Does anyone know about the IMPCO LP system on older buses. i have a 2000 GMC conventional, 454 engine, with this system and it won't run full throttle under load. Bogs down to about 25mph going up a hill. Only can push pedal down halfway or it will buck and jerk and not gain any speed. Anyone been around long enough to have any ideas? I had a MAP sensor code but have replaced that and shows no codes now. Ed
A carbureator system correct? I would make sure manual liquid fuel shut off valve on tank is fully open. Check vent opening on the vaporizer to make sure it is open, no hosing from this port to any location. Also make sure any fuel filters, usually in fuel lockoff, are not retricted.
havent seen it on a bus, but had similar issues with a forklift. the cause was leaking vacuum hoses to the throttle body and leaking diaphragms in the vaporizer.
I don't know if you call this carburetor type or not. It has a vaporizer then a mixing chamber before going onto intake manifold. It is a 2000 model GMC. I have checked pretty much everything else for trouble spots. I have oil in the mixing chamber. The retired mechanic said to check hose from vaporizer to see if it had oil in it but I can't get it off very readily so pulled off cover of mixing chamber and found the oil. I'm guessing that a diaphragm is bad in the vaporizer as stated here from other post. ED
As I recall finding oil in the vapor fuel chambers and lines was quite common.
If this was an aftermarket conversion the factory timing specs may not be correct for the fuel.
Ignition system has to be spot on for LP as its harder for spark to jump the plug gap. Make sure advance mechanism is not froze and cap, rotor and wires are in excellant condition.
I know this sounds elementary but it sounds like it's starving for fuel. Wonder if you have a rubber line collapsing? I'm not familiar with these old systems so just using mechanic logic. lol
IMPCO LP SYSTEM
Posted - 11/18/2016 : 12:05:38 PM
