Plug gaps, HT leads and lpg....

Plug gaps, HT leads and lpg....

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2blackhats

Original Poster:

446 posts

156 months

Monday 20th September 2010
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As some of you know I run lpg on my Ro 6 litre vxr and although it drives fine - I've never had any actual problems, I frequently get the check engine light thing. Various attempts have been made to remedy it, so far without success.(NB it only does this on gas never on petrol)
I recently came across this info in the FAQ's of a lpg installers site and I'm wondering if it might be the answer to my issue, I will start by re-gapping th plugs as they suggestand if that doesn't help maybe replace the HT leads, but any comments and thoughts on this would be most welcome. Here's what they say....

'Misfiring', when reported in OBD terms, means something quite diffrerent to a failure to fire. It means that the cylinder the trouble code relates to has fired, but the result of the firing (combustion) was out of parameter. This is why we don't feel a reported misfire when driving. The cylinder involved hasn't failed to fire, although it may be firing out of parameter because the resulting combustion is incorrect.
The number 1 and 2 causes of true misfiring ( in the OBD sense as described above) are spark plugs and coils. This happens because incorrect ignition will often leave some fuel unburnt and the engine management system will see that cylinder as running too rich as a result. If this isn't the case, a reported misfire in OBD terms can also mean that the fuelling of the cylinder is out of parameter which could be due to incorrect amounts of fuel being injected. A cylinder that is running with fuel too rich or too lean is Misfiring.
The path to cure will be a process of elimination, but it is always best to begin with the cheapest and easiest things, the spark plugs.
'Gas/air mix is much harder to ignite than a petrol air mix.
As a result, the voltages reached within the HT components (just before the spark occurs) can become far higher when running on gas as opposed on petrol, typically 12-15 Kv's on petrol and up to 30 - 35 Kv's on gas.
This means that the insulation of HT components is at least twice as likely to break down when running on gas, often resulting in tracking, leakage, misfiring etc.
This is the point where we often hear the statement 'It doesn't misfire/backfire/judder/stall on petrol'.
In the light of the above, it wouldn't.
To help reduce the potential for problems when running on gas, set plug gaps to .030" (.75mm).'
To show this effect in action you need to see what a reduction in plug gaps does on a 'scope.
Too wide = High voltage.
Reduce gap = Reduced voltage.
No one says that reducing the plug gap will dramatically remedy backfiring, but it will certainly reduce the risk.
Another factor often missed is that once HT leads etc. have been exposed to higher than normal voltages for some time they will have had their insulation damaged to the extent that a later reduction in plug gaps cannot stop the leakage. Misfiring and the ensuing backfire will still occur. 'Tracking' or 'Shorting' is, after all, mini lightning. You'd expect something to be damaged by this if only by the inherent erosion. Such damage makes just the place where damp likes to dwell, making things even worse.
If that is the case, only replacement of the damaged components will cure the problem (if the backfiring is really due to ignition faults in the first instance).

stevieturbo

14,787 posts

202 months

Monday 20th September 2010
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The ignition system on an LS1 is very powerful, and you have no need to mess with any of it for gas.
And it runs circa 50-60kv, nowhere near the low numbers you mention.

Standard parts can easily handle 20psi boost, so firing a little LPG mixture will pose no problem at all, even if the plugs had 100k on them.

I'd be more inclined to check the LPG system is actually providing sensible mixtures in order to be ignited.

What sort of AFR's is it running ?

Edited by stevieturbo on Monday 20th September 20:02

2blackhats

Original Poster:

446 posts

156 months

Monday 11th October 2010
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Well, I tried altering the plug gap as detailed above. Result: MASSIVE IMPROVEMENT. Check Engine light warnings have all dried up. Car drives perfectly on gas or petrol with no issues. It DOES make a HUGE difference. I've now ordered a set or Irridium plugs and Magnecor KV85 leads to make sure I'm getting the zappiest spark possible.
TBH I'm fair dancing a jig over this discovery as the engine check has been driving me nuts. Over the last year I've remapped the car, gas fuel trims have been adjusted a million times all to no avail. Finally regap the plugs and problem solved.
So if you have lpg and have this issue, give it a try!

ringram

14,695 posts

203 months

Monday 11th October 2010
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As discussed before Iridium is one of the worst metal conductors in the world, copper is way better.
Its only benefit is longevity.

Glyn84

661 posts

135 months

Tuesday 12th October 2010
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Interesting read this, thanks for sharing your findings! I've got similar issues myself, and recently developed a misfire on LPG and was advised by an installer to check the plugs and replace them with decent ones. I've got a part number from the NGK American website of IZTR5B11 for the Laser Iridium plugs. When you fitted yours did you go with a cooler plug or just stay standard?

2blackhats

Original Poster:

446 posts

156 months

Tuesday 12th October 2010
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I've actually yet to replace the plugs, but have a set of NGK irridiums ITR6F13 on order. I also have the Magnacore leads on order. All I've done is regap the bog standard plugs as specified and I've already had a big improvement. I may have to try a number of combinations until I get the best result, but at last I know I'm barking up the right tree with the ignition components.
I'll report further as my experiments progress.
NB: I'm not suggesting this will fix ALL lpg engine light issues, but on my car it certainly seems to be the culprit and if you have similar issues its worth a try. Certainly workling for me.

wallsjay

408 posts

153 months

Tuesday 12th October 2010
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who did your lpg conversion and would you recomend them ?

djwilk

1,652 posts

124 months

Tuesday 12th October 2010
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As far as I remember same as the ones that did it on mine.
Recommend? NO. Mainly for the bad customer service after they've taken the money...

