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 Post subject: Spark plug gap
PostPosted: Sun Dec 13, 2015 12:58 pm 
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Joined: Fri Nov 15, 2013 4:09 pm
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Gonna be changing the plugs in my 2011 Subaru outback soon. The car was converted in the summer and its got 30 k miles on it. It's got ngk in it at the mo and I've got a set of the equivalent denso iridium's to go in. I've seen talk on here of gapping the plugs at .8/.9 mm for Lpg, but the denso plugs are at .7 mm out of the box. Will these be ok to drop straight in ? The ngks were not gapped down on conversion, and the car runs lovely. Cheers, paul


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 Post subject: Re: Spark plug gap
PostPosted: Sun Dec 13, 2015 1:46 pm 
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Joined: Wed Jul 27, 2011 7:21 pm
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Gapped at .7 will be fine. They ain't so fussy about dwell. Unlike fords for example who run an insanely big plug gap.


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 Post subject: Re: Spark plug gap
PostPosted: Sun Dec 13, 2015 2:32 pm 
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Thanks tubbs!


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 Post subject: Re: Spark plug gap
PostPosted: Wed Dec 16, 2015 7:02 pm 
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Joined: Wed May 30, 2012 8:42 am
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is it NA or turbo?


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 Post subject: Re: Spark plug gap
PostPosted: Thu Dec 17, 2015 1:02 pm 
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 Post subject: Re: Spark plug gap
PostPosted: Fri Dec 18, 2015 1:28 am 
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I changed the plugs today on my 95 Jeep XJ Cherokee 4.0 and i've never seen such worn plugs! They were NGK V-Groove and it was impossible to tell where the groove had been, such was the wear on the central electrode!

Is this kind of wear normal on LPG-converted engines? I've only owned it since June and so far only done less than 2000 miles. However, there is no service history whatsoever with it, the mileage is a little on the high side (247k) but not out of the way for one of these.

PS - sorry if this is a bit of a hijack but it's hopefully a relevant question!

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 Post subject: Re: Spark plug gap
PostPosted: Fri Dec 18, 2015 12:33 pm 
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You'd have to know how long the plugs had been in for really Dave, if they're like that after being in 100K then they'd have done really well, if like that after 2k then they wouldn't have faired so well. Have to see how the new plugs go...

One of the aspects I was talking about on the recent thread about plugs... http://www.lpgforum.co.uk/viewtopic.php?f=33&t=13975
Fit el-cheapo £2 each nickel plugs or fit £6/£8 iridium plugs? Since it's easy to access and change plugs on your engine it might make sense to fit el-cheapos, particularly if your old plugs were el-cheapo and had given good results for 20000k.

Simon

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 Post subject: Re: Spark plug gap
PostPosted: Fri Dec 18, 2015 9:38 pm 
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Thanks Simon, that's a good point and it's odd you mention 100k miles as that's how long i would estimate they had been in! It's a wonder the thing ran at all! When i first got it i had to renew the dizzy cap, rotor arm and HT leads as it ran like a bag of spanners in a tumble dryer. I should have checked the plugs then but they looked (on the outside anyway) bright, shiny and new-ish. How wrong was i!!!! :oops:

Jeep recommend changing the plugs at 30k and the HT leads at 60k (with the rotor and dizzy cap) as service items. I know the previous owner had it 3+ years and i think maintenance for him just about stretched to adding oil when the engine rattled! Slight exagerration, he probably did actually use the dipstick every so often but you get the gist.

I can't find any MoT history for it before the MoT i had done (it had a valid certificate when i bought it, or at least it seemed valid) which is kind of worrying.

https://www.check-mot.service.gov.uk/

So maybe he did 60k in threee years and it was due new plugs when he bought it. That would make 90k. The plugs are fairly easy to change on it, yes, except 1 & 6 - 1 because the A/C compressor and radiator top hose are in the way and 6 because the bulkhead and a 3" diameter bit of loom is in the way.
Other than that it's a little fiddly on all 6 because they sit deep in a recess.

