BMW Z4 Engine Sounds Like Small Stones Thrown At A Window - Then It Stalls..

[MEV Z4]

Yep I put some new plugs in during the last few days, the others had been in there since the 'dawn of time' and one of them was 'odd' with a single terminal.

I'm convinced the remaining problem is the fuel pressure regulator - When the pumps failed on my E36 2.5 & E46 330 the car spluttered like mad (Not that). With this Z4 you can rev it up to 6k while standing still (Or Rolling in neutral / or in gear with clutch down) or drive perfectly well until you over 50% throttle when after half a second it hesitates (It's OK even at high revs in low gear) - If you back off then it recovers OR if you keep the foot down it's limp mode. If you rev it hard in neutral while rolling then hold the revs and slowly let the clutch up then it's limp mode - This problem is only ocurring under engine load.

I think that's because the engine needs more fuel when under load - and there's some mechanism to tell the Pressure Regulator to let more through to maintain the constant 50psi required. (The ECU commands it on the Z4 but a vacuum pipe makes it happen on the E46).

At standstill I'm getting 50psi at the fuel rail but I cant think of a safe way to test the fuel pressure while driving on full throttle!

[Mike6]

Hmm. Did you mention fuel pump which could be failing under load, or perhaps the fuel filter.

[MEV Z4]

Hi! Got to the bottom of it - I put a Foot Pump on the cars Schraeder valve and used it's guage to read the fuel pressure. With ignition on the fuel pressure was 50 psi and it stayed there when started and idling. I took off the Foot Pump, started the car and accelerated hard along my drive in 1st gear until it cut out (After only15ft). As it cut out I immediately turned off the ignition, got out and re-attached the Foot Pump to read the fuel pressure after a stall. Zero psi. Then I turned the ignition back on and the the guage went from zero back up to 50psi.

This car is definitely stalling because of a fuel delivery problem which is not apparent unless the engine is under load. I've got anew fule pump / regulator assembly and the good news is that the Pump & Regulator are in one unit, the bad news is they're horrific to get at and it requires draining the tank. The fuel filter is in an even worse position- If I can't replace it then I'll just flush it back and forth with carb cleaner.

The only other possible causes are the wiring to the Fuel Regulator or the ECU sending it faulty / no commands - Don't know how to test that.

It's true i got this car really cheap and part of the reason I got it was to learn how to fix a 'modern' car - Got my wish, I've only had three days use out if it in nearly 4 months.... But I've learnt loads.

[enuff_zed]

Hi! Got to the bottom of it - I put a Foot Pump on the cars Schraeder valve and used it's guage to read the fuel pressure. With ignition on the fuel pressure was 50 psi and it stayed there when started and idling. I took off the Foot Pump, started the car and accelerated hard along my drive in 1st gear until it cut out (After only15ft). As it cut out I immediately turned off the ignition, got out and re-attached the Foot Pump to read the fuel pressure after a stall. Zero psi. Then I turned the ignition back on and the the guage went from zero back up to 50psi.

This car is definitely stalling because of a fuel delivery problem which is not apparent unless the engine is under load. I've got anew fule pump / regulator assembly and the good news is that the Pump & Regulator are in one unit, the bad news is they're horrific to get at and it requires draining the tank. The fuel filter is in an even worse position- If I can't replace it then I'll just flush it back and forth with carb cleaner.

The only other possible causes are the wiring to the Fuel Regulator or the ECU sending it faulty / no commands - Don't know how to test that.

It's true i got this car really cheap and part of the reason I got it was to learn how to fix a 'modern' car - Got my wish, I've only had three days use out if it in nearly 4 months.... But I've learnt loads.

All I can add is that as this forum moves forwards we gain more experience amongst us. Whilst this is a royal pain in the ass for you, it will greatly assist someone in the future, so thank you for documenting it.

[patriot66]

Hi! Got to the bottom of it - I put a Foot Pump on the cars Schraeder valve and used it's guage to read the fuel pressure. With ignition on the fuel pressure was 50 psi and it stayed there when started and idling. I took off the Foot Pump, started the car and accelerated hard along my drive in 1st gear until it cut out (After only15ft). As it cut out I immediately turned off the ignition, got out and re-attached the Foot Pump to read the fuel pressure after a stall. Zero psi. Then I turned the ignition back on and the the guage went from zero back up to 50psi.

This car is definitely stalling because of a fuel delivery problem which is not apparent unless the engine is under load. I've got anew fule pump / regulator assembly and the good news is that the Pump & Regulator are in one unit, the bad news is they're horrific to get at and it requires draining the tank. The fuel filter is in an even worse position- If I can't replace it then I'll just flush it back and forth with carb cleaner.

