Hesitation problem / 4x2 drive

[RoyMacDonald]

Originally Posted by 4wheeldriver

Ive only had the go then stop on about 5 or 6 occassions but it is pretty random where it does it. It has done it in the local shop car park but there's less desperation to move there so eventually it does go again with more gas but when it does go it still leaps forward with a surge in the revs! Again delay can be anything between 1 and 2 seconds depending on the extra gas it requires you to feed through the pedal. The day with the bus incident it went to the floor and I prayed it would catch but would reckon took sameish time to go. Mechanic in Shrewsbury DID notice hesitation once but then he was being hard on it to hear the knocking from under the bonnet that day.

The surge almost sounds like a problem with the common rail system. I used to have that kind of thing all the time with my Golf TDi (I know it's a Pump Duess system before anyone posts) but that system was notorious for it. First time it happened it threw the car really wide on a corner because I wasn't expecting it.

Roy

[RoyMacDonald]

Originally Posted by Clan

The highlighted part above is part of the reason ,
if you take off with small throttle and as it starts to move press down further but slowly but progressivly as you get moving you will find it takes off alot better ... Its aknack yes but try it ..

That's how I've always driven. I've never experienced the problem.

Roy

[4wheeldriver]

This is how I try to take off same as I have with any other auto ive owned, but theres nothing then suddenly it goes with a heap of revs and an almighty jump. This is with feeding in the throttle progressively and waiting for it to go then BAM you're off! Yes. Hands up!! The other day when it came to a standstill in front of the bus I DID nail it!! Wouldnt you with a bus bearing down on you?? CAn you explan further Roy about the Golf problem?? When I put it to the dealer I KEEP telling them its the throttle that does nothing and they keep checking the gearbox settings!! The gear is engaged, it's the engine that does nothing other than a couple of hundred more revs than idle.

[NCS XC90]

Yep,
I've been out tonight trying the to understand the hesitation. I have found that there is a hesitation of about 1 second on my car when I floor it. As I have written earlier this is something I have not done before. In the secondish delay before the car pulls off the revs don't rise or anything, its as if the car is prepairing itself for what is coming next. I actually find its faster if as Clan states and take of with a small throttle and progressively apply more pressure (which is my normal driving style). I also noticed that If when driving at about 30 or 40 I take my foot off the throttle and just let the car "glide" for a few seconds and then floor it there is the same hesitation. To be honest the last part does not supprise me as I have had this experiece when overtaking in other auto cars. Not had and did not get the go - stop -go type of hesitation.
To be honest I'm nt convinced my car is any different to other automatic cars but then as I said I may not have it as bad as others.

[RoyMacDonald]

Originally Posted by 4wheeldriver

CAn you explan further Roy about the Golf problem?? When I put it to the dealer I KEEP telling them its the throttle that does nothing and they keep checking the gearbox settings!! .

Trouble is it dosn't have a throttle in the coventional sense, it's more like a computer game exept your input tells the computer what to do and it controls how the car interprets your command.

The lack of controlability of the Pump Duse engines is pretty well documented I belive. Run a search on Pump Duse and you'll find posts like this...

The main reason for makers prefering CR because, in this, the pumping and injection is more or less independant of each other. Therefore, a more flexible injection program can be incorporated into the system. The combined units like PD, the injection is locked with pumping and there it is difficult to control injection. (Makers have experimented with tandem pumps and dual injectors but it has not been popular). Therefore CR can give a higher RPM bandwith and more even distribution of torque. Also the pollution control can be better over the entire rpm range

The PD engine gives good fuel consumption but poor fine control. The XC90 Common Rail was a real relief after the Golf which was just nerve wrecking.

Roy