You might not even be able to find replacement parts/kits for this regulator/vaporizer.............one site I glanced at states that it is "non-serviceable". That is kinda the norm with some component assembles that carry a C.A.R.B. certification these days.

I'm not familiar with your exact regulator, but I can tell you that a faulty regulator can cause multiple symptoms, some more prevolent than others.

Also- a warm engine is more tolerant of fuel mixtures being overly lean/rich than a cold one. The older impco regulators had no provisions for cold fuel enrichment. If the electric "trim" device you speak of is malfunctioning, do yourself a favor & replace the entire regulator (with the fuel trim solnoid) attatched- you'll save alot of frustration in the long run.

Here's an update and additional questions...

Most of the ignition system (coil, module, pickup, cap, rotor, wires, plugs) has been replaced. A local tech told me it was likely the mixer - I replaced that - still having the problem.

Last night I was here late - quiet so I could hear things. I noticed that as soon as I turned on the key - I could hear a hiss. I found it was coming from the gas line going into the mixer. The truck finally has completely stopped running and hasn't ran for more than a week now. I turned the gas off and bled all of the gas out of the line. Then I just cracked the valve on the tank - truck started and ran like a champ. After the truck warmed up, I opened the valve just to see what would happen - truck ran fine - no issues. I shut it off - it started right back up.

The truck has an Impco CS4-30772-004 regulator on it. The regulator has a device attached that has a two wire harness and vacuum line attached. I'm sort of thinking this a some sort of fuel trim???

Since after it warmed up, it ran fine, do you think it's the regulator? It doesn't really make sense to me that it would be bad since it's just a diaphragm it should either work or it shouldn't, right??? If my assumptions are correct that the attached "valve" is a "trim" device I'm leaning in that direction as the culprit.

This is all sort of beginning to make a little sense - too much fuel fouls a plug - get a miss that seems to be intermittent - replacing the plugs seems to help. But as I've said all along that was just masking the real problem...maybe???

Any help would be greatly appreciated since none of the local techs seem to be able to figure this out.

Thanks!

Don't know if you have fixed this issue or not but from the outside looking in, I would ask, Is it always the same cylinder missing or does it move. Same cylinder would indicate things like a valve sticking or a lifter collapsing or not pumping up. Maybe the new tuneup parts just mask the issue..

I have had this problem with these engines and with alot of the cheaper aftermarket ignition parts,

The fix i found was matching it with the better automotive cross overs:
- if it has the spider style igntion cap its a 1999 GMC Safari
- if it has the tall cap its a 1995 GMC Safari and buy decent cap and rotor

as for plugs get the 1995 GMC Safari AC Delco Non-Platinum plug (i find they with stand the heat of especially propane trucks)

Has anyone checked or replaced the coil? Maybe this is your problem with the truck,just another possibility to look at,with the engine running take a spray bottle of water and wet down the coil and see if you get any arcing or if it starts missing. might have a crack or carbon tracking in the coil someplace that acts up at times
Have you done a compression check on the engine,to see what the compression is like?
Is there an LP injector/injectors on the truck? Possibly an injector sticking closed? Just because there is a miss dosent mean that it is Igniton system related,it is the highest probabliity but not the only thing to look at.
One other thing has any one checked the pickup in the distributor????

I would think that the MAP & CTS would throw a code if they were faulty. As far as the HEI module, usually when they go bad, they're done. Not usually an inconsistant issue.

I personally would take the cap & rotor down to the local NAPA store & have them match them up for you. I have used the following #'s on a Hyster with the V-6: RR203 cap, RR173 rotor, 700322 wire set & AC plugs- R44TS. The cap is fairly large (probably about 6" in diameter)- if you have a small cap (about 4" in diameter), the cap & rotor #'s are incorrect for your application

I've always had great luck with NAPA igntion parts. Usually the dealers sell aftermarket ignition parts which have always been a headache for me. Hope that helps.

2 Sets...

Latest thought is maybe the HEI module is bad? According to the latest mechanic, there are only 2 sensors - MAP & CTS that the ECM uses. Sound right???

What about the spark plug wires?

To be honest - I'm not sure. I have a service contract with Yale Carolinas - that's where all of the mechanics have been from and where the parts are coming from...

You say that by replacing the cap/rotor & plugs, the symptoms go away for maybe 2 months? What is the brand of these items?