The only other possible causes are the wiring to the Fuel Regulator or the ECU sending it faulty / no commands - Don't know how to test that.

It's true i got this car really cheap and part of the reason I got it was to learn how to fix a 'modern' car - Got my wish, I've only had three days use out if it in nearly 4 months.... But I've learnt loads.

I used a length of old hosepipe and siphoned the fuel from the tank which I had already run down to a minimum beforehand. To be honest once you get to the fuel tank itself then the job of removing and replacing the filter/pressure regulator and the separate fuel pump is fairly straightforward. I bought a specific Laser Tools fuel tank lockring tool to avoid damaging anything. The trouble is getting to the fuel tank is a bit of a PITA...exhaust system and heatshields need to be removed

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This is the combined fuel filter/pressure regulator that is secured by the lockring

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You can see the fuel pump still inside the tank below

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Job done !

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[MEV Z4]

I put in a new fuel pump (?) but I'd like to confirm that there wasn't meant to be some pipe that push fitted onto the Regulator.

It does look like there should be a pipe on the Regulator but there wasn't one when I took the pump (?) out - so I put it all back in the car without thinking.....

1) Did you find a pipe on your regulator OR is it meat to be open to the air / air pressure?

My old Pump (?) was completely full of black 'stuff' like some rubber component had dissolved inside it. I blasted carb cleaner through and it came out the other end black.

2) Thinking further about it - The part we've replaced (White plastic thing in the side of the tank) might be just the Regulator & Filter assembly and not the Pump. The RealOEM website and Pelican Parts website (Z4M Model) say it's only the filter and then show the pump coming out after. Is the Fuel Pump joined to the Level / Float mechanism and they sit further in the tank? However lots of other sites / breakers picture that part and describe it as a fuel pump- Can they all be wrong? (I might break my old unit apart to confirm if it's just a filter).

NOTE - In some discussions they say you have to take off / move the driveshaft -Not True for the Z4 E85 2.5 model. (Yes the complete exhaust does have to come off).



These forums are very helpful but please stick to this particular topic and answer only the questions raised above.

Please don't ask things that are irrelevant like - What codes I've got and if I've changed the spark plugs.
No unhelpful comments like "Should have got a Mercedes LOL" + laughing emoji....

[patriot66]

Referring to my photos the part B in my hand is the combined fuel filter/pressure regulator (secured by the lockring in the first photo) and you can see all it's electrical and fuel line connections internally and externally in the first two photos. There are 2 fuel lines connected internally at 1 and 2. The fuel pump (with integral fuel float/ level sender) is secured to the base of the tank and is visible circled in red and marked A in the third photo. The Pelican Parts fuel pump replacement shows what you are asking about https://www.pelicanparts.com/techarticl ... cement.htm

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[MEV Z4]

HI!

Thanks for the pictures, yes that bit is just the filter / regulator and the pump is further in the tank.

The x2 main fuel pipes were attached correctly to the filter on mine - Should there also be a pipe on the OTHER side of the regulator as indicated in my picture?

[patriot66]

HI!

Thanks for the pictures, yes that bit is just the filter / regulator and the pump is further in the tank.

The x2 main fuel pipes were attached correctly to the filter on mine - Should there also be a pipe on the OTHER side of the regulator as indicated in my picture?

No. No pipe attaches to that side of the regulator. Photo of mine as it came out of the tank before I undid any connections.

20220209_142932.jpg (111.43 KiB) Viewed 153 times

Photo of standard 3.5bar press.regulator on the right and high press.reg on the left. The high press.reg doesn't have the small pipe that you're wondering about. This was fitted as part of my Supercharger kit and has been running perfectly for over 2 years/10k miles now

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[MEV Z4]

Thanks! A New Fuel Filter didn't solve it (Yes the old filter was full of black silt).

Next steps -

1) New upstream O2 sensors (Engine sounds extremely rich and revs itself which is why i thought it was the fuel regulator - Could be upstream O2 sensors giving a rich mix).
2) Re-do the fuel pressure leak down test with the new regulator fitted, see if it anything is different now?
3) Injectors to be removed / tested for leaks and then cleaned. (Leaking injectors can also result in a rich / surging condition).
4) Fuel feed line and rail to be cleaned out (Filter was full of silt so maybe they are as well?).

If it's not any of the above then I've run out of ideas.....

This car has had EVERTHING on it either cleaned / tested and or replaced.

[enuff_zed]

So you still have low fuel pressure at the injector rail?
I'm sure you will have checked already, but if other work has been done in the engine bay, is it possible the feed pipe to the rail has been kinked?