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

[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

[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.

[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?

[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

[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?

[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

[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.

[Chad speed]

Cheers for your help Pete, I guess you know first hand how frustrating it is. I'm on the verge of taking it to Austec or RG now as I'm going nowhere, but one thing still bugs me. The adaptives on both banks go + right in the rev range where it hesitates pointing to an air leak but I'm damned if I can find one. I used Blue Hylomar to seal the throttle bodies to the head, do you think its worth taking them off again and sealing with RTV silicone? or could it be ignition. Dont want to do all that work again if I can avoid it.
Thanks for the support again - much appreciated.

[Chad speed]

PetrolHeadPete said:

Where abouts are you?

Horsham, West Sussex

[Chad speed]

PetrolHeadPete said:

Can you pm me the adaptives for the two banks
If you are saying the adaptives peak up at around 2k that might be similar to mine

Horsham is a little way from me in portsmouth

Thanks Pete, the only way I can make the diagnostics run is on a flakey old laptop I have, will try and transfer the maps from it to my PC and mail to you. Appreciate you are a way from me, would offer to drive down but the lean running on long runs makes me feel nervous about potential damage elsewhere in the engine. Look out for mail in the morning.
Cheers

[Chad speed]

PetrolHeadPete said:

Can you pm me the adaptives for the two banks
If you are saying the adaptives peak up at around 2k that might be similar to mine

Horsham is a little way from me in portsmouth

YHM
Chad

[Chad speed]

I bit the bullet at lunchtime and decided to remove the throttle bodies and check the sealing faces. I'm glad I did, all the Blue Hylomar had been squeezed out (as I think PetrolHeadPete found) and more tellingly, there were traces of fuel/Hot Start etc in the joint. I also tested all 6 throttle body for air tightness on the bench - they were all excellent, no leaks through bearings/injector O ring/or other connections. One other point of note was that when I removed the fuel rail I spilt fuel into body No.6 and it stayed above the throttle butterfly for a good 30 seconds until I mopped it up? I.e. at tick-over no air was passing via the butterfly so it must have been coming from somewhere else!
All bodies are now back on with automotive petrol duty RTV silicone sealant and I am much more confident about the integrity of the seal. One final curve ball that's been thrown at me is all but one fuel rail/injector O rings have been damaged on assembly even though I was as careful as I could be and there were no fuel leaks. It is proving to be a right SOB to assemble them without shaving the o/d of the O ring, good job I have some spares.
Chad

[Chad speed]

Warming up the 'O' rings/fuel rail/injectors made assembly much easier, I think the 'O' rings were two hard to deform enough first time round. I now have it all assembled and been for a test drive and it's 60% better but not 100% yet. There were small flashes below 1 or 2 butterfly's before I re-sealed the bodies, there are none now and it was very easy to balance them (all adjustment screws ok thanks RobertJP). After a test drive I had a look at the real time graph for Adaptive/AFR, the trace for each bank is now, more or less, one over the other where as before, 456 was always above the other by about 5mm, I think this proves to some extent that I did have some small leaks between throttle body and head.
One thing that I did noticed is the throttle pots are now diverging by as much as 5% at 30% open, not sure if they did before but I will put a couple of new ones on tonight (just delivered from TVR Power). NCE61 the air temp sensor looks to function ok but its a good point.
If I cant get to the bottom of it soon I think a RR session to fault find/re-map may be on the cards. I am beginning to think the original TVR maps were less than ideal - anyone done this and care to comment?
As ever thanks for your contributions.
Chad

[Chad speed]

I have made significant progress in resolving the hesitation and will post a resume of what worked and what didn't in due course but for now a little more advice please.
I had the engine re-mapped which improved the hesitation but didn't cure it. I have noticed now that I have a constant AFR fault on 456 and an intermittent AFR fault on 123. Installing a standard chip myself for comparison instantly cured the AFR faults (adaptive's on the std chip range between 0 and +16. With the re-mapped chip -7 to -35). I will take the car back and have the re-mapped chip altered as clearly something is wrong and I have an MOT due soon as well.
The question for now, is the re-mapped chip doing the engine or lambda's or Cats any harm? We are off on a touring trip at the end of next week and I would prefer to leave the re-map chip in as it drives better with it, but obviously not if there is risk of any damage?

[Chad speed]

Since starting this thread I've spent 10 months on and off hunting down the cause of hesitation or a very slight misfire at light throttle openings (it seems a few other SP6 owners have the same issues as well). With the help of fellow Tivers on PH I’ve done the following that has improved things but I’m not there yet:
• Roller bearing throttle bodies
• Plugs, leads, coil pack, crank sensor, throttle pots
• Injectors cleaned and balanced
• Re-map (general improved driveability but little effect on the problem)
• Engine loom plug connections cleaned
Next I guess is to replace the Lambda sensors but the software graphs show all to be ok with them. Before doing the Lambdas, which is £300+, I have noticed a certain pattern to the problem which I’d like to get to the bottom of first.
The hesitation almost disappears after re-fuelling but gradually comes back after about 5 minutes. I’m not sure if it’s related to switching off the ignition, venting the fuel tank, or a rise in under bonnet temperatures.
Any thoughts welcome, I’m getting thoroughly hacked off with it now.