Grrrrr.......Fuc£ing misfire!!!!!

[scorcher]

Quick recap....Dizzy cap,rotor arm,magnecor leads ,extenders plugs all renewed at service about 16 months ago.Car then got an occasional cough where it would just miss a beat randomly.Never really got to the bottom of it and just lived with it.Car ran like a dream otherwise.
4 months ago had another service and new stealth cam and ACT induction kit and car pulled 306 horses on the rollers eveything running ok but still had the occasional missed beat.Played about with the coil/dizzy lead and replaced with a std one and that seemed to sort it.
New problem( related / unrelated ???)
Went out on a run about 3 weeks ago and had a rev limit of about 2900rpm and car would just stop revving as if it had hit a rev limiter.Push the clutch down and car would run ok,stop on side of road and rev and car would happily go up past 2800rpm but not under load.Took std dizzy lead off and replaced with magnecor and reseated dizzy cap checked seating of other leads and reset ecu and car now revs upto 6000rpm but seems to go fluffy /misfire around about 4000rpm.This morning I fitted a new bosch coil,an ignition module and a new dizzy cap and it still misfires about 4000rpm.Got some new plugs to fit tomorrow when its cooled.
Any other ideas/suggestions for me to try before I start travelling to the TVR garage??
Thanks in advance
Scorcher

[Bluebottle]

I get similar symptoms accasionally, which is usually cuased by No.1 lead arcing (on my 3rd magnecor lead now) have you done the "bonnet up in the dark" thing to see if you are getting any visible arcing? My vacuum advance hoze has a habit of drooping and resting on the leads and this cuases the Mangycraps to arc across to it.

[steve-V8s]

Is it definitely RPM related or is it Speed related ? In other words does the fault occur at the same revs in different gears.

Just wondering about intermittent road speed sensor. I guess you would see the Speedo acting up, but if it really is intermittent you may not notice.

[GreenV8S]

First thing to check is the engine speed trigger from the dizzy to the ECU. This is usually a single wire running along the nearside rocker cover, under the throttle body and joining the main loom by the throttle assembly. Make sure it's routed well clear of the HT leads and check the connection at the coil end. If this signal is playing up or picking up a false signal from the HT leads then the engine can run rich or lean, which can cause all sorts of funny behaviour including misfires. You should find a resister in this line too, check that the connections are secure. This fault can be load sensitive because the spark changes when the engine is under load so you can get more HT interference. Problems like this can also be caused by a weak spark caused by a faulty coil, ignition amp or HT lead.

Edited by GreenV8S on Monday 10th December 17:48

[g500]

I would say its your coil amplifier 70 pounds change it

[D14 AYS]

I had a similar problem,and after changing everything electrical it turned out to be the induction hose from air filter to Afm,the internals of the pipe was lose closing up with increased air intake,i got the ACT smooth bore intake good bit of kit problem gone.

Good luck Dean

[nicktowe]

TVR Power told me that magnecors can cause misfire, try standard Land Rover leads.

[Johno]

Buy Moroso leads from Real Steel.

Much better than OE Land Rover and far better than Magnecrap. Got fed up with replcing them and got put on to Moroso, have run them for twice as long as Magnecrap would last and till going strong.

You can also cut them to the length you want, even better.

[scorcher]

Done the bonnet up in the dark thing and couldn't see anything.
Done the ignition amplifier module this morning.
Done ACT induction.Definitely RPM related.Will check wiring in the morning.Also I'll check the plugs to make sure they are a nice colour.Think I'll invest in a set of std leads to see if that makes any difference before buying a set of more expensive ones again .Are the leads just a set of Range Rover Classic 3.9 leads or another specific model?.
Thanks again.

[Petros]

nicktowe said:

TVR Power told me that magnecors can cause misfire, try standard Land Rover leads.

Agree with that, have found standard leads far more reliable then magnecors.

[blitzracing]

Power dissapearing under load, could be fuel supply related. Things like fuel filter, kinked pipes, failng pump etc or you mean it runs to 6000 rpm under load, but only hiccups around 4000 ?

[scorcher]

blitzracing said:

Power dissapearing under load, could be fuel supply related. Things like fuel filter, kinked pipes, failng pump etc or you mean it runs to 6000 rpm under load, but only hiccups around 4000 ?

