z4 broken down - thought please

[rob davey]

Hello all,

Unfortunately the Z4 let me down last night, which resulted in a 4 hour wait for the AA to come and rescue the car with a flat bed truck.

I would like your thoughts as to what could be the problem if you dont mind.

What happened…
The car had been on a 50 mile run round the m25 and i stopped at my office for literally 5 minutes to pick up some post. When i came back the car would turn over but did not fire.

The AA mans thoughts…
The starter motor is buggered, the motor has a clutch to engage it to the engine and this was probably faulty as the motor was spinning freely with no resistance therefore it seemed it was not engaged to turn the engine.

BMW Sytner High Wycombe’s thoughts…
It’s not the starter motor, on initial check they can see the timing chain moving so now they want to do a compression check to see if the engine has any compression. They also think the timing chain may have slipped so want to take off the cam cover to look. The catch is it was £95 for the initial check and it will be over £300 odd once they do the next steps of diagnostics mentioned before any thing is fixed.

Any ideas or similar problems? I can see this getting very costly at this rate

 

[cj10jeeper]

Almost impossible to diagnose such things at a distance without endlesss Q&A, but the starter motor woudl have been very obvious and you'd have heard it whizzing round at speed if it was not driving hte negine.

What I'm suprised at is BMW going for compression test first. I'd be looking for a spark and fuel getting to the engine (wet plugs if nothing else) before I ever thought about the internals having failed. - Odd

 

[un1eash]

Could be any number of things, i take it they ran a diagnostics check? Could be the crank sensor?

 

[rob davey]

Almost impossible to diagnose such things at a distance without endlesss Q&A, but the starter motor woudl have been very obvious and you'd have heard it whizzing round at speed if it was not driving hte negine.

What I'm suprised at is BMW going for compression test first. I'd be looking for a spark and fuel getting to the engine (wet plugs if nothing else) before I ever thought about the internals having failed. - Odd

My thoughts exactly and the only logic I see is to do the expensive diagnostics stuff first to ensure i have a hefty bill!

Could be any number of things, i take it they ran a diagnostics check? Could be the crank sensor?

If i remeber rightly the codes of the Diagnostics said co2 sensor, vvt sensor

 

[jonnyfive]

No mechanic here but its not your starter motor , it might be worth checking if you are getting a spark at you plugs or could be your fuel pump ( check fuse and filter )

Not quite sure what a compression test is going to tell you especially if the car was fine with no over heating or running rough before you stopped, a sudden lost in compression is very rare, i think there taking you for a ride a little .

I bet its your fuel pump fuse.... but like i said no expert but if it is you owe me a beer.

to test fuel pump turn key to position 1 and see if you can here the fuel pump come on. Normally a couple of seconds weering its very quiet but you should be able to hear it.

 

[aquazi]

How many miles has the car covered?

I'm also amazed a compression test so early on... unless all 4 cyclinders have gone it wouldnt cause a siezed engine.

 

[bigshurv]

I think I'd prefer an indy to look at it. Main dealers are good at replacing loads of expensive parts, BUT, they don't tend to like repairing things as they cannot charge loads of wonga for it.They will follow manufacture guidelines all the time which will ALWAYS recommend replacing parts whereas an Indy will try to fix the direct problem. However if the car in under a BMW warranty, you have no choice.I bet it's nothing major.Good luck with it, I hope it is an easy fix.

 

[fraserbottomley]

My dad had a Rover 75 which would suffer the same symptoms, especially common if the car was still warm from driving when trying to start the engine. It would turn over but not fire.

Anyway this was a fairly common problem on the Rover, and turned out to be the cam/crankshaft position sensor, I can't remember which one exactly but they were both only £10 parts so we replaced both. Prolem solved!

Now with your fault codes reading 'vvt sensor', and with BMW being involved with Rover at the time of the 75 it might be a
similar issue! I'd certainly be looking at something simple like this and not a compression test.

 

[EdButler]

So does it sound normal when cranking? If the starter wasn't engaging, you'd get just a high pitched buzz from the motor like CJ10Jeeper said...

If the engine is cranking, just not firing, Im gonna join the froserbottomley camp and think it is probably something to do with the Camshaft Sensors. There was someone on here recently who had similar error codes (O2 Sensors, Misfires, Vanos timing error) and it is usually to do with camshaft sensors or a bad vanos. As yours plainly wont start, I believe it could be the former.

I agree with others in taking it to an Indy, a compression check certainly should NOT be the first port of call... And if you wanted to do it... DIY, its easy!

 

[rob davey]

Thank you for all the feedback, I’ve had to stick with the dealer as I have no other way of moving the car and worse still the longer it is off the road the longer I can't do my job and earn an income

The compression test found that there was low compression across all 4 cylinders. I’ve been told the problem is an electric motor under the cam cover that has failed, this has something to do with the vanos but with my limited knowledge I’m not sure what. They are replacing the motor and then timing the engine and it should, should be fixed.

That would also explain why the vanos sensor fault was on. Fingers crossed.

 

[rob davey]

To update the car was fixed on Friday... AND BROKEN DOWN AGAIN TODAY!

It's symptoms are exactly the same as before. :headbang:

 

[fraserbottomley]

Did they change the VVT/Cam sensor?