Spark plugs and lead quiry?

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biggerbinns

Member
Posts
46
Hello everyone.

Recently changed the plugs on my 4.6 p38 as I was getting a slight misfire from cold which cleared fairly quickly but happened mainly when it had been stood for a couple of days.

It looked as though the plugs had been in their for some time but I am still getting a bit of a misfire when cold.

Firstly, what are the reccomended plug gaps for a 4.6 and do they suffer if their out a bit?

Secondly, I was going to replace the leads to see if the problem could be sorted sooner with their replacement.
Had a very obnoxious guy in a Landrover specialist say that only Landrover genuine part leads would do (funny enough thats all he had to sell).
Can anyone reccomend some other leads of reasonable quality that come in a lot cheaper?

On another note, all the problems I had with the p38 losing it's key code and getting flat batteries seems to have been sorted with the disconnection of the reciever.
I was fortunate to have Mtech available to look over the Becm again to check for any further problems but all seemed good so fingers crossed.

Cheers for now. :)
 
biggerbinns said:
Hello everyone.

Recently changed the plugs on my 4.6 p38 as I was getting a slight misfire from cold which cleared fairly quickly but happened mainly when it had been stood for a couple of days.

It looked as though the plugs had been in their for some time but I am still getting a bit of a misfire when cold.

Firstly, what are the reccomended plug gaps for a 4.6 and do they suffer if their out a bit?

Secondly, I was going to replace the leads to see if the problem could be sorted sooner with their replacement.
Had a very obnoxious guy in a Landrover specialist say that only Landrover genuine part leads would do (funny enough thats all he had to sell).
Can anyone reccomend some other leads of reasonable quality that come in a lot cheaper?

On another note, all the problems I had with the p38 losing it's key code and getting flat batteries seems to have been sorted with the disconnection of the reciever.
I was fortunate to have Mtech available to look over the Becm again to check for any further problems but all seemed good so fingers crossed.

Cheers for now. :)
Click to expand...

Most likely to be leads fouling each other, it is critical they are installed so as to not touch each other and keep them away from as much of the metal components as possible by use of lead spacers correctly installed.:)
 
Misfiring from cold but clearing quickly can also be a symptom of a failing head-gasket. Moisture gets into the cylinder & dampens the plug but the combustion chamber heat rapidly dries it out once the engine is up & running. Sus. out which cyl. is missing & the when the car has been standing (& stone cold) look for signs of water on the relevent plug. Hope I'm wrong & it is just an ignition fault.
 
Cheers for that, I will have a look for the failing cylinder and see what needs to be done.

Any clue on the plug gap whilst I am looking into it?

Also any reccomendation on leads apart from genuine ones?

Cheers.

:)
 
0.8 fer gap i think, some people swear by magnecor leads... they aint cheap leads but neither is owning a 4.6
 
Ideal.
I have heard others mention those leads so I may try with them first dependant on what spare time I have.

Thanks again
 
Do yourself a big favour, don't go pulling anything apart or racing off to get things tested until you carry out this test.

To be done at night where there is no light, total darkness is best.
Preferably while your engine is cold as this is when you are having the trouble.

Lift your bonnet then start your enging and look around all of the spark plug leads and coil leads for blue glow or sparking around the leads. if any exists this will be your problem.

As for the leads, it does not seem to matter what quality they are if they are not installed exactly as per the specifications they will foul each other.

Many of the workshop manuals (rave does) have a schematic drawing of the dizzy cap and lead layout, it is imperative that you install and run each lead as it is depicted in the drawing and this includes them being installed into their lead support spacers. Ank keep them from touching anything metal.

Just go and do it, you may be surprised.
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Would do what ssmn says,
But you'll have to wait to at least 4.30pm until it gets really dark :D;)

I had a lil trouble before relating to electrics and done the night test. Turns out one of the leads to the solenoid was shorting against the new exhaust fitted. Prob solved :):)
 
Assuming plugs and leads have been changed, listen to the engine with the bonnet up when started from cold. Do you heard a slight 'chuffing' noise. Last 4.6 I had in that had a 'mis-fire' was in fact an inlet gasket leak.
 
ssmn1234 said:
Do yourself a big favour, don't go pulling anything apart or racing off to get things tested until you carry out this test.

To be done at night where there is no light, total darkness is best.
Preferably while your engine is cold as this is when you are having the trouble.

Lift your bonnet then start your enging and look around all of the spark plug leads and coil leads for blue glow or sparking around the leads. if any exists this will be your problem.

As for the leads, it does not seem to matter what quality they are if they are not installed exactly as per the specifications they will foul each other.

Many of the workshop manuals (rave does) have a schematic drawing of the dizzy cap and lead layout, it is imperative that you install and run each lead as it is depicted in the drawing and this includes them being installed into their lead support spacers. Ank keep them from touching anything metal.

Just go and do it, you may be surprised.
icon7.gif
icon7.gif
Click to expand...

I KNOW THIS WELL , FUNNY THOUGH HOW THIS HAS NEVER APPLIED ON ANY OTHER CAR I HAVE EVER HAD, IN ONES WTH LONGER LEADS, WHY IS THIS? (oops sorry I had caps lock on lol)
 
Recently changed my coil ( thor engine), then the leads to Magnecore and then the plugs..... at first i did not set the gap on the plugs, put them straight in from the box, it ran OK just like it did previously, however took them backout and checked the GAP it was 0.75, the recommended for the 4.6 is 0.95 - 1.05, so I set mine to 1.00, instantly better and the MPG went up from 18 to 22 MPG on long runs.....so yes it will make a difference.......

However it is still running slightly rough , so I will check out the positioning of the leads tonight before I leave work and see if it makes a difference on the way home......

will let you all know later....

P.s. Forgot to mention this is on LPG
 
Right, checked under the bonnet when it got dark and found I had my own mini firwork display going on due to sparks from the leads pinging off here their and every where.

Going to get some leads off ebay, Lucas leads, £25 and look fine for what i need.

Cheers for the tip.
 
I can recommend magnecor blue leads, dont go down the cheap option. Ive recently put these on my p38, much smoother and did make a slight increase in economy.
 
i would also go along with jonny427 and have been running on magnecor blue for about 6 months and you will notice the differance in your car.most definatley do not go down the cheapo lead road..good luck
 
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