94 K1500 Converting from Propane to Gas

[04silvyhotrod]

Needing some info on what all is needed to change a 94 k1500 over from propane to gas?

I've found a deal on a real solid 94 K1500 that came from the factory setup to run on propane.

It's got the 350 and nv4500 in it and the way the guy talks; used to be a company truck and has ran on propane ever since 94. It looks to be all original and solid as they get.

He told me it wasn't hard to change it back over to gas. That he had everything needed to change it over. He said all you had to do was put the gas tank, sending unit and fuel pump back in it and hook the fuel lines back up to the throttle body.

I've never seen or messed with one but wouldn't think it would be that hard to change it back over. But don't see how you wouldn't have to change the ecu in it to one out of a gas truck.

If anybody has seen or did this swap some opinions is appreciated.

 

[stutaeng]

@Pinger has a LP setup. Not sure if bought his truck like that though. There may be another guy that also has a similar setup that recently joined.

Both are in Europe IIRC.

Good luck.

 

[Pinger]

My truck was converted to run on propane 3 years after it left the factory so a completely different system to GM's - though the operating principles could be the same.
On mine, all the gasoline kit remains (it can run on either fuel and gasoline is used for cold start) and the electronics are 'fooled' into thinking it's running on gasoline when running on propane.

For yours to be a straightforward change to gasoline the electronics to control the fuel injectors will have to be there. I can't say with certainty that they weren't used to control the propane system. Unlikely in 1994 that injector signals were used but if a closed loop system (probable) then the O2 sensors will have been used. This is kind of important as with the aftermarket system I have, if the mixture is wrong when on propane, the gasoline fuel trims can shift and running on gasoline then becomes erratic (until they correct again).
If you can get a photograph of the system - look for a 'mixer' in the inlet tract between MAF sensor and TB and a 'stepper actuator' in the propane feed pipe to the mixer. That would give a clue to the type of system (ie, closed loop single point mixer).

What has me slightly confused though is that there's no mention of the ability to run on either fuel (dual fuel). If the injectors aren't there for that then it's a bit of a stretch to imagine an ECU there configured for gasoline operation. If dual fuel operation is there - then all the tank. sender, and pump should already be there. Including a gasoline gauge on the dash. Then, all that is required is to throw a switch for gasoline operation and discarding the propane components is entirely optional.

I have a bit of lit on the GM system. I'll try and find it and if there's anything of use, post the details or document here.

 

[04silvyhotrod]

My truck was converted to run on propane 3 years after it left the factory so a completely different system to GM's - though the operating principles could be the same.
On mine, all the gasoline kit remains (it can run on either fuel and gasoline is used for cold start) and the electronics are 'fooled' into thinking it's running on gasoline when running on propane.

For yours to be a straightforward change to gasoline the electronics to control the fuel injectors will have to be there. I can't say with certainty that they weren't used to control the propane system. Unlikely in 1994 that injector signals were used but if a closed loop system (probable) then the O2 sensors will have been used. This is kind of important as with the aftermarket system I have, if the mixture is wrong when on propane, the gasoline fuel trims can shift and running on gasoline then becomes erratic (until they correct again).
If you can get a photograph of the system - look for a 'mixer' in the inlet tract between MAF sensor and TB and a 'stepper actuator' in the propane feed pipe to the mixer. That would give a clue to the type of system (ie, closed loop single point mixer).

What has me slightly confused though is that there's no mention of the ability to run on either fuel (dual fuel). If the injectors aren't there for that then it's a bit of a stretch to imagine an ECU there configured for gasoline operation. If dual fuel operation is there - then all the tank. sender, and pump should already be there. Including a gasoline gauge on the dash. Then, all that is required is to throw a switch for gasoline operation and discarding the propane components is entirely optional.

I have a bit of lit on the GM system. I'll try and find it and if there's anything of use, post the details or document here.

I asked him about the dual fuel but he wasn't making much sense to me. I don't know if he's meaning it was and he took all the stuff concerning gas out or it wasn't and he has the stuff to convert to gas. He said all the wiring and plugs is there for the throttle body.

He sent me this pic of the propane setup, I've never seen one or been around any propane vehicles. So I'm clueless as to what system them is.

You must be registered for see images attach

 

[Schurkey]

Ten years ago--more-or-less--I bought gasoline-fuel equipment taken off of 8.1L trucks by the company contracted to convert them to Propane.

At least that company--and others, I suppose--were gutting the gasoline system during the Propane conversion.

I ended up with a couple of fuel pump modules, a set of injectors and fuel rail, some ignition coils, and a front cover with crank sensor. All of this was to be used to get my 8.1L engine running. I'd bought an eBay 8.1L, used, with a heap of miles on it. It was missing all the fueling system including the throttle body, and some of the sensors.

