LPG tune issues after air cleaner replacement

[mark2]

I've just replaced the aircleaner element (fairly large Donaldson type) on my V8 running twin SU's.

I dont know how old the old element was (it was on the vehicle since I've had it) but I presume it was fairly restrictive as its been in there for years and was quite dirty. I have blown it out with air and emptied the dust trap periodically but never replaced it until now.

Prior to replacing it ran fine on lpg and petrol. It would idle easily on lpg when turned to a very lean setting on the idle mix. The mixer is an older Landi Renzo type, rated at 100kw, my engine probably puts out a bit more than that (4.3 stroker)

After replacing the air cleaner elment, it runs noticably better on petrol (more power, more responsive) but will not idle at all on lpg unless the idle mixture is set to almost the richest setting (fairly loud hiss with ignition on and engine off) and the cold start solenoid is on all the time. The high speed mixture screws also needed to be turned out a few turns to get rid of a flat spot just off idle. Adjusting the idle up wasnt really an option as it would effect the idle speed on petrol. Prior to richening the lpg mixture, the performance on lpg had not improved - I havent yet had a chance to roadtest the performance on lpg after this 'tuning' effort.

I tried it with the old element back in to eliminate the possiblity of a blocked converter due to dirty fuel - it was back to 'normal' and idled well on a very lean setting and with no need for the cold start solenoid to be activated.

With the new element in, placing a few fingers over the air inlet on the cleaner body to block it by about half 'solved' the problem - making it like run like it did with the old elment in, at a much leaner idle setting.

Does this sound like a problem with my converter, the setup or just point towards the fact that the tuning over the years may have been adjusted to compensate for a progressively more restricted element.

I'm concerned that my fuel consumption may go up a lot due to the much richer setting but am also thinking that the better air flow may compensate.

In any case, I'm amazed how much of a difference a new air cleaner element has made, both to the performance on petrol and the tune on lpg.

[scarry]

Lpg systms are extremely sensitive to airflow,inlet manifold air leaks,etc.I wouldnt fiddle with it,you may end upwith burnt valves:mad:,and or bad fuel economy.Sounds like it was tuned with a dirty element
Get a tune at a reputable gas place with the new air cleaner fitted,it will be money well spent.It will then run well until the air filter needs changing again.

You would be unlucky for the converter to be faulty,although ihad to have one replaced last week,they dont seem to last as long as they used to.

Hope the above helps

[PhilipA]

I am aware of this pressure drop issue. Apparently the mixer type LPG units need a pressure drop across the filter. This is the reason you cannot use K&N filters etc on LPG mixer ring type units. I understand it is also a NO NO to have a snorkel. It is to so with the relative atmospheric pressures enjoyed by the regulator in the engine bay and the gas ring in the inlet manifold.
Just have it retuned with a new element.
BTW its always a good idea if you are having any tune done to have a new air filter, fuel filter plugs etc etc.
Regards Philip A

[p38arover]

I understand it is also a NO NO to have a snorkel.

I ran a snorkel on my old mixer ring LPG system on the previous RR. No problems were encountered.

However, I don't remember if the snorkel was fitted before or after the LPG system.

[Freestyler]

I have my 110 running on gas and runs great. The best thing I did was to fit a oxygen sensor in one of the extractors close to the engine. I have built up a kit from jaycar that the tells you the fuel mixture ( about 15.7:1 for LPG ). You can buy gauges already made up and calibrated if you don't have the experties to build one. Another secret is is there is normally a balance pipe from the vacuum side of the carbies to the converter which then puts bias on the converter. Gas converters run on diaphrams and are very sensitive to vacuum changes, if this pipe is connected then as you filter slowly blocks the balance pipe will adjust the mixture as required. With this pipe connected they run even better with a snorkel. It also doesn't matter what type of air filter you fit. I have a mate who is running gas on a landie with K&N pod filters and runs great. I'm running an impco gas carbie off the side of an EFI manifold on a Leyland Terrier 4.4 it runs realy well and is cheaper to run than the Isuzu but alot more fun. I am getting the gas injection fitted to my truck early next year.
Tim

[mark2]

Thanks for the replies.
I will have to look into this balance pipe thing - none fitted at present and looks like there is provision on the convertor for one.

Took it for a drive this morning - runs a lot better on lpg but smells rich at idle - previously you couldnt even smell the exhaust.

[mark2]

Just hooked up a balance pipe between engine vacuum and mixer diapraghm.

It idles (still needs a rich mixture) but engine will not rev at all if any vacuum is applied to the diapraghm.

Looks like this may not be an option for me.:(

[rovercare]

Balance pipe goes from the breather on the convertor, to a closeish point to the start of the intake, i.e. the base of the snorkel where it comes in the engine bay, to accomodate for the difference in the vacuum created

[mark2]

Balance pipe goes from the breather on the convertor, to a closeish point to the start of the intake, i.e. the base of the snorkel where it comes in the engine bay, to accomodate for the difference in the vacuum created

OK. I dont have a snorkel so am I right in saying that the inlet piping between the throttle plate and the clean side of the air cleaner (its a fairly long pipe on my setup) will have lower pressure than than the rest of the engine bay due to pressure drop accross the air cleaner?

[350RRC]

Balance tube on mine goes from the air cleaner housing to the breather on the convertor. I would think that from from anywhere on the 'clean side' of the air cleaner would be fine.

DL

[rovercare]

OK. I dont have a snorkel so am I right in saying that the inlet piping between the throttle plate and the clean side of the air cleaner (its a fairly long pipe on my setup) will have lower pressure than than the rest of the engine bay due to pressure drop accross the air cleaner?

Near enough, stick it in and see what happens;)