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LPG Conversion of a 1993 Jeep Cherokee

This article was written and kindly contributed by our British 60th Registry member Simon. If you have a question on this conversion, see Simon's page and email him directly. I have not modified his writeup in any way at all, so monetary values and units of measurement may be in metric and British Pounds.

Back in 1998 finally bought a Jeep Cherokee, a vehicle I had been hankering for sometime. I already had sat in my garage an ex-British Army 1942 Willys MB, bought back in ’92 in preparation for going over to Normandy for the 50th Anniversary of D-Day with my father and father in law both landed D-Day +1 and D-Day +2. We had also bought a 1981 LHD CJ7 in 1995 so it was logical to add a current model to the line up.

The particular Cherokee was a 1993 4 litre Limited. As expected it had all the bells and whistles but lacked the leather. After several months of driving it, it become blatantly obvious that I was not going to get the MPG I had anticipated. It got to the point that every time we went anywhere we were calculating the cost of the fuel. During 1998/99 the cost of fuel in Britain had started to escalate which meant the Jeep was become just too costly to run. However salvation was at hand.

In the summer of 1999 we went to the Ardennes in Belgium and stayed in Bastogne. Whilst travelling around the region visiting the various battle sites of the Ardennes offensive, we couldn’t help but notice the cost of LPG (Liquid Petroleum Gas) or PGL as they call it. It got us thinking, could we have the Jeep converted?

rear side photo of 93 XJOnce back in England I started to investigate how I could go about making the Jeep economically viable. I seemed to be making little progress when one Sunday we went to my brother in laws house for a BBQ. When we got there he had set up his gas BBQ but discovered he had run out of gas. We got out the yellow pages to see who supplied bottled gas and who might be open on a Sunday. Whilst looking through the list an advert leapt out of the page at me, not only did this advert say they sold bottled gas but it posed the question ‘Does your car run on LPG? You can now fill it up here’, this was the breakthrough I was after. Unfortunately they weren’t open on a Sunday so my quest had to wait until the following day. In the end after driving around to various places that we thought might have bottled gas we eventually got one from a neighbour, so the BBQ was on.

Monday morning saw me on the phone first thing to talk to Accy Gas whose advert I had found in the Yellow Pages. Just how much is LPG? 36 pence a litre, less than half the price of petrol. Things were definitely looking up. Did they know anyone who converted cars to run on LPG? ‘Yes’ came back the reply. As soon as I had put the phone down I was on the phone to Len Morris, the man who could help me keep the car I had instead of selling it and buying some none-descript box on wheels. I arranged to meet up with him so that he could have a good look at the Cherokee and explain to me what was involved with the conversion, including the cost, some £1400 (at the time around $2200). But the calculations of the mileage I did and the savings on fuel meant I would recoup the cost of conversion in a little over 12 months. The decision was made that we would go for it.

Having made that decision we had to decide on whether to go for the very large tank (100 lts of water/80 lts of gas) put in the boot (sorry trunk) across the back of the back seat, or did we go for a much smaller tank mounted underneath. The later would involve removing the main petrol tank and replacing it with a smaller custom made one. I decided to go for the bigger tank as at the time I only knew of the one place to fill up with gas, so the bigger the tank the greater the range, the fewer visits to fill up. Interestingly Len who had converted a good number of vehicles had never converted a Jeep, so he was looking forward to doing it, and it stood him in very good stead. I booked the Jeep in for the following week with it estimated to take three days.

Tank installed in cradleThe tank was fitted to a special cradle that had been bolted to the floor and to the wheel arches. The inlet/filler pipe was routed from the side of the tow hitch into the boot, and the outlet pipe was routed through the floor along the underside of the vehicle into the engine bay. These were the only holes made in the conversion, everything else was fitted using existing holes, bolts etc. Once the piping was fed into the engine bay it was mated up to the gas converter. LPG is stored under pressure and so is in liquid form. The converter transforms the liquid to gas, but to do this it needs a heat sourced to prevent it from freezing up. To prevent this a ‘T’ feed of hot water is taken from the heater hose and returned to return flow pipe. The newly converted gas is then fed to the air inlet using a special collar which is fitted to allow the gas to be mixed with the air from the filter. Everything is control electronically with the ‘brain’ of the gas system talking to the Jeeps ECU. Two more extra electronic units are fitted which ‘talk’ to the fuel injectors when the Jeep is running on gas, because the injectors are telling the vehicles ECU that they aren’t getting any petrol, these boxes effectively tell the injectors that they are. One more final unit is fitted in the cabin which acts as fuel gauge and also acts as a switch if you need to switch back to petrol from LPG.

Gauge - SwitchOnce all the gear is fitted the vehicle is a dual fuel vehicle, meaning it can run on both petrol and LPG, extremely useful if you can’t get to fill up with LPG. When you start the car it starts on petrol. If you blip the accelerator so the revs go above 1700 revs when they begin to drop off the system switches over to LPG. If you don’t do that it doesn’t matter, when you drive off and the jeep changes to second gear the system switches over automatically.

That’s the technical bit so how does the vehicle perform? Well actually very well. There is a slight drop in performance but on the ’93 model Jeep I over came that by selecting the ‘Power’ setting on the gearbox as opposed to the ‘Comfort’ mode. Running like this and not paying any attention to economical driving the Jeep was returning just over 3 miles per LPG litre, which was the same as petrol. So what advantage is there I hear you say, well it is the cost. Just 36 pence a litre of LPG as opposed to 75 pence per litre of petrol, so half the cost. However you do use slight more LPG, an Imperial gallon of petrol is 4.5 litres, and LPG gallon is 6.1 litres, so you use a third more LPG. This aid it is still a considerable cost saving over petrol. Since this very first conversion of a Jeep Len has converted many, including second hand vehicles being offered for sale by the local Jeep dealership with a free LPG conversion thrown in to make them more attractive to buy.

Apart from cost of fuel there are other advantages that help the overall running costs of what is now a true ‘gas’ guzzler. The pollutants from out of your exhaust are reduced quite dramatically which helps save our environment by helping to reduce greenhouse gases, as LPG burns that much cleaner. As a result of the cleaner burning, there are less pollutants in the engine oil which helps extend its working life. If you change the oil at the usual 7,500 miles the oil comes out virtually the same colour as it went in. Particularly in the ’93 Cherokee the delivery of power seemed that much smoother than petrol which meant there was much less snatching of the transmission. There is a safety issue as well, an LPG tank is rigorously tested and the welding done to extremely high standards, as a consequence in an accident the LPG is less likely to rupture. Also because of its position, usually very close to the rear axle, it is well away from the point of impact if rear ended. The petrol tank is more likely to rupture and/or explode. There is also a security issue, because of the closed system you won’t suffer from fuel theft! All in all there are far more advantages than disadvantages of running on LPG. Obvious where the price differential isn’t as great then financially converting has to be questioned.

Since the conversion the Jeep has covered just short of 80,000 miles with none of the faults it has suffered from being attributed to running on LPG. I have just traded in the old horse for a younger model, a 2001 60th Anniversary Cherokee, this particular Jeep wasn’t already converted to LPG but by the time you read this it will have. This time I have gone for the smaller LPG under the floor, this decision was made as there are considerably more LPG filling stations in the UK than there were four and a half years ago. The new Jeep seems also to be a little more fuel efficient than its predecessor so hopefully I won’t lose out too much with the mileage from the smaller tank. Once I have driven the newly converted Cherokee for a while I will let you know how I’m getting on.

‘LPG, it’s a gas!’

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Page created on 7/9/2004
Last updated on 7/17/2005