Juddering in slow traffic - Any clues?
Discussion
Recently brought a '95 Griffith 500. Runs well out on the open road but tends to judder in slow/town traffic? Any ideas why? Somebody did tell me it could possibly be the Idle Stepper Motor? - what ever or where that is! My knowledge under the bonnet is somewhat limited! So I leave it to the experts - like you.
Had the timing checked - spot on. As I said, the open road, no problems at all.
Thanks for your help
Had the timing checked - spot on. As I said, the open road, no problems at all.
Thanks for your help
V8 GRF said:
Low speed driveline shunt TADTS 
Yep, I'd go along with this option. I believe the original 340bhp (as if!) version did this as standard but the situation became a bit better when they trimmed them down to 320bhp.Mine shunts but as mentioned, you learn to accommodate this with your driving style over time.
It can be overcome in town centres by permanantly wheelspinning and revving at 5,000rpm and drifting your way to the other side of town to the tune of a thumping V8 baseline.
Edited by lazyitus on Wednesday 29th October 08:30
Thanks guys, I was told it could be a number of things. However, pretty certain I was told it wasn't the drive line shunt. I will get the various suggestions looked at. Thanks for your input, much appreciated. Any other suggestions, welcomed!
Edited by marz92 on Wednesday 29th October 08:37
Are you talking about a problem that has been there since you bought the car or one that has recently developed?
Do you know what profile of camshaft is fitted to your car?
There is a tendency for people to fit different camshaft profiles, and some make the much more prone to shunting in traffic. The payback is more performance when you find a clear bit of road. The compromise may be perfectly acceptable to someone who does little traffic driving.
I bought my car and found that the cam fitted was wild. I don’t do much traffic, but was never truly happy with the low speed manners. The option was to fit a milder cam and lose performance, or fit a mapped ignition system and gain performance and better low speed manners. I chose the latter.
This isn’t cheap, so eliminate all the potential little faults that it might be. Get someone who has driven many Griff’s to take it out and see how different to other cars it is.
If it’s all working as well as it can and the issue is just the character of the car, then go for a mapped system for improved manners.
Do you know what profile of camshaft is fitted to your car?
There is a tendency for people to fit different camshaft profiles, and some make the much more prone to shunting in traffic. The payback is more performance when you find a clear bit of road. The compromise may be perfectly acceptable to someone who does little traffic driving.
I bought my car and found that the cam fitted was wild. I don’t do much traffic, but was never truly happy with the low speed manners. The option was to fit a milder cam and lose performance, or fit a mapped ignition system and gain performance and better low speed manners. I chose the latter.
This isn’t cheap, so eliminate all the potential little faults that it might be. Get someone who has driven many Griff’s to take it out and see how different to other cars it is.
If it’s all working as well as it can and the issue is just the character of the car, then go for a mapped system for improved manners.
Uncle FesterQUESTION: said:
Are you talking about a problem that has been there since you bought the car or one that has recently developed?
MY ANSWER: The problem has been with the car when I brought 3 weeks ago. Some people tell me that Griff 500 do this. one person in the 'trade' has looked at it quickly and wonders if more BHP was added early in its life thus causing it to judder at slow speeds.
QUESTION: Do you know what profile of camshaft is fitted to your car?
MY ANSWER: Don't know, I will have to look into that one
QUESTION: There is a tendency for people to fit different camshaft profiles, and some make the much more prone to shunting in traffic. The payback is more performance when you find a clear bit of road. The compromise may be perfectly acceptable to someone who does little traffic driving.
MY ANSWER: Yeap, just want the TVR expert said to me!
QUESTION: I bought my car and found that the cam fitted was wild. I don’t do much traffic, but was never truly happy with the low speed manners. The option was to fit a milder cam and lose performance, or fit a mapped ignition system and gain performance and better low speed manners. I chose the latter.
MY ANSWER: Looks like I MAY follow your 'route' of advice.
QUESTION: This isn’t cheap, so eliminate all the potential little faults that it might be. Get someone who has driven many Griff’s to take it out and see how different to other cars it is.
If it’s all working as well as it can and the issue is just the character of the car, then go for a mapped system for improved manners.
