Hesitation 2000-2700 rpm

[Chad speed]

Gentlemen, your advice please.
I have a 2001 Tuscan 4.0 which in my ownership has always had a slight hesitation at light throttle openings between 2000 & 2700 rpm. It had a TVR Power rebuild 6k ago, throttle body roller bearings recently fitted and today a 6k service and tappet shim adjustment by Dan at Taylor TVR which included throttles re-balanced, adaptive's re-set etc. Each of these has improved things but its still noticeable.
So the question is what to try next, coil pack and leads perhaps but I would expect the fault to get worse as rpm rises, not clear? My thoughts are its fuelling not ignition but I could be wrong, so perhaps a re-map or chip?
Anyone been there, done that?
Any help much appreciated.
CHAD

[Tom 8]

Has it got wet? Silly question I know, but I had the same and after drying out plugs, perfecto! Really silly and annoying but you can get a build up of moisture.

[Chad speed]

Tom 8 said:

Has it got wet? Silly question I know, but I had the same and after drying out plugs, perfecto! Really silly and annoying but you can get a build up of moisture.

Have got it wet a few times in the past and had plug leads shorting etc and no its not that. This has been present for 18 months and the car is kept in a dry garage. Good point though.
Thanks

[TUS 2 CON]

Is your speedo working ok?

[Chad speed]

TUS 2 CON said:

Is your speedo working ok?

Yes speedo ok, you suggesting it could be related to the sensor on the diff?

[Chad speed]

Cheers RM75, some useful pointers. Did you diagnose your faulty lambda sensor with a meter or just find out it was at fault through process of elimination? I've read somewhere how to test them with a meter but cant find it anywhere now.

[Quentin1]

Chad,

Dan would have recognized a faulty lambda spot on when hooked to the Laptop. Do you have one yourself?

Anyway, that somehow sounds like the coilpack or plug leads to me.

Björn.

Edited by Quentin1 on Friday 10th December 11:07

[Chad speed]

I spoke with Dan yesterday (as friendly and helpful as usual) and he confirmed the lambda sensors were performing as expected according to the laptop and that during the service the plugs were changed and the leads tested. His feeling is its most likely to be the injectors that are dirty or faulty or possibly the coil pack but that was also inspected (apparently coil packs tend to show visible signs when breaking down). As it happens I have a spare set of injectors so the first step is to have these cleaned and tested and replace the ones on the car.
Just a final thought, I filled the car with petrol yesterday and the pressure in the tank was somewhat higher than normal - could this be related?

[Robertjp]

Did you replace the throttle pots when you did the throttle bodies? The internals wear quickly if there is wear in the TB's.

Injectors sounds like a good call after that, fuel filter could also be due a change but unlikely to cause the symptoms you suggest, but possible i guess? It may be that at lower pressures the fuel flow isnt consistent through a dirty filter? Clutching at straws to be honest.

When you did the throttle bodies did you check that they all sealed against the head and that there was blue hylomar used to seal them? That can also cause a problem - you think you have balanced them and find out there is more air getting in than you thought!!

[Chad speed]

Robertjp said:

Did you replace the throttle pots when you did the throttle bodies? The internals wear quickly if there is wear in the TB's.

Injectors sounds like a good call after that, fuel filter could also be due a change but unlikely to cause the symptoms you suggest, but possible i guess? It may be that at lower pressures the fuel flow isnt consistent through a dirty filter? Clutching at straws to be honest.

When you did the throttle bodies did you check that they all sealed against the head and that there was blue hylomar used to seal them? That can also cause a problem - you think you have balanced them and find out there is more air getting in than you thought!!

The throttle pots seemed ok when removed during the body rebuild and Dan says they looked good on the laptop at the service. I think the bodies are sealed to the head but will check when back up and running (easy check to run a little fuel around the joints while the engine is running - if the rpm changes there's a leak). Dan also re-balanced them although they were pretty close.
Just received the injectors back from Jason at TVR Power (very helpful chap), I sent both the originals and the spare set which was just as well as a couple were a bit ropey, Jason has made a matched set but also numbered for each cylinder. Apparently cylinders 1 & 6 like injectors with either slightly higher or lower flow - cant remember which. So fingers crossed this will be the cure but not got the time to assemble it all until Monday - will let you know.

