LPG Discussion Forum

Jeep Commander 5.7
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Author:  Ian_Fearn [ Mon Feb 05, 2018 10:07 am ]
Post subject:  Jeep Commander 5.7


I've just bought a Jeep Commander with the 5.7 Hemi engine. It has a Prins LPG conversion, completed in 2009 (50k ago) with the original certificate, paperwork and manuals etc.

It seems to run perfectly, switches from petrol to gas, no warning lights, no hesitation and as far as i can tell stays on gas all through the rev range.

I collected it from Guildford where the owner told me he had brimmed the LPG tank "maybe 50 miles ago". I drove back to Derby and filled (75 litres) near home another ~130 miles on. So if the previous owner was correct i've managed 10.8 mpg.

This seems a little high for a clear motorway run and whilst I had a little fun occasionally, I was generally tired and just kept to speed limits.

As far as I can tell from the paperwork, the gas conversion has never been serviced. Anybody got any thoughts?

Author:  hitman [ Mon Feb 05, 2018 11:09 am ]
Post subject:  Re: Jeep Commander 5.7

Aye the original owner was bullshitting you :-)
You'll know soon enough aftrr a couple of fills the real situation

Author:  Ian_Fearn [ Mon Feb 05, 2018 12:59 pm ]
Post subject:  Re: Jeep Commander 5.7

I've just checked the trip computer thingy and its saying 16.0mpg which seems more like I was expecting.

Author:  Gilbertd [ Mon Feb 05, 2018 5:00 pm ]
Post subject:  Re: Jeep Commander 5.7

If it does 16mpg on petrol and it is still saying 16 mpg when run on gas, there's nothing wrong with the gas calibration. The trip computer calculates fuel consumption from the petrol injector pulse lengths and, as the gas system slaves off the petrol system, the injector pulse lengths (the fuel trims) should not alter when on gas. The difference is that you will use a bit more gas than petrol so the trip computer is pretty much redundant on gas except as a check on the calibration. 180 miles on 75 litres sounds a bit heavy but may be about right. My 4.0 litre Range Rover on a long motorway run cruising at 75 ish in the UK would do about 210 miles on a tank which is 65 litres. You've got a car of similar weight and aerodynamics but a bigger engine so I would expect it to use a bit more. Reset the trip meter whenever you fill the tank and you'll soon get used to when you'll be needing to fill it again.

Author:  Ian_Fearn [ Thu Feb 08, 2018 12:00 pm ]
Post subject:  Re: Jeep Commander 5.7

Whilst I can't see anything wrong with the gas system, i'd like to keep it that way so I want to do some LPG servicing, i.e. change the filter/s before taking it to an LPG person with the software to check the parameters.

As far as I can see, there is a Prins filter (twin outlet) mounted just above the reducer but the replacement kit seems to come with 2 filters. Can anybody explain what the 2nd filter is for?

AND then..... I'm unclear as to how gas is delivered. Is there some kind electrovalve at the tank that only switches on when gas is selected or are the lines pressurised upto the reducer?

Should there be a manual shut off valve at the tank so i can safely remove the filter?

I've found a receipt for a reducer rebuild shortly after it was fitted, is that a service consideration or should it be fit and forget until something goes wrong?

Thanks in advance.....

Author:  Gilbertd [ Thu Feb 08, 2018 5:16 pm ]
Post subject:  Re: Jeep Commander 5.7

There are two solenoid valves, one at the tank and the other at the reducer and both of these open when running on gas. The one at the reducer incorporates a filter which is the other smaller filter element that comes in the kit. You can see it in your picture with the blue solenoid coil. There will be a manual shut off at the tank as well as the solenoid. You can shut that off (or simply disconnect the power to the solenoid valve) and run the car on LPG for the few seconds it will run on what liquid is left in the pipe from the tank. Or just slacken the incoming line to the front solenoid and bleed the pipe run of gas before undoing the filter housing.

If the reducer has been rebuilt properly, it should be good for another 100,000 miles.

Author:  Ian_Fearn [ Thu Feb 08, 2018 6:37 pm ]
Post subject:  Re: Jeep Commander 5.7

Thanks for the information. I've ordered the filter kit so will get onto it once it arrives.

Author:  LPGC [ Thu Feb 08, 2018 7:05 pm ]
Post subject:  Re: Jeep Commander 5.7

The pressure sensor attaches to the vapour filter on Prins systems, simple matter to shift it onto the new vapour filter.

Author:  Ian_Fearn [ Sat Mar 10, 2018 7:24 pm ]
Post subject:  Re: Jeep Commander 5.7 Hemi

Brief update on this:

I've now completed a full fluids change, transfer box, axles, engine, autobox etc and also changed the 2 LPG filters. The 16 spark plugs are a right pain to change! Luckily they only need doing every 30k. The gearbox fluid and filters change is a pretty horrible job too without a ramp, my hair still stinks of ATF!

Given there was nothing obviously wrong with it before, its continued to be fine after the LPG filter change. As far as I know it stays on LPG throughout the whole rev range.

I drained the gas by removing the inlet connection to the vapouriser as I had a coolant leak from the heater hoses into the vapouriser and needed to raise it for access. Fingers crossed some new nicely tightened jubilee clips have sorted that.

I bust open the plastic filter housing, interestingly, both filters (9 years old) visually, were spotlessly clean.

I should be doing a couple of longer journeys in it over the next few weeks to get a feel for MPG. Its an amazing car, I really love it. Would highly recommend one should you want a big comfortable cruiser for very little money.

Does anybody have any long term reliability experience of the Prins VSI ECU or vapouriser or the Keihin yellow dot injectors?