2blackhats

Original Poster:

446 posts

156 months

Tuesday 12th October 2010
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wallsjay said:
who did your lpg conversion and would you recomend them ?


Capital Autogas did the work. Would I recomend them....Tricky. The install is neat and they were competitive priece wise. My experience was that they tried extremely hard to fix my check engine light issues. They had the car back on numerous occassions. However, they ultimately failed and never once were ignition components ever even considered as a possible cause of the trouble. Only my own researches and the random stumbling over the article above has set me on the right track.
However, they have since converted several other LS series V8's with varying degrees of success and so have a fair bit of experience with them. Mine was their first.
So in conclusion, they're ok, but you might do better and also worse.... If someone knows an LPGA installer whos a whizz with LS V8's I'd be very pleased to hear about them too.

Glyn84

661 posts

135 months

Wednesday 13th October 2010
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I called the NGK technical people today and they knew all about Monaros and VXR8s which surprised me, but was very reassuring. He was explaining various things to me and I quizzed him on the LS2 engine running with LPG. He said the plugs to go for are the IZTR5B11 laser iridium ones with an extended tip. He also mentioned they have some new plugs out called LPG5 which are better suited to LPG and will last longer, although how long is a case of how long is a piece of string. 60,000 miles was a figure mentioned for a normal car but will obviously be less on a high performance engine.

The LPG5 plugs are also gapped differently and just happen to be very close to 0.3" from the factory which is the same as the 0.3" you found worked really well. I've ordered myself a set from Opie Oils so will post how they work.

Please keep posting your findings 2blackhats as it makes for interesting reading smile As a matter of interest, which LPG equipment are you running?

Edited by Glyn84 on Friday 15th October 20:31

Glyn84

661 posts

135 months

Monday 18th October 2010
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Installed my NGK LPG5 plugs at the weekend. It took me about 2 hours, but then again spanners scare me. The left side of the block is fairly staight forward and took just over 30 mins, but make sure there are no minors around when you're doing the right side. Access is tight, you will scrape your nuckles, and you WILL swear smile

The plugs I pulled out were NGK V-Power approx 10,000 miles old. These aren't OEM quality plugs, but the chepest of the regular plugs. Initial impressions were the engine is significantly smoother and the throttle response is noticeably sharper too on petrol. On LPG things are even better than before so I would highly recommend them.

At £14.50 a plug (when buying 2x packs of 4) they aren't cheap, but worth it in my opinion.

http://www.opieoils.co.uk/p-64073-ngk-spark-plug-l...

Edited by Glyn84 on Monday 18th October 14:20

2blackhats

Original Poster:

446 posts

156 months

Monday 18th October 2010
quotequote all
Very interesting Glynn. Are you still getting the check engine light on lpg, or has it cured it?
This saturday I installed Magnecore 8.5mm HT leads and the car deffo runs smoother. I've still got the original plugs regapped as described. I'm getting the check engine light, but it seems pretty random. Some days I don't get it at all, other days I'll get several check engine signals.(Before messing around with the plugs I got check engine every day).
Regardless of signals the car always runs smoothly.The next step for me will be to install the irridium plugs and see if I get any further improvement...and yes you're right about access to the rear of the right hand bank of cylinders!

Glyn84

661 posts

135 months

Tuesday 19th October 2010
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I'm still getting the check engine light coming up once in a while, but it's hard to tell if it's less frequent or not. As you say some days it doesn't come on at all, where others it constantly does it. I've only had the new plugs in 2 days so it's too early to say if it's any better or not, but by the end of the week I'll have a better idea.

Scottcav2000

72 posts

81 months

Tuesday 17th December 2013
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Hi guys, just stumbled upon this trying to rectify a very slight rough idle on my LPG. I've had it checked over by an LPG guy and all is well but has recommended changing the plugs, so I've changed with some Bosch plug sand it's still the same.

I'm going to try and reduce the gap as you mentioned, but the standard gap on these plugs is 1.5mm so dropping to 0.75 seems a lot of gap change. Were yours at 1.5 before you adjusted? Have you had any issues with it since you done this?

Thanks

Glyn84

661 posts

135 months

Tuesday 17th December 2013
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I haven't adjusted any plug gaps because the NGK LPG plugs are iridium, so you can't adjust them. They have a gap of 1.1mm. They've been in for 25,000 miles and still working well.

SteveMJ

919 posts

151 months

Tuesday 17th December 2013
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I run my VXR8 on LPG, coming up to a total of 50k miles, ~40k since LPG conversion.

I had a few 'engine warnings' early on , but nothing now.

I can't tell the difference in the car's performance (except 14 sec run at Santa Pod insead of 13.5 on petrol) but I do notice a differenc at the fule station's check out!!

Stevbe

snowwolf

11,500 posts

130 months

Tuesday 17th December 2013
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Copper is good like ringram mentioned above, but wear pretty quick and need changing every 10k max , what I have found is when changing plugs it is very easy to damage the HT leads which I think where most problems occur, they may look perfect but def not.

IMO I would go for iridium from monkfish or other reputable company, eBay is full of fake plugs but I am sure there are many good sellers on eBay, if your leads are over 25k miles change them or wait till you change the plugs and do them all at same time, job done for 50k miles but avoid touching the leads until the next change,.

If you change the leads to after market leads make sure none rub against anything, on the R8 the rear right lead will rub, best to cover where it rubs with silicone hose and cable ties.