places. If the idle speeds up, you've found the leak.

 

Yea I may do that. Does anyone have some idol and engine off MAP readings ?