Uncontrollable lurching at low speeds

[CanadianGriff]

I have the 4.3 in my 1993 Griffith and at low speeds you either have to ride the clutch to control it from lurching. It's like when you slow your car in to high of gear. This start at any RPM below 2200 RPM. It starts to lurch and it won’t stop until you depress the clutch.
The mechanic thinks the throttle cable is to short and when the engine does the first little twist and pulls the cable it just continues. I think I’m baffled.

Any thoughts?

[carsy]

This is known as shunting. Loads of threads on it just do a search. For starters Make sure there are no air leaks around the plenum. I have a 4.3 and it doesnt really suffer from this.

[Simon says]

Think i might review your mechanic situation too

[EGB]

Dave. If your car has power steering, check that bolts on the power steering oil resevoir are not loose on the plenum. This can let air into the plenum as Carsy said. Also, if it has a Stepper motor, then give it a clean.

Edited by EGB on Monday 6th February 22:39

[blitzracing]

Just try uplugging the stepper to see if it improves things, as there have been some mutterings about the TVR ECU control circuitry coming into play at the wrong time causing the stepper to try and control the idle when the car is moving. I can also be caused by poor ignition, mixture errors the ECU is trying to correct, or the fact that the system has an AFM combined with a plenum chamber and perfromance cam- these are a bad mixture design wise.

[Aandytvr1]

Initial clean the stepper motor , in addition , you may need to increase the springs to two,
Check site for accelerator return spring

The main spring , some models have one or two
I have two and prefer it , makes pedal feel firmer ( some don't like)

If you whilst the engine is off feel the tension in the springs and increase the acelerator (engine bay) Ypu may feel the pinch point , it should be smooth and return quickly


Please don't confuse with third spring ( smaller)

Andy

[domV8]

Just for the record, check your driveshaft bolts - loose bolts exacerbate the effects of shunting a lot, and this in turn shakes the bolts loose further etc etc...

Easy to check, and can make a world of difference.

HTH,

Dom

[EGB]

One main throttle spring working is sufficient.

[blitzracing]

Not when it snaps.

[blitzracing]

If its the typical shunting a lot of cars suffer from, it occurs at around 1700 rpm is high gears and very light throttle, and will dissapear the moment you open the throttle a bit more. Unfortanately there is no specific fix for this, as its basically poor combustion that can be caused by a multitude of reasons from poor ignition to cross contamination between cylinders of exhaust gas during the valve overlap period (this is why a plenum is a bad idea if you run a high performance cam). Basically anything that can impove the combustion is likley to help. Unfortuately if you are running catalysts you cant alter the mixture, otherwise getting the engine to run a bit richer frequently helps.

[cavebloke]

I have the exact same problem on my 4.3 and I was told it was a worn camshaft that needed changing (£1500). Mechanic said they only last 50k and as mine has done 75k it was probably the cause. Of course there's no easy way to even check if it's worn without spending a lot or DIY.


Since I didn't have the cash I'm living with it for the moment and avoiding town centres. Some of these posts make me think it's worth checking some other things first though.

[Aandytvr1]

You missed the point with the single spring , by having two ' increases the tension and it will effectively not stick as much and return a lot quicker .

But note if cable weak it will certainly make it snap

[Aandytvr1]

You missed the point with the single spring , by having two ' increases the tension and it will effectively not stick as much and return a lot quicker .

But note if cable weak it will certainly make it snap

[EGB]

Aandytvr1 said:

You missed the point with the single spring , by having two ' increases the tension and it will effectively not stick as much and return a lot quicker .

But note if cable weak it will certainly make it snap

If cable is weak, it will snap before the spring! There is another spring on the throttle butterfly shaft to close it if the spring, or the cable snaps. This should be enough to close the engine to tick over. Important to check this one is functionable or else!!!Two springs can make the throttle pedal too heavy for some and probably more likely to snap the cable.
I queried the single spring set up with a well known TVR repair shop. He said many, many TVRs have only one spring. The jury is still out! Rimmers of Lincoln for throttle springs. I have a part number but check with them.
Dave in Canada. How are you getting on? Cheers Eddie.

Edited by EGB on Tuesday 7th February 20:46

[blitzracing]

cavebloke said:

I have the exact same problem on my 4.3 and I was told it was a worn camshaft that needed changing (£1500). Mechanic said they only last 50k and as mine has done 75k it was probably the cause. Of course there's no easy way to even check if it's worn without spending a lot or DIY.


Since I didn't have the cash I'm living with it for the moment and avoiding town centres. Some of these posts make me think it's worth checking some other things first though.

Camshaft wear is certainly an issue, but not the route cause of shunting on its own. If the cam is changed for one with less valve overlap it may well resolve the issue as the engine breaths much better at low speed, and you get less exhaust contamination back in the plenum, plus the AFM and ECU can control the mixture more acurately. The down side is the engine will loose its ability to rev so well, and you will loose some peak horsepower in the process. A 5ltr I saw had a cam so worn it had no lift at all on one of the lobes, it shunted, so it had a new Stealth cam fitted, and it still shunts just as badly.

[PeteGriff]

cavebloke said:

I have the exact same problem on my 4.3 and I was told it was a worn camshaft that needed changing (£1500). Mechanic said they only last 50k and as mine has done 75k it was probably the cause. Of course there's no easy way to even check if it's worn without spending a lot or DIY.


Since I didn't have the cash I'm living with it for the moment and avoiding town centres. Some of these posts make me think it's worth checking some other things first though.

I have this slightly on my 4.3, but it does not bother me to much at all. In town or traffic I keep in a lower gear therefore allowing more revs, other than that I trickle the clutch a little and she is OK and nobody else notices. I believe they all do this a bit so treat it as a characteristic. Pete

[marz92]

blitzracing said:

A 5ltr I saw had a cam so worn it had no lift at all on one of the lobes, it shunted, so it had a new Stealth cam fitted, and it still shunts just as badly.

Yep that'll be me!! Hi Blitzracing - trust you are well. Griff currently hibernating and will soon be ready for its interior make over courtesy of D & C boys

Blitzracing are you coming to the Neil Garner Open Day on Easter Saturday which I am organising? Look on the TVR Events Page - near the top under Neil Garner, would be great to see the Yellow Peril there! - If so, do please stick your name down. TVR or no TVR - super cars and performance cars welcome.

[blitzracing]

Linky?

[marz92]

blitzracing said:

Linky?

YHM. Blitzracing

[BliarOut]

EGB said:

Aandytvr1 said:

You missed the point with the single spring , by having two ' increases the tension and it will effectively not stick as much and return a lot quicker .

But note if cable weak it will certainly make it snap

If cable is weak, it will snap before the spring! There is another spring on the throttle butterfly shaft to close it if the spring, or the cable snaps. This should be enough to close the engine to tick over. Important to check this one is functionable or else!!!Two springs can make the throttle pedal too heavy for some and probably more likely to snap the cable.
I queried the single spring set up with a well known TVR repair shop. He said many, many TVRs have only one spring. The jury is still out! Rimmers of Lincoln for throttle springs. I have a part number but check with them.
Dave in Canada. How are you getting on? Cheers Eddie.

Edited by EGB on Tuesday 7th February 20:46

We lost one griff due to it only having one spring and it failing