Never did finish that project.

 

[TechNova]

I had a dual fuel big block apart many years ago. It was the cleanest 100K engine I had ever seen. There was no carbon and I was later told propane did not wash the cylinders like gas running rich. This meant the bearings would be in better shape due to oil not being contaminated.

 

[Pinger]

Found the document I was referring to. It refers to a Vortec so as well as not being appropriate to a 1994 truck, it is also a crate engine with no mention of it ever being in a truck from new.

The system on the truck you have seems to be a 'carburettor' one. Google 'Impco carburettor' for more info. Almost certainly an open loop system ie, no feedback from O2 sensors. Unless either you can see wires to the 'carb' or there's an actuator/stepper at the other end of the propane supply pipe (out of camera shot).

Usually, with a propane conversion gasoline operation is retained not least for cold start when there is no heat in the coolant for the propane vaporiser.

I'd dig deeper as to what GM offered - if it's true that it came from the factory propane ready. I'd also heed Shurkey's comments about gasoline system parts being jettisoned. If no info on the former, familiarise yourself with everything required to make a TBI run on gasoline and check that the parts are present - or can be obtained (at an acceptable price to you). ECU included.

Or - assuming adequate propane supply in your area - consider continuing with propane. It's a good fuel with a high octane number, doesn't need cold enrichment, doesn't wash oil off bores and self pumps as a pretty simple and reliable system. It has a lower energy density than gasoline so less MPG but it should also cost less.

 

[04silvyhotrod]

Found the document I was referring to. It refers to a Vortec so as well as not being appropriate to a 1994 truck, it is also a crate engine with no mention of it ever being in a truck from new.

The system on the truck you have seems to be a 'carburettor' one. Google 'Impco carburettor' for more info. Almost certainly an open loop system ie, no feedback from O2 sensors. Unless either you can see wires to the 'carb' or there's an actuator/stepper at the other end of the propane supply pipe (out of camera shot).

Usually, with a propane conversion gasoline operation is retained not least for cold start when there is no heat in the coolant for the propane vaporiser.

I'd dig deeper as to what GM offered - if it's true that it came from the factory propane ready. I'd also heed Shurkey's comments about gasoline system parts being jettisoned. If no info on the former, familiarise yourself with everything required to make a TBI run on gasoline and check that the parts are present - or can be obtained (at an acceptable price to you). ECU included.

Or - assuming adequate propane supply in your area - consider continuing with propane. It's a good fuel with a high octane number, doesn't need cold enrichment, doesn't wash oil off bores and self pumps as a pretty simple and reliable system. It has a lower energy density than gasoline so less MPG but it should also cost less.

Appreciate all the info buddy, I'm going to look at it tm and will get better pics of everything.

I'd really like to bring the truck home for the price. For $2000 I honestly feel like it's a good deal considering it's a rust free RCSB truck. And it having the NV4500 just makes things better.

As far as keeping it on propane that's not outta the question yet. I'd have to check around on prices and see how many places offers it.

 

[Pinger]

Being in the UK I've no idea if that's a good price or not! But it's a running truck and if you buy it I'll give you something to check on the propane system that if it's been neglected will need doing and will benefit it (it's very simple and costs nothing).

If the propane prices are good.... and anyway, it's a runner while you make the gasoline conversion so no down time. Stick with the propane and you'll never have to be concerned with that GMT400 Achilles heel - the in-tank gas pump!
Ask the current owner what MPG he gets. If it's less than 3/4 (due to lower energy density) of what you'd expect, that could point to a primitive propane system with poor metering and changing to gasoline could be beneficial after all. Ditto propane prices. 3/4 of gasoline or lower.

 

[04silvyhotrod]

Being in the UK I've no idea if that's a good price or not! But it's a running truck and if you buy it I'll give you something to check on the propane system that if it's been neglected will need doing and will benefit it (it's very simple and costs nothing).

If the propane prices are good.... and anyway, it's a runner while you make the gasoline conversion so no down time. Stick with the propane and you'll never have to be concerned with that GMT400 Achilles heel - the in-tank gas pump!
Ask the current owner what MPG he gets. If it's less than 3/4 (due to lower energy density) of what you'd expect, that could point to a primitive propane system with poor metering and changing to gasoline could be beneficial after all. Ditto propane prices. 3/4 of gasoline or lower.

I've got 2 other K1500s, a 88 k1500 and a 89k1500. The 89 has a stout 400 in it and the 88 is all orginal with 109k miles. Just like these body style trucks and that 94 is clean, be a good addition to the other two.

I found a article browsing around on the web and do believe this truck still has the TBI and all the wiring and stuff to still run gas. This impco kit in the article looks similar to the pic he sent me. https://www.rasoenterprises.com/propane/35-conversions/53-dual-fuel-tbi