P38A 4.6 Thor Misfire

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R

robster_1981

Member
Posts
36
Yet another misfire thread!!
So I’ve got a steady misfire that is present at idle and all through the Rev Range. I’ve done limited testing so far, as I have been having a near meltdown of myself and the engine, as per my other thread :rolleyes::D

I’ve checked the plugs, and they seem to be half black and half brown/white, but all seem the same. The gap is just over 1mm, probably 1.2, so outside spec, but not by miles. Anyway, earlier on, I decided to have a go pulling a wire at a time while the engine was running to try and narrow it down, and when I pulled the leads on 1 and 2, the spark jumped out of the end of the lead onto the head, probably across a gap of 20mm or so. On the other leads, this did not happen. My question is, does that mean faulty insulation on the lead/s or is this expected?
I would happily just swap the leads, but as you all know, it’s not a 5 minute job :rolleyes:
 
Btw, car has 145000 miles. Has no service history, and the inside of some of the leads have evidence of slight corrosion, but nothing major. I am going to service the car fully, but want to make sure it’s nothing sinister before I dive in
 
On my Thor with LPG every time it ran "Lumpy" it was yet another HT lead beginning to fail. Or, a coil pack on its way out.
I got fed up with the "death by a thousand cuts" approach of the Indie and just told them to replace BOTH coil packs and all HT leads.
Problems solved. Could be different on yours.
 
Thanks for that! That’s obviously what I’m hoping for, I’ve just got that awful feeling that I’m going to end up throwing good money after bad! They don’t half get under your skin though these beasts!! :cool::eek:
 
I’m going to pull all the plugs tomorrow to double check them. I’m fairly sure they all looked pretty much the same, but it was a couple of weeks ago, so I need to do it again and wrote everything down!
 
If a coil pack is failing, you'll get two cylinders missing.

Corroded contacts and HT leads on the coil pack can happen.
 
Well I pulled the plugs tonight, and sure enough, number 6 was black and stank of petrol, and didn’t spark when held against the exhaust manifold. There were sparks arcing out from between the lead and the plug though, so could be a combination of the plug and lead.

However, I think someone has been butchering before me :rolleyes: the plug in cylinder 4 was tight all the way out, and tricky to get back in and tight all the way back in, so damaged thread me thinks :( I think someone is trying to tell me something!!!
 
Oh ffs, looking further, it seems somebody has fitted plugs for a GEMS engine (NGK PFR6N) I used a 5/8 socket to remove them, and the new plugs I’ve bought are a bigger size, although the same thread, so the leads won’t fit, so it seems it has the wrong leads too :rolleyes::eek:
 
Pics may help what you took out and put in..

Some need the little cap taken off the top of the plug.

J
 
79349614-C8-BC-4-A20-B909-79-F128281547.jpg
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Not sure if this image will work!
There is an obvious difference in size between the two, so not sure what (if any) difference this makes?
 
marjon said:
And your plug leads caps?

J
Click to expand...
Ahh sorry, they’re on the car, I’ll get a picture tomorrow. They are a pretty tight fit on the smaller plug though if that helps? I’m wondering if someone has just fitted plugs/leads from a Gems without realising?
 
kermit_rr said:
The top of the plug should be the same size regardless of socket size required, all plug leads are the same size?
Click to expand...

Thanks for that :cool:

Right, had a couple of hours this morning before going on nights, so I’ve changed the plugs. All bar one that had the dodgy thread, I dare’nt touch it! The misfire has all but gone and the difference in the power was big :cool:
Strangely, one of the plugs wouldn’t fit in cylinder 8 (nearest the ABS). It seemed to go in on a slightly different angle than the others, so it seems I have two dodgy plug holes :mad: unbelievably, in the set of 8 plugs I bought, one was the smaller socket size, so went in nicely :D

My decision now it’s running well is thus...spend more time and money getting it spot on, or cut my losses on what seems to be a car that everyone else has helped along to it’s current state :(
 
When you say they won't fit do you mean socket jams in plug hole or you have to change socket size I had to buy a thin wall snapon to get mine in without jamming or possibly cross thread...PO had put long reach in and last one snapped in head...
 
Yes, the socket jams against the head. I was going to get a thin walled socket, but there wasn’t much more than a couple of mil gap :confused: like I said, one of my new plugs (same part number) was the smaller type for some reason, so I got away with it this time. I might have to factor in a couple of thread inserts before the next service.

Oh, and yes, after hearing that V8 roaring away, I really REALLY want to keep it :D:cool:
 
robster_1981 said:
Yes, the socket jams against the head. I was going to get a thin walled socket, but there wasn’t much more than a couple of mil gap :confused: like I said, one of my new plugs (same part number) was the smaller type for some reason, so I got away with it this time. I might have to factor in a couple of thread inserts before the next service.

Oh, and yes, after hearing that V8 roaring away, I really REALLY want to keep it :D:cool:
Click to expand...

It's not the plug its the angle and the head casting...a standard plug removal socket fits the plug BUT as I found out jams in the plug recess my mechanic mate didn't believe me till he tried...pulled out his snapon and bingo out came the ones that jammed...when he was back in uk getting his tools serviced he bought me one...can't remember cost think it was 90€...will post pic of it tomorrow...
 
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