Acceleration Issue?!

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Spitfire01
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Acceleration Issue?!

Post by Spitfire01 » Wed Oct 11, 2017 8:04 pm

Good Evening All,

So yesterday I visited Mike (Ducklakeview) and he very kindly fixed my broken roof wiring and relocated my roof motor in exchange for some money!! As posted previously, bloody nice bloke and bloody good workmanship! However, while there I was having a look at his own Z and I mentioned a slight accelerator issue and wondered if anybody else has had the same issue? So Mike's 3.0l has a pedal that hits a slight 'stop' and of you want to flat out accelerate and push your foot to the floor, it feels like you push a little switch when the pedal hits the floor??

My 2.2l doesn't have this feature but I've noticed the following on mine for a while:

If I accelerate with the pedal maybe 10mm off of the stop, it flies but when you push the pedal to the 'stop' there is a definite lag or loss of acceleration??? To try to explain the severity of this issue, I think if I didn't tell you about it, you might not even notice so it isn't massively pronounced but neither is it a figment of my imagination!!!! It's just annoying that if you fancy a bit of pedal to the metal action, I feel like I have to find the sweet spot with the pedal....normally in 5th gear on the motorway....

Any suggestions folks??

Thanks in advance!

Mike

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Acceleration Issue?!

Post by Chris1981 » Thu Oct 12, 2017 11:47 am

Is Mikes 3.0l an Auto by any chance? my old e46 M3 SMG had a small switch on the accelerator which was for the kick-down you need with an auto... if it's a manual then not a clue!?

Acceleration issue could just be systematic of port injected petrol engines... a layer of fuel builds up in the inlet which is compensated for by enriching the fuel mixture at wide open throttle, when you back off the accelerator that unburnt fuel gets sucked into the engine giving a slight burst in acceleration known as 'acceleration overrun', this is also what causes pops and bangs in the exhaust which can often be tuned by adjusting fuel trims, particularly for forced induction engines! It may explain why you feel a surge in acceleration when you lift off the throttle on motorways following a burst at full throttle.

However if this is not the case it could be any of the numerous engine management sensors, throttle position sensor (2 of these, one on the pedal and one on the throttle body), MAF sensor, MAP sensor, Lambda sensor (4 of these, 2 pre and 2 post cat), any of these can start to operate at a less than optimum rate which would have an impact on engine performance, however still function within parameters so may not throw an engine code until completely broken). As our cars are now pretty old it's likely the case they are under performing however replacing them won't be cheap, a MAF on my e86 is in the region of £300, lambda sensors are probably around £150 each so could get expensive just throwing parts at it without really understanding what is wrong... someone with decent diagnostic software should be able to view the output of these various sensors and validate whether they are within spec or not, I only have Carly which doesn't give live data on my N52 engined Coupe! :thumbsdown:

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Acceleration Issue?!

Post by ph001 » Thu Oct 12, 2017 12:52 pm

Won't be any of the lambda sensors as these are ignored under WOT, but all the other sensor suggestions are valid as is the Vanos.
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Acceleration Issue?!

Post by Marlon » Thu Oct 12, 2017 12:58 pm

Chris1981 wrote:
Thu Oct 12, 2017 11:47 am
Is Mikes 3.0l an Auto by any chance? my old e46 M3 SMG had a small switch on the accelerator which was for the kick-down you need with an auto... if it's a manual then not a clue!?
Yes - Mike's is an Auto
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Acceleration Issue?!

Post by Chris1981 » Thu Oct 12, 2017 1:33 pm

ph001 wrote:
Thu Oct 12, 2017 12:52 pm
Won't be any of the lambda sensors as these are ignored under WOT, but all the other sensor suggestions are valid as is the Vanos.
Good point!

Just been thinking a bit more.... how about fuel pump or filter? a clogged filter won't allow as much fuel to get through and given the larger quantity of fuel required at WOT it may not be getting enough? Similarly the pump failing won't be able to deliver enough fuel... or would that throw a lean mixture code?

