Hi. how did you manage to notice that to much end play on the crank??
thanks

Update: Problem was too much end play in crankshaft. Causing slight misfire at idle only.

commen problem to match play on the distributor axle and distributor cap internal flashover

You mentioned you tried an ECM from another truck- I'd take readings from the sensors on the truck that was operating ok & compare them to readings on this truck. I would think that there would be a code stored if there was a sensor issue.

Running rough could be a timing or a EGR issue. They would be my next targets

ok, so not an LP truck, my mistake
without a serial number it will be hard to give an accurate suggestion as to what the problem might be.

got one on this truck?

We just tried that but it is hard to tell because it runs so bad at idle. I can't tell any difference in the idle performance by unplugging or pinching them off either on the new ones that are on it or with the originals. There are two new ones on it because they broke the originals when they took them out to look at them.

What do you make of this: We have 12 volts at the cam sensor and 5 at the crank sensor - shouldn't these be similar voltages? We can take the cam sensor off and no change in the idle....it even starts right up without the cam sensor plugged in. We have had two seperate OEM techs out to look at it three different times.

It still sounds to me like the injectors are faulty. I've found that they stick in the open position, causing one or more cylinders to run too rich at idle. Try unplugging 1 injector at a time while the engine is idling. Good injectors that are unplugged cause an immediate notable miss, while the faulty ones take a few seconds before the miss happens.

If you do find a faulty injector, bite the bullet and replace all the injectors. I've never replaced just 1 injector without the rest needing replacement shortly thereafter.

The truck has about 9000 hours on it. I assume the injectors are the original. No change in idle after running at high rpm for about a minute. We did clean out the lpg regulator though it was not dirty. Also, we tried another ECM from another truck and this did not fix it either.

How old are the fuel injectors? If you run the engine at high rpm for about a minute, then return engine to idle- does the miss go away for a short while?

Thanks, but this model doesn't have a mixer, it has injectors and all that jazz for EPA emissions. It has an electronic throttle body which we replaced with new. We are thinking vac leaks but can't find anything obvious.

if you've done all this to the ignition system and all is good then i doubt the ecm is bad. it sounds more like maybe a mixer issue?
have you cleaned out the mixer and the seat in the diaphram in the mixer?