[Chad speed]

Injectors back in and up and running. Even with the zero degree ambient temperature and water temp at only 5 degrees the engine is a lot smoother at tick-over and through the rev range. Just got to wait for some decent weather before I can test it under the right driving conditions - whenever that happens!
Thanks for the pointers, I'll let you know as soon as I can.
Chad

[Chad speed]

Managed to get out for a sneaky test drive yesterday and the cleaned and calibrated injectors are noticeably smoother and more responsive but the hesitation/missing at 2000-2700 rpm is still there damn it.
So hooked up the laptop and on screen 2 have 'AFR 456 - BAD' and 'Lambda 1 - fault log'. Problem is of course that Lambda 1 trims the fuelling on cylinders 123 so is it possible the lambdas have been connected to the wrong plugs in the loom? Or would the ecu display Lambda 1 & 2 and AFR 123 & 456 faults if this was the case?
A somewhat frustrating situation but at least the fault is now showing on the diagnostics where as it didn't before.
Have a good day all - cheers

[Quentin1]

Honestly, get the airflow checked on each throttle. Was the problem with my car, showing exactly the same symptoms and error logs. One of the cylinders was way out so the adaptives for that bank went out of range. Worth a try. Even if Dan says he synchronized the throttles, could easily be out of balance again.

Björn.

[Chad speed]

Quentin1 said:

Honestly, get the airflow checked on each throttle. Was the problem with my car, showing exactly the same symptoms and error logs. One of the cylinders was way out so the adaptives for that bank went out of range. Worth a try. Even if Dan says he synchronized the throttles, could easily be out of balance again.

Björn.

Worth a third check I suppose, but I balanced them when I rebuilt the throttle bodies with roller bearings, and Dan re-checked/adjusted them at the service.
Doing the family thing today but hope to play tomorrow, would be nice to replace the Lambdas one at a time without having to buy them - £150 each! Anyone in the Sussex/Surrey area have a know good spare I could borrow?

[dvs_dave]

What's so special about the TVR lambdas? As they're not wideband sensors, I was under the impression that you can use pretty much any lambda sensor as they all work in the same way. i.e they either signal a rich or a lean mix.

Edited by dvs_dave on Sunday 26th December 11:42

[Chad speed]

dvs_dave said:

What's so special about the TVR lambdas? As they're not wideband sensors, I was under the impression that you can use pretty much any lambda sensor as they all work in the same way. i.e they either signal a rich or a lean mix.

Edited by dvs_dave on Sunday 26th December 11:42

From what I understand, and I'm no expert, the TVR Speed 6 Lambdas are Land Rover items modified to operate at higher temperatures - hence the higher price. I think others have tried standard 3 wire Lambdas and whilst they work for a while, eventually they fail.

[Chad speed]

Ok for those who are still with me on this one the latest is that the earlier Lambda 1 logged fault has not returned after clearing it and going for a good run, so I am concentrating on cylinders 456.
I'm now thinking that Björn may have suggested the next place to look - leaks between throttle body and head. My reason for thinking this is the AFR on 456 faults within a few seconds of start-up and the adaptive's at idle on throttle 2, in the region of +18%, would seem to be linked - so my question (before I pull the whole lot apart again), is + on the adaptive's richening the mixture or weakening it? As a comparison, throttle 1 shows about -3% adaptive at tick-over.
As ever your comments much appreciated.
Chad

[Basil Brush]

Chad speed said:

dvs_dave said:

What's so special about the TVR lambdas? As they're not wideband sensors, I was under the impression that you can use pretty much any lambda sensor as they all work in the same way. i.e they either signal a rich or a lean mix.

Edited by dvs_dave on Sunday 26th December 11:42

From what I understand, and I'm no expert, the TVR Speed 6 Lambdas are Land Rover items modified to operate at higher temperatures - hence the higher price. I think others have tried standard 3 wire Lambdas and whilst they work for a while, eventually they fail.

The early 3 wire lambdas are modified LR units. The explanation I got was that the internal cable insulation material is removed and replaced with a harder rubber material, as the standard insulation melts with the heat of the S6 engine bay. I know the standard LR units fitted (in error ) by a certain ex main dealer didn´t last very long in mine.

[PetrolHeadPete]

+ is towards rich, so large + values imply too much air. Air leak is very possible. I posted up about my woes of trying to seal the throttles to the head

[Chad speed]

PetrolHeadPete said:

+ is towards rich, so large + values imply too much air. Air leak is very possible. I posted up about my woes of trying to seal the throttles to the head

Thanks Pete, read your thread a number of times, and all the other related one's doing a 'search'. I am pretty sure I have no leaks between throttle body and head or through the new bearings, I sprayed Easy Start around the joints and no rpm change or lambda trace change on the real-time graph. The engine ticks over very smoothly and pulls like banshee to the red line, its just the slight missing at light throttle openings. Two thinks of note this morning however:
1. If I blip the throttle from tick over, on the 4th screen 'dthrottle' shows no control for a few seconds but is perfectly ok if the revs are increased slowly. - Is this normal?
2. On the Ignition real time graph, the white trace which is the ignition has lots of small spikes mainly above and some below the normal line at tick over (and throughout the rev range). - Again is this normal?
Although I'd always thought the fault was fuel/air related I'm now questioning the ignition system. Getting towards the end of my patience now and if I dont make any progress soon will take it to a specialist, shame the two nearest to me Racing Green and Austec have been closed all week.