Engine keeps and displaying underpower.

[dpostelnicu]

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References to systems which are not approved to be installed in the United States have been removed from this thread
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I bought a GMC Envoy with an aftermarkt system {reference to uncertified system removed}. The system seems to work ok but seems to be out of adjustment.

Has anyone done any adjustments on these systems for a 6 cyclinder 4.2l or close?

the problem I have is that the CNG works just fine at idle and low end just fine. It seems to bog down and go only to 3500RPM, not to talk about the fact that it is simply gutless. I can entualy get it to speed like 40MPH or 60MPH on the highway. After a fre minutes I get Loss of Power error on GM Envoy and it idles only, no more throutle available till I shutdown the vehicle and restart it on reg gas.

I can't seem to be able to start the vehicle when warmed up on CNG either. I can however change over once started on reg gas. The problem I have is that even the timing advance kicks (I hear the click on the relay for timing advance) when I touch the gas pedal, it seems like it is not advanced enough. I though with CNG the timing needs to be set to 12.

Any ideas?

Thanks,

[larrycng]

Re: Engine keeps and displaying underpower.

I've seen a couple of {reference to uncertified system removed} kits, and they would not be my first choice. It sounds as if you are not getting enough fuel. A couple of questions:

Did you have a qualified technician (one with experience on CNG) install the kit or is it a do it yourself?

How many of {reference to uncertified system removed} extra "fix boxes" were used on the installation? (these extra boxes are like the autotronics (dual curve) boxes of the early '90's used to cure little problems like check engine light, change the advance curve, etc)

Also, are there any intercepts in the installation that re-rout a signal through the {reference to uncertified system removed} control system and back to the OBD II computer? These can cause problems (conflicts) with the OBD II system operation, including reduced power.

Does the vehicle run normally in terms of power, performance, and fuel miliage when on gasoline? If it does, you have problems with the installation. If it doesn't you may still have problems with the installation especially if there are intercepts in the system wiring.

OBD II looks at and compairs readings within the system. It also looks at rates of change of various sensors. OBD II has a rationality check to determine if under a given set of circumstances the engine readings correlate in an expected manner. If they don't the system will "throw a code"

Suggest you take it to a good technician for an evaluation on each fuel, and not to the guy who installed it -- you need a second opinion.

I would suggest that you consider replacing it with a EPA approved kit.

Hope this helps

Larrycng

[Lakewood90712]

Re: Engine keeps and displaying underpower.

If the vehicle was purchased from a car dealer, the best thing would be to get your money back and find a vehicle with an oem system.

The gm pushrod v-6 is a very good engine,especially for low rpm torque. I have seen them used for towing . However , even on gasoline it doesn't have a lot of horsepower.

[dpostelnicu]

Re: Engine keeps and displaying underpower.

I apreciate the quick response. The vehicle works just fine on Regural Gas. The system was installed by a profesional so I thought. I purchased the vehicle with the conversion on it already. The reason I question the profesional statement is because this vehicle does not have a TPS and the PROFESIONAL hoked it up to the Throutle wireing. It had negative voltage beeing sent to the sensor. Further study I found out that this vehicle does have Pedal Position Sensor and I hoked up to that. The installation is in questions because of this discovered mistake. I did purchase the PC interface cable/box and software(spanish.....Dang).

This install does have 2 paralell units installed I belive, that you are asking about.

This system was about $3000 installed with the tank and I hate to throw it out without going through some more troubleshooting. In Utah is allowed to have NON EPA aproved installations as long as it passes safety inspection on the proper installation and smog test passes on both gasoline and Nat gas.

I was hoping someone had some more documentation on setting these systems up on 6 Cyl vahicles.

[larrycng]

Re: Engine keeps and displaying underpower.

Seems I forgot to ask an important question, What year is this Envoy?

Since you say it has a pedel position sensor, it sounds like a late model with "fly by wire". If I remember correctly, the pedel position sensor basically tells the system what the driver wants. There should be another sensor signal that tells the actural throttle opening that resulted from the driver's command. Many systems have dual PPS for safety reasons; If one goes out you won't be stuck in the middle of an intersection with the engine at idle and no throttle -- John Deere had that problem. I would have to see the wiring diagrams on both systems before I could go any farther.

If the vehicle has a distributor that can be moved to set timing (on some vehicles with distributors, moving the distributor does not change timing), check timing advance with the vehicle on gasoline and on CNG to see if you are getting additional spark advance on CNG.

I agree with Lakewood. I would give the previous owner a chance to have it fixed at his expense or give you your money back. It depends how much you like the vehicle.

If you read and/or speak Spanish, you could call {reference to uncertified system removed}

Probably not much help

Larrycng

[Lakewood90712]

Re: Engine keeps and displaying underpower.

If this is a 2007 or later, it is an inline 6 with variable valve timing. Not going to be easy to get this properly working on a {reference to uncertified system removed} system.

[cowboy]

Re: Engine keeps and displaying underpower.

kiss ( keep it simple stupid ) check all wires and hoses and fuel filter make sure the tank valve is all the way open I always try the simple first as it is cheaper and just one loose wire or hose can drive you crazy good luck

[dpostelnicu]

Re: Engine keeps and displaying underpower.

