Constant Throttle Misfire...

[Dai Capp]

Yet another misfire one!

This one is at a constant throttle, most noticable between 3200 and 3900 rpm in 5th and 2200 and 2600 rpm in 4th. However on a bad day (and yes severity does vary from day to day) you can feel it missing in these rev ranges on acceleration.

All makes for a very lumpy drive on motorways etc!

It has had new leads, new throttle pots and new throttle bodies all in the last four weeks but still no cure. I have checked for vacuum in the fuel tank and none is present. When the dealer has had it back and made changes eg replaced the throttle pots it runs OK for around 100 miles and the reverts back to its old habits. Most recently it had the throttle bodies re-set up following bedding in ran OK for a bit then went back to being lumpy.

Anyone got any bright ideas...

Many thanks

DC

[andyvdg]

Reshim the valve clearances.

[judas]

Ditto what Andy said - had the same problem. Lots of stuff looked at including new HT leads. Sorting the valve clearances did the trick

[TVR5]

Dai Capp said:

Yet another misfire one! This one is at a constant throttle, most noticable between 3200 and 3900 rpm in 5th and 2200 and 2600 rpm in 4th. However on a bad day (and yes severity does vary from day to day) you can feel it missing in these rev ranges on acceleration. All makes for a very lumpy drive on motorways etc! It has had new leads, new throttle pots and new throttle bodies all in the last four weeks but still no cure. I have checked for vacuum in the fuel tank and none is present. When the dealer has had it back and made changes eg replaced the throttle pots it runs OK for around 100 miles and the reverts back to its old habits. Most recently it had the throttle bodies re-set up following bedding in ran OK for a bit then went back to being lumpy. Anyone got any bright ideas... Many thanks DC

Have exactly the same problem on mine. Bet it's the valve clearances.

[Dai Capp]

Sounds pretty conclusive...

Thanks for your help folks, I'll get the dealer to check the valve clearances and we should be all again!!

Cheers

DC

Edited to say do you know how regularly the valve clearances need reshimming...

>> Edited by Dai Capp on Tuesday 24th June 08:46

[andyvdg]

Every 12000 miles. Officially, that is.

[Ianf]

My car suffers the same. Now has 33,000 miles on it and has had everything changed!

I like others are now looking at the issue of worn throttle body bearings. If you are in the Nort West I would suggest that you ring SFR Engineering (Ex TVR Race Div) 0161 480 0101

[Dai Capp]

Im off to the factory on July 10th for them to have a look at the problem so I'll update on the results. John Ravnescroft suggested throttle balancing and did a bit of a at valve clearances, so we shall see...

Cheers

DC

[lee02]

My griff used to do this when i got stuck in london traffic to long.The plugs used to carbon up unfortunatly NGK plugs will not clean up the only answer was to change them.This may not be the answer but a new set of plugs is not a lot of money just make sure you get the right gap it is critical on performance engines.
Also try a compression test or cylinder leak down test this is cheaper than checking the valve gaps and should prove conclusive.
all the best lee

[dai capp]

Blimey, disappear for three weeks and the last topic you read is a million pages back!

Anyway, got the problem sorted, I now have an X reg Grigio Titanio Tuscan which drives just lovely thanks!

Dealer was amazing after the factory said there was no fault, agreeing to take the car back and change it for this one!

Sorry I couldn't dig out a really effective solution but my gut instinct says that it's either throttle bodies, cam related (my old car dynoed at 380 bhp without red rose conversions and rattled like a bugger) or something to do with the purge system/ECU/emissions...

All the best

DC

[swilly]

I had the same, but about 2 weeks ago TVR Power changed the leads at its 18k service, and all is well.

No constant throttle hesitation/jerkiness/misfire.

[tvr totty]

well done DC, what a result. best not to leave these misfire to long chaps, not good for the cat apparantely, which may not be good for the engine,.

ours is back, but going back into the dealer monday as at 30pmh steady, and 40mph and 50mph, pulling back - changes from day to day how bad, but want to get it checked.

see you soon

[TVR5]

Mine had a hesitation mainly apparent when going up hill, or on a flat throttle.

Turned out it was movement in the throttle bodies (ie air going into the engine was not quite what it measured it was....I think).

It's fine now.