Yes it will pull to 6000rpm but under protest.Feels like its dropping back onto 7 cylinders just past 4000rpm.Had a couple of plugs out and they are a fairly nice brownish colour.May have to go in to be diagonosed after Xmas when I've got a bit more time to take it.

[ngr]

GreenV8S said:

First thing to check is the engine speed trigger from the dizzy to the ECU. This is usually a single wire running along the nearside rocker cover, under the throttle body and joining the main loom by the throttle assembly. Make sure it's routed well clear of the HT leads and check the connection at the coil end. If this signal is playing up or picking up a false signal from the HT leads then the engine can run rich or lean, which can cause all sorts of funny behaviour including misfires. You should find a resister in this line too, check that the connections are secure. This fault can be load sensitive because the spark changes when the engine is under load so you can get more HT interference. Problems like this can also be caused by a weak spark caused by a faulty coil, ignition amp or HT lead.

Edited by GreenV8S on Monday 10th December 17:48

Same as above I have found the speed trigger from the coil to the ecu tied together with the HT lead cause this exact symptom.

Edited by ngr on Thursday 13th December 09:27

[FFMan]

i had occasional issues with speed trigger wire also.

Its a bit flaky, single wire running from dizzy into the loom by the AFM. Connector was corroded and caused intermittant symptoms. You can run without the resistor for a while just in case its that also.

I made up my own replacement housed in shrink wrap etc and a proper weather proof connector.

[blitzracing]

I would not rely on general plug colours as a definitive measure of fueling over 4000 rpm. You need to hold the engine at the desired RPM for a short period, then kill the engine on the ignition switch and coast to a stop, to get a true reading. Its not that easy, and if your engine is lean it could do serious damage to the piston crown as it overheats, so not really recommended. You could monitor the lambda outputs (black and white wires)with a analogue test meter, but you need to used screened cable, extended into the cockpit, for someone to view in the passenger seat under load. You need .7 volts or more over 4000 rpm. The ECU should give you fault codes if its fuel related, so its probibly worth hiring a code reader before you throw lots of money at it. It wont pick up EHT faults, but Id seriously throw the magnacors away. They glitch the HT coil primary, and ignition amp, as the coils secondry discharge is much faster with the low resistance leads. You just dont need them, standard Landie leads are fine. (I payed £12 for the last set of Lucas Speedlines no problems so far).

Mark

[v8 racing]

make sure your rotor arm is a genuine lucas part, if it doesnt say lucas on it then throw it away and buy one that does, it may cost you £20 for one but trust me pattern parts on these engines are the bain of my life. also the magnecor leads can/have caused problems in the past, my preference is definetly oe ones or an upgrade to moroso. BUT i will state again again MAKE SURE YOUR ROTOR ARM IS GENUINE and people selling pattern ones should all be hanged.

[dwgriffith]

v8 racing said:

make sure your rotor arm is a genuine lucas part, if it doesnt say lucas on it then throw it away and buy one that does, it may cost you £20 for one but trust me pattern parts on these engines are the bain of my life. also the magnecor leads can/have caused problems in the past, my preference is definetly oe ones or an upgrade to moroso. BUT i will state again again MAKE SURE YOUR ROTOR ARM IS GENUINE and people selling pattern ones should all be hanged.

One thing to be aware of when buying "genuine" Lucas arms; many of the later ones (post 1993?)can simply be re-badged CI components. They may come in lucas boxes with lucas printed on the side of the arm but are no different to the £4 item sold at most motor factors. The original proper one's have lucas cast into them on the top face with the code number 54401050. Be aware also that the similar arms for older type distributors with code number 54402689 when fitted, stand too tall on the shaft, the cap will not fit on with these unless you modify them by grinding out the stepped ring in the mounting hole. This operation is surprisingly easily done with a dremel or similar tool and as they can picked up for couple of pounds, you may find it worth doing?

[Ballistic Banana]

I had a similar problem looked at the rotor arm (along with the other things mentioned) which wasnt a lucas one adn looked ok, still couldnt diagnose problem so and went over evrything again and found the the strip on the arm was loose. i imagine it was perhaps lifting when spinning. Changed it and ay ok

BB

[optimax sniffer]

Might have something to do with the weight of the stable in the rear of the car...

[Number55]

Or it could be the socks that Sam got him for Christmas stuffed in the engine somewhere ...