MY ANSWER: A mapped system? What sort of cost are we talking about?
MY ANSWER: Many thanks Uncle Fester for your help
MY ANSWER: The problem has been with the car when I brought 3 weeks ago. Some people tell me that Griff 500 do this. one person in the 'trade' has looked at it quickly and wonders if more BHP was added early in its life thus causing it to judder at slow speeds.
QUESTION: Do you know what profile of camshaft is fitted to your car?
MY ANSWER: Don't know, I will have to look into that one
QUESTION: There is a tendency for people to fit different camshaft profiles, and some make the much more prone to shunting in traffic. The payback is more performance when you find a clear bit of road. The compromise may be perfectly acceptable to someone who does little traffic driving.
MY ANSWER: Yeap, just want the TVR expert said to me!
QUESTION: I bought my car and found that the cam fitted was wild. I don’t do much traffic, but was never truly happy with the low speed manners. The option was to fit a milder cam and lose performance, or fit a mapped ignition system and gain performance and better low speed manners. I chose the latter.
MY ANSWER: Looks like I MAY follow your 'route' of advice.
QUESTION: This isn’t cheap, so eliminate all the potential little faults that it might be. Get someone who has driven many Griff’s to take it out and see how different to other cars it is.
If it’s all working as well as it can and the issue is just the character of the car, then go for a mapped system for improved manners.
MY ANSWER: A mapped system? What sort of cost are we talking about?
MY ANSWER: Many thanks Uncle Fester for your help
Edited by marz92 on Wednesday 29th October 17:19
Edited by marz92 on Wednesday 29th October 17:21
The best person to talk to is probably http://www.track-car-solutions.co.uk/
The cost can vary quite a bit, depending on how good you are at DIY mechanics, which make and other options you choose.
The cheapest route is Megasquirt, which is very DIY. There is plenty of support on the web for this and others have fitted a Griff with it. Before going for Megasquirt you should be very confident of your abilities to finish. You will have to solve problems yourself.
The alternative is to buy a kit and fit it yourself or have it professionally installed. There are several on the market. These offer a variety of features and prices. To this add labour costs for professional fitting. In all cases you will need a mapping session on a rolling road.
One option is to have a short connector loom that plugs into the existing ECU socket. A much better solution is to replace the engine loom with a dedicated new loom for the new system. This costs more and there is additional labour in the fitting.
The original TVR loom was a modified Range Rover loom. This was much less satisfactory than a dedicated loom. The original loom has had some years in a very hot and hostile environment. In some cases this will have chafed and degraded. This can cause problems and no wire lasts forever. It may be worth taking the opportunity to replace the original with a dedicated new loom.
I went for the new loom and an Emerald ECU.
You will have parts removed from your car that can be sold to recuperate some of your outlay.
In addition, the expense should not be considered as just the cost to remove some shunting. The benefits of a mapped system are many. Improved economy and power, faster throttle pick up, smoother running. The ability to tune the engine is improved. This can lead you onto a slippery slope of spending more to get more power. One big consideration is that the engine can be mapped to run on 95 octane instead of the more expensive fuels. This will also help repay the initial outlay.
Remember, look for the basic problems. If you can cure it simply and cheaply now then do so. Fit a mapped system later if you want to.
But don’t make the mistake of spending a fortune chasing a problem without success, only to spend the money again on fitting the mapped system. Remember, you will be fitting much of, if not all of, an entirely new system. It can be cheaper to ‘cut the Gordian knot’ and undertake the modernisation from the beginning.
ETA
If the problem is cam profile, the alternative is to change the cam. That would be costly too.
The cost can vary quite a bit, depending on how good you are at DIY mechanics, which make and other options you choose.
The cheapest route is Megasquirt, which is very DIY. There is plenty of support on the web for this and others have fitted a Griff with it. Before going for Megasquirt you should be very confident of your abilities to finish. You will have to solve problems yourself.
The alternative is to buy a kit and fit it yourself or have it professionally installed. There are several on the market. These offer a variety of features and prices. To this add labour costs for professional fitting. In all cases you will need a mapping session on a rolling road.
