LPG Fuel economy with injected Gas

Submitted: Sunday, Apr 06, 2008 at 21:26
ThreadID: 56380 Views:6511 Replies:5 FollowUps:5
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I promised to post this a while back. I now can.

Our new Ford Courier 4L V6 was fitted with a Prins, Sequential Vapour Injected Gas System about a month after we got it.

Describing it as simply as I can it makes the engine run on LPG as it does on ULP. As opposed to the older style LPG systems that effectively changes a fuel injected engine back to carby one when running on LPG, hence the dramatic increase in consumption running on LPG with the old system.

As near as I can work it out, the Courier uses about 10% more on LPG than ULP. I do however put some of this down to the extra weight of the LPG tank and the fact I have put the spare wheel on the roof rack which cannot be helping the aerodynamic drag.

To offset that, it still uses some ULP on start-up; the system will not switch to LPG until the motor is warm, typically about 3 km on a chilly Melbourne morning.

So, on balance, I reckon the modern LPG system uses around 10% more than ULP. This stands scrutiny, as I had an RB30, 3L Petrol (Carby) GQ Patrol years back and too had it converted to LPG and the difference was about 10%. That is, on two "like for like" LPG conversions the 10% is constant.

Anyway, at around 20L/100 Km with LPG at 60c/L and Diesel at $1.45/L, I would need to find a diesel Twin Cab Ute that could return 8L/100Km. They don't exist. Certainly not with 154kW and the way I drive. I'm no lair (these days LOL), but neither have I ever driven with economy in mind.

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Reply By: John S (NSW) - Sunday, Apr 06, 2008 at 21:35

Sunday, Apr 06, 2008 at 21:35
Are those consumption figures city only ?
AnswerID: 297056

Follow Up By: Jim from Best Off Road - Sunday, Apr 06, 2008 at 21:39

Sunday, Apr 06, 2008 at 21:39
Yes John.

It has been the only "constant" comparison I can make.

Figures with the old GQ were ULP from Townsville to Mellbourne and LPG on the trip back.


FollowupID: 563104

Reply By: Jim from Best Off Road - Sunday, Apr 06, 2008 at 21:37

Sunday, Apr 06, 2008 at 21:37
Forgot to add, I'll do some performance testig soo and post it.

No, not 0-100km/h or standing quarter times.

My plan is to put the camper trailer on the back and time how long it takes to go from 70-110 km/h in both third and fourth gears on both types of fuel.

AnswerID: 297057

Reply By: Member - Kiwi B - Monday, Apr 07, 2008 at 01:01

Monday, Apr 07, 2008 at 01:01

Interesting but I can't understand why your vehicle is set-up to start on petrol then switch to LPG. I'm of the understanding that an engine is at its worst operating condition cold and bore wash from wet fuel etc. Areal benefit of LPG is its ability to provide dry gas to a cold engine thus preventing this wear potential. I'm aware that there were some cold start porblems with vane type air flow meters but is your horse using one of these?

Perhaps somebody can enlighten us please.
AnswerID: 297094

Follow Up By: bruce - Monday, Apr 07, 2008 at 10:48

Monday, Apr 07, 2008 at 10:48
A vehicle can start on LPG , but it will take some time to do so and probably flatten the battery...LPG is frozen and has to be warmed up before it enters your motor...my most recent experience with this was last week, my car was running to cold and the gas was not being " unfrozen " or was refreezing before it got to the motor..the car was losing power and chugging .....a new thermostat was fitted and the problem was fixed ....that is why it starts on petrol to warm the motor up......cheers
FollowupID: 563155

Reply By: Robnicko - Monday, Apr 07, 2008 at 08:51

Monday, Apr 07, 2008 at 08:51
20l per 100k still seems alot, My 1995 80 series auto returns between 18-20 lp100k on lpg. And it is the older style Impco system. I would have thought that being injected you would be getting better than 20 l/100k?
Is the v6 4l engine very thirsty? Or is the vehicle weighed down?

AnswerID: 297121

Follow Up By: Jim from Best Off Road - Tuesday, Apr 08, 2008 at 06:57

Tuesday, Apr 08, 2008 at 06:57

Most V6's are pretty heavy on juice and the Ford 4L V6 (out of the Explororer) iis not exactly the most modern or technically advanced V6 on the market.

Combine the engine's failings with the fact that the car is carrying a fair bit of weight and factor in the way I drive; the economy is about what I expect.


FollowupID: 563329

Reply By: kktdw - Monday, Apr 07, 2008 at 14:00

Monday, Apr 07, 2008 at 14:00

I recently had my 2001 4.5ltr LC100 converted to LPG with Sequential gas Injection. Runs great - a little down on power - but runs very smooth and dependable. Consumption is surprisingly similar around town but a little more gas on the open road. Best I ever measured was 16l/100klms on trip to Canberra from petrol - travelling at the speed limit. A recent trip to Cuttaburra Bore on LPG returned 19l/100klms.

Car starts on petrol and switches to LPG in less than 1klm typically. At this rate I use a tank of petrol per year if I get lucky! I do mostly short trips around Melbourne so get to use more petrol than I would if I were doing longer trips.

I was told the starting on petrol was for efficiency reasons because the LPG settings can be leaner if calibrated to run only at engine operating temp.

Any which way, I love the Cruiser now and don't even think about the cost of fuel whereas before i was always thinking about fuel consumption etc.. when running on petrol.

Valve recession is apparently an issue and I will be doing all my own valve adjustment to manage this.

Regards Ken
AnswerID: 297171

Follow Up By: Blaze - Monday, Apr 07, 2008 at 21:54

Monday, Apr 07, 2008 at 21:54
Gday Ken,

You mention you will use one tank of ULP a year if lucky is great... I have owned dual fuel vehicles for the last 14 yrs, 4bys and family cars with only a faulty reg problem.

One thing I thought I should point out, is with ULP (unlike leaded) has a very limited shelf life. I seen a ULP tank the other day out of dual fuel vehicle which looked nearly like a bottle of black Clag (glue). It goes really yucky. Just a thing to look out for.
FollowupID: 563295

Follow Up By: kktdw - Tuesday, Apr 08, 2008 at 09:19

Tuesday, Apr 08, 2008 at 09:19
Will keep an eye on that.

The guy that does my engine work also told me not to keep ULP too long

Many thanks

FollowupID: 563351

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