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.
Car stalling on cold start
- Thread starter igeak691
- Start date
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?
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?
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?
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.
igeak691 said:
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 said: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.