Sounds like a Hydraulic Issue to me.

#1 Check that the pump is outputting the correct pressure/flow. if there is a case drain on your pump, you should check how much flow you have on the drain line... a lot of flow would indicate a failed pump, a little trickle is normal... but this is only the case if there is a separate drain line for the case.

If you reduce the main relief valve pressure to a much lower than operational pressure and your problem goes away (except for the new problem of a screaming relief valve). You can assume you have a problem downstream of the pump IE valves/motors etc. If the problem persists, you may have a problem with your pump.

I suspect if your problem is with multiple functions, it would most likely be a bad pump, but I really don't know enough to give you an educated answer at this point.

Thank you for your direction. I will check out further...

I am not familiar with the model of forklift you have. Is it gasoline or propane powered? If so, the symptoms you describe are what you would find with a problem of not sufficient voltage to fire the spark plugs under increased load (cylinder pressure).

It could be plug gaps that have worn over time.

It could be plug wires that have become brittle and are leaking voltage to ground. Both of these would bring on the symptoms very gradually.

It could be the rotor allowing voltage to ark through it. same for a distributor cap. Don't rule out an ignition coil, or even points or condenser it old enough. Good luck.

I get the feeling, from his post that the engine is actually running ok, but it's the functions on the lift that cause the engine to stall, which would indicate to me something in the hydraulic end of things causing a higher than normal load on the engine. However, if the engine is indeed the culprit, that's a whole different set of troubleshooting issues, and should be independent from the hydraulic functions on the lift.

Engine bogged down or stops when load is put on it..I.e. Maxing out steering wheel,or putting in gear to drive.

Running the steering against the stops would indeed allow maximum pressure build up, and noticeable engine loading symptoms could be normal. But just putting it in gear should not cause excessive hydraulic pressures to build. That is what I read into the message. JMHO.

I read no performance under load. If it's propane, maybe a kink in the feed hose, or a regulator flaw. More information, please!

these might b the causes....

1) Engine too weak.

2) un due load of hydraulic pressure..

3) Gear box problem.

check them and hope you will b doing well.......................

research indicates this is an LPG engine? Weak spark or fuel flow. Unfortunately, could be any number of things. Unfortunately, the newer engines are WAY more complicated than the older ones that only required a main pressure regulator and the other regulator that senses venturi vacuum and meters the fuel accordingly. If you are lucky enough to have the old style, make sure both regulators are functioning properly. There should be a simple mixture adjustment screw on the carburetor. You can try adjusting that. If the mixture is too rich or spark really weak you'll know it by the smell of unburned propane.

a bad ignition coil will perform normally when you first start it up from stone cold and performance will progressively degrade as long as the engine is running. shutting off the engine after running for a time and attempting a restart will be problematic or futile. That is because the coil is an oil-filled transformer and will actually go into a condition similar to thermal runaway as the short in the coil causes the oil to get hot which further degrades the insulation leading to worsening of the short which heats the oil further....

Weak spark can be checked with a regular #2 pencil or you can actually get a test light to test spark pretty cheap.

Don't forget to check for vacuum leak(s).

Vacuum leaks suck.

I once bought a car that was sold as having a defective lock up converter because it would run just fine till put in gear. It would stall out immediately in any drive position. Trans shop said "no lock up converter on that model". Further checking showed the distributer cap and rotor looked like they had been hit with lightning. After replacing them, the car ran fine for a couple of years till my daughter decided to test the limits of the temp gauge.

We had the same issue on our toyota LPG towmotor dying when the wheels were turned fully when standing still. We had a combination of too low idle setting and hyd.p/s return line kinked creating too much back pressure for the low idle of engine to handle.

Good luck.

we had a problem with our fork truck a Toyota and the main problem was traced to a bad plug wire. The forklift had all the same symtems as this article. would sit and idle but you could not load the engine with-out missing and backfire. hope this helps.

You demonstrate why it is poor policy to fix your problem, with someone else's cure.

While I realize that not everyone has access to an oscilloscope, your problem, and the OP's problem would show up easily on one.

BTW, welcome to the insanity.

I don't have 1 of these forklifts but I searched & found on the internet that your model forklift have a 4Y engine in them, am I correct? If I am look HERE 3/4 down the page is the link to a torrent for the service manual for the 2Y-4Y engine apparently also used in the Volkswagen Taro, which was a rebadged Hilux.

So If I got it all right the manual I found for that engine shows it as a points Ignition system so if that is the case & you have the same ignition I would be checking the condition of the points & make sure they aren't pitted & adjust them up as they should be I would be inclined to replace them, also check the condenser on the points as the same problem can be caused by a faulty condenser & as with any time you adjust or replace points, check & readjust the timing as needed.