TVR 5.0 Shunting
Discussion
All
After much mechanical work on my TVR and a bit of chassis cleaning , my attention has now shifted to stopping this annoying shunting at low revs. So basic summary is
TVR 5.0 recent work has been.
Replaced all ignition system components, including removal of spark plug extenders and replaced with ceramic HT lead ends.
New stealth cam ( shunting was seen before and after this work)
ACT induction kit, new air filter.
New fuel pump and adjustable fuel regulator with fuel pressure set at 38 psi.
So my research to date has led me ECU/ engine management upgrades and i am considering this but i wondered what everyone else would advise. I am booked in for a rolling road tune which I am hoping may improve things.
Many thanks
Andy
After much mechanical work on my TVR and a bit of chassis cleaning , my attention has now shifted to stopping this annoying shunting at low revs. So basic summary is
TVR 5.0 recent work has been.
Replaced all ignition system components, including removal of spark plug extenders and replaced with ceramic HT lead ends.
New stealth cam ( shunting was seen before and after this work)
ACT induction kit, new air filter.
New fuel pump and adjustable fuel regulator with fuel pressure set at 38 psi.
So my research to date has led me ECU/ engine management upgrades and i am considering this but i wondered what everyone else would advise. I am booked in for a rolling road tune which I am hoping may improve things.
Many thanks
Andy
May be worth trying the move to full manifold vacuum first as it's more or less a free modification.
Have a read here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Have a read here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
What do you define as shunting?
I ask because there's a whole range of symptoms described as shunting, from light hesitation when <2000rpm to a full blown on/off hysteresis through the drivetrain that just gets worse unless you dip clutch/accelerate etc.
On mine, You can feel slight hesitation on even throttle at around 1800rpm but no driving sympathy/correction is required and I think that's about as good as it gets.
My engine and ignition mods and spec sound very similar to yours, ceramic leads, ACT stuff etc. I'm also running the full manifold vac advance as Belle427 mentioned.
Where do your symptoms lie on the spectrum?
I ask because there's a whole range of symptoms described as shunting, from light hesitation when <2000rpm to a full blown on/off hysteresis through the drivetrain that just gets worse unless you dip clutch/accelerate etc.
On mine, You can feel slight hesitation on even throttle at around 1800rpm but no driving sympathy/correction is required and I think that's about as good as it gets.
My engine and ignition mods and spec sound very similar to yours, ceramic leads, ACT stuff etc. I'm also running the full manifold vac advance as Belle427 mentioned.
Where do your symptoms lie on the spectrum?
Edited by KevtheRev on Saturday 6th April 18:16
If you're still on the 14CUX you're pinned to 14.7:1 which really is quite a bit leaner than the engine wants.
Leaner mixtures burn slower so advancing the ignition timing can help a lot, if you are able to run a richer map too you'll see even greater benefits.
However, a Thor inlet manifold would of course be the ultimate solution
Leaner mixtures burn slower so advancing the ignition timing can help a lot, if you are able to run a richer map too you'll see even greater benefits.
However, a Thor inlet manifold would of course be the ultimate solution
lancelin said:
I found richening mine in the shunting area has helped. A different inlet manifold sounds interesting provided it doesn’t reduce the power. The other option might be the gems system but nobody offers this as a kit or drive in drive out solution.
You point out 2 posts up how after market Ecu can’t always stop shunt but somehow the gems might! . Thor is for pulling tree stumps up and a total non starter in a Tvr imo
I have cured shunt with Ecu and Dif replacement as one ain’t much good without the other if your car has been cangarooing for years.
Cam choice is probably critical to the issue too.
Im no expert and much of the work on my car has been done by experts ( Powers Performance) and or very informed TVR friends ( Thankyou Guys ) so I never really thought I’d cure shunting any more than anyone else has,,, Dif was the icing on the cake after engine rebuild, MBE Ecu new clutch and gord knows what else, the Dif made the biggest difference.
I might have a few hp less than many cars but I’d never forsake the smooth drive I have now as things like my gear stick knob stays cool even on long runs when it used to get very hot, this is a step change in both maintenance and performance going forward.
The car accelerates properly now too, if I do provoke slip in a straight line two tyretracks are left on the road.
Thanks guys. I hadn't thought of Diff but now that you mention it , I have had a noisy diff since i bought her last year. It is on my list of jobs to do once i have money together. I have done a diff oil change immediately after buying her but then notice a drip of fresh oil afterwards on the garage floor.
Chimpongas, i have read much about the car set up too lean from factory. Is it possible to adjust this with the standard Lucas ECU set up or will i need an aftermarket ECU that has more freedom to adjust? I have been looking at Lloyds Development Canems offering as they are drivable distance from me as i live in Devon. Reviews seem good and you have one don't you? Would love to be able to go up and see Jules at Blitzracing but its just too far for me. I also wondered what you think on the diff contributing to the shunting. I wonder what came first, the diff problem or the shunting due to lean fuel which then caused the diff wear?
Chimpongas, i have read much about the car set up too lean from factory. Is it possible to adjust this with the standard Lucas ECU set up or will i need an aftermarket ECU that has more freedom to adjust? I have been looking at Lloyds Development Canems offering as they are drivable distance from me as i live in Devon. Reviews seem good and you have one don't you? Would love to be able to go up and see Jules at Blitzracing but its just too far for me. I also wondered what you think on the diff contributing to the shunting. I wonder what came first, the diff problem or the shunting due to lean fuel which then caused the diff wear?
andymc1966 said:
Chimpongas, i have read much about the car set up too lean from factory. Is it possible to adjust this with the standard Lucas ECU set up or will i need an aftermarket ECU that has more freedom to adjust?
