Car stalling on cold start

Rufus59 · Post by **Rufus59** » Thu Apr 06, 2017 1:49 pm

I would check air parth, maf, coils, plugs and then the fuel system including sender and rail pressure. I think you should be able to read off rail pressure using diagnostic software and perhaps throttle position too.

A visual inspection of the above would be a good start, connections etc and then failing that is get it to a garage for a more thorough investigation.

groovy_hippy · Post by **groovy_hippy** » Sat Apr 08, 2017 8:47 am

Agree with Marc-j.

It's something to do with the engine being starved of something - could be fuel, air, or 'ignition'. It's not firing on all of its cylinders... Hence - check anything to do with that - coils, fuel system, spark plugs, any other electronic gubbins that control any of the above.

It sounds just like mine did - it would start, then as it warmed up a bit, it'd cough and splutter, and if you could keep it going with tiny careful throttle inputs, it would eventually warm up completely and run ok. Ultimately it wouldn't even start smoothly - the final straw was when it sounded like an old tractor and needed nannying to get going...

groovy_hippy · Post by **groovy_hippy** » Sat Apr 08, 2017 8:51 am

A further clue to the fact it's not firing correctly is the unburnt/smokiness coming out of the exhaust. Not a happy engine.... and yes, it will rattle and shake horribly because there are ignitions going on at the wrong time, and most probably in the wrong place (in the exhaust system...). Not something to keep doing - unburnt fuel on the catalytic converter and lambda sensors could kill them (queue lots of cash to fix...)

igeak691 · Post by **igeak691** » Mon Apr 10, 2017 6:05 pm

Further update.. today, I tried looking at the injectors and fuel rail, check some vacuum hoses. Didn't really find much but car did same thing on first start, then it started and idled fine on the second start. It is pretty warm today compared to other days.. but I went driving, and cruising in fifth gear the car started to die again, like I was giving it gas but it was still dying. Eventually I pulled off to the side and when I let in the clutch the car died like it would've if I was at a stand still. Anyway, after a few startups it didn't happen again, and I also put some chevron fuel system cleaner in the tank. I'll be doing another bottle with the next fillup. What's surprising to me is that it happens when the car is "warm" now too. I think perhaps fuel filter related? Car gets starved of fuel intermittently I'm guessing, which leads to the misfires and knocking and stalling. Hoping the fuel cleaner will take care of it. If it does or doesn't I guess I still need to swap the fuel pump/filter assembly? Still very confused, but saw another thread on a forum (http://forum.e46fanatics.com/showthread ... 131&page=4) very similar and it was fixed with a fuel filter.

Rufus59 · Post by **Rufus59** » Mon Apr 10, 2017 8:47 pm

If you can, get it to a garage to take a look. They might charge £100 to fault find but they'll have the right gear to get to the bottom of the issue and save you replacing something you don't need to. If you want to have a go yourself some more, get it on a BMW dis or inpa to get the codes off and read the vitals from the modules. Fuel pressure, air fuel ratio, mass air flow, injector status

igeak691 · Post by **igeak691** » Mon Apr 10, 2017 11:17 pm

I am familiar with DIS and INPA. Is there a guide somewhere I could follow in terms of hunting for codes? As I understand, the modules store codes that don't necessarily show up as check engine lights. Like I remember seeing certain errors and error counts once when I was digging through some modules but it's been awhile. Any direction for diagnosis is appreciated as here in New York, there are specialty shops that would be doing the same thing I can do. Not to put them down as they are more experienced than I am but I have seen some shops do their thing and I'd only be paying for their time since I own the tools to perform the same diagnostic tests they do.

igeak691 · Post by **igeak691** » Thu Apr 13, 2017 9:30 pm

News! Got a fuel pressure gauge today and mounted it onto the fuel rail. When I start the car the fuel pump primes and goes to 46psi which i think is fine. However when the car starts stumbling and then stall, the fuel pressure is exactly in sync so I think I got a faulty fuel pump! Fuel pressure at the rail should never jump around right? The fact that it is oscillating exactly at the same rhythm as the idle makes me believe I need a new fuel pump. Am I on the money or am I missing something?

Rufus59 · Post by **Rufus59** » Fri Apr 14, 2017 11:21 pm

I'd avoid doing any more starts, sounds like some of the cylinders aren't firing so might be causing some minor damage each time. Get it down to a garage that can investigate and diagnose properly. Unfortunately it could be any number of things, fuel, induction, spark. It's a frustrating expense but at least the car will be fixed

Edit just read the above post. Yeah that does sound odd, as far as I know rail pressure should be pretty much constant. Not sure of the exact system the z4 has but perhaps it could be some kind of pressure garage/regulator at fault?

Behr · Post by **Behr** » Fri Apr 14, 2017 11:55 pm

Don't discount the power supply to the fuel pump either. It could be a poor contact or wiring/earthing issue causing a reduction in the pump circuits' current carrying capacity.

igeak691 · Post by **igeak691** » Sat Apr 15, 2017 3:05 am

I've since gone ahead and ordered a fuel pump and fuel filter/pressure regulator. Hopefully swapping them out will fix it, if not.. it was time for them to be swapped anyway. Im not sure how I'd trace electrical issues leading to pump failure, if you or anyone else knows how I'd appreciate advice and guidance on that.

Behr · Post by **Behr** » Sat Apr 15, 2017 11:16 pm

igeak691 wrote: ↑Sat Apr 15, 2017 3:05 am I've since gone ahead and ordered a fuel pump and fuel filter/pressure regulator. Hopefully swapping them out will fix it, if not.. it was time for them to be swapped anyway. Im not sure how I'd trace electrical issues leading to pump failure, if you or anyone else knows how I'd appreciate advice and guidance on that.

Easy way to see if the pump is getting the required voltage would be to put a multimeter "across" the fuel pump terminals and observe the voltage reading under fault conditions. It sounds from your posts like the fault happens when idling and is easily repeatable so should be a quick test to do. If you don't have a multimeter then a 5 or 12w test bulb and some leads could be made easily and is arguably more reliable (bulb starts to dim then you have a problem).

Alternatively you could connect a standalone power supply to the pump for test purposes, taking care when doing so. Petrol and sparks are only fun when they happen inside the engine

Either way, hope you get it sorted.

igeak691 · Post by **igeak691** » Thu Apr 20, 2017 11:02 pm

Swapped it out and sure enough the car runs fine even from a cold start now!

I think it was a combination of a weak fuel pump plus a clogged fuel filter. When I tested the fuel pump on the bench it worked, so likely it was mostly the fuel filter that was clogged.

Behr · Post by **Behr** » Thu Apr 20, 2017 11:25 pm

Nice one. And thanks for updating with the outcome

10Terp · Post by **10Terp** » Tue Jan 30, 2024 3:03 pm

igeak691 wrote: ↑Thu Apr 06, 2017 12:33 pm Anyone can venture any ideas? Can't drive the car and it really sucks

Posting for posterity as I own this car now, and hopefully it'll help somebody else who may stumble on this post. I got the car in November of 2023 with 116,500 miles on it, and it was still stalling on cold start (but it would stay running after a while). Certainly could be a combo of the fuel issues outlined above and what I found as well. The problem was a combination of things:

1) The car had a MASSIVE vacuum leak. The IAT bellow on the air intake boot had a huge crack in it.
2) The DISA was completely shot. The valve flapper was free spinning on the shaft.

Replaced the intake elbow and rebuilt the DISA and it no longer dies on cold start. Fires right up and idles great.

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