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throttle hesitation or flat spot v6 255 help!

S

Spike

New Member
Am a new member and looking for some help or info,
have purchased a v6 255 and have a flat spot when pressing the throttle sharply, not fully just a quick blip, if you are gentle there is no problem, this only happens from idle. no ecu lights on, no fault codes, new plugs, new coils, new battery.
engine seems to go momentarily weak for 1/4 (ish) of a second, (shown on gas analyser) like it needs a jot of fuel , then picks up ok. i have tried two other cars, one the same one not, has anyone come across this?
thought the throttle valve was opening too quickly so removed and found the throttle valve to be out of spec, 600 ohms across pins 3 & 5 ( should be 1200 +/- 250) so ordered another, new one has the same spec????? this is starting to get expensive.
car drives fine once rolling with no loss of power. does not stall. just annoying.
any help appreciated.
 
Welcome to you Spike.

Put "flat spot" into the search above and read the various posts. I'm sure some of the technical guys will be along soon to help futher.

James
 
My Vee always felt "lumpy" whist pulling off.
In fact, I used to stall it a lot...

It sounds like your problem is more technical, but mine was simply me not realising how heavy the little critter was (tried pushing one?).
In the end it was either a case of giving it more welly to pull off or plumb for a RSTuning remap. I chose the latter and the fueling is much improved.

As I say, your problem sounds more technical - but bare the "normal misgiving" in mind. :approve:
 
It sounds like the 'fly by wire' system is suspect ...

'fly by wire' relies on two key components, the throttle pedal sensor and the throttle actuator. Both of which need to be setup correctly although I understand there is a self calibration feature which I can't quite recall how to engage it, I think the throttle actuator self calibrates when you turn the ignition (the clicking and whirring you can hear in the engine bay) ... I believe it is still important for both units to be installed and aligned correctly for the system to function correctly.

Sorry if the above is a bit vague as I am working from bits of memory ...

I have read that throttle pedal sensors can become faulty also.

Martin
 
THANX FOR THE REPIES
the throttle actuator checks out ok, as i said the thottle body does not, the recalibration sequence has been followed and setup was ok, a point to note is that if the sequence is not carried out the cruise and speed limiter will not work until the ecu has re learned the system, i know this as i tried to con the system by not recalibrating but it relearned in about 50 miles.
my reasoning behind the throttle control valve (tcv) opening too quickly is that i placed a camera in the inlet, stabbed the throttle and watched the action, the resulting display was like a carb with the acc pump not working. this backed up with weak signal on gas machine! the fly by wire system should surely not allow this to happen (emissions etc).
my biggest issue is with the specs for the tcv, bosch will not give the spec saying its dealer only, and my local bosch dealer cannot get the spec from bosch technical, the only spec i can find is in the clio v6 motronic manual (renault dealer or these pages, both same). bosch dealer is going to order another tcv in case the one supplied is faulty, i dont hold much hope! anyone got access to bosch specs for part # 0 280 750 154 tcv.
another question is what does the tickover speed normally settle to, this one seems quite low, aux air valve working, is it adjustable via ecu interogation?
 
Hi,

Just bought a MK2 and I noticed this the first time I "blipped" the throttle.
The revs seem lazy to rise, just the first 1/4 second or so like you say, also to drop too.
Being brought up on bikes I had assumed it was the big engine spinning up and slowing down.
I havn't really had a chance to look into it and it definately does not effect the drive, it is there though.
Like you have suggested, I was going to try and increase the tick over (if that's possible) to see if it reacts the same from slightly higher revs.

Not really too bothered about it, but interesting none the less.

Cheers,

Matt
 
INTERESTING REPLY TO MY POST, I TOO AM USED TO THE INSTANT RESPONSE OF A BIKE, BUT ALL THE SAME BECAUSE THE FAULT IS THERE IT WILL BUG ME, MAYBE A RISE IN TICKOVER WOULD HELP?
I HAVE JUST BUILT A RIG TO TEST THE FUEL PRESSURE, WILL POST MY RESULTS LATER.
 
Just to clarify my terms ...

Actuator = throttle valve (tcv)
Sensor = throttle pedal

If both check out OK that is good ...

My car has perculiar behaviour in that the throttle response is VERY sharp and almost seems to anticipate my pedal behaviour, but the Bosch 'fly by wire' ECU, as I can see that you know, is very sophisticated and only uses the throttle pedal position and swipe speed as a 'torque request' taking into account many other factors - so it is not suprising with this type of ECU that each car should feel a little different.

I also remember other owners reporting flat-spots in the standard ECU map. Some have had re-maps which are claimed to remove some flat spots.

Martin
 
JUST SPOKE TO BOSCH TECHNICAL, QUOTED FIGURES IN MOTRONIC MANUAL ARE WRONG, BOTH MY THROTTLE BODIES (NEW AND OLD) ARE CORRECT, THEY HAVE SUGGESTED MAP SENSOR, OR FUEL PRESSURE / DELIVERY FAULT.
BIT THE BULLET AND BOUGHT NEW MAP SENSOR: NO, ITS NOT THAT!
CHECKED FUEL PRESSURE, AND AM GETTING 46 PSI (3 BAR-ISH), CONSTANT, BOSCH TECH COULD NOT GIVE ME THE CORRECT VALUE FOR THIS AND, TO THROW A SPANNER IN THE WORKS THERE ARE TWO FIGURES QUOTED IN THE MOTRONIC DATA HELD ON THIS SITE AND BY THE DEALERS, SOME QUOTE 4 BAR, SOME 3.5 BAR, ANYONE KNOW WHICH IS CORRECT.
 
I had a similar fault to this - when the car reached 3.5 through to 4.5k under hard acceleration it would stutter then continue to rev, it felt like a misfire / flat spot

Eventually it was traced to a broken fuel pump - the dealer had the car on his forecourt for many months and left the petrol tank low, meaning the petrol pump wasnt covered in the tank and actually rusted to bits - thats why the manuals recommend running at over 2 gallons at all times

Hope this helps
 
WONGY":2ctynks0 said:
I had a similar fault to this ...................

Eventually it was traced to a broken fuel pump - the dealer had the car on his forecourt for many months and left the petrol tank low, meaning the petrol pump wasnt covered in the tank and actually rusted to bits - thats why the manuals recommend running at over 2 gallons at all times

Hope this helps
Click to expand...

Interesting info there Wongy.... :approve:
 
Well the dealer had the car for 2 weeks - at first tried to tell me nothing was wrong and it was the rev limiter kicking in at 4k rpm! I'd already done the usual stuff changing coils and spark plugs cos I'd just bought the car so got it serviced.

I called Clarkiev6 from here, he said if there's nothing on the ECU then its likely to be fuel related so they put a clip on to monitor the car when driving and check the fuel pressure.

When they took out the tank it has rusty bits floating around plus the fuel pump itself when you shook it sounded like it had sand in it!
 
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