It is a 2004 GMC Envoy. It does have two modules in parallel. Like I mentioned it seems to run just fine at idle and low speed. The issue is that the engine gives the underpowered light and the rest is history.

Does anyone on this forum has any install instructions for these units. I do have a Few and will post them for anyone else who might have a difficult time.

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References to systems which are not approved to be installed in the United States have been removed from this thread
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[larrycng]

Re: Engine keeps and displaying underpower.

I'll look at some of the material between football and turkey, maybe I can come up with something.

If you have time, put a "T" in the low pressure line and hook up a pressure gauge (I don't think you will need over a 50 psi gauge) with a length of flex tubing (use hose clamps, etc.) and tape it the windshield so you can see it. Drive the vehicle on NG and note the pressure; at idle, at low cruise, and when it starts to go "south". If there is a pressure drop of over 10 to 20% from idle (and I'm ball parking), you are starving for fuel. No fuel = no power.

It's an old, crude trick, but it will give some valuable diagnostic information. It can be applied to any system.

Many of these "off shore systems" will switch back to gasoline under heavy load. If that is the case with this system, its not switching back to gasoline.

You can check injector pulse width or Injector on time percentage with a good automotive digital volt/ohm meter such as a Fluke 88. Compare your reading with manufacturer. If the pulse width or on time have are near maximum, (under heavy load) the injector is too small or NG pressure is too low. Not enough fuel for the power requested by the throttle.

Just shooting from the hip; i.e., SWAG

Larrycng.

[Franz]

Re: Engine keeps and displaying underpower.

From what I read of the provided installation instructions,this is a venturi draw system with computer defeat boxes, and a single complex style regulator. There is no low pressure line, unless you want to call the vapor hose a low pressure line, but then, it will be reading vacuum in inches of water column and not in PSIG.

This system does not have EPA certification, nor does, I suspect, the fuel system meet either DOT or NFPA standards.

On this forum, we have seen this system installed before in some of the most extraordinary conditions (and I dont mean in a favorable way!)

Franz

[Molerpa]

Re: Engine keeps and displaying underpower.

Sorry to answer being so new, but I would like to explain a few things:

In some cases (and is not only in your country) the CNG regulator is not proper for the vehicule. In fact, if the {reference to uncertified system removed} that is in your vehicle is {reference to uncertified system removed} (the one shown on the image here) has 14 +-2 cubic meters per hour. This means, is not for more than 1.6... maybe 1.8 engines (100 horsepower max)

What happens in this case? after a % of flow demand (example, 2/5 throttle, 3000 RPM) the mixture is EXTRA, HYPER, SUPER LEAN, as the reducer cannot deliver enough gas.

A way to test this, is with the oxygen sensor (if you have it on your car, most of the EFI/MPFI have it) the normal sensors (narrow type) are 0-1 volt. connect a multi-meter to ground and to EGO sensor (Exhaust Gas Oxygen Sensor, known as plain "oxygen sensor" or "Exhaust sensor") signal. On gasoline, you'll find that it varies from 0 to 1 (some cars also uses 0.8 to 1.6 or 0 to 5... some rare cars 5-0, others 0 to 2.5)... Anyway. If on gasoline goes from 0 to 1 normally (slow driving, low power demand, idling), on cng should copy this.
if on half/more than half throttle, on gasoline remains rich (0.7-0.8... 0.9) on cng should be the same. Full throttle, the same.
If on gas (CNG) any of this conditions, the oxygen sensor level goes near 0v, you are running lean mixture. This translates on: head overheating (normally doesn't change the engine temperature, is only noticed on the short lifetime of the cylinder head)

and, obviously, will show the warning light as you said before due to the lack of power.


Hope it helped.

[larrycng]

Re: Engine keeps and displaying underpower.

Thanks for the information Molerpa.

I might add one thing, you need to use and multimeter (digital volt meter) with a 10 mega ohm impedence. If you use an analog meter or something with less impedence to measure O2 voltage you won't get an accurate reading because the meter will draw too much. An O2 sensor doesn't produce much current. Also, take the reading on the sensor before it goes into any "box"; before it is modified.

Larrycng

[John Mitton]

Re: Engine keeps and displaying underpower.

In Utah is allowed to have NON EPA aproved installations as long as it passes safety inspection on the proper installation and smog test passes on both gasoline and Nat gas.

Non-approved fuel conversion systems violate the Clean Air Act in all 50 states, Utah included. The poster likely is referring to a recent Utah court decision to strike the requirement for evidence of EPA certification when vehicles are in for safety inspections. Many Utah counties require EPA certification for emissions testing, discussion threads here:

http://www.cngchat.com/forum/showthread.php?t=3137
http://www.cngchat.com/forum/showthread.php?t=2709

While it is unfortunate the original poster was lead to believe the conversion for his vehicle was done professionally and legally, the reality is the emission system of this vehicle was tampered with via use of a non-certified fuel conversion kit -- including the installation of an emission control defeat device which activity is clearly illegal in the United States under the Clean Air Act.
http://www.epa.gov/oecaerth/resource...aa/casper.html

We wish the original poster the best of luck in getting the problem resolved with the shop who sold the conversion and are going to have to close this thread in accordance with our forum Terms of Service.
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