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Thread: P38 on LPG - plugs!

  1. #1
    Join Date
    Feb 2010
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    P38 on LPG - plugs!

    Hey guys

    I've had a read, so from what I gather when getting plugs for a dual fuel engine, the general consensus is to go up one heat range and drop the gap by 1 - 2mm.

    I've pulled out one of the current plugs (champion RC10PYP4) and th tip is worn and to be honest it looks like the engine may have been running lean to me (not sure why!!)? Should I go up another heat range or is that chalky and worn tip a common thing on gas engines?

    I've had this particular P38 for just over a year, and owned many before, but I'm new to gas.

    EDIT: it's a High Compression 4.6

    Cheers
    Keithy

    Green 2000 P38 Range Rover HSE - Gone
    Blue 1999 P38 Range Rover HSE - Gone

    Silver 2002 P38 Range Rover HSE - Sequential LPG, BCDC Charger, TPMS, Rear Locker, Wheel Carrier, Bullbar & Spotlights, General Grabber AT2's, Too Much to Mention!

  2. #2
    Join Date
    Apr 2009
    Location
    Crafers West South Australia
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    Your research results look a bit odd to me. Lower heat range, not higher, ie one step colder. Different plug manufacturers use different number ranges that go in different ways. In Champion you'd want a 9, NGK a 6 and Bosch a 7. "Brisk" make a LPG specific plug that seems to be good, I've fitted a couple of sets of DR15YS and they're running well. Available here.

    Gaps should be around 0.7mm to 0.8mm for LPG. And stock standard OEM style plug leads are best, Roverlord sells them. Racing type leads have too little electrical damping and resonances can cause all sorts of grief.

    If you don't read the newspaper, you're uninformed. If you read the newspaper, you're mis-informed.
    Mark Twain

  3. #3
    Join Date
    Feb 2010
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    Townsville, QLD
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    You're right, I went to the 6 in NGK (colder plug, or up in heat range). It's gapped at 1.1mm like standard. First impression on petrol was instantly noticeable better idle and low rpm response. I'm filling up the gas tomorrow and heading off on a big drive, so will see!

    If it's off on gas, I'll re-gap the plugs when I get home to about 0.9mm and go from there. They are platinum plugs. The old champions were all very worn!

    Cheers
    Keithy

    Green 2000 P38 Range Rover HSE - Gone
    Blue 1999 P38 Range Rover HSE - Gone

    Silver 2002 P38 Range Rover HSE - Sequential LPG, BCDC Charger, TPMS, Rear Locker, Wheel Carrier, Bullbar & Spotlights, General Grabber AT2's, Too Much to Mention!

  4. #4
    Join Date
    Feb 2010
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    Townsville, QLD
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    First big drive on gas, it drove ok on gas, but the "hesitation" that prompted me to check and replace the plugs is still there. It feels as though there is a slight miss every now and then on steady throttle at low to cruise rpm. Under load while above 2500rpm it's not noticeable.

    By changing the spark plugs I've gained an extra 25km (nearly 10%) in fuel range on LPG. My best tank range was around 300km prior (cruising at 100km/h, steady). Just yesterday I got 325km and I was moving, and I'm heavier now too (probably not far off GVM actually).

    I'll try one thing before I go chasing anything else.

    I'll change my LPG supplier. I've only noticed it recently, and funny enough I changed where I buy LPG from at the same time. It's 30c/litre cheaper than everywhere in town, hence the change - both places were Coles Express servos, but one was 89.9cpl, about the standard price here in Townsville, the one I'm going to now is 59.9cpl. LPG quality can't vary that much surely?

    It doesn't "hesitate" or "miss" on petrol. Although it doesn't do it often or constantly on gas, maybe once per minute, it's noticeable to me (but not to my passengers), and it feels down on power a little on gas as well. Goes like a rocket on 95 octane petrol though ;-)

    Cheers
    Keithy

    Green 2000 P38 Range Rover HSE - Gone
    Blue 1999 P38 Range Rover HSE - Gone

    Silver 2002 P38 Range Rover HSE - Sequential LPG, BCDC Charger, TPMS, Rear Locker, Wheel Carrier, Bullbar & Spotlights, General Grabber AT2's, Too Much to Mention!

  5. #5
    Join Date
    Apr 2009
    Location
    Crafers West South Australia
    Posts
    9,784
    Quote Originally Posted by Keithy P38 View Post
    First big drive on gas, it drove ok on gas, but the "hesitation" that prompted me to check and replace the plugs is still there. It feels as though there is a slight miss every now and then on steady throttle at low to cruise rpm. Under load while above 2500rpm it's not noticeable.
    This is the point at which I once again have to point out that LPG and petrol have different ignition requirements and anything other than OEM leads will have resonant effects at particular speeds and loads. As petrol requires about 30% less voltage to form a spark it rarely appears on that fuel.

    Anyway, by all means try your different fuel supplier, while there definitely is a big difference in LPG mixes across the world, I'd expect a smallish city to be supplied from the one primary source. Then tell me what sort of ignition leads you're running. I have this battle of words with virtually every vehicle owner on coil pack ignition and LPG. Most aftermarket leads are unsuitable for LPG even if the box says "LPG compatible" on it. OEM is best. Pretty blue leads from a certain manufacturer are the worst.

    If you don't read the newspaper, you're uninformed. If you read the newspaper, you're mis-informed.
    Mark Twain

  6. #6
    Join Date
    Feb 2010
    Location
    Townsville, QLD
    Posts
    2,444
    Thanks for the reply!

    My ignition leads are standard issue!

    Cheers
    Keithy

    Green 2000 P38 Range Rover HSE - Gone
    Blue 1999 P38 Range Rover HSE - Gone

    Silver 2002 P38 Range Rover HSE - Sequential LPG, BCDC Charger, TPMS, Rear Locker, Wheel Carrier, Bullbar & Spotlights, General Grabber AT2's, Too Much to Mention!

  7. #7
    Join Date
    Feb 2010
    Location
    Townsville, QLD
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    I guess I should wrap this thread up given it was quite some time ago.

    In the end the miss was still present. I plugged the nanocom in and it showed cylinder #4 was almost constantly missfiring, a few others on occasion.

    I replaced both coil packs (Thor P38), issue sorted. I used Britpart coils. No issues.

    Recently drenched my air filter after taking on water from a massive storm while driving, welcome back light missfire/lack of power. I'll have to sort a way to stop the snorkel from taking water in during heavy rain. For now I've put a sock on the head. I'm leaning towards MAF for my issue, however it seems to have improved slightly after inspecting and re-adjusting the intake pipework - where it mates to the throttle body was on the **** a little. When I took on the water the engine coughed and spluttered when given a little berries, but I managed to drain the water from the filter and limp it the 300km home that night. I'll give it more attention when I get the chance! The miss is on both fuel types, and under load only, seems ok at cruise.

    Cheers
    Keithy

    Green 2000 P38 Range Rover HSE - Gone
    Blue 1999 P38 Range Rover HSE - Gone

    Silver 2002 P38 Range Rover HSE - Sequential LPG, BCDC Charger, TPMS, Rear Locker, Wheel Carrier, Bullbar & Spotlights, General Grabber AT2's, Too Much to Mention!

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