I'm thinking that the ECU has to know that the engine is running in order to activate the assist solenoid when the engine needs more power under load. Your accelerator pedal tells your throttle sensor that it needs to open farther when you step down on it. Then the ECU will respond and open the assist or boost solenoid to compensate for the extra load being applied. Still thinking the holder is plugged. Just in case the ECU p/n's have to be exactly the same. You can't just change one over from just say a dual fuel unit. Part numbers would have to match.

The main issue I have is this LPG assistor that has power going to it. If I put direct power to it you can hear propane and smell getting shot from the injector. Without direct power to it it has a very subtle smell of propane. I checked voltage on it and I don't have any volts going to it at all. I pulled back all the electrical tape and even checked almost all the spots going back to the ECU and still nothing. I'm curious if it is just an ECU issue as I see those wires going to the ECU. I can't find much information on these K21/K25s but they do repairs on these ECUs for a reason.

Well now you know that it is able to run with the starting fluid sprayed into it. Your fuel from the vaporizer is suppose to be high pressure which it is to the injector holder. Your injector turns it into low pressure to feed the motor. If it was high pressure it would flood the engine and then it wouldn't start either. If it isn't supplying very much fuel through the injector holder then I would say that it is still clogged up with tar since you can't smell much propane. As I stated earlier sometimes even soaking the holder assy. will not breakup the tar inside. Solvents or brake cleaner usually will not break it up and get things unstuck. That sensor with the spring and plunger will actually boost fuel when the engine needs it when you step on the gas pedal. I tried something once, I fed propane from a propane torch into the air intake to see if it would start and run. If I remember it did start and ran but you have to feed it enough to get it started. ALWAYS BE CAREFUL WHEN WORKING WITH PROPANE!! Tar builds up inside a vaporizer and needs to be drained at times when the engine has been run and everything is hot. The tar turns into liquid form and can be drained. I'm wondering if you could pull the injector housing off and gut the sensors and injector out of it and dip it in boiling water for awhile and see if any tar softens to liquid and maybe it will get unplugged. I've never tried this ever before but it might be worth a shot. You have a lot of expensive parts already installed so it might work possibly. Hopefully it will start and run for you.

Ok, so when turned off the LPG and sprayed starting fluid into the air box while cranking and pumping the gas pedal it will start.

I don't know how the LPG coming out of the injector is supposed to look like but it does not smell nearly as strong as the LPG that comes out of the inlet pipe from the vaporizer and that has a white misty appearance to it. I'm not sure if that sensor to the right of the injector is the problem. I cleaned out the injector housing with brake cleaner and still the same problem. The sensor that I'm talking about is called the LPG assistor that has a plunger with a spring in it.

I removed the intake air pipe that goes to the throttle body, when I turn the key it does push air out but it barely smells like propane and has no color. It doesn't look like the vaporized LPG coming from the regulator at all. It looks like something is plugged up in that injector holder and it hardly lets any LPG pass through to the injector. Just looks like straight air blowing out of it and hardly smells like propane and once I undo that fuel line from the regulator that feeds into the injector housing it seems like a lot of pressure is built up from that propane having nowhere really to go since it is plugged up somewhere.

When I sprayed some starting fluid into the air box after I mounted everything back up it does start after pumping the gas consistently.

Put it all back together and spray it right down into the inj holder. If you have spark it should do something. I've never had a timing chain go bad on a K21 OR K25 but anything is possible. I think you can remove the oil fill cap and look inside to see if you have any rocker arm action when you crank it over. You mentioned earlier that you thought it wasn't getting any air into the cylinders. If the chain is off your valves don't open and no fuel or air gets inside.
Motors with timing belts are bad for that problem. This engine has a chain. Somewhere it has an issue that just needs to be located. Everyplace there is a brass colored cap on the inj holder there is a spring and check ball that you can't remove , sometimes you can clean it enough to make it work and other times you can't. Did you spray inside all the port holes of the holder? Thats where the tar clogs everything up. Good Luck

Yes, I changed out all 4 spark plugs and ignition coils. The fuel screen I did locate and I cleaned it out. You're saying I should spray some starting fluid down the throttle body and try to start it? Without the injector holder and all that plugged up or should I leave it plugged in.

Yes so it does have that small whining noise and the throttle body opens up when the key is turned on. Then it closes back up again. I'm just not sure if its supposed to stay open while cranking or not.

