The Impco system only has around 8-9in vacuum at the fuel cutoff. The big hose has to be connected to get vacuum IIRC. Take the big hose off and the vacuum line, connect a vacuum pump (brake bleeder type) to the vacuum line and see if you get propane. The primer button on the vaporizer is there to jump some vaporized propane before the coolant kicks in to vaporize the propane. The propane cools the vaporizer, so to get a continuous vapor out it needs the coolant, but with just starting up the ambient temp is enough to vaporize some propane. Don't assume the impco stuff is faulty.
As for spark, check it like you would any vehicle, verify with an extra spark plug connected to one of the leads, you should get a hot blue kernel.
The GM HEI modules are either 4 pin or 7 pin, since this is carbed, I'd assume it's a 4-pin. These modules can go bad as can the VR sensor in the distributor body.
I would check each sub component. Try some starting fluid in the intake too, if the engine kicks, it's a fuel problem, if it doesn't kick at all, it's a spark issue. Don't get too crazy with the starting fluid, it can do bad things to engines.
I'm not "assuming" the Impco vaporizer is faulty, via conclusive tests, I know absolutely it is...read my posting on the matter more carefully.
Originally Posted by Perry Harrington
Sorry this isn't about your problem Don, but maybe someday it will be...
If you run low on water (blockage, bad pump, low level...etc.) the thingy with the button will freeze up. It needs running water.
I found this out after having my forklift start and run for between 30 seconds and couple minutes and then stall out. The thingy was always cold or frozen...a state in which it won't work.
Certainly unrelated, but might be useful one day.
Its been a few yrs. since I have worked on one, but I don't ever remember running into a fuel circuit being incorporated into the ign. module. Maybe they have changed since then. Also thought Perry's advice was good on checking the vaporizer. I don't remember Don saying anything about having applied an external vacuum source to see if the propane would flow. My guess is get your spark back and it will run on one of the two units, maybe both.
The fuel circuit is not incorporated into the ignition. Someone in this thread speculated it might be, but even without a wiring diagram I can see there is no way that it is.
Originally Posted by J. Randall
Then re read more carefully. Vaporizer advice was good, but moot as I already know the status of the vaporizer. Also, he was flat out wrong about vacuum not working "with the big hose disconnected". If that were true, how is it that LP does flow out the big hose when I press the button on the vaporizer ? If there was no vaccum, the fuel lockoff would not allow fuel to flow to the vaporizer and out the big hose.
Also thought Perry's advice was good on checking the vaporizer. I don't remember Don saying anything about having applied an external vacuum source to see if the propane would flow.
Re the ignition module...absolutely you must use and refresh the dielectric grease every couple (5) years. The ign module gets hot and the bottom aluminum base of the distributor is its heat-sink. The dielectric grease is a conductive agent that bridges any gap or irregularities in the surface contact.
Mine are thoroughly greased as such and I have never had one fail in 2 TBI pickups, approx 150k miles between the two on my watch. However, I do carry a spare one with me
Also, the crank sensor is more or less a prox switch which "triggers" the ignition event, I think there's only 1 prox hit per crank rev so there's some "multiplier" that compensates for the number of cylinders, I think you might get a spark event on the exhaust stroke too, it's just "wasted" but nobody really cares...not 100% sure how the multiplier part works. The ECM in a pickup sends what I think is an analog signal to modify spark (advance or retard) but I bet for a forklift its something simple such as pure vacuum advance as I doubt there's any knock sensing capability...the spark table is just setup so there's no possibility of a knock event. The strange thing that boggles my mind is that the ECM modification for spark has no mechanical way to realign the distributor cap and rotor to compensate...the spark is simply "hot" enough to jump whatever rotational misalignment exists internally between the bar on the rotor and the pin in the distributor cap for that particular cylinder.
Fixed it... electrical side anyway...she runs when I press the vaporizer button but sputters out when I let off...so still gotta clean that out....but at least I know what the issue is there.
Shall I spill the beans or let you guys guess what the "no spark" problem was ?
1. It wasn't the ign coil
2. It wasn't the ign module
3. There is no crankcase position sensor
4. No fuses blown
5. No oil pressure interlock, or other limit switch type components involved
6. It wasn't something simple like a loose wire. A component did burn out.
What was the component ?
This may be hard, because it may be an electrical component found only on gas and LP forklift engines. The only way I figured it out (sans schematics or any books) was finally reaching a knowledgeable CAT forklift repair tech on the phone. And even then I didn't actually fix or replace the component but bypassed it via jumpers I figured out via his faxed schematic of that area.
And FWIW, tech thinks although this component would normally tolerate 15 volt high start current (i.e. large battery charger hooked up), he thinks sure enough that could have been the straw that broke the camels back on a weak component near failure anyway. So, sure enough, two problems at once...lucky cuss, ain't I ? :rolleyes:
all the best.markj
My only good guess is a neutral-start safety switch or another limit switch which monitors parking brake operation.
However, these might be limit switch devices which were ruled out.
On edit that can't be it because it would inhibit cranking the engine.
Epsi and Matt....No and no
Tachometer/rev limiter? Something downline of the coil?
Electronic La-cuukoratcha horn?
Kinda hard to guess without ever even having seen one.
That's a good guess as it could have been that...but wasn't. I've heard of situations where there was 12 v getting to coil when you turn key "on" but during actual cranking, no 12 v...due to faulty key switch...but not the case here. Note I said "burned out" component...as in shorted. Sean is close when he said something downline of the coil...
Originally Posted by Ralph_P
"Shall I spill the beans"
Capacitor? (as in shorted)
The terminal "R" is the relay terminal used as the starter bypass on old stuff. Not sure if it even applies on these new fangled machines
We know that Don!
OK, the answer is the "5 second delay timer" of course ! Little black potted square about 2 x 2 x 1/2 inch thick with 5 terminals. I have only a vague notion of what it's actually for...something about keeping the starter pinion from engaging the ring gear at inappropriate time and destroying the pinion or jaming the ring gear.
I should probably call the tech back and get him to explain it in more detail, but it is apparently for a pretty rare occurance and ok to bypass it temporarily. I straight wired the 12v+ wire from starter solenoid to the wire on the timer going to the coil and now she runs.
Some may remember I was previously measuring 12v at the coil but this was with negative probe on one of the ignition module wires as ground and I now know it has to be with frame as ground otherwise no "real" 12v to coil....was getting a "fake" reading previously.