Outer Limits 4x4 Board

Hi All,
Almost a year ago, I installed an lpg kit in my Disco'. I got it certified afterwards to make sure it was all fitted OK which it was. I had installed a 70l tank with an impco system using the 425 mixer. I still have petrol as well.

Initially, I was getting 300k's to the tank on LPG but in the last couple of months it has dropped to 250 and the last tank only gave me 225k's.

I had noticed that raginRover and some of you others had been talking in the past about different plugs ( NGK BP6RES .7mm gap? ), and advancing the timing up to 12btd.

I made a call to Impco and they are telling me that the 425 isn't really suited to the Disco' and that I should be using the 225 Impco mixer. To me I don't know if this is right as it still would not explain the drop in mileage.

Are there any of you using the 225 mixer and what are your results?

Or, is it perhaps time to swap out plugs, perhaps a new dizzy cap and new leads instead?

I figure theres got to be a reason. Wondering also whether I can "by ear" manually tune the idle mixture on the 425 myself or whether I have no option but to go and get it Dyno'ed.

TIA.
Cheers, Pete'

The 425 may be too big and supplying too much gas, the 225 or 200 model mixer is used on 4.2 patrols and 4.5 cruisers so will be up to the job.
Its almost impossible to tune gas by ear as gas will run smoothly with varying mixtues, its only in the long run where you will see problems ocurr that can be traced back to lean mixtures.

The 425 is definitely too big, that was my first thought as soon as I read it, before I saw what Impco said to you. Somewhere in the mid 200s is about the norm for Rover V8's, including 4.6's.

What my guess would be, and it is a bit of a guess, but as your plugs have worn down, the richness of your mix has started to become more and more of a problem, because your plugs are not capable of burning the mix efficiently. That is one theory which could perhaps explain your mileage drop, but there is probably holes in it somewhere.

There is, however, one other thing that can happen. For some reason (can't remember what it is exactly), converters seem to get richer and richer over time, to such a point when you adjust the mixture at idle, you actually can't lean it off to the correct spec, at which point you need to install a lean idle shim inside the converter (very thin plastic ring) to allow the mixture to be set lean enough.

Another possibility is wax in the converter - there is an amount of wax in the gas, which tends to build up over time inside the converter. If you carefully pull the side plate off the converter, and look inside, you should be able to see any wax deposits.

Spark plugs. Yes, this does change on a gas car, and you are correct - NGK BP6ES with a .7mm gap is what most gas rovers run.

As far as swapping your leads + dizzy cap - I'd hold off on that. If you had a major problem here, you should be able to hear and feel a misfire. Not saying that its not contributing, but its unlikely to be the overall problem.

My first step would be to take out the plugs, have a bit of a look at their condition, then chuck them and fit the NGKs. Go through a tank of gas, and see if its any better. If that doesn't make any difference, I'd recommend taking it to a workshop with experience in gas, one with a scope and an exhaust gas analiser.

Its not neccesary to take it to a dyno, since I'm assuming its not a computer controlled system. Obviously it wouldn't hurt, but dyno time is expensive.

My belief would be, if the plugs don't fix it, or only improve it halfway to where it used to be, the problem lies somewhere in the tune or condition of your converter. The size of the mixer probably doesn't help, and perhaps a smaller mixer, combined with a good tune, might even push your economy up past what it was - I doubt it though, 300kms sounds pretty spot on for 70l of gas.

Hi Guys,

I am now in the process of getting a brand new 225 to replace the secondhand 425. I did have an analyser on whilst tuning and we couldn't get it below 7.99% Co2 ( I think), which is obviously WAY too high. There was lots of "meat" left in the idle screw on the mixer, just couldn't get that percentage down though.Should be down around 3% if possible, or so I have been told.

I am hoping with the new 225 that I will see a marked difference.

Just as further b/g on this, I bought this kit 2nd hand from a guy that had it in his HSV SS Commodore 5 ltr . I installed it myself and then went and got it certified by a gas installer. I didn't ask how long the previous owner had it in, but it had done a few years at least.

I might also look at the converter after I have run the 225 for a couple of tanks and see if there is any wax deposits as well.

Thanx for the advice guys, I'll keep you posted on the outcome.

Cheers.

Definitely keep us posted, will be interested to see the results. Interesting that you had travel left on the idle mixture screw and still couldn't get down to 2.5 - 3.0% CO (Not co2), definitely doesn't sound like it needs a lean idle shim.

OK, Got the 225 mixer and installed it. Didn't change main jet settings or anything else, simply removed the 425, installed the 225 with adaptors and away I went.

Have just finished the 2nd tank of gas and have averaged 265k's per tank, up 40k's from when the 425 was installed.

I noted that idle revs were higher ( approx 11100-1200rpm ) when in park or neutral and 800 when in drive.

Have now adjusted main jet as mix was too rich and will now run that as idling is now much better ( 750-800rpm in park or neutral ). Will run this for 2 tanks and see what happens.

Any thoughts or comments are welcome, otherwise stay tuned.

Cheers.

Glad to hear you re geting it sorted, with this setup you should be able to get approx. 300 - 350 k's per tank - thats what i was getting on my old 81 rangie .

Have now completed running through two tanks of fuel with an additional main jet adjustment. Am now averaging 320k's per tank. Obviously I'm much happier than the days of 225k's per tank on the 425 mixer.

I will make some further adjustments and see if I can mileage up a bit further.

Torden wrote:Have now completed running through two tanks of fuel with an additional main jet adjustment. Am now averaging 320k's per tank. Obviously I'm much happier than the days of 225k's per tank on the 425 mixer.

I will make some further adjustments and see if I can mileage up a bit further.

Nice job mate, you are a regular impco expert now, where did you end up getting the 225 and can you give me a ball park figure and one last thing, where did you get access to the co2 meter for the exhaust ?

Cheers mate

Tom

Good work, i had been having probs with the lpg on my carby rangie, turned out the dash pots on the strommies were dry, a top up with oil and its back to running sweet and with still over half a tank of gas (70 ltr useable) have done 180 k's.

Hi Tom, OK, I got the mixer through Barralong Mechanics in Erina NSW as through them it was $195 and through another installer it was $400! The $400 guy obviously thought I wouldn't get a quote elsewhere. ( What a dill!)

Barralong also has the gas analyser but I have one of my own too, a handheld jobby called an AIM 3600 which displays a bunch of different gases and their concentrations.

And talk about followup service, barralong has not charged me one cent to make the additional adjustments, gas testing or additional hose fittings that were required to fine tune the gear. He's even said to come in again to see if we can get the milage up to about 400!

I know someone whose getting bourbon from santa this year!