Misfire under load

[sidpinup]

I went for a drive yesterday and I have started to get a misfire under load. I guess its HT leads but any suggestions would be welcome.

Thanks

Ed

[KillerJim]

If it happens when she is hot I would check the collant levels in the swirlpot..

[sidpinup]

It is not temp dependent. Gentle acceleration is ok but as soon as you apply a bit more it misses on one cylinder. It feels like a HT lead has broken down to me so have ordered a new set. I will let you know the results.

Thanks

Ed

[triac]

KillerJim said:

If it happens when she is hot I would check the collant levels in the swirlpot..

- how does that cause a missfire ?

[shep1001]

sidpinup said:

I went for a drive yesterday and I have started to get a misfire under load. I guess its HT leads but any suggestions would be welcome.

Thanks

Ed

I say HT leads, your fault is the same as what I had. Also get missfire if you rev the engine whilst stationary at about 2K. Leads are cheap about £45 but dealer will charge double this to fit!

[sidpinup]

I have ordered a set of 10mm racing specification leads from ACT and a new coil pack and plugs from Clever Trevor. They should be here today. I thought it was worth doing everything just to be sure. Also ordered an up rated oil pressure sender as mine is leaking.

Thanks for your help.

Ed

Edited by sidpinup on Thursday 30th April 09:21

[sidpinup]

It was the HT leads. I put on a new set of Magnecor KV85 racing leads from ATC at lunchtime and it's now going how it should. It also seems quieter and a lot more enthusiastic. If anyone is sufferering from a misfire. lumpy engine or flat spots in the rev range try a new set of leads.

Ed

[icraigmy]

sidpinup said:

It was the HT leads. I put on a new set of Magnecor KV85 racing leads from ATC at lunchtime and it's now going how it should. It also seems quieter and a lot more enthusiastic. If anyone is sufferering from a misfire. lumpy engine or flat spots in the rev range try a new set of leads.

Ed

Just seen this post Ed. I had this and it was my HT leads too. Had them changed and it's now

[SP6 Animal]

I have a similiar problem misfire at 300 revs ish worse when cold.
Bought some nearly new silicon leads and it seems to have made it slightly worse.
It's a rebuilt engine and i picked it up from power yesterday and he say's it could be a throttle pot or more likely just needs caning.
Engine pulls well just this misfire but as i say more noticable from cold.
Where are the TP's and why a blue and a white one i assume a easy fix?
As said engine only done 1k so i assume plugs ok air filter looks used so i may aswell replace that.
Thanks for any advice.

[sidpinup]

I did have another misfire about 2 years ago and it was an injector or rather the signal wire to the injector so ended up being a simple fix. It did cause a misfire all the way through the rev range so if its OK when you rev higher it is liekly to be something else.

[SP6 Animal]

Sorted it
Power supplied me both throttle pots they were convinced that was the problem cheif mechanic bet his house on it!
Well he kept his house the car doesn't stutter at any speed.
Learning more about this car as i take bits off it found the fuse it's a 125 amp has that been upgraded or std?
Well chuffed

[thainy77]

SP6 Animal said:

Sorted it
Power supplied me both throttle pots they were convinced that was the problem cheif mechanic bet his house on it!
Well he kept his house the car doesn't stutter at any speed.
Learning more about this car as i take bits off it found the fuse it's a 125 amp has that been upgraded or std?
Well chuffed

Well done on sorting the problem. The standard fuse is 100amp so it's been upgraded.

[BirleyDan]

What kind of price are we talking for the throttle pots?

I'm just wondering about my own.

[SP6 Animal]

There on powers website £65+vat.
Can't begin to tell you what a difference they made.
Easy job takes a hour.

[Robertjp]

SP6 Animal said:

There on powers website £65+vat.
Can't begin to tell you what a difference they made.
Easy job takes a hour.

Was it throughout the rev range you had a misfire? i have one about 6k rpm, and you have me wondering...

[SP6 Animal]

Robertjp said:

SP6 Animal said:

There on powers website £65+vat.
Can't begin to tell you what a difference they made.
Easy job takes a hour.

Was it throughout the rev range you had a misfire? i have one about 6k rpm, and you have me wondering...

Yes more of a stutter rather than misfire.
Appears to have been fuel shut off and then on again rapidly.
Town driving and motorway any speed but constant speed it was noticable accelerating no problem.
It was explained to me these pots are controlled by the ecu if there faulty or out of range they send the wrong signal ie too much or not enough fuel hence the shunting.
If you floor it you get full fuel so problem it's when you want a constant speed it shows up.
HTH
Paul

[VARLEYHYD]

SP6 Animal said:

Yes more of a stutter rather than misfire.
Appears to have been fuel shut off and then on again rapidly.
Town driving and motorway any speed but constant speed it was noticable, accelerating no problem.
It was explained to me these pots are controlled by the ecu if there faulty or out of range they send the wrong signal ie too much or not enough fuel hence the shunting.
If you floor it you get full fuel so problem it's when you want a constant speed it shows up.
HTH
Paul

Could be worn throttle bodies too?

G

[BGB autosport]

Graham, i have read on here about fitting bearings to the throttles and also in your manual, is this something you have done?, obviously this requires the machining of the throttle bodies for the new roller bearing, do you know the commonly used size for the bearings?