HUNTING SHUNTING

[EGB]

Hello experts. On trailing even throttle 30-45mph, 3 or 4th gear now experiencing some hunting, shunting. (seems a not uncommon experience on RV8) Creates some annoying backlash on prop. On acceleration through the gears, and cruising at 70mph in 5th, no problems.
Simple symptoms. should be a simple diagnosis? Thank's everybody for a simple cure?

[Chimpafrolic]

Well worth taking 10 minutes to adjust your Throttle Position Sensor.

Two screws hold it in it's fixed position, so a screwdriver & a test meter are all you need.

If the screw holes don't allow enough adjustment you can elongate them with a needle file or a Dremel.

Scroll down the page on the following link to find instructions on how to set up the Throttle Position Sensor:

http://www.actproducts.co.uk/2011/lucas-14cux-fuel...

Edited by Chimpafrolic on Tuesday 6th September 11:17

[EGB]

Thanks Dave. Will try, and also read the ACT. I sometimes feel our TVR RV8 engine is let down by all this electronic bolt/clip ons. We never had these difficult to diagnose problems with the original P6S V8 running on SUs or Weber carbs. There is a real need for a family tree, step by step symptoms=diagnosis=cures=longer life prognosis. It would save a lot of time and money doing all these hit and miss replacements. It would be a useful new chapter for Steve's Bible.
Cheers...........Eddie

Edited by EGB on Monday 12th September 22:52

[Toffer]

Eddie...are you and the Griff joining PH at Norwich this weekend?

Checkout the East Anglia forum!

[blitzracing]

Just do a search for shunting on this or the chim' forum, loads on it. Basically a high performance cam does not work well with a plenum chamber due to the poor low speed breathing, and exhaust gas's getting blown back into the plenum when the valves overlap, so the inlet charge gets contaminated. Having said that, anything that improves the burn can help, or as mentioned the various the various sensor inputs and fuel control can all affect it.

[ruaricoles]

There always seem to be loads of potential ways to make it better, but in my case (a Griff 500 with a V8D "stealth" cam) a transformation occurred when Sportmotive fitted an SC Power plenum spacer for me earlier this year. The shunting hasn't quite disappeared, but has gone from relatively bad to not really an issue at all. Might be worth a try if tuning what you've got doesn't help much.

Ruari

[domV8]

Shunting is exacerbated by a worn diff, as the play allows movement (read: banging) back and forth and this accentuates the shunting motion...

I reckon a diff rebuild would minimise a lot of affected peoples symptoms...

Dom

[TVR Beaver]

I found shunting to be more like 'missing' when the RPM was around 1600 / 1800?.. if its that bad its hammering the drive train its well bad!!... The plenum spacer is one option but it can loose you torque low down....
I've got a 885 Power cam in mine now, set up by Mark Adams and its as sweet as anything.. not a shunt in sight... and making over 310 BHP???

[blitzracing]

Another element is how the ECU deals with the emission requirements, as it holds the mixture a bit leaner than the engine really likes, as not forgetting the the engine was never designed to be emission compliant. The non catalyst fuel map is a lot better, but it may cook the catalyst if you run it, so you cant really win. If you fit an after market ECU you can program it to the engines requirements (Just like the old 14CUX does in non catalyst mode), but if you let the mixture swing say between 12.5 and 15.5: 1 air fuel ratio it exceeds what the catalyst can deal with and may cause overheating. Time will tell however on the likes of Emerald and Megasquirt on this one, as it may simply be scare mongering. The other issue on the non catalyst fuel map on the 14CUX, is its likely to be a Range Rover map, and not optimised for a TVR that breathes a lot more air, so you need to get the correct map. I have one of Mark Adams Tornado chips in my Ginetta, and the non cat fuel map is spot on with no shunting at all, (his chips have both maps set up correctly) but when you switch to the catalyst map a small amount shunting becomes apparent, but I dont have any catalysts to worry about, so Ive stuck with the non catalyst map.

[EGB]

Thanks Beaver and Blitz. I think I have cured my HUNTING, ! Solution, a change to new plugs, 35thou gap. Hunting may have been due to a faulty plug?
See pic of rubber tubing to start screw in of plug to help prevent cross threading.

[EGB]

[blitzracing]

" Having said that, anything that improves the burn can help"

[SILICONEKID340HP]

You are very limited with the 14cux

Its so easy to cure on the Megasquirt ,all you need to do is follow the dot on the live AFR table and just change the AFR ratio bit by bit until its ironed out..
Mine shunted at very low speeds below 30mph an was running around 14.7 adjusted it to 14.2 and it drives smooth as silk

[Simon says]

SILICONEKID340HP said:

You are very limited with the 14cux

Its so easy to cure on the Megasquirt ,all you need to do is follow the dot on the live AFR table and just change the AFR ratio bit by bit until its ironed out..
Mine shunted at very low speeds below 30mph an was running around 14.7 adjusted it to 14.2 and it drives smooth as silk

Their all different Daz,mine still shunts unless I am running a 13.5ish AFR in that 1700rpm area its horrible at 14.0 or leaner in that same area its OK for people to just say drive through it but the trouble is in the real world your passing through it quite a lot no matter how short a time

Edited by Simon says on Monday 12th September 22:09

[SILICONEKID340HP]

Its about time some one made a plenum which works without spending a fortune on carbon fibre plenums ....Can`t they be made from a cheaper matarial.....LS use cheap plastic pipes..

[Simon says]

SILICONEKID340HP said:

Its about time some one made a plenum which works without spending a fortune on carbon fibre plenums ....Can`t they be made from a cheaper matarial.....LS use cheap plastic pipes..

More to do with the firing order in relation to the inlet trumpet positioning Daz i.e cross contamination and that plenum's dislike big duration cams I gather the more knowledgeable posters on here have known about this phenomenon for quite some time now my richer fuel mix masks the problem but its not gone away the solution goes deeper than just fuel or ignition timing but it certainly makes it no longer a pain to drive at low speeds like approaching roundabouts/slow moving traffic for example

Edited by Simon says on Monday 12th September 22:18

[EGB]

Thanks guys for your help. Is there a good PH thread somewhere on HUNTING.
Can it be a caused by dirty injectors. Perhaps a cure for this could be Polyether-amine, BG44K (Chevron Techron) Alledgedly also used by BMW in USA. Said to be superior to all other additives. Any Griffs out there who have used this additive.

[blitzracing]

Im told you can spot dirty injectors from an uneven colour on the plug electrode insulator, as the fuel becomes more of a jet than a spray, and ends up cleaning part of the plug. Its not number 1 on the list of what makes your car shunt.....

[EGB]

Thanks Mark. My insulator looks ok, same as other plugs. Used Halfords "LASER" LED to show all the new plugs are firing and HT leads are ok. FLASHTESTER shows a flash of at least 12mm sent to plugs, set at 35thou, so plenty of 'umphh' from coil and pre amp on tickover. Therefore, leads, plugs and coil are ok. That leaves testing AFM, Throttle pot, ECU, Lambdas,Injectors. May try BG44K, but will speak with BMW first. Anything else?

[EGB]