1.8T Light load stumble - about to go on holiday.. help!

[Hogwarzt]

Originally Posted by ianqv

I thought the hesitation was being caused by the new coil, sadly after a couple of days it has returned!
The hesitation happens around 2500rpm on light load.
I'm starting to wonder if it may be a calibration issue?

Anyway.... I have just re set up the tps (turned ing to position 2 and pumped the throttle 5 times).

Lets see what happens on the way home tonight.

I will keep you posted

Ian

Ian,

Quick test for you is to see if it behaves ok when you first start up from cold. My guess is the Lambda sensor under the bonnet upsetting the fueling.

From cold start-up the ecu ignores any signals from the lambda til the engines warms up. That's the reason I mention from cold.

I imagine this could be quite dangerous when trying to pull away from a junction etc?

regards
Rich

You should be able to disconnect completely and force ecu to use default sensor values. Anyway, something for you to try.

[marinabrian]

Originally Posted by Hogwarzt

Ian,

Quick test for you is to see if it behaves ok when you first start up from cold. My guess is the Lambda sensor under the bonnet upsetting the fueling.

From cold start-up the ecu ignores any signals from the lambda til the engines warms up. That's the reason I mention from cold.

I imagine this could be quite dangerous when trying to pull away from a junction etc?

regards
Rich

You should be able to disconnect completely and force ecu to use default sensor values. Anyway, something for you to try.

No, you can't disconnect the upstream HO2 sensor, as even when the ECM is in "open loop" it's relying on lambda input.

Closed loop fuelling is achieved once the coolant temperature sensor reaches 88 deg C, and the downstream HO2 sensor is used as a "fine tune" for injector pulsewidth and ignition timing.

In answer to the OP, I have only encountered this phenomenon once, and it turned out to be defective wiring to the MAP sensor, where the wiring enters the plug housing.

Brian

[Hogwarzt]

Hi Brian, ive seen this twice before and it was obvious from the obd readings that there was a problem during ol and cl. I would still investigate even if not disconnected.
Regards
Rich

[ianqv]

@ MG Tom - yes it sounds like we have the same concern.
It only happens with 30% throttle (measured using datalogger).
And yes if I am on a slight gradient – this can make it worse / last longer!

I know what you mean re the suspension – you have to be on a smooth surface to pick it up, or you could think its suspension/bump related.

But I think the gradient thing just keeps it in the zone for longer.
If I use any more than approx. 30% throttle, you cannot feel the hesitation (you are outside the range when it happens).

I have now chucked a load of injector cleaner though the engine – has not made any difference.
I also reset the TPS last night – sadly, has not made any difference either.


@ Hogwartz – I’ll give it a go when cold! Thanks for the tip.

Thinking of kicking it in to http://www.chelmerrovercentre.com/ as I feel I’ve chucked enough parts at it now, and I’ve reached the end of what my OBD2 code reader can give me.
You never know, T4 may give us something else to go on.

All other suggestions welcome!! J

Cheers

Ian

[ianqv]

Yes its still there when cold!!

Cheers

Ian

[MG Tom]

Mine has recently been T4'd, and after a thorough interrogation by Phil it was given a clean bill of health.

My emissions at MOT were absolutely superb.

I have a new pre-cat lambda (genuine NTK, not a universal crappy one).

I have had some odd rev-counter issues on occasion where it reads half actual rpm, so I have ordered a new crank sensor and will see if that improves things.

Please do update this thread with any progress though as I am following with interest!

[ianqv]

Just a quick update.....

The light load stumble is still there.

Will try and get it T4'd shortly

Cheers

Ian

[MG Tom]

Looking forward to hear how you get on Ian