Coverting my 4.4i x5 to gas/compress natural gas (CNG)

[avonside]

Just wanted to share a few pictures of my LPG instal that I had done just over 3 years ago, did have a few issues at first but it is running pretty well these days and with petrol here in the uk at $8 a USA gallon LPG is half that so it makes sence even if living with LPG does have some annoying quirks ..it took us about 18 months to get our money back cos the install was $3500...but on a run it great to know your on half price fuel..its also cleaner about 20% on the emmisions

[reg]

Nice! I like that the tank replaces the spare tire and you don't loose any trunk space. How is the range on propane?

[avonside]

Its a 90ltr tank but in reality ive never got more than 65 in...which gives me about 250 miles...the gas is ok in the summer but it doesnt like the cold and takes longer to get up too working temp to be able to switch over from petrol,can be very jerky to drive around town on low revs and does have a habit of stalling under load ...but recently we have decided that when we are doing the around town school runs etc, a mile here and there type of thing we leave it on petrol and it is perfect..then as soon as we are out of town on a run, over to LPG runs like a dream...it is not quite as perfect as I had imagined but without it we would have had to sell the beloved X ..so for its few issues its well worth it....lovely feeling when your on a run to be paying 50% fuel costs

[JCL]

Originally Posted by IanP

Take it the CNG means it is still in gaseous form in the tank? Can you not get LPG Stateside?

We can certainly get LPG, which we just refer to as propane, but it is more expensive than CNG. There have been propane conversion kits here, but most conversion kits are for compressed natural gas (CNG). Range is reduced due to the tank pressure limits, but it is cheaper than gasoline. It is why there are often dual-fuel conversions, so when you run out of CNG you can get to a fuel station on gasoline.

The other risk with propane/LPG is that it is heavier than air, so it settles and collects in enclosed areas. CNG is lighter so that it rises and dissipates. Our fire codes typically ban any propane/LPG vehicles from entering car parkades, which can be a hassle in the city.

[JCL]

Originally Posted by reg

It is going on a 2001 x5 4.4i so it is exempt from my local emissions testing as Illinois EPA only test cars ten years and newer. I still believe it is going to pass as CNG is a cleaner burning fuel over gasoline.

I don't think it is a true carburetor as the CNG is already in a gaseous form. It is called a mixer and the system delivers the CNG using the same fuel injectors installed in the vehicle. The system only costs $599.99 plus you need a tank so for around $1000.00 I think it is a viable option over $5.50 permium gas.

Below is their FAQ


EWS Conversion Kit
These kits are low cost and easy to install.
This kit is available for all gasoline engines including all EFI throttle body or multiport, carburetor, and even turbo or super charged engines.
This is how it works:* A mixer (venturi) is installed in the air intake before the throttle body which provides single point fuel injection.* An oxygen sensor on the engine's exhaust is monitored by the CNG controller which controls an electronic valve (stepper motor) installed on the low pressure CNG fuel hose going to the mixer to provide the proper fuel ratio at all times.
On all gasoline engines the combustion air has always been controlled with a throttle plate so it makes sense to bring the fuel in with the air letting the oxygen sensor adjust the fuel ratio.* This provides the best mixing of the gas and air which provides excellent engine performance.* The engine idles and runs the same as it does on gasoline without the intense programming and adjusting needed with sequential injection conversion kits.* There is more information on sequential kits above.* The mixer does restrict the air flow some when running on gasoline, but not enough to effect the performance or fuel economy.
The instructions are written for the car owner to install with many tips, "how to" information and a trouble guide.
No programming is needed as we have each controller programmed for your engines requirements.* Computer cable and software is available if desired.
All you have to do is adjust the idle screw on the regulator and observe the indicator lights that let you know it is adjusted properly.
Our controller features self adjusting electronics which always provides peak performance.
The control on the dash indicates which fuel you are using and how much CNG is in your cylinder.
This kit allows you to run on either gasoline or CNG with the push of a button on the dash.
Our kits for 8 or 10 cylinder engines come with high output regulators for more power and better performance.* You can upgrade your smaller engine kit to a high output regulator for an additional fee.
If you run out of CNG you will begin to loose power so you just push the button on the dash and you will switch to gasoline and continue driving. *You should always refuel before you run out of either fuel.* Read the features of both our EWS and Millennium kits to decide which kit you would prefer.

