Cold start rough

[marioz4]

Thanks - today we conected the car and it gave reading that low presure fuel pump is spinning like mad, so i will chnage the LPFP first and while his work is beeing done will take this oprotunity to ask them to take spark plugs out and check them.

I forgot to ask them if they can see in car history when they did diagnostic what code car gave when CEL light came on ( it came on only once some 10 day sago and it vent away afer 1 min.)

Will keep you posted

Just back from BMW

Injectors 13 53 8616079 300 euros each, you mention that revision 12 are the latest, so this one 13 i guess is totally new version?
Also they qouted me 420 euros for low pressure fuel pump...

13 is fine aswell, I am confused as to how they are quoting you for a low pressure fuel pump when the Z4 doesnt have one?

Model 35i - yes it has low presure pump, item number: 16 14 7363076 - i just found one on internet for half price.. not original bmw but i am sure it will be just fine

[ph001]

Yes, the N54 certainly does have both a low pressure and a high pressure pump. The LPFP sits in the tank and is electrically powered - it is used to 'prime' the fuel rail to around 70psi (so not that low pressure)! The HPFP is mechanically driven from the engine and boosts the fuel rail to over 2000psi (around 700psi at idle).

It is rare indeed for the LPFP to fail but it is not unheard of for the LPFP pressure regulator to fail. You need to look at log of fuel pressure to confirm, but basically the correct operation is for the LPFP to come on with ignition and prime the fuel rail to around 70psi, then turn ignition off again and check fuel rail stays at around 70psi. Even the next day it should be above 50psi. If fuel pressure regulator is bad then the 70psi drops off very quickly when ignition is switched off.

Normally, a bad LPFP pressure regulator causes long delay in starting - maybe 5-10 cranks of engine, but when it does start it usually runs OK. Bad / rough running from cold is nearly always an injector problem.

[marioz4]

Yes, the N54 certainly does have both a low pressure and a high pressure pump. The LPFP sits in the tank and is electrically powered - it is used to 'prime' the fuel rail to around 70psi (so not that low pressure)! The HPFP is mechanically driven from the engine and boosts the fuel rail to over 2000psi (around 700psi at idle).

It is rare indeed for the LPFP to fail but it is not unheard of for the LPFP pressure regulator to fail. You need to look at log of fuel pressure to confirm, but basically the correct operation is for the LPFP to come on with ignition and prime the fuel rail to around 70psi, then turn ignition off again and check fuel rail stays at around 70psi. Even the next day it should be above 50psi. If fuel pressure regulator is bad then the 70psi drops off very quickly when ignition is switched off.

Normally, a bad LPFP pressure regulator causes long delay in starting - maybe 5-10 cranks of engine, but when it does start it usually runs OK. Bad / rough running from cold is nearly always an injector problem.

Thanks - bit late now but hey... when they conected the car to PC it gave off scale reading for low presure pump, i can also hear it buzzing like crazy, as fuel filter is attched to the pump i decided ( as there is no extra labor cost) to change the fiter as well ( 60k miles).

I found injectors for 1/3 of the price from bmw thanks to another member here who advised alternative BMW original injectors.. so if changing the pump dos not solve the issue...next thing would be injectors...my feeling is that its the pump as issue with rough start ( even when car is hot revs are very low ) is that its the low presure fuel pump...( or leaking injector) as i am off for holidays most likely all of this will be done in January.

[ph001]

Is the fuel pressure regulator attached to the pump? If the pressure was off the scale then the regulator must be duff. You can’t have a bad pump and a good regulator giving you those symptoms if you know what I mean.

The other member specifying the alternative injector part numbers was me!

[R.E92]

There's no pressure sensor for the low pressure line on the Z4 so it's hard to diagnose the low pressure pump.

My advice would be to get the genuine parts. Go with either index 12 or 13 injectors, everything else will cause you headaches.

[marioz4]

Is the fuel pressure regulator attached to the pump? If the pressure was off the scale then the regulator must be duff. You can’t have a bad pump and a good regulator giving you those symptoms if you know what I mean.

The other member specifying the alternative injector part numbers was me!

Oh, it was you! Fantastic great, i am in Germany now and will go to BMW to ask about difference between two injectors. THANKS A lot for sharing this info with us.

Presure pump in 35i dos not have any sensor that will let you know that pump is now working OK - i can hear the pump struggling and its very noisy and when we did test it was off scale spinning...anyhow i ordered new one and original air filter both in total for £300 - not cheap. Not sure how long is needed for this to be replaced..where is access to the pump

[marioz4]

UPDATE: I have changed coils and car works like new! i ordered 6 coils on line for 140euros and changed them myself - 15min job. It look like this was the main issue.

I have pending replacement of LPFP as that buzzing is driving me mad, i should say - more mad

[marioz4]

UPDATE: I have changed coils and car works like new! i ordered 6 coils on line for 140euros and changed them myself - 15min job. It look like this was the main issue.

I have pending replacement of LPFP as that buzzing is driving me mad, i should say - more mad

[enuff_zed]

UPDATE: I have changed coils and car works like new! i ordered 6 coils on line for 140euros and changed them myself - 15min job. It look like this was the main issue.

I have pending replacement of LPFP as that buzzing is driving me mad, i should say - more mad

So mad you wrote this twice

[marioz4]

UPDATE: I have changed coils and car works like new! i ordered 6 coils on line for 140euros and changed them myself - 15min job. It look like this was the main issue.

I have pending replacement of LPFP as that buzzing is driving me mad, i should say - more mad

So mad you wrote this twice

Nop... no so mad - crazy as coconut but... did not wrote this twice - i guess IT glitch