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E36/7 Z3 (1996-2002)
E36/7 Z3 Roadster, Z3 coupe, Z3 M Roadster and Z3 M Coupe talk with our gurus here.

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  #1  
Old 04-13-2005, 08:53 AM
Black Buggy Black Buggy is offline
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Mein Auto: Z4 2.5
'03 Z4 2.5 Engine problem(s)

I'm hoping someone here might be able to help me to determine if several engine issues are related. My husband and I have a 2003 Z4 2.5 with 20,000 miles that over the last three months has been serviced for engine problems and I'd like to know if any of the repairs may have impacted our current problem -- chips out of the pistons that will require a repair not covered by warranty to the tune of $8,600!

The first service was required after the service engine light came on, with the car sputtering and having no power for acceleration. Service included:
- replacement of pulse generator on the exhaust camshaft and FC 28AC specified torque monitoring restored
- Installed new DME

The second service was when the check engine light came on and the engine was running very rough. Service included:
- Removed and replaced 6 IGN coils

And now for the "fun" part...

My husband was driving the car on the highway Friday at 6pm - fairly heavy traffic- going about 70mph and a car cut in front of him. In order to avoid an accident (Thank you BMW driving school!) my husband stood on the brakes and downshifted from 5th gear into 3rd gear, thankfully avoiding contact with the other car. After the downshift, the Z lost power to accelerate and he pulled over in the breakdown lane and the car stalled and failed to restart. We towed it to our dealership and told them what happened.

They are saying it was an over rev situtation and not covered by warranty. Shouldn't the car be able to handle a downshift like that? Or aren't there any safety overrides that should have kicked in to protect the engine? Could any of the prior service issues had an impact?

I'm just trying to understand it all better because I would have thought the car should have been able to handle it without blowing the engine - pistons!!
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  #2  
Old 04-13-2005, 09:24 AM
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kyfdx kyfdx is offline
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Quote:
Originally Posted by Black Buggy
I'm hoping someone here might be able to help me to determine if several engine issues are related. My husband and I have a 2003 Z4 2.5 with 20,000 miles that over the last three months has been serviced for engine problems and I'd like to know if any of the repairs may have impacted our current problem -- chips out of the pistons that will require a repair not covered by warranty to the tune of $8,600!

The first service was required after the service engine light came on, with the car sputtering and having no power for acceleration. Service included:
- replacement of pulse generator on the exhaust camshaft and FC 28AC specified torque monitoring restored
- Installed new DME

The second service was when the check engine light came on and the engine was running very rough. Service included:
- Removed and replaced 6 IGN coils

And now for the "fun" part...

My husband was driving the car on the highway Friday at 6pm - fairly heavy traffic- going about 70mph and a car cut in front of him. In order to avoid an accident (Thank you BMW driving school!) my husband stood on the brakes and downshifted from 5th gear into 3rd gear, thankfully avoiding contact with the other car. After the downshift, the Z lost power to accelerate and he pulled over in the breakdown lane and the car stalled and failed to restart. We towed it to our dealership and told them what happened.

They are saying it was an over rev situtation and not covered by warranty. Shouldn't the car be able to handle a downshift like that? Or aren't there any safety overrides that should have kicked in to protect the engine? Could any of the prior service issues had an impact?

I'm just trying to understand it all better because I would have thought the car should have been able to handle it without blowing the engine - pistons!!

If he downshifted into 3rd gear at 70 MPH, then he wouldn't have over-revved it, I don't think..(not sure, though.. I'm guessing redline in 3rd gear would take you over 70 MPH) My guess is he downshifted into first gear, thus blowing the engine... It is a manual transmission.. when you are accelerating there is a rev limiter, which cuts engine power... but, even if you are coasting at 70 MPH with the engine off, you would over-rev it, if you shifted it into 1st or 2nd gear.... It is a mechanical hook-up, and there is no way for the car to prevent it..

The OBD computer records over-revs.. I think you are going to be out of luck.. I don't see how any of the other problems would affect this, especially when you have another explanation..

regards,
kyfdx
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  #3  
Old 04-13-2005, 10:22 AM
Black Buggy Black Buggy is offline
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Quote:
Originally Posted by kyfdx
If he downshifted into 3rd gear at 70 MPH, then he wouldn't have over-revved it, I don't think..(not sure, though.. I'm guessing redline in 3rd gear would take you over 70 MPH) My guess is he downshifted into first gear, thus blowing the engine... It is a manual transmission.. when you are accelerating there is a rev limiter, which cuts engine power... but, even if you are coasting at 70 MPH with the engine off, you would over-rev it, if you shifted it into 1st or 2nd gear.... It is a mechanical hook-up, and there is no way for the car to prevent it..

