Going from CNG to Gasoline

[ut_bill]

I just bought a 2001 bifuel F150. I wanted to see how far I could go on a single CNG fillup. I got about 144 miles when the truck converted over to gasoline. I heard a thump or bang and felt a slight hesitation as it converted over, then it ran okay. Is that normal? I would appreciate any help you could provide. Thanks.

Bill
Centerville, UT

[rtry9a]

Re: Going from CNG to Gasoline

yes, the hesitation is normal as is your range. If you haven't figured it out yet, you have to stop and turn off the ignition to change between fuels manually.

[ut_bill]

Re: Going from CNG to Gasoline

What about the thump or bang I heard? I was driving about 50-60mph.

[Luke]

Re: Going from CNG to Gasoline

It is typical that the engine misses a cylinder or two as it switches fuels; this is especially noticeable at high speeds. On my bi-fuel vehicles there is a noticeable click sound as it transitions from CNG to gasoline; this click is normal. If yours is quite loud, you may have an issue with your pressure regulator or compuvalve.

How loud was the sound that you heard? How many miles does your truck have?

[Kevin Fern]

Re: Going from CNG to Gasoline

Has the issue happend since? There is a fuel lockoff valve, usually on the fuel tank and/or the fuel regulator, you may want to check for leaks, ie. if the fuel line is empty, there is a point where the fuel must fill the lines (if empty) this may be where you are getting the bang from? It is advised that you switch fuels when stopped and not going down the road, Kevin

[ut_bill]

Re: Going from CNG to Gasoline

This has happened only once (the first time I ran it out of CNG). It hasn't happened since because I am still running on the second fillup of CNG. I have about 20K miles on the truck. I just had the truck in the shop and the compuvalve and a coil pack were replaced. If the empty fuel line is the issue could I check this by running on gasoline then switch back to CNG just before the truck runs out of CNG? If there is no bang/thump then that would be my problem. As a general rule though, I should not let the truck switch over fuels as I am driving, is that correct?

[rothstar]

Re: Going from CNG to Gasoline

The "thump and hesitation" (officially referred to as buck/jerk?) is painfully familiar to me. My truck has a tendency to do this at 50-60 mph under moderate acceleration up a hill only when I am running on CNG and not necessarily when the truck is switching over to gasoline, so my problem may be completely separate from yours.

I believe that this buck was partially responsible for predisposing my truck to eject the #3 spark plug. After a lengthy repair of the sprak plug threads (Time-Sert Ford Triton #5553 kit) and replacing all of the coil packs, spark plugs, seals and o-rings I expected great things...

The truck now runs great on either gasoline or CNG with smooth idle and strong acceleration, but at random intervals while beginning steady acceleration at 50-60 mph on CNG, it bucks. The anticipation of this happening is enough to make all the miles of smooth running and fuel savings evaporate into an expletive and extremely high blood pressure.

Tomorrow my new coalescent filter should arrive, and there may be a glimmer of hope that a new filter will fix the problem. I have noticed that the fuel gauge dips slightly right before the buck happens.

Go ahead, tell me I need a new compuvalve--I'm tough.

Samuel

[maxman]

Re: Going from CNG to Gasoline

Bill,
I assume from your name, you are in Utah. Where did you get the Compuvalve replaced at and how much does it run? (I may have to do mine)

You said you only had about 20K miles on it. Did you mean on the truck total, or the compuvavle? Also, did your check engine light come on? My son's 2001 keeps kicking his light on when it changes fuels.

If your truck only has 20K miles TOTAL miles, it might still be under warranty.

Max

[Devo]

Re: Going from CNG to Gasoline

Yes, if it's a factory installation, it should have an 8 year / 80,000 mile warranty on the CNG components (don't let them tell you that it doesn't because it does). Champion Ford in Sandy officially works on them.

[ut_bill]

Re: Going from CNG to Gasoline

The bang/thump only occurred when the truck ran out of CNG and transitioned to gasoline and I was driving at about 50-60 mph. I haven't heard the bang/thump since or before.

I had my compuvalve replaced at Ed Kenley Ford in Layton, UT. It was under warranty. They told me the compuvalve runs about $2500. I guess I would check with a few dealers to find the best price if you're not under warranty.

[darress]

Re: Going from CNG to Gasoline

My truck (2001 f150 7700) has the same buck/thump/bang/thud...when switching over from cng to gas. It is more noticeable with higher speeds as others mentioned. My truck also has a jerk at times when at high speed, constant or accelerating, seems a bit random. I suspected the transmission due to an occasional torque converter shudder, and in researching, this shudder appears to be yet another frequent issue with Ford trucks. It sounds like it can be fixed with programming shift points, transmission flush, or a high performance valve upgrade. Do any of you have the tranny shudder at times along with the fuel switching?