More rough running! Help!!!

[helipilot]

I had my car serviced in July and have done 2000 miles since. The car has started running slightly rough when only very light throttle is applied between 2-3000 rpm. Its fine on full throttle or when coasting just not when the throttle is depressed to maintain around those revs. The car judders like it is kangarooing. I have cleaned the stepper motor with no difference. I am leaning towards some electrical problem and have ordered some new HT leads which i hope will cure it. Anyone else got any ideas?

[iandbeech]

It does sound similer to ours and I`m going to check the stepper motor at the weekend. Also, we were running on unleaded but changed to optimax and the stuttering seems to have occured once we running on Optimax so are going back to unleaded to see if that helps.

[derf]

Mine does this to.. please keep me posted.. I just thought it was due for a good service. New plugs etc...

Richard

[david beer]

My Griff does(did) this, it would be smooth going up hill or if test with handbrake on. Disconnect the vaccum advance pipe, too much on partial throttle at low revs.

[neal1980]

Hi,

I really have to rate optimax!! my 4.0 chim i've tried with various super unleadeds and you get god and bad fills. It really takes a hammering on performance and drivability on a bad tank...I have capped off the vac advance and fill up every time with optimax now and its an absolute flyer!....Its so good I drive 16 miles to fill up at the nearest shell garage!...

Failing this get super then ass an octane booster I found this good as well but gets kinda expensive.

Treat your TVR with optimax it will LOVE YOU!

[helipilot]

Mmm. Disconnecting the vacuum advance pipe. Anyone think this is a bad idea. Should it then be blanked off. What are the pros and cons of doing this?

[david beer]

You should get the "big guys" coming on and saying that very often they are disconnected, after all its only for cruising fuel economy, whatever that is in a TVR. As soon as you put your foot down, the vacuum is removed and you have no advance. Of course it may not be "the problem" but its got to worth a go.

[helipilot]

I disconnected the vacuum advance pipe and drove the car home (only 10 miles).. but seems to have sorted the problem completely, in fact it feels like a different car!! So next questions. Do I just leave the pipe off?...do i close both end connectors? What effect will it have on the car by leaving it off? Why did the car run fine 2 months ago and not now? Would a clean of the airbox sort the problem? So many questions!!

[iandbeech]

helipilot said:

I disconnected the vacuum advance pipe and drove the car home (only 10 miles).. but seems to have sorted the problem completely, in fact it feels like a different car!! So next questions. Do I just leave the pipe off?...do i close both end connectors? What effect will it have on the car by leaving it off? Why did the car run fine 2 months ago and not now? Would a clean of the airbox sort the problem? So many questions!!

where is this vacuum advance pipe then?

[helipilot]

Very thin (3mm or so) pipe that runs from the plenum chamber to the metal flying saucer shaped item next to the distributor cap (about half a metre in length) !! Give it a try.

[Ballistic Banana]

I had a rough running problem while driving down to Limousin in France, had yea olde bible with me.
Started car and looked in the engine bay while dark and found a HT lead shorting on to the manifold wouldnt have seen it engine off in daylight as from above it didnt look like it was on the manifold pipe.

I have heard of the vacum pipe been taken off before.

BB

[neal1980]

Just a quick note, if you disconnect the advance pipe block the end up at the inlet, if you dont you have effectively got an air leak...

Mine runs much better, my mate from TVR says they do this on most there cars and there racers...

[iandbeech]

neal1980 said:

Just a quick note, if you disconnect the advance pipe block the end up at the inlet, if you dont you have effectively got an air leak... Mine runs much better, my mate from TVR says they do this on most there cars and there racers...

Do you mean block the plenum end? And leave the other end open? Or the other way around?

[helipilot]

The bible says block the plenum end and leave the distributor end open. Did it help on yours?

[neal1980]

Just a quick one before I get busted at work under the "no personal internet use policy!"...

Block the plenum end up and leave the dizzy end open..

Thanks

[iandbeech]

Yet to try but now I know which end to block will have a go at the weekend. Thanks.

[neal1980]

Hi,

You will probably find your vac advance unit is shafted mine is. Disconnected it from plenum end and put it in your mouth and sucked. Stick your tongue over the end if it has pressure there, its more than likely fine, if nothing then chances are its gone.

Ive spoke to a guy who changed 3 during the time he owned his car. Thats why its like a different car, when its capped up it flies due to no air leak. Then when connected runs much slower i found. New ones are around £50quid i think but im not tempted to fit one as its not pinking or doing any harm to the engine.

Try it and let us know the results of the suck test..

Cheers

[iandbeech]

neal1980 said:

Hi, You will probably find your vac advance unit is shafted mine is. Disconnected it from plenum end and put it in your mouth and sucked. Stick your tongue over the end if it has pressure there, its more than likely fine, if nothing then chances are its gone. Ive spoke to a guy who changed 3 during the time he owned his car. Thats why its like a different car, when its capped up it flies due to no air leak. Then when connected runs much slower i found. New ones are around £50quid i think but im not tempted to fit one as its not pinking or doing any harm to the engine. Try it and let us know the results of the suck test.. Cheers

So if I suck and then my tongue gets pulled into the tube, it`s working! Think I`ll try it by driving it first I`ll let you know how I get on though!

[david beer]

Um, cross perposes here i think. If the vacuum is working correctly, getting advance, you might get lumpy partial throttle. If its knackered there will be no advance. If its knackered you should get less MPG. Reason for it being like it after a service is that the timing will of been adjusted. I always do the "get it to pink and slowly retard until it stops" method. Of course without the vac advance.

[iandbeech]

Quite incredible, feels so smooth and is indeed like a different car. Have tried provoking to stutter etc and it just won`t

Pg64 of bible for details.

So if there is anyone thinking of selling their Chim and saving up for a Tuscan cos they want a different car, try removing the vacuum hose and invest in a bit of insulating tape instead!! It`s far cheaper