JLG 26mrt scissor lift Drive issues.

I have a 1998 JLG 26mrt dual fuel (gasoline-propane) scissor lift. The issue is when I start either engine the drive system will not function until the engine has been running for at least 15 min. I have to run the lift up and down, and steer the wheels back and forth numerous times during the 15 mins until the engine is warm. Once I have done that it drives fine for the rest of the day. I have to do this every morning. I have changed all the filters and fluid, check the power to solenoids, and replaced the control joystick. I hope there's someone who may know what the issue is. Thank you.

Does it just not move or does it kill the engine?

The engine runs fine during the warm up but it doesn't drive ( move) until the engine is at peak temp... Or hydro fluid is warm enough. So it seems.

heat the hyd fluid faster by turning and just holding it into the relief for a few minutes. then you will know if its fluid temp related.

Is there any control on the coils or pressure in the drive circuit?

Have you checked or replaced the drive pump charge filter element?

I will try it all today, and let you guys know ASAP

The coil has power when the lift drives and when the lift is trying to drive; the pressure in drive circuit is 1400psi max is 1500psi for the steering & lifting functions according to the book; while the drive is 400psi max is 500psi. The drive pump filter was replaced less than 5 hrs ago, as well as the cutout relay at the same time... But do the coils get weak even though there is adaquite power to it?

I'm not sure why our manuals differ, but the diagram I'm looking at says the lift relief if set to lift 120% of rated load, 2000 psi +/-, steering has crossover reliefs set at 1850 psi, drive pump charge pressure regulating valve set at 300 psi, and drive pressure circuit reliefs set at 4500 psi.

When no lift