Author:  Gilbertd [ Sat Mar 10, 2018 11:28 pm ]
Post subject:  Re: Jeep Commander 5.7

I can't comment on the ECU or vaporiser although don't recall hearing too many complaints about them but the Keihin injectors are one of the best. In fact it is the choice of injectors that gives the Prins system it's high end reputation.

Author:  Ian_Fearn [ Wed Mar 14, 2018 11:42 am ]
Post subject:  Re: Jeep Commander 5.7

So i've just filled up after 100 mixed miles.

I put 66 litres in, 14.6 gallons.

Thats 6.8mpg.

Surely something must be wrong? Time to get it on a computer?

Author:  LPGC [ Wed Mar 14, 2018 12:35 pm ]
Post subject:  Re: Jeep Commander 5.7

Ian just called me for a chat and is going to see what mpg he gets on petrol.

Something I didn't mention in the chat is the potential for uneven cylinder fuelling.. . If any cylinder(s) has a problem injector then that cylinder will get different fuelling to other cylinders - If this cylinder is lean it will cause the other cylinders to run rich (and vice/versa) because lambda and fuel trims reflect average fuelling over all cylinders on a cylinder bank. It is possible to have say 1 cylinder on a bank providing say 30% rich mixture causing other 3 cylinders on the bank to run 10% lean mixture, this wouldn't necessarily cause MIL light problems etc but would affect economy.

Author:  Ian_Fearn [ Wed Mar 14, 2018 1:30 pm ]
Post subject:  Re: Jeep Commander 5.7

Simon, thanks a lot for your time, really appreciate it.

Will run it on petrol for a few hundred miles and see what happens.

Author:  Ian_Fearn [ Fri Mar 23, 2018 9:14 pm ]
Post subject:  Re: Jeep Commander 5.7

Right, firstly panic over.....

It turns out that whilst I was servicing the Jeep, I left it in Neutral overnight with the key in the ignition. This flattened the battery and it reset the trip meter so i'd actually done more miles. Having sat down and worked out where i'd been in it, i came up with 150 miles so forget that first test.

I've just done 374 miles in it purely on LPG. So new figures are in:

First tank: 135 miles on 36.5 litres (52.9p/l). The first 20 miles were local shorter runs, the rest was one steady run. So 16.5mpg :D

Second tank: 239 miles (tank fully empty a mile before the gas station) on 79.35 litres (61.9p/l) so 13.4mpg. The first ~140miles of this tank was slow pottering around the lanes of north Wales, the latter ~100miles a steady run (generally with fast accels from roundabouts).

So i think that's about right. The first tank was done at 44% of the petrol cost equivalent at the same station and the second tank 49%. I've proved it really is cheaper to run on this basis than the equivalent diesel.

Looking at the USA Commander forum, MPGs of 10-15 is par for the course with the Hemi.

The main thing now is that i'm happy the car is running right and the wife isn't nagging too much about fuel costs!

Thanks again to Simon for his advice, if I decide to go for that 6.4 SRT8 next i'll know where to get it converted!

Author:  Gilbertd [ Fri Mar 23, 2018 10:07 pm ]
Post subject:  Re: Jeep Commander 5.7

Ian_Fearn wrote:
Looking at the USA Commander forum, MPGs of 10-15 is par for the course with the Hemi.
Don't forget they will be talking about US gallons which are smaller than real ones (a US gallon is 0.83 UK gallons, or 3.785 litres compared to 4.54 litres for a UK gallon). Your mpg figures sound about what I'd expect from a heavy, un-aerodynamic, V8 powered vehicle so nothing to worry about.

Author:  Morat [ Sun Apr 15, 2018 5:07 pm ]
Post subject:  Re: Jeep Commander 5.7

I'd love to see a jeep commander. I was tempted briefly but ended up with a p38 Range Rover instead. It would be interesting to compare notes!

Author:  LPGC [ Wed May 09, 2018 7:18 pm ]
Post subject:  Re: Jeep Commander 5.7

SRT8 Jeeps are very quick indeed, I've converted loads of them.

Author:  agostino [ Mon May 14, 2018 10:53 am ]
Post subject:  Re: Jeep Commander 5.7

LPGC wrote:
SRT8 Jeeps are very quick indeed, I've converted loads of them.

Simon have you done patriots as well? the 2.4L petrol is interesting...

Author:  LPGC [ Tue May 15, 2018 8:58 pm ]
Post subject:  Re: Jeep Commander 5.7

agostino wrote:
LPGC wrote:
SRT8 Jeeps are very quick indeed, I've converted loads of them.

Simon have you done patriots as well? the 2.4L petrol is interesting...

Yes but it's been a few years. If memory serves there's nothing out of the ordinary with them but fitted AEB124s on them, though might not be needed with more recent LPG ECUs.

Author:  Ian_Fearn [ Fri May 25, 2018 7:45 am ]
Post subject:  Re: Jeep Commander 5.7

Been a couple of months since my last update on this. I've been chasing an intermittent ABS/BAS/ESP fault that I finally tracked down to a simple fuse for the brake lights that had corroded. This was after changing the ABS sensors as this seemed to be the most common cause.

Also had 1 rear brake calliper piston split in half when trying to retract it for new pads and another brake calliper seize on me.

Still getting a consistent 13mpg local running about and 16mpg on a longer run. Whilst I'm no racing driver my driving style is much more progress orientated than for economy. I'm still amazed what a great car this is. The driving experience is so far beyond any other SUV I've ever driven especially considering the price.

My current issue is the Prinz vaporiser appears to be leaking from the joints where the coolant pipes go in. Initially it just looked like a case of loose hose clips but the leak seems to be at the vaporiser where the ferrules exit the casing. I see you can buy a rebuild kit that comes with the new ferrules and seals. It's only a very minor weep, I rarely have to top up at the moment.

Does anybody know if the vaporiser is rebuildable as a DIY proposition?

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