Given the location of the fuel filter and pump on a Z4 i doubt very much many have had them changed... might be worth throwing a bottle of decent fuel system cleaner through before looking at the expensive and frustrating task of changing sensors or having a vanos rebuild!?

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Acceleration Issue?!

Post by Spitfire01 » Thu Oct 12, 2017 2:35 pm

As ever, thank you to all for your comprehensive replies! I wish I was a bit more technically minded re cars in general and had the ability to tinker more! Not sure my bank balance would appreciate it though! Having just thrown £1200 at it recently, I think the acceleration Issue can wait...I've just had ABS sensors done, oxygen sensors, track rod ends, front shocks.....and roof fixed....it's crippling me 😅...

I've even considered getting rid for a euro box that is zero to tax and 70mpg etc but when the Z is cleaned and polished and the sun's out, you can't beat it can you??!! She stays for a little while longer me thinks!

Thanks once again, it certainly gives me some food for thought and some more things to research!! 😎

Mike

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Acceleration Issue?!

Post by Bing » Thu Oct 12, 2017 6:03 pm

Marlon wrote:
Thu Oct 12, 2017 12:58 pm
Chris1981 wrote:
Thu Oct 12, 2017 11:47 am
Is Mikes 3.0l an Auto by any chance? my old e46 M3 SMG had a small switch on the accelerator which was for the kick-down you need with an auto... if it's a manual then not a clue!?
Yes - Mike's is an Auto
My auto had this too.
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Acceleration Issue?!

Post by ranski » Thu Oct 12, 2017 7:30 pm

I had this on my 3.0 autobox 2 years back (70k) I had the transmission fluid changed and 15k later its not reappeared
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Acceleration Issue?!

Post by Mr Tidy » Thu Oct 12, 2017 9:39 pm

Another happy "dlv" customer here - rear brake pipes replaced and a new flip key cut and coded a week or so ago!

And as Marlon says Mike's is a 3.0 Auto, but I'm pretty sure he said he had cleaned out the DISA valve and it improved mid-range response no end so that might be worth thinking about - after all Mike charges very sensible rates!

I wouldn't go euro box zero tax OP - you'll just lose money on depreciation without getting any enjoyment. :roll:
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Acceleration Issue?!

Post by Ducklakeview » Thu Oct 12, 2017 9:45 pm

Mike, this really needs to be live monitored in order to determine what's happening with the fuelling/ignition etc. Don't think it'll be the DISA, as yours was nice and quiet, but on the VANOS test, it did fail for both the inlet and exhaust.

I know you've had the oxy sensors replaced, so can prob rule them out, as mentioned under WOT the emissions side of things is pretty much ignored.

Just needs a bit of time spending tracking down the fault, possibly testing component outputs with the oscilloscope etc.

Mike

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Acceleration Issue?!

Post by Mr Tidy » Thu Oct 12, 2017 9:49 pm

Ducklakeview wrote:
Thu Oct 12, 2017 9:45 pm
Mike, this really needs to be live monitored in order to determine what's happening with the fuelling/ignition etc. Don't think it'll be the DISA, as yours was nice and quiet, but on the VANOS test, it did fail for both the inlet and exhaust.

I know you've had the oxy sensors replaced, so can prob rule them out, as mentioned under WOT the emissions side of things is pretty much ignored.

Just needs a bit of time spending tracking down the fault, possibly testing component outputs with the oscilloscope etc.

Mike
Well there you go OP, from the Z4 guru!
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Acceleration Issue?!

Post by Ducklakeview » Thu Oct 12, 2017 9:51 pm

Thinking about it, I reckon this could "just" be the throttle position sensor in the car.. I'd start with getting a scope on it to check it's output. Not sure what type it is, probably not a potentiometer, more likely to be a hall sensor of some sort. A used part shouldn't be much from a breaker to swap and eliminate it as the cause if you want to try it?

£13.50... http://www.ebay.co.uk/itm/BMW-Z4-E85-20 ... SwPK1ZXP4n

Mike

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