Hesitation/shunting help.

[natben]

Hi Guys, can anyone help?

Recently my car has started to hesitate /shunt/stutter when driving between 2,000-3,000 rpm.
I had it hooked up at to the laptop at my nearest TVR service centre and they adjusted the tickover as it was stalling and is now ticking over ok ,cold and hot. They didn't notice anything unusual and I got it back but it is still shunting/stuttering.

So any ideas.
It isn't a misfire as it would have shown up on the diagnostic software at the garage so I take it that rules out plugs/leads/coil pack??.

Engine mounts?? there is a bit of vibration from the engine area when I am reversing into my garage. How do you know engine mounts need changed?.

Throttle bodies worn? Costly at around £1k to change and wouldn't like to spend this cash if it isn't the fault having not long spent almost £8k on a rebuild.

So can anyone advise me what I can check. I am a novice mechanic but I'll give it a go!
Thanks in advance
George

[Cockey]

I'm sure they would have done this, but if playing with the idle speed they need to reset the throttle using the ecu software, otherwise it can run quite badly. Not sure if you're supposed to do this, but I reset my adaptive map the other day which sorted out a bit of lumpy running at low revs.

[natben]

Hi yes they had it hooked up to the software and ajusted the throttle bodies to allow them to ajust the idol and they did say they were quiet a bit out, It ticks over ok now but still has the hesitation/shunting.

I'm thinking engine mounts but wouldn't that be more noticable on sharp accelaration?
Sensor came loose somewhare?
Throttle cable sticking but it is only really noticable between 2-3000k rpm especialy in a higher gear wouldn't it be right accross the rpm range?

Or throttle body bushes (ouch £1k, upgraded bushes only available from Racing Green I think).

Anyone changed bushes, what were the symptoms?

George

[Challenger C4s]

Did they reset the TPS (throttle position switches) after resetting the idle. you have one at each end of the throttle banks. they are an position adjustable linear resistance switch and the output voltage at tick over I believe should be 0.29 volts (anyone else verify this??). if they are not set right then the ECU can never understand exactly what it should be doing with the fuel metering.

[m4tti]

HT leads breaking down, coil pack issues. Have they been visually inspected at least.

Or like you say un metered air getting past the throttle bodies, but would have thought you'd have odd idling issues.

Edited by m4tti on Thursday 9th August 06:52

[Robertjp]

could be a few things but as said throttle bodies would be one of the suspects.

If the spindles have worn the throttle bodies it doesnt take long for them to go back out of tune. At light throttles in a high gear, i believe its most obvious, the spindle vibration can translate to funny thottle pot readings and that could be having an effect. I had a misfire at 5k rpm due to throttle spindle bibration that would result in ECU shutdown for an instant - not fun.
Str8 Six used to do the throttle body upgrade to roller bearings for around £500 fitted.
RG used to do a throttle body set with bearings for £350 ish but you have to return your old ones and you will get no support from them...so you pays your money...makes your choice!

Im not saying it is that though - but it could be contributing. It does sound air / fuel / ignition related though, so if you have replaced coil, HT leads and plugs recently then its worth investigating.

[Fad Sucker]

I had the same problem, srt8six had a look and found that the throttles linkages to 4,5 and 6 were all loose, they tightened them and car now running without any problems

[natben]

Thanks for that Fad, worth checking, But what does a throttle linkage look like?, Can anyone post a picture for me? .Is it the link between each throttle body?. I will remove the airbox tonight and have a look.
George

[natben]

I removed the air box and checked the HT leads were all pressed home into the coil pack, seemed OK
I sprayed some WD40 on the linkages between the throttle bodies.
I started the engine and let it idol up to temperature, when I pressed down on the throttle and held it at about 2000-2500rpm throttle 3&4 spat some flames very slightly where as all the other throttles were ok. Is this anything to suggest it's the culprit/misfire?
Anyone know what the purpose is of the black pipe that runs below the throttle bodies and connects at the far right hand side.

[Basil Brush]

Spitting flame from the throttle can be a sign of a lean mixture. I'd check for air leaks around the inlets and get the throttles re-balanced. It might be the angle of the picture but it looks as though throttles 3&4 are more open than the outers.

[natben]

Thanks for the replies guys, I think I will change the coil pack as a first step as the leads were changed last year so in theory should still be ok.
If this doesn't cure it then I will get new HT leads, but wouldn't any of these items shown up as faulty when the garage had it connected to the software.
George

[crypto]

Basil Brush said:

Spitting flame from the throttle can be a sign of a lean mixture. I'd check for air leaks around the inlets and get the throttles re-balanced. It might be the angle of the picture but it looks as though throttles 3&4 are more open than the outers.