One option is to have a short connector loom that plugs into the existing ECU socket. A much better solution is to replace the engine loom with a dedicated new loom for the new system. This costs more and there is additional labour in the fitting.
The original TVR loom was a modified Range Rover loom. This was much less satisfactory than a dedicated loom. The original loom has had some years in a very hot and hostile environment. In some cases this will have chafed and degraded. This can cause problems and no wire lasts forever. It may be worth taking the opportunity to replace the original with a dedicated new loom.
I went for the new loom and an Emerald ECU.
You will have parts removed from your car that can be sold to recuperate some of your outlay.
In addition, the expense should not be considered as just the cost to remove some shunting. The benefits of a mapped system are many. Improved economy and power, faster throttle pick up, smoother running. The ability to tune the engine is improved. This can lead you onto a slippery slope of spending more to get more power. One big consideration is that the engine can be mapped to run on 95 octane instead of the more expensive fuels. This will also help repay the initial outlay.
Remember, look for the basic problems. If you can cure it simply and cheaply now then do so. Fit a mapped system later if you want to.
But don’t make the mistake of spending a fortune chasing a problem without success, only to spend the money again on fitting the mapped system. Remember, you will be fitting much of, if not all of, an entirely new system. It can be cheaper to ‘cut the Gordian knot’ and undertake the modernisation from the beginning.
ETA
If the problem is cam profile, the alternative is to change the cam. That would be costly too.
Edited by Uncle Fester on Wednesday 29th October 22:30
On the cars Ive looked at, its caused by the mixture running lean at around 1500 rpm. The ECU is pretty clever, and sets the overall mixture to be spot on at tickover dependent on the lambda feedback and this is the long term fuel trim value. As the RPM rises the ECU then constantly tweaks the mixture on about 1/2 second intervals, but can only make small adjustments and this is the short term trim value. Problem is if you run a high performance cam, the low speed airflow is poor and The ECU backs of the fuelling to match this "low" airflow, so the engine runs lean. The ECU picks this up via its Lambda feedback and tries to correct it, but runs out of "short term" fuel trim, that causes the car to shunt badly. What you feel is the ECU richening the mixture, but not far enough to get a correct reading, so it keeps trying, so the power keeps pulsing. This is a problem really associated with the way the catalyst fuel map works, and in some cases can be eliminated by switching to the non catalyst fuel map (this is just a resistor change), but this may fail emission tests or damage the catalyst. Apart from this there are multiple things that might improve it, basically anything that will improve airflow to richen the mixture,(like induction kits) or anything that will help ignite the very lean mixture, such as better HT leads, new plugs, rotor arms etc etc. Remapping is a possibility, but its expensive, and only a last resort after you are sure everything else is spot on. There is a huge post on what some people have done.
http://www.pistonheads.co.uk/gassing/topic.asp?h=0...
Mark
http://www.pistonheads.co.uk/gassing/topic.asp?h=0...
Mark
Another problem can be if your stepper motor is sticky - you will be trying to drive through traffic at a very fast idle speed which will cause shunting. Mine is lazy sometimes and when I come to a standstill it idles at 1500 for a few seconds and then slowly drops back to 900 (it should ideally drop to about 1100 or so when moving and then about 900 once you stop)
Talking of steppers, I have now perfected a way of getting them to bits to clean, without damage:
1) get the car warm
2) Remove the stepper from the plenum and reconnect it.
3) Block the hole that the stepper came from with some sort of bung.
4) Hold the stepper in your hand, so you can catch the central cone and spring when it comes out.
5)Get someone to start the car. Without the stepper inplace it will rev at around 2k, but the ECU will try to slow it down by powering the stepper motor and pushing cone outwards. It will do this in a series of pulses, a few seconds apart, until the cone and spring drop out.(assuming they are not completely stuck). Stop the engine.
6) clean all the muck of the shaft, and lightly lubricate the screw thread inside the motor.
7) To reassemble, wind the shaft back into the motor so far, but align the slot in the shaft with the plastic keyway as best you can by rotating the shaft.
