Help with choosing spark plugs for V8 HO with LPG

I bought a Jeep.

I've only had it about 3 weeks and have been replacing and servicing bits here and there. It's a 2002 Grand Cherokee Overland V8 4.7L HO with injection LPG. It goes like a rocket on petrol, but when switching to gas I get a random infrequent misfire, nothing major. It's been suggested I try replacing the spark plugs.

So I pulled out one of the plugs today and found a warn over-gapped NGK ZFR6F-11G. Before replacing them I thought I'd check what it should be running and this is were I get lost. Very lost.


This site says to only use platinum plugs, but the plugs already in it aren't; http://www.wjjeeps.com/service/sparkplugs.htm#REMOVE47

I've been to a couple shops today to try and find an answer and they call said "ummmmm, hmmmmm".

So which plug do I need to use on the V8 HO when it runs on both petrol and gas?

Would love to hear what people out there are using.

[turbomart]

Ive got a 4.7L on lpg though its not a HO that doesnt really matter. I run the regular plugs with the gap reduced slightly. Never had an issue and they last for a long time anyway.
Dont forget to coat the threads in anti-sieze before fitting.

[WJBRUTE]

I don't have the HO either and I run LPG on standard plugs, no chang to gap and it runs excellent. The link you have posted gives you the champion plug number to suit the HO engine. Most auto parts will stock or be able to get these in for you. Cheers

Thanks guys, the only reason I hesitated getting the Mopar/Champion plug was the LPG. Everyone keeps telling me you need 'colder plug' for LPG.

I'd left it too late to buy new plug yesterday, so I pulled out and re-gapped all the current plugs a little smaller than spec. All of them a bit warn and had a massive gap. Took it for a good run afterwards and it didn't miss a beat. I'll still replace the plug, but I might just chuck the cheaper NGK plugs in. Will talk to a gas fitter first.

[Hammertone]

I'm in a very similar position, just bought a HO4.7 and i'm about to get LPG installed. I've been giving the car a full service and have looked into replacing the plugs.

Originally Posted by turbomart

Ive got a 4.7L on lpg though its not a HO that doesnt really matter.

From what Mopar say, it does matter. They're very specific about using only the Champion platinum in the HO and the general consensus on the web is that there's no substitute brand that can be used.

I've also been told that platinum is no good for LPG which leaves me in a pickle. My car is booked in at the Sprintgas R&D workshop on Monday. I'll ask them their opinion and try to get a good explanation about it and will report back with my findings.

I spoke to a few people about it and the general response was "if the current plugs work, stick with them and just gap them a little small then spec".

So I've ordered 8x NGK ZFR6F-11G, same as existing, and will just gap them down a bit smaller. 0.04" down to 0.038" or 0.036". It's possible the previous owner didn't even adjust the gap. I'm told it's pretty common thing people miss.

It's been running on the 'gas-friendly' NGK plugs since November 2011. But I'll will now check the condition of the plugs each service.

P.S. Congrats on the HO purchase, I've had my Overland for about a month and LOVE IT!! It's so much more capable and comfortable off-road then my 1999 Pajero was.

[bleetnblurt]

is not LPG a dry gas ? and is more explosive than unleaded ?