yucan2
Well it finally happened. I get to work on a unit hooked up for propane. Not many hereabouts. Would happen now, it's freezing.

Customer has a model #052420 attached to a mobile food service vehicle. No, not an RV generator, but a home standby. (I'll get pics when I go back). He has a whole fleet of em.

Anyway, called us. Unit will only start by using starter fluid. Said had another company out and they said he needed a new "Gas Valve", his words not mine. However even after being given the go ahead to make the repair, they never returned. Called us...

Now realizing he probably means fuel regulator, I head out. After hearing the details and listening to him tell us he knows he needs a "Gas Valve" because the other company said so, I politely informed him that we would be happy to give him what he wants, but to be advised that it may not solve his problem. We need to do our own diagnostics. He agreed.

I immediately notice a new fuel regulator hanging from the propane tank. I inquire as to why. He said that the other company said that the one we had was wrong. No low pressure output. OK is my response. After all what do I know, I'm groping here, but I have enough available resources to solve this issue.

I check pressure at regulator in unit. 12" of WC. Battery at 9V. Remove battery. Quick Charge for 15 minutes. Now at 13.1V. Unit cranking very strongly but won't start. Choke opening and closing at 2 second intervals. Appears normal. Aha!!! Stepper motor pretty much frozen. Takes significant effort to get it to move.

Now here's my question. I know the stepper motor controls speed regulation and therefore to some degree voltage output, (btw, I didn't have a spare stepper motor for that unit), but would it prevent the unit from starting?

The owner did mention that even after getting the unit to start by using the starter fluid, the voltage oftentimes would be too low for some items to operate. Frozen stepper motor, OK, this makes sense. But what role does it play in starting.

Time for an old dog to learn something new :D
Quote
bronco
At rest the stepper motor is at wot(wide open throttle) to give all the gas and air it needs to start. Then the controls move the stepper to close and slow the engine to the right speed.
Quote
yucan2
bronco;8001 wrote:
At rest the stepper motor is at wot(wide open throttle) to give all the gas and air it needs to start. Then the controls move the stepper to close and slow the engine to the right speed.


Excellent explanation, thank you very much.
Quote
yucan2
Installed new stepper motor. Goes to wide open throttle, cranks strong but won't start. Very cold outside. Hit with starting fluid, starts right up. Shut it down after a few minutes. Place in manual and starts right up.

Is this inherent with propane? Hard start or no start when very cold?
Quote
Skip Douglas SkipD
yucan2;8042 wrote:
Installed new stepper motor. Goes to wide open throttle, cranks strong but won't start. Very cold outside. Hit with starting fluid, starts right up. Shut it down after a few minutes. Place in manual and starts right up.

Is this inherent with propane? Hard start or no start when very cold?
The impression I get is that air may be getting into the fuel system when it's shut down for a while. Thus, extended cranking or starting the engine with an alternate fuel (the starting fluid) is needed to pump the air out of the fuel line until fuel finally gets to the carburetor.

Is the propane being delivered under pressure to the generator all the time or is it shut off between intended runs?
Skip Douglas
Quote
yucan2
SkipD;8043 wrote:
The impression I get is that air may be getting into the fuel system when it's shut down for a while. Thus, extended cranking or starting the engine with an alternate fuel (the starting fluid) is needed to pump the air out of the fuel line until fuel finally gets to the carburetor.

Is the propane being delivered under pressure to the generator all the time or is it shut off between intended runs?


Its being shutoff so what you suggest may in fact be occurring.

I also received a suggestion that I may want to "Close the spark plug gap a bit. Cold propane is a lot harder to fire across than starting fluid is."

Anyway, the owner says that they've always started them that way when cold or at least have for quite some time, until the stepper motor failure.

He's happy so all is good, just thought it odd and unsatisfactory in my mind.
Quote
ceb58
yucan2;8044 wrote:
Its being shutoff so what you suggest may in fact be occurring.

I also received a suggestion that I may want to "Close the spark plug gap a bit. Cold propane is a lot harder to fire across than starting fluid is."

Anyway, the owner says that they've always started them that way when cold or at least have for quite some time, until the stepper motor failure.

He's happy so all is good, just thought it odd and unsatisfactory in my mind.


I have several that do the same when they are "cold"


Quote:
The impression I get is that air may be getting into the fuel system when it's shut down for a while. Thus, extended cranking or starting the engine with an alternate fuel (the starting fluid) is needed to pump the air out of the fuel line until fuel finally gets to the carburetor.


I agree with Skip along with the fact that after the unit sits for a while the gas vapor has evaporated and must be pulled from the flow reg. to the carb.
You mentioned that you had 12" WC the regulator could be turned up a little to around 14" this will give a little more pressure but I dont know if it would make that big of a difference
Quote
yucan2
ceb58;8045 wrote:
I have several that do the same when they are "cold"




I agree with Skip along with the fact that after the unit sits for a while the gas vapor has evaporated and must be pulled from the flow reg. to the carb.
You mentioned that you had 12" WC the regulator could be turned up a little to around 14" this will give a little more pressure but I dont know if it would make that big of a difference


Thanks for the input.

On a related note, owner now informs me that he has 2 other vehicles that have been out of service for awhile. They also have the same generator mounted on the rear of the unit.

He says that he's fairly certain that one of them needs a new fuel tank regulator and he doesn't know the status of the other, but he'd like us to check them both out.

My question: Do I need a high pressure regulator mounted on the tank or can I just go with a low pressure regulator being as the tank is only inches away from the generator?

I think I answered my own question while typing but I think I'll leave it out here anyway.
Quote
ceb58
yucan2;8046 wrote:
Thanks for the input.

On a related note, owner now informs me that he has 2 other vehicles that have been out of service for awhile. They also have the same generator mounted on the rear of the unit.

He says that he's fairly certain that one of them needs a new fuel tank regulator and he doesn't know the status of the other, but he'd like us to check them both out.

My question: Do I need a high pressure regulator mounted on the tank or can I just go with a low pressure regulator being as the tank is only inches away from the generator?

I think I answered my own question while typing but I think I'll leave it out here anyway.


It probably has a duel stage regulator. A single stage secondary (low pressure) reg cannot handle the line side pressure from the tank with out a primary regulator.
Another thought about what you said about reducing the gap in the plugs. You could have a auto parts store cross reference the plugs you have and give you hotter firing plugs.
Quote
yucan2
ceb58;8049 wrote:
It probably has a duel stage regulator. A single stage secondary (low pressure) reg cannot handle the line side pressure from the tank with out a primary regulator.
Another thought about what you said about reducing the gap in the plugs. You could have a auto parts store cross reference the plugs you have and give you hotter firing plugs.


Thanks Ceb.
Quote
VHF
If these units are mounted on a vehicle, what size is the propane tank? Is it a horizontal or vertical tank? Could it be that the tank is not able to provide sufficent vaporization at cold temperatures?

Does the generator run OK under load once started?
Quote
yucan2
VHF;8076 wrote:
If these units are mounted on a vehicle, what size is the propane tank? Is it a horizontal or vertical tank? Could it be that the tank is not able to provide sufficent vaporization at cold temperatures?

Does the generator run OK under load once started?


I'm just guessing, 100 lbs. maybe? It's an upright tank. Runs fine under load once started.
Quote