Need to decide between keeping LPG or going injected.

[Ki Areese]

I've read over a bunch of threads about the pros of TBI and am pretty sure that's the root I'd go if I ditch my LPG set up. The problem is, I've finally got my Scout on the road (even got an inspection sticker) and I just don't have a lot of time to be taking on another sizable project.

The reason I'm considering it, is that after taking my scout around town a couple of times, my LPG tank, that had 7 gallons in it, is on E.... I've put 21 miles on this 7 gallons, and while it still has some left, its a bit concerning having no idea how much I actually have, and the possibility that I may be getting somewhere in the ball park of 3 miles to the gallon...

The specs look like this:

Tuned up 345 w/727
33" x 13" swamper tires
Dana 44s with 3:73 gearing (I think...)

The timing was already advanced a bit more than it should have been with gas, I could probably advance it more, but I'm trying to decide on this before I go a tweaking.

Also, I have a wiring harness and ECM for the TBI swap. I'd need to get a new gas tank, the throttle body and a chip to tune. The fact that Propane is pricing out at $4.50 a gallon is more motivation, but, time and cash flow are kind of limited. If I can get this thing to some level of respectable fuel economy (10-12 mpg would work), then I can sell my car have a bit more cash flow.. but 3-4 mpg is a little scary..

So, thoughts or suggestions would be very appreciated. What would you do??

[Mark Ashford]

No way you should be getting 3 mpg. Even racing I wasn't drawing that much with my 392.

Either your gauge is off, or the tank wasn't full, or you have a leak somewhere.


Drain a tank, weigh it with a scale (i.e. the bathroom scale), write the weight on the bottom. Then take it to have it filled. Take note of how much fuel they put in it (should be about 8 gallons if your using forklift tanks), then weigh it again.

Now you can tell how much fuel is in at any one time by just weighing the tank.


If your going to use this as a driver, rig up two tanks. Either two removable forklift tanks, or two fixed tanks. One can even be smaller than the other. Rig up two electric cut-off valves and a couple of "empty" lights. When the light goes on, flip the switch to change to the "other" tank. If its the smaller tank then call it the reserve so you know you need to get fuel.


Start with a known full tank, then carry a spare till you get to know your range. Use the soapy-water trick to find any leaks, and I like to get in the habit of shutting the main valve if/when I'm going to park, especially if you don't know if you have a leak yet.



However, with your LPG prices, I'd be thinking about efi as well, especially on a driver. Mines a trail rig, so other than bulkier fuel storage, I don't have to worry about running out of fuel on the intestate.

[Ki Areese]

Thanks for the reply. I was thinking the same thing about the 3 mpg, but this is a new tank so I was assuming that the gauge wasn't screwed up... I'm probably wrong or its just a really coarse gauge... It could be a leak, but I've let this system sit for a long time, so unless its leaking a lot faster when driving, I can't imagine its causing that kind of mileage reduction.

Yeah, the price is pretty daunting, but, my commute is usually only about 14 miles round trip so I wasn't too concerned... Right now the time and money it would take to change back to gas is also pretty daunting, so if I can stick with this for a while anyway it would be better.

I don't suppose you have any leads on where I could pick up the electric shut offs. I was searching McMaster for propane/LPG stuff and wasn't finding much. I'm not 100% what valves and gauges are good for propane. I was considering machining up some manual shut offs and rigging them up with pressure gauges to know when to switch tanks, but if I can source some electric ones that would be great.

[bmacguyver]

you can get most of it from intrupa, there a forklift parts outfit. the low fuel light is operated by a pressure switch. was your lp system new or used when installed? it could be a diaphram leaking in the vaporizer or a leak in the throttle body aswell not just the lines.

hth

mac

[Ki Areese]

Thanks for the info, I'll check them out.

The system was used, but I did rebuild the vaporizer. I guess I'll have to get a kit for the mixer and vacuum lockout.

[Doc Stewart]

Propane fuel can function on a lot of advance. Try 15*BTDC.

Out here in CA, propane fuel prices are unregulated. In my area, it can be found for as low as 2.99 and as high as $6.00 / gallon. Shop a bit.

My propane set up on a 74 345 pickup has a fuel gauge. Dunno anything about it except that it works. The tank is 100 gal. I get just over 7 mpg: 4 speed manual with 4:10 gears and 32" tires.

[Paul "Misterfixit" Schulz]

Have you put a sniffer up the tail pipe and set the mixtures for propane properly????

should be 2% co at idle and 0.5% at around 2000 rpm.

[Ki Areese]

Paul, No, I have to tune the mixer in a bit more, I didn't think it would cause that much inefficiency, but after reading up on it more, I'm sure it isn't helping.

Doc, while I'd like to get better than 7 mpg, at this point that seems like a great goal to achieve. I'll be looking up other propane filling stations in the area over the next few days and getting some prices. Hopefully I can find some closer to the going gas price of $3.45...

Thanks again for the replies. Now I'm off to read up on tuning the mixer... At least that doesn't require a computer .