GM Impco wiring

[Yroc]

Does anyone know where the wires on the low pressure regulator are supossed to be connected? Someone clipped these to disable the CNG system on this Jimmy. Thanks in advance.

[BRodri]

Re: GM Impco wiring

i think that is actually your low pressure fuel lock off. it just takes a positive and a ground with a 3 amp capability. you can test to see which one is positive and which one negative with a battery charger. if you see two other wires near there. then that is where it is connected at.

[larrycng]

Re: GM Impco wiring

Brodri is right it is a low pressure lock-off. It is an insulated unit so it doesn't which wire goes where

One wire should go through a lock-off switch which can work on engine vacuum or to a oil pressure switch that is normally open and goes to ground. The use of one of these switch ensures that there will be no gas flowto the engine if the engine is not turning over.

The other side should go to the ignition switch (dedicated vehicle) or to the switch over control for power. This low pressure lockoff should only be on when the engine is running on the gaseous fuel and should be off when the engine is off eventhough the ignition is on.

NFPA 52 -6.6.3 "a valve that automatically prevents the flow of gaseous fuel to the engine when the engine is not running, evenif the ignition is switched on, shall be provided in the system."

This requirement could also be meet with a high pressure lock-off, but the Low pressure lock-off is more effective.

Larrycng

[Yroc]

Re: GM Impco wiring

Thanks that is all good to know. I don't actually have the vehicle yet, so I'll check that out when I get it. They guy we bought it from said he ran 12V to the switch and it would run on CNG for a minute and then die, I'll have to check into it when I can see it.

Thanks again!!

[Yroc]

Re: GM Impco wiring

So I ran 12V to the solinoid and it switched on and gas flowed freely through the regulator. Does this mean it needs a new reg? I heard there is a rebuild kit for these? ANyone know where I can get one? It's am Impco Model E low pressure regulator.

Also, how to the buttons work inside to switch from CNG to gasoline? There is a light that is lit when it's running on gasoline, when we pressurized the system, the light went out, but it won't start or run on CNG. So we tried to switch it manually to run on gasonline, but it wouldn't. I had to turn of the valve under the driver door and then power the solinoid until all the pressure was gone, then the light came back on and it started on gasoline. Shouldn't it be able to be switched manually??

[BRodri]

Re: GM Impco wiring

Ok i got my rebuild kit for the regulator from a local propane company. it wasn't very expensive but if it is flowing freely through the regulator there could be a problem at the mixer. but once again i am not an expert in this category but maybe someone with more experience can help.

[larrycng]

Re: GM Impco wiring

check the diaphram in the mixer and the passage that sends the air valve vacuum signal to the diaphram (assuming a 300a or 425 mixer). Make sure everything works freely.

You can download the whole Impco master catalog from the Impco website. It has a whole lot of good information that can be useful. Page 102 has the breake down of the 425.

I was going to attach the catalog but its a 10mb pdf files and 5 is the limit

Larrycng