MAF & LPG

[Battler]

Does the MAF have anything to do with fuelling an LPG injected v8?

[bee utey]

If the LPG is a sequential vapour injected system then yes, it's following the petrol signals which rely on the MAF to be functioning perfectly. D1's and RRC's with simple mixer systems have no need for a MAF signal.

[Battler]

Thanks Bee Utey,

Yeah it's sequential injected.

Is it also the case as with say plugs and leads that any symptoms with the MAF is a lot worse on LPG than on petrol?

[bee utey]

Is it also the case as with say plugs and leads that any symptoms with the MAF is a lot worse on LPG than on petrol?
If a MAF is bad then I assume you'd notice it on petrol as well. LPG is much more difficult to run on if you are using stock plug gaps and have extra lean mixtures due to a tuning fault. Plug leads should never be the low resistance type favoured by boy racers. NGK leads for example have not played well with the last two injection systems I've had in for servicing. Magnecore and Bosch are better, so is OEM. Your plug gaps should be around 0.7mm to enable them to fire under load with lean mixtures too. Plugs should be at least one heat range colder than stock too, and correctly tightened. The number of vehicles I see coming here with finger tight plugs worries me sometimes about the skills of mechanics in general. ;)

Then there's the final interesting fault I've had a few instances of, where LPG injection systems have too short main delivery hoses and develop resonance inside them. That means that at particular combinations of load and revs standing waves form inside the hoses causing a loss of gas pressure at some injectors. I've successfully added another inline filter and a short length of extra hose and improved these vehicles. All good fun when you dabble in modern tech, hey. :)

[Pedro_The_Swift]

Your thoughts on genuine plugs for LPG?
and the difference from 4 - 4.6?
one grade colder will be a ten yes?

[Battler]

It runs great on petrol. On LPG it idles great and cruises alright. It will also run ok if you gently get up to speed. But if you push it just bit hard it bogs down with misfires on all cylinders. The plug leads are new Eagles for LPG and the plugs are new NGK 6BPR6ES at .8mm.

I'll pull the plugs tomorrow and reduce the gap to .7mm. I'll also check to see if the water flow is good.

Thanks for your help Bee Utey!

Cheers

[bee utey]

Your thoughts on genuine plugs for LPG?
and the difference from 4 - 4.6?
one grade colder will be a ten yes?

I assume the plug specs that you showed are for multi electrode ones, ie surface-air-gap. They are designed to do a very specific job, and that is to be self cleaning under very cold running conditions, as carbon fouling of the insulators is burned off quickly by the spark running across the carbon. They really have no other advantages. As they aren't adjustable I won't use them on LPG. Single point standard, platinum or iridium plugs are better suited to LPG. Heat range wise I'd run two heat ranges colder than those, ie N9YC or equivalent. That's apart from the fact that I haven't fitted a Champion plug in 20+ years as I've used almost all Bosch plugs for LPG.

Oh and there is too little difference between a 4.0 and a 4.6 to justify different plugs, it's the design of the heads that controls the heat flow, the compression ratio might be more of a factor.


It runs great on petrol. On LPG it idles great and cruises alright. It will also run ok if you gently get up to speed. But if you push it just bit hard it bogs down with misfires on all cylinders. The plug leads are new Eagles for LPG and the plugs are new NGK 6BPR6ES at .8mm.

I'll pull the plugs tomorrow and reduce the gap to .7mm. I'll also check to see if the water flow is good.

Thanks for your help Bee Utey!

Cheers

Every time I see Eagle leads on a rack the boxes scream " boy racer" at me, just my opinion. Check the resistance of the longest lead with a multi meter, if it's under 2000 ohms it's electrically like a too stiff spring and will have trouble performing under load. Good quality leads have a resistance of around 4000 ohms on the longer ones.

Your plugs should be OK at those settings.

[Battler]

I'd have to take the plenum off to do the ohms test as the boots on the Eagles are slightly longer and are bloody hard to get on. I did however compare the longest magnercore lead I took off to the same length Eagle lead and there was a significant difference. I can't remember the exact figures but it was something like 4 for the magnecore and 11 for the Eagle. The magnecores have done about 160k and about 12 years old.

But it is under load when it bogs down with misfires.

[Battler]

The MAF was the cause of all the trouble!