What kind of maintenance is required

[Keithy P38]

Hi guys

I've got a sequential gas system on my P38, it's the first time I've ever dabbled in the gas game (and I bought it with the gas fitted in May this year).

Just wondering if it ever needs attention? Perhaps the occasional tune? It's running very well albeit a slightly rough idle on either petrol or gas compared to my other P38 which could balance a 50c piece while idling. Perhaps the P.O. had a camshaft installed to suit the gas conversion?

I'm pretty happy with it so far, getting about 20L/100km on gas around town and 16.5 to 17L/100km on petrol.

Cheers
Keithy

[bee utey]

The most important maintenance is to replace the vapour filter/s between the converter and the injectors. In some markets the gas is so dirty that replacement every 20K is recommended, in SA I do them around 60-80K and have few problems. The price of filters can vary wildly between suppliers, from around $20 to $100+ for factory genuine GMH or Ford. Ebay has a range of filters which may or may not suit your system. Many filters have replaceable inner cartridges, some of which are interchangeable across a surprising range of filter brands.

Next most important is to occasionally check the screws holding your converter together for tightness, as the rubber components relax water and gas leaks might occur. Check any exposed rubber edges for perishing, if the bit you can feel is crumbling then there's a good chance that the internal sections are getting old and could do with replacement from a rebuild kit.

After running on gas, turn off the engine and disconnect any vacuum hose off the converter. Any gas leaking quietly into the engine will make restarting harder and is a sign of rebuild time.

Plugging it into a computer occasionally will be useful if the wielder of the software is skilled in its use. Untrained fitters can do more damage than good. I recently had an old fella bring his BF falcon ute in for tuning. I had a good look and reset a number of basic parameters and then did a tune, the difference was amazing. The guy simply had never experienced it in top condition and thought it was just normal except for a few changeover quibbles.As for your rough idle, I'd suggest you do a compression test and look at the plugs, you may have a bit of carbon build up from a slightly dodgy valve stem seal. Nothing to worry about, just it's worth checking.

[p38arover]

The most important maintenance is to replace the vapour filter/s between the converter and the injectors. In some markets the gas is so dirty that replacement every 20K is recommended, in SA I do them around 60-80K and have few problems. The price of filters can vary wildly between suppliers, from around $20 to $100+ for factory genuine GMH or Ford. Ebay has a range of filters which may or may not suit your system. Many filters have replaceable inner cartridges, some of which are interchangeable across a surprising range of filter brands.

Jilden, what are the symptoms of dirty filters? Mine (one for each bank) have never been changed in the 8 years mine has been on injected gas (not sure of km, I'd need to boot up another computer to find out). I have pulled them apart and they looked pretty clean and I could blow through them easily.

I had a look on eBay and some filters are damn pricey. I'll pull them out to see if I can identify them. I might need to take a pic and ask you.

[bee utey]

Dirty filters tend to let more semi liquid contaminants through, these may end up causing the injectors to stick and wear abnormally. A larger capacity filter seems to hold these back better than a small sized one. You'll know when it's too late for your filter change, the injectors may already be stuffed when you feel a change in running.

[p38arover]

Ok, thanks Jilden. Mine is idling very roughly on LPG but seems to run ok once the revs come up. However, fuel consumption is now quite high, e.g., 26 l/100km on the highway. That's much higher than when running on petrol (13-16 l/100km).

The next question is - how do worn injectors affect running?

[bee utey]

A new injector contains a steel plunger with a rubber seat that travels a precise distance (around 0.5mm) in a very precise time when the current regime is applied by the LPG ECU. The opening and closing times are a significant fraction of the total time the injector is open, particularly at idle. So any wear that increases the friction of the plunger in its bore will change the opening time and affect the mixture delivery. At WOT the injector open times are typically 5-10x that of idle time so a worn injector will affect the idle mixtures more than drive mixtures.

There are also the effects of leaking injectors due to worn seats that add extra fuel and this becomes more noticeable at idle too. Some injectors have a rubber end buffer to quieten them and if these wear out or break the travel increases and the mixture increases. So unless your worn injectors are repairable with rebuild kits that replace all affected components, they're often bin jobs. I've had some success with cleaning injectors by back flushing them with solvents but worn out ones go straight into the rubbish.

Unfortunately LPG injectors are expensive in Australia (around $600-$1200 for a typical V8 set) but I've recently bought new ones from the UK for around $200 a set that seem to be good value and have a 2 year warranty too.