However i used my special home-made tool to make life easier. Basically an old #2 Pozidrive screwdriver (1/4" dia shaft) with a length of 1/4" bore fuel hose, about an inch longer than the blade pushed all the way over the blade. This gives about an inch of hose at the end to grip the nodule/nub/pip on the end of the plug and turn it until it's fairly near home then can be nipped up with the good ol' 1/2" drive ratchet - an absolute God-send on my Rover (Honda C27) V6s, especially on the rear bank! These are the plugs i used, not exactly el-cheapo make but el-cheapo price :

http://www.ebay.co.uk/itm/351166414610? ... EBIDX%3AIT

Other than the fact i like NGK plugs with Bosch being my second favourite, they were a like-for-like replacement, except the gaps weren't 3mm wide! The previous owner was a bus driver - he obviously drove his bus through the plug gaps! Not measured the gaps on the old ones yet but certainly approaching, if not bigger than 2mm.

So with that lengthy explanation of why i don't know how long they'd been in and a hypothetic working out of the probable life they had, i think they did extremely well. I feel a bit like Old Mr Grace - "You've all done very well!" :lol: :lol: :lol:

I think for now i'll go for checking them at 10k and renew when they show signs of failure. The tell-tale brown ring round the bottom of the insulator is usually one of the first (and worst!) signs of failure. All 6 of the old ones had that to some extent.

The "proper" NGK LPG plugs are something like £40 each and don't appear to last any longer than the "official" service interval.
Given the fact i bought the Jeep sort of on a whim (i'd always fancied one, it had LPG already so was probably cheap to run and i wanted something for the winter to protect my Rovers, one of which was hit twice last week :evil: :evil: :evil: by some unconcious incompetent congenital idiot who got their driving licence off a corn flake packet :evil: :evil: :evil: ) i don't want to go mad on £40 a pop plugs (£240 a set for a kick off, could almost buy another Jeep! :roll: :shock: :lol: ) but run it not on a shoestring but as economically as possible for any given circumstance.

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 Post subject: Re: Spark plug gap
PostPosted: Tue Feb 02, 2016 11:24 pm 
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My XJ is happy on standard NGKs and LPG :)


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 Post subject: Re: Spark plug gap
PostPosted: Wed Feb 03, 2016 12:23 am 
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Joined: Sun Aug 09, 2015 12:45 am
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Morat wrote:
My XJ is happy on standard NGKs and LPG :)


So is mine now after some tweaking to the cooling system and the LPG system - it had previously been icing the vap on tickover! Now it does what it's meant to and i'm not sure on economy - last tank returned a scary 11mpg! That said, it spent about 4 hours idling between tweaking the LPG system and warming it up while waiting for the hounds to return after walkies and other things. Reckon that used half the tank so in reality probably more like 22mpg but i'll check it properly this tank.

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 Post subject: Re: Spark plug gap
PostPosted: Thu Feb 04, 2016 1:11 pm 
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Joined: Wed Jul 27, 2011 7:21 pm
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Location: Midlands
As I'm sure I've said many times before. To get a proper idea of mpg. You need to fill up from the same pump. As the shut off pressures differ from pump to pump. For example. Mostly I fill up bang on 41 litres. The other day on the m25 I had run out of gas. Pulled in for a refil. And it only took 36 ?
When I got home. Filled up from empty from the usual pump. And it took the standard 41.


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 Post subject: Re: Spark plug gap
PostPosted: Fri Feb 05, 2016 12:36 pm 
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Tubbs wrote:
the shut off pressures differ from pump to pump
Agreed.

Though when I manage to put extra litres in than usual I have to wonder if pump calibration is correct.. In some cases I find I get no more mileage from the metered higher quantity (so think calibration is wrong), in other cases I do get more mileage (so think shut-off pressure is higher).

Depending on delivery rate, I expect pumps with higher shutoff pressure to slow towards the end of the fill from the point where a lower shutoff pressure pump would stop, as this is the point where the tank fill valve will be partially closed.

A number of factors will effect fill quantity, not least tank and gas temperature (in the tank and in the fill) - a tank that has just been run empty can take a little more gas than a tank that has been empty for some time as it will be cooler than atmosphere (lower tank pressure / tank cooling gas that enters tank)? I haven't done the maths but have noticed the effect.

Another thing with pumps, think I'm right in saying, they measure volume not mass - may get a bit more gas for the money when gas from forecourt pumps is cold (unless some pumps compensate for temperature?). In these ways temps can have a double whammy effect - More gas in less space combined with lower tank pressure?

I'd better lay off with the procrastinating now, got another Citroen petrol ECU to repair and a Subaru H6 engine to strip/repair... :( Tubbs, I know you're into Subaru's a bit.. Know where I can get a piston and cylinder head for an 06 3L H6?


Simon

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Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
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2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240


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