It's definitely possible to make fuel map changes to the Lucas ECU, but an aftermarket ECU makes it so much easier and also gives 3D control over the ignition side, as such it's a significantly better solution.However, TVR wouldn't have sold many Chimaeras and Griffiths if they shunted from new, I've also driven quite a few Chims and Griffs on the original Lucas 14CUX and distributor setup that drive super smoothly, this includes my mates 1996 5.0 litre. This evidence tells us if everything is set up correctly and the car is in good health the original Lucas 14CUX and distributor setup is perfectly capable of giving excellent results, the reason so many don't can be attributed to a number of things...
1. An awful lot of Chims and Griffs have ignition problems due to poor servicing/maintenance
2. Poor setup, elements like correctly setting up the throttle butterfly air gap, the TPS and base idle are often overlooked. Finding someone who truly knows how to properly set the system up is your challenge here, I believe Jules fro Kits & Classics is one of the few.
3. The engine loom and how its spliced to the the poorly executed TVR loom is getting very old now, there's a lot of heat in the engine bay which is not wiring friendly, sensor/engine earthing is often poor on our cars too.
andymc1966 said:
I have been looking at Lloyds Development Canems offering as they are drivable distance from me as i live in Devon. Reviews seem good and you have one don't you?
Yes I have a Canems Dual Fuel System that offers both petrol and LPG management, on LPG my TVR averages the petrol cost equivalent of 48mpg which is game changing so I would never go back to the Lucas 14CUX. However, be aware all the petrol only aftermarket ECU packages do the same thing and are essentially the same engine management technology. It doesn't matter if you go with a Canems, an MBE, a MegaSquirt or an Emerald it's all essentially mid 1990's engine management technology running EDIS wasted spark (think Mk3/4 Ford Fiesta or Mk4/5 Escort) with some user friendly software to make the mapping process easier.In many respects the quality of the wiring you get with your aftermarket ECU is actually more important than the ECU itself, you also need to consider after-sales support as you wouldn't want to end up with a system where the manufacturer has gone out of business or there's only one company in the UK that can map it.
andymc1966 said:
Would love to be able to go up and see Jules at Kits & Classics but its just too far for me.
Kits & Classics may be a long way for you to drive but do factor in an aftermarket engine management system is going to cost you anywhere from £2,500 to £3,500, no one can argue the 14CUX and distributor arrangement is the last word in technology but it clearly worked just fine from new so it can be made to work well again. If you took a day off work and had Jules go right through your TVR I wouldn't mind betting it'll be the best money you'll spend on the car with results that give you a solution to your current frustrations while delivering a massive saving over an aftermarket engine management installation. As with most decisions in life there are lots of options and at the end of the day what you go for will be largely governed by budget, however if you're working on the principle of best value there is nothing to rival working with what you have already and making it work as designed.
andymc1966 said:
I also wondered what you think on the diff contributing to the shunting. I wonder what came first, the diff problem or the shunting due to lean fuel which then caused the diff wear?
Slack in the drive train is certainly not going to help, but I would shy away from diagnosonmg your issue over an internet forum without even driving your car. This is where a trusted specialist comes in, by far your best bet is to find someone honest who will fully appraise the car and provide a report on their findings. Be aware it's very tempting for a small business to add jobs that may not be essential, I've seen many cases where the owner goes in for one thing and ends up being talked into a lot of largely unnecessary work.Again Jules of Kits & Classics seems to score well here, I've never used his services but do I know a lot of people who have and they all say he's a straight up guy who's focused of giving his customers good results at a realistic price, I'm also reliably informed he will not try to ratchet the list of jobs as others seem to do.
Shunt causes and effect.
1 poor fuelling/timing and Cam choice.
2 drive train slack once its all worn and above are no longer in perfect harmony.
If that’s the case then no Ecu alone can remove all of the shunt now mainly caused by slack gearbox/ Dif internals.
If your gearbox has survived and the effect is most felt at the furthest point from engine namely the Dif it needs sorting to fully remove shunt at low revs.
If I had a bad case of shunt I’d look at the rear of the car as much as the front.
To many experts in the past fettle this or offer that and totally ignore the effect shunt has had on the Dif.
These dif come with a low set preload at around 30psi I seem to recall, a racing Dif will be preloaded to about 70 or 80 so with all the power Tvr have its no surprise if a few diff are tired.
1 poor fuelling/timing and Cam choice.
2 drive train slack once its all worn and above are no longer in perfect harmony.
If that’s the case then no Ecu alone can remove all of the shunt now mainly caused by slack gearbox/ Dif internals.
If your gearbox has survived and the effect is most felt at the furthest point from engine namely the Dif it needs sorting to fully remove shunt at low revs.
If I had a bad case of shunt I’d look at the rear of the car as much as the front.
To many experts in the past fettle this or offer that and totally ignore the effect shunt has had on the Dif.
These dif come with a low set preload at around 30psi I seem to recall, a racing Dif will be preloaded to about 70 or 80 so with all the power Tvr have its no surprise if a few diff are tired.
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