I did take the injector holder off to clean out with brake cleaner but it does not look that dirty on the inside. I have new sensors ordered as well, fuel injector is new so no need to replace that. I tested it and it works without problems.

I changed out the harness to the crank and cam sensors and still to no avail.

I'll check again with the air filter removed to crank it and see if it smells like propane. I have dozens of other projects I am working on so hard to remember if it does!

With the air cleaner air horn off and cranking it over did you smell any propane? If not I would try spraying the starting fluid directly into the throat of the throttle body to see if it will start. If it does start then the injector housing is probably plugged with tar. It sounds like your throttle body is working properly. The small whining noise is when the throttle plate opens slightly when the key is turned on. From earlier messages you said you have spark to the plugs and a blast of fuel to the injector housing thats the way it's suppose to work. Did you locate that fuel screen yet????? Have you pulled the plugs and checked their condition? If you haven't be careful because they can bind up and strip the threads out in the head!! Be careful doing this!! The new plugs are not threaded all the way to the bottom of the plug to stop that issue.

It did not die on me. I used it one day and the next day I went to start it and it did not want to start. I'm starting to think it may be an issue with no air getting into the combustion chamber. I did just check the throttle body and removed the cover to see if it opens. In start position it moves around by itself and stops. When cranking only when pushing the pedal it opens up, otherwise it remains closed. Not sure if that could be the issue. It's very strange that it would not start the next day when I had it running the day before. That's why I was thinking it was some sort of electrical issue. Before that it ran without hiccups.

Yeah, it should be under the sensor that goes down into the inj holder or depending on a s/n break there could be a metal indented cover held with 2 screws on top of the inj holder. About the size of a quarter. I would also try spraying starting fluid all around the intake manifold while cranking it over. You might have a major vacuum leak somewhere. If you do and it attempts to run then it might be cracked. I had one once. I am also not sure if it died on you while driving or just wouldn't start the next day for you.

I haven't checked out those other parts of the engine just yet but will mess with it later today. I did check the voltage going to the cam sensor and it drops to 4 ish Volts when cranking. On they key in the start position it gets battery voltage both the cam/crank sensors.

I do notice a slight whining sound coming from the throttle body. Fuses are all good even the fuse in the fuse holder on the injector red wire. Is the mesh fuel screen in the injector holder part of where the injector is bolted to and where it bolts to the top of the throttle body?

Another thing to check is the throttle position motor. When you turn the key on the throttle plate in the throttle housing should make a slight whining noise for a second or two. If you don't hear it then it may have a bad wire in the connector or the throttle motor may have died. Broken wires in the plugs was always an issue. Did you ever locate the fine mesh fuel screen in the injector holder?? It should be under the sensor going down in the holder or there could be a metal indented cap with 2 screws on top of where it's located. S/N break. If it's plugged with tar it will not start for you either. And the injector housing could still be the culprit. There are check **** and springs that get stuck with the tar and won't feed fuel. I would double check the fuse in the red wire of the LPG fuel injector. Should be a 3 amp mini style. You have fuel to the inj holder and spark to the plugs so probably a issue with fuel not getting into the engine. Listen for that throttle motor to make it's small whining noise. That is located under the inj housing and on top of the intake manifold.

Do you have any idea of where else I should check voltage at to see if maybe it's a bad sensor or part of the harness that isn't open? All 4 ignition coils I have power at as well.

Well, unfortunately the cam and crank sensors did not solve my issue. I have a fully charged battery on the forklift right now.

I should be getting full battery voltage now with two brand new sensors on it so at least that side is solved. This forklift was seldom used and is kept inside my warehouse. All the wires look to be intact and there are no frays, breaks, etc on any of the wires I have seen.

I'm just confused as to how I got it started before when I changed out the crank sensor and cam sensors and now it does not want to start at all.

That harness that leads to the crank and cam sensors is the only short replaceable harness on the whole machine. There is a connector for it about in the middle of the block down under the coils and the cyl. head. You might look at that too, sometimes that harness will be bad or it could have a poor connection. I didn't see any code or hours where the hour meter is. A crank code would be an E-27 but maybe with the low voltages it may not trigger a code. Hopefully you discovered what the real issue is and can get it fired up and back to work again. Sometimes tracking these things down can be a real pain. Hope you get it going!!!