Misfire / Hesitation (after fitting new HT leads??)

[JimsTVR]

Im hoping someone can offer a few words of wisdom to help me with this puzzling problem with my 2000 4.0l Chim.

I treated her to a New set of Magnicore 8mm leads and an ACT induction kit yesterday, but since fitting she has a nasty misfire/hesitation under load or acceleration.

Ive checked the lead connections, the extender connections, i wired up one by one to the correct cylinders. The induction pipes have no splits or leaks, and there is no where for air to escape/enter between the MAF sensor and the manifold.

Can fitting these low resistence leads cause another part of the ignition system to fail? What else could i possibly of done wrong? She was running beautifully before, but now she is like this!

Maybe not related but for the last few miles of this evenings drive the fuel pump 'hummed'. Im really quite worried im causing her some damage so ive parked her up and come here for advise. So if anyone has any ideas, or has seen this before, please offer a quick reply.

Thanks
James

[gf350]

I think the plug extenders you use for the magnecor leads are different, as when I had mine serviced I had to have them changed and I was told the new ones were half the price they would have been as I had magnecor leads on.
Not sure this would cause a problem though. Maybe disturbing the extenders broke one? Maybe the leads are earthing on the engine block?
Also check you put all the leads back in the right place, theres a diagram in the bible somewhere.

[victormeldrew]

Not true, I have Magenecor leads fitted and all other ignition components are standard. No misfire in the five years they have been fitted. I replaced the plug shrouds with new ones at the same time as the leads were fitted, but mostly for cosmetic purposes, as the originals were a bit manky.

These are 10.4 mm leads, but the 8.5mm are similar.

Not much chance of the leads earthing through all that silicone by the way. You can bundle them together and lay them directly on the heads with no adverse effects - bundling standard leads would give all sorts of problems with induced sparks, and would short to the engine. I am fitting lead separators to mine again purely for cosmetic reasons; they have given no trouble lashed together with cable ties and draped on the heads since I fitted them.

You have changed more than one thing at a time, which isn't helping. If you have the original leads, refit them to help you isolate the problem.

>> Edited by victormeldrew on Sunday 19th February 10:21

[baz1]

I hope there is some answers to your problem as i fitted the 8mm Magnicore leads and have encounterd a missfire when first driven after cold,which i dident have before.
If i run the car untill hot then leave for 10 mins or so it is then fine.
Also put new plug extenders on to no avail.

[JimsTVR]

Thanks for all your replies, they really do help.

Ok, its not the leads, i put the old ones back on and checked the connections again, and all seem fine.

I now wonder if ive disturbed/damaged one of the extenders, so i guess i will be calling ACT for some new ones.

I did spot one other thing though, i took the induction pipes off (again) to check them, and where the long pipe joins the filter side of the MAF sensor i might of done the jubilee (sp?) clip up a little too tight as it made an indent on the ring. Although its the filter side so air escape/entering wouldnt cause huge problems, is it likely that this mis-shape could be causing an diturbed air pattern hence the hesitation/misfire problems?

Thanks again, more replies appreciated.

[griffter]

There are resistive extenders/shrouds and non-resistive. Standard (Vauxhall) are resistive. Both are visually identical. If you're using Magnecors I think you really want non-resistive extenders (available from ACT). Using the originals in conjunction with Magnecors could yield a weak spark - maybe not in all cases, but possibly so in yours.

[Painey]

When I had the knackered leads on my Griff replaced with Magnecor ones it was misfiring on the way home so called the garage who suggested I try resetting the ECU by simply unplugging it, leaving for a few minutes and then reconnecting it. Did the trick for me!

All the best - Chris

[GreenV8S]

griffter said:

If you're using Magnecors I think you really want non-resistive extenders (available from ACT).

Interesting, because I was about to suggest the opposite. The original RR ignition system uses high resistance leads, and so do TVR. However, TVR also fit resistive extenders which I think were not used on the RR. If you're having trouble after changing to low resistance /non-resistive components throughout then I'd be inclined to put some resistance back in. Also consider whether the different electrical characteristics of the low resistance setup may be showing up a fault elsewhere in the system, such as the wrong spec coil or the beginning of an HT insulation breakdown.

The Magnecor leads have an inductive layer which helps reduce inductive coupling between adjacent leads, but it is still not a good idea to let them touch. There will still be *some* coupling which can only be bad, more important any mechanical contact with the leads will accelerate the insulation breakdown. This applies to strapping them to each other, having them pressing/resting against the engine or even (to a much smaller extent) simply handling them roughly.

[JimsTVR]

Hello

Well problem solved!

I will invest in some new extenders anyway, but the culprit was the Aif flow sensor.

After fitting the Induction kit id routed the wires running from the Air flow meter under the 90' tubing leading to the manifold. It seems that this was a little too tight and it had actually pulled a wire from it terminal. Refitted, and routed above the pipe and all seems to be working ok now.

Thanks for all of your replies, it nice to know so many poeple out there are willing to help. I highly recommend the ACT induction kit, although im sure the car isnt more powerful, response and pickup below 2000rpm has improved (and she sounds better too!)

Cheers!

Jim

[gf350]

Please let us know what type of plug extenders Tim recommends as I'm pretty sure its the non restricted ones fitted on mine since the change which may not be right.

[GreenV8S]

On mine, Tim recommended and supplied the non-restrictive extenders with Magnecor leads, and it worked fine for many years. But it's possible that the reduced resistance could have some effect on other cars if your coil or ignition amp are a different spec. Of course it's also possible that the extenders or leads have been wrongly fitted, or damaged through mishandling while fitting. Sometimes the connectors need a little force and it's very easy to have them held on by the boots and not properly engaged, or to damage the HT lead by pulling on the lead instead of the boot.

[gf350]

GreenV8S said:

On mine, Tim recommended and supplied the non-restrictive extenders with Magnecor leads, and it worked fine for many years. But it's possible that the reduced resistance could have some effect on other cars if your coil or ignition amp are a different spec. Of course it's also possible that the extenders or leads have been wrongly fitted, or damaged through mishandling while fitting. Sometimes the connectors need a little force and it's very easy to have them held on by the boots and not properly engaged, or to damage the HT lead by pulling on the lead instead of the boot.

Many thanks, what sort of coil should I be using. Mine is the original one.

[GreenV8S]

gf350 said:

Many thanks, what sort of coil should I be using. Mine is the original one.

Land Rover PRC6574 (Bosch part # 0221 122 392-740) or Lucas DLB198 (but these have a reputation for being unreliable), should be around £50+VAT. But to be honest if it is the original coil it is very likely to be the correct spec, the worry is more that some previous owner has replaced it with something that is not quite right, but happens to work OK with the original leads. In the past I've used the wrong coil as a 'get you home' repair and the engine ran OK but spluttered a bit under full throttle.

>> Edited by GreenV8S on Sunday 19th February 17:10