I hope I'm not writing s**t here but if I remember it correctly then :
The cylinder fires when inlet & outlet valves are closed, the first to open after firing is the outlet valve (for a full stroke) until the inlet opens. Number 3 & 4 fire 360 degree apart.

The ignition coil-pair for 3&4 are together, i.e. the sparks 3&4 fire both at the same time, wheras only one cylinder has air/fuel in it and the other is just getting air/fuel (one of the sparks is waisted).

Flames coming out would mean that the "waisted" spark fires what ever just got into the cylinder ??
Are the distances of the spark plug(s) correct ? I assume you use standard high octane 98 fuel ?
Maybe this helps too :
http://www.mytuscan.co.uk/problems_main.php#misfir...

[Hollowpockets]

crypto said:

I hope I'm not writing s**t here but if I remember it correctly then :
The cylinder fires when inlet & outlet valves are closed, the first to open after firing is the outlet valve (for a full stroke) until the inlet opens. Number 3 & 4 fire 360 degree apart.

The ignition coil-pair for 3&4 are together, i.e. the sparks 3&4 fire both at the same time, wheras only one cylinder has air/fuel in it and the other is just getting air/fuel (one of the sparks is waisted).

Flames coming out would mean that the "waisted" spark fires what ever just got into the cylinder ??
Are the distances of the spark plug(s) correct ? I assume you use standard high octane 98 fuel ?
Maybe this helps too :
http://www.mytuscan.co.uk/problems_main.php#misfir...

I would have thought 3 and 4 fired at the same time being at the same part of the stroke at the same time.

As well as the spindles wearing in hte pots the sealant between the throttle pots and the head can also deteriorate causing air leaks in behind the butterfly, this could cause the uneven running, perhaps also the slight flaming, I guess bad timing set up or a chain jumping a tooth would allow the inlet valves to be open during ignition, dont drive it, get it checked out asap.

[crypto]

Hollowpockets said:

... I would have thought 3 and 4 fired at the same time being at the same part of the stroke at the same time ....

looking at the cam it can't be (ignition sequence is 1-5-3-6-2-4) ...
http://www.thetvrshop.com/pop_image.asp?image=PTVR...

Edited by crypto on Monday 13th August 19:29

[Hollowpockets]

The picture would suggest valves open/close at different times but look at a crank though, the pistons 1+6, 2+5 and 3+4 will be at the top of the stroke at the same time in pairs, so why would 3 and 4 fire at different times from each other? would that not reduce the effectiveness of the combustion?

Im no expert, just trying to understand a bit more about how they work

Edited by Hollowpockets on Monday 13th August 20:22

[Filos Hippos]

I would also suggest to check all earthconnections as this could cause some of the faults you discribe.

[Basil Brush]

Hollowpockets said:

The picture would suggest valves open/close at different times but look at a crank though, the pistons 1+6, 2+5 and 3+4 will be at the top of the stroke at the same time in pairs, so why would 3 and 4 fire at different times from each other? would that not reduce the effectiveness of the combustion?

Im no expert, just trying to understand a bit more about how they work

Edited by Hollowpockets on Monday 13th August 20:22

Each cylinder fires every other revolution though. Just because the big ends are aligned doesn't mean they are on the same stroke. Ooo er missus.

[Hollowpockets]

I see, makes sense now! Thanks

[nrick]

If the throttle bodies aren't balanced then it will spit back through the bodies. Check with a Syncrometer (ebay) and they should all be about the same value. If after you check it they go out of sync quickly then it is likely to be the throttle body bushes (or lack of them). Another culprit can be that the bodies aren't sealed , OEM is a flexible sealer which isn't good. Power now do a thermal gasket which is a better idea. Sorry if all this has been said before, but it is a good place to start. If the car start misfiring at 3k then it is most likely the coil.

HTH

[natben]

SORTED

Massive, massive thanks to Dom at TVR Power, one quick chat with him and he had the issue diagnosed!! Throttle pots!!! he sent me them up (2) I fitted them, then using the software and the help of local TVR owner who brought his old lap top to allow the software to run, the addaptives were re set and all is well again. The car idols perfectly and is silky smooth.

So no need to spend £1k on new throttle bodies! thank feck!!.

Thanks Dom.