‘03 z4 starting issues.

C

carlsson

Member
 Los Angeles, CA
I haven’t used my z4 for a week and decided to use it this afternoon as weather was really nice. Started right up, idled smoothly, lowered the top and off I went to my first stop...a drug store 2 blocks away. When I came back it just won’t start...cranks really good but just won’t start. Figured might be my key...got my spare key but still no start. Any ideas?
 
Probably ignition switch... assuming you haven’t run out of gas! Immobiliser another possibility but ignition switch is a common failure point.
 
Hi ph001, was thinking fuel pump relay or crankshaft sensor. Will look into the ignition switch too. Anyway, went to my car this morning and I was tempted to start it..it fired up and is idling smooth as if nothing happened. Drove it on the freeway and the car works fine. Now I’m in a dilemma...I never found out what was wrong and it could happen again anytime anywhere. :cry:
 
ph001 said:
Probably ignition switch... assuming you haven’t run out of gas! Immobiliser another possibility but ignition switch is a common failure point.
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Surely the immobiliser is separate to the ignition switch? I'd expect no starter motor action if the ignition switch was duff.

[ref]carlsson[/ref] I'd be thinking along those lines you mentioned too. It could even be the fuel pump itself on its way out, or a faulty immobiliser. Tricky one!
 
Ii always hear a slight hiss a few seconds before I start my car..figured it’s the pump priming the fuel system...didn’t hear that noise last night when it failed to start. Will check tomorrow if I hear that hiss again.
 
wonkydonkey said:
ph001 said:
Probably ignition switch... assuming you haven’t run out of gas! Immobiliser another possibility but ignition switch is a common failure point.
Click to expand...
Surely the immobiliser is separate to the ignition switch? I'd expect no starter motor action if the ignition switch was duff.

[ref]carlsson[/ref] I'd be thinking along those lines you mentioned too. It could even be the fuel pump itself on its way out, or a faulty immobiliser. Tricky one!
Click to expand...

No, easily the ignition switch and exactly what happened to mine. Would crank but not fire. Position 2 had gone duff so no ignition lights, but you don’t tend to notice that when you usually just get in and turn the key.

Intermittent problem that got worse.

£10 fix for replacement from quarry motors via eBay.
 
carlsson said:
Ii always hear a slight hiss a few seconds before I start my car..figured it’s the pump priming the fuel system...didn’t hear that noise last night when it failed to start. Will check tomorrow if I hear that hiss again.
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Interesting. If it is a fuel pump matter, hopefully it's just a tired relay (or fuse - but then you'd be wondering why it blew a fuse).
 
Won’t start again this morning. Checked fuel pump relay and it’s working fine. A pain in the ass to reach if you are somebody my size... :D Anyway,noticed that my temp guage sweeps all the way to the red zone when I turn on ignition..i don’t think it did this before the starting issues...
I doubt it’s an ignition issue...all dash lights turns on when I put it in position 2.
 
Checked fuel rail and it’s dry. So fuel pump is not working...but will a faulty crankshaft sensor cause that? Tell the ecu not to put fuel on the engine?
 
The car started this afternoon...this time I was really observant.... :D
When the temp needle goes all the way to the red zone on a cold or warm engine then it will not start...just cranks. If the temp needle stays on the blue line on a cold engine or center on a warmed up engine the car will start. One time the temp needle went all the way to the red line but went back to center so the engine started...I’m scratching my head here..will a faulty engine temp sensor or radiator sensor cause starting issues?
 
That is interesting. An ECU will tell the injectors to give the engine more fuel when the coolant is cold, but it'll also request significantly more fuel during start-up cranking. Even on a hot start-up cycle I'd expect you'd be getting enough fuel for a cold engine to start, but perhaps it's not QUITE enough? Is it trying to cough into life? Or merely cranking with no attempts to fire up?

The fact that you only encounter this issue when trying to start the engine (and not when the engine is already running and you're on the move) makes me think the issue lies with the control of the fuel pump, rather than the mechanical functioning of the pump.

What diagnostic goodies do you have access to? It would be helpful to see if any errors are being logged.
 
Not often you hear of new unique problems on these cars given the history of this forum... but I’m pretty sure this is one of them! An intermittent coolant temperature sensor would be odd indeed but I think it’s something you are going to have to eliminate. Do a careful check of the connector and wiring to it when you are down there. I didn’t think an ‘apparently’ overheating engine would also cause the ecu to cut the fuel pump either, but maybe it does!
 
Issue appears only while trying to start...when it starts engine runs smooth.
It just cranks and cranks if the temp guage is at the red line. If its on the blue line when I turn the key then it starts right up.
I have a creator c310...bought it to check/reset minor stuff.
 
I’ll try replacing the engine temp sensor tomorrow and see what happens...a cheap part indeed but replacing it seems like a pain to do.
 
Bizarre behaviour from electrical components can often be sourced to an unreliable current return (earth) path. I'd have thought you'd have more issues than this one if you had a poor earth somewhere, but again, this is guesswork on my part.

ph001's advice to check the connector and wiring to the coolant temp sensor is wise. Perhaps the ECU forbids engine start if the coolant sensor output is out of range? An ECU can default to safe running if it loses a temperature sensor, but maybe if it looks for a temp sensor at startup and doesn't find it, it prevents the engine from firing? If one day it "sees" the sensor and starts the engine, but another day it doesn't, that might point you more down the road of a wiring issue.

I'm obviously just thinking out loud with you here in an attempt to get more brains on the job!
 
BTW when the engine IS running and you're driving about, does the coolant temp stay solid? If it does flick high again, do you notice any change in the engine running? More crackles/backfires on overrun?
 
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