The OBD computer records over-revs.. I think you are going to be out of luck.. I don't see how any of the other problems would affect this, especially when you have another explanation..

regards,
kyfdx
Thank you for responding. How do I go about finding out what the OBD computer reported? Is it something I can ask the dealer to print out for me? Again thank you for your thoughts.
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  #4  
Old 04-13-2005, 10:44 AM
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LA525iT LA525iT is offline
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I think the gearing is different between the 525 and the Z4, but a 5-3 downshift at 70 does not cause an overrev. Must be (1) something else or (2) accidental shift into 1st.
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  #5  
Old 04-13-2005, 11:53 AM
99flhr 99flhr is offline
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Unhappy

Quote:
Originally Posted by kyfdx
If he downshifted into 3rd gear at 70 MPH, then he wouldn't have over-revved it, I don't think..(not sure, though.. I'm guessing redline in 3rd gear would take you over 70 MPH) My guess is he downshifted into first gear, thus blowing the engine... It is a manual transmission.. when you are accelerating there is a rev limiter, which cuts engine power... but, even if you are coasting at 70 MPH with the engine off, you would over-rev it, if you shifted it into 1st or 2nd gear.... It is a mechanical hook-up, and there is no way for the car to prevent it..

The OBD computer records over-revs.. I think you are going to be out of luck.. I don't see how any of the other problems would affect this, especially when you have another explanation..

regards,
kyfdx
production "crotch rocket" motorcycles employ "back torque limiting" devices in their clutch setups which inhibit the ability of the rear wheel to "drive" the engine, this allows multiple gear downshifts (i.e. 6th to 2nd) without over revving the engine or causing the tire to slide. This of course doesn`t help the unfortunate lady above. For $8600 I hope she gets a new short block
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  #6  
Old 04-13-2005, 01:53 PM
bmw325 bmw325 is offline
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Quote:
Originally Posted by 99flhr
production "crotch rocket" motorcycles employ "back torque limiting" devices in their clutch setups which inhibit the ability of the rear wheel to "drive" the engine, this allows multiple gear downshifts (i.e. 6th to 2nd) without over revving the engine or causing the tire to slide. This of course doesn`t help the unfortunate lady above. For $8600 I hope she gets a new short block
Interesting. So, on one of these motorcycles if you did a multi-gear downshift that would, lead to an engine spped that's too high, what happens? The engine just goes to redline in those cases?
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  #7  
Old 04-13-2005, 05:06 PM
99flhr 99flhr is offline
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Can`t say for sure as I`ve never had a bike with this feature, the main idea is to allow you to the utilise the tremendous brakes these bikes have, esp. on a track where you would encounter a tight turn at the end of a straight. Come in @ 110, brake and downshift for perhaps a 40 mph entry speed and not have the back end break loose while the bike is leaning into the turn.Beyond my skill level, pucker factor way to high!!!
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  #8  
Old 04-13-2005, 06:05 PM
MyCoupe MyCoupe is offline
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I thought that all BMW's had a rev limiter so that something like this would not happen.
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  #9  
Old 04-13-2005, 06:17 PM
99flhr 99flhr is offline
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Quote:
Originally Posted by MyCoupe
I thought that all BMW's had a rev limiter so that something like this would not happen.
Please reread kyfdx`s excellent explanation in post #2
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  #10  
Old 04-13-2005, 07:31 PM
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TR6 TR6 is offline
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Quote:
Originally Posted by Black Buggy
How do I go about finding out what the OBD computer reported? Is it something I can ask the dealer to print out for me?
Ask the dealer to show you the code(s) that the computer spit out indicating an over rev. But that sounds like the culprit.
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  #11  
Old 04-14-2005, 07:31 AM
///MDex ///MDex is offline
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I would think a synchro would prevent shifting into 1st at 70mph, and if he stood on the brakes at 70mph, then downshifted, even into 3rd, he wasn't doing 70 when the clutch was engaged.

I too would DEAMND proof of the over rev if they are going to deny warranty coverage on that alone

Also, get in touch with BMW USA ASAP.
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  #12  
Old 04-14-2005, 08:21 AM
99flhr 99flhr is offline
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Quote:
Originally Posted by ///MDex
I would think a synchro would prevent shifting into 1st at 70mph, and if he stood on the brakes at 70mph, then downshifted, even into 3rd, he wasn't doing 70 when the clutch was engaged.

I too would DEAMND proof of the over rev if they are going to deny warranty coverage on that alone

Also, get in touch with BMW USA ASAP.
The syncromesh is actually what ALLOWS you to complete this mistake. They allow the chosen gear wheel to be accelerated up to the rpm of the the gear that you are "leaving".
Without syncro`s the gears would clash and grind and the lever would shake so hard in your hand that you would stop the attempt. That`s why old non-syncro trannies are called "crash boxes"
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  #13  
Old 04-14-2005, 08:28 AM
///MDex ///MDex is offline
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Quote:
Originally Posted by 99flhr
The syncromesh is actually what ALLOWS you to complete this mistake.
Interesting. Perhaps I used the wrong terminology. In any event, with a previous Honda manual transmission, you could *not* downshift into a gear that would cause damage to the engine; I thought the preventive mechanism there was the synchro.
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  #14  
Old 04-14-2005, 04:18 PM
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As a general practice (which hopefully doesn't happen often), if I am facing a panic stop situation in a manual transmission car, I stab in the clutch with my left foot while I stand on the brake with my right. I would not attempt to downshift to slow the car rapidly. Too risky (as evidenced in this case).
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