8) Let the engine cool, then reconnect the stepper motor. Power cycle the ignition, (dont start) and the ECU will try to pull the shaft back in each time the ignition is turned OFF. This is the slightly tricky bit, as if the keyway and shaft are not quite aligned it wont pull home, so you may need a few attempts.
mark
1) get the car warm
2) Remove the stepper from the plenum and reconnect it.
3) Block the hole that the stepper came from with some sort of bung.
4) Hold the stepper in your hand, so you can catch the central cone and spring when it comes out.
5)Get someone to start the car. Without the stepper inplace it will rev at around 2k, but the ECU will try to slow it down by powering the stepper motor and pushing cone outwards. It will do this in a series of pulses, a few seconds apart, until the cone and spring drop out.(assuming they are not completely stuck). Stop the engine.
6) clean all the muck of the shaft, and lightly lubricate the screw thread inside the motor.
7) To reassemble, wind the shaft back into the motor so far, but align the slot in the shaft with the plastic keyway as best you can by rotating the shaft.
8) Let the engine cool, then reconnect the stepper motor. Power cycle the ignition, (dont start) and the ECU will try to pull the shaft back in each time the ignition is turned OFF. This is the slightly tricky bit, as if the keyway and shaft are not quite aligned it wont pull home, so you may need a few attempts.
mark
In agreement with Uncle fester for me.
I had low speed shunting (late 94 500), went down the route of checking timing, adjusting throttle pot, AFM trim, new HT leads etc, which made a slight improvement. However replaced the camshaft which was fairly well worn to a MC1 and low speed shunting basically eliminated.
oz
I had low speed shunting (late 94 500), went down the route of checking timing, adjusting throttle pot, AFM trim, new HT leads etc, which made a slight improvement. However replaced the camshaft which was fairly well worn to a MC1 and low speed shunting basically eliminated.
oz
I seam to remember reading that was problem with some cars and TVR down tuned the later one’s from the claimed 340bhp to 320bhp (course I might be talking complete b
ks).
You also don’t say if this is constant, mine is a 97 and is not good but it’s OK, however when the fans kick in, which in slow traffic is every couple of minutes or so, I get a major hiccup. To help with this and the marginal cooling in warm weather I fitted a fan override switch and when ever I come into traffic I switch this on. You do learn to watch the temp gauge in a Griff.
Cheers,
Simon.
ks).You also don’t say if this is constant, mine is a 97 and is not good but it’s OK, however when the fans kick in, which in slow traffic is every couple of minutes or so, I get a major hiccup. To help with this and the marginal cooling in warm weather I fitted a fan override switch and when ever I come into traffic I switch this on. You do learn to watch the temp gauge in a Griff.
Cheers,
Simon.
I had a look at the car in question today. Firstly I connected up a monitor to both lambda probes, and put in a switchable tune resistor to I could compare fuelling with and without the lambda feed back. On the catalyst setting, the engine was running lean, and you could see the ECU trying to correct it, but it would still drop below lambda range (lean) for about 3/4 of a second and the car hesitated. Switching to the non catalyst map, the fuelling became very much richer and the fault disappeared (This is only for test only for a short period- just to prove the point), so I could rule out non fuel related issues. I then put a 1 ohm resistor in the earth wire of the AFM. This has the effect of putting about an extra 100mv the AFM output by lifting the earth point in relation to the ECU. This can be done as about 100ma passes down the AFM earth to feed the electronics. This fools the ECU into thinking there is more air going in, so the ECU adds more fuel. I made this switchable to the results could be easily be seen on the Lambda monitor, and the effect on the shunting could be compared as the resistor was switched in and out. 1 ohm worked pretty well, with the car dropping back into the correct Lambda range, and the ride becoming much smoother. I tried going to 1.3 ohms to see if any more gains could be had, but at this point the one bank started to over fuel slightly, so we went back to 1 ohm. We where being pretty harsh on the car, running it down to 1000 rpm in 5th, and although there was still a slight snatch, it was not fuel related, and probably just down to the cam duration. I hope to get some feedback over the next few days to see how much difference this has made in traffic / town conditions when the problem was at its worse. For anyone thinking of doing this, it is MOST IMPORTANT that the lambda outputs are monitored to get the value of resistor spot on. values are in the .5-1.5 ohm range, and small steps make a big difference.
Mark
Mark
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