I agree that CNG is cleaner burning, but if the air fuel ratio is not correct it wouldn't be cleaner than on gasoline. Not a problem if you don't have to get it tested though.

The fuel is described as being admitted through a venturi (restriction in the air flow) that speeds up the air, and the fuel is drawn in. That results in a fuel/air mixture that then goes through the intake manifold and into the combustion chamber. That is the definition of a carburetor IMO.

It is impossible for the existing gasoline fuel injectors to deliver the fuel, since they are metering fuel and not air. The CNG is not mixed with the gasoline. The CNG is mixed with the air. The air/CNG mixture doesn't meet the gasoline until it is in the combustion chamber. The advertisement is very misleading, as it says that the mixer provides single point CNG injection. There is no injection, there is mixing. It seems like purposeful confusion, to me. They try to make it sound like the fuel injectors have something to do with it, when they don't. Since they have spelling mistakes in their advertisement, though, perhaps it isn't clear to them.

They even comment on their site that they don't like using fuel injectors, because they are too complicated and you have to mess with programming the ECU. Yup, that is how it works.

So when you follow the instructions and adjust the idle screw and the lights go out, meaning that you have the correct air/fuel ratio, then how do you turn off the vehicle warning lights on the dash that are lit up for the same reason, bank one and bank two being too lean or too rich? They are latched, and I would think that would require a service tool to reset. Each time the air fuel ratio goes out of range.

They go on to say that once you set the mixer control, then you have the correct air/fuel ratio and it will stay there, or self-correct at least. One of the limitations of carburetors (or mixers, if you prefer) was that the air/fuel ratio changed at different rpms due to the properties of the venturi. Historically, cars solved this with multi-barrel carburetors, separate idle jets, and so on. They don't seem to think this is required. Maybe it isn't, but I would wonder about it. Precise fuel metering over different rev ranges and conditions was the reason manufacturers went to fuel injection, though. And you will still have the vehicle fuel injection there working, trying to correct for conditions that it won't expect.

It is cheap, and it may work fine, so try it and let us know. As you say, CNG is cheap now, largely due to increased reserves brought about by increased shale gas fracturing. But don't expect the refinement of your current engine control system, IMO.

I provided the info on the WING system for new Ford pickups just as a counterpoint. That is what an engineering fuel injected CNG kit looks like. It is installed on a new truck prior to delivery, and it carries the same warranty as a new Ford pickup. Due to the characteristics of CNG, namely that it is drier and provides less lubrication than gasoline, the engine is hardened for the kit. That includes different valves and valve seats to prevent the valves pounding in (recession). There may be other engine changes, but that is the one I know about. CNG works best as a fuel when it is integrated into the engine and engine control system, not when it is simply plumbed into the intake manifold. Just my $0.02

[IanP]

I think my LPG conversion is basically the same as Avonsides. The LPG ECU piggybacks the original ECU and uses the same input signals. There are separate LPG injectors for each cylinder, when it goes from LPG to petrol and back you cannot tell the difference. LPG has less heat value than petrol so you get less mpg (about 15-20% less, but as has been said LPG is half the price in UK so its a no brainer. I had the engine apart for tensioner related issues and it was very clean after 80000 miles, about 20000 of which on gas,

[avonside]

Hi IanP , does your x struggle with the cold when its on LPG, I find it drives very lumpy when its just at the cross over point in temp and revs ( about 1200) and it has stalled frequently when driving in traffic around town.We have decided to leave it on petrol only when around town then it drives perfectly.

[IanP]

Hi Avonside, no it has no problems, it might take a wee bit longer to change over when it is really cold (well cold for the UK anyway), but most of the time I dont notice it changeover. The car is only only petrol for startup and when it gets a good thrashing as the system isnt big enough for a 4.6 at full throttle. Works well enough up to about 5000 rpm. Maybe your gas system just needs a service and the filter changing?

[JCL]

Avonside and IanP, I think you may be helping answer the original poster's questions. If your much more complete kits have occasional drivability issues (tolerable, but noticable) then I suspect that a kit that is less than half the price may exhibit the same sort of issues, if not more.

[phil47]

I suspect the LPG drivability issues are mainly related to cold weather. CNG doesn't suffer the same problems in severe cold as LPG as it is already gaseous. We have converted a large portion of our operations fleet to CNG and they are handling temps in the -20s and -30s with no driveability problems whatsoever. These are not purpose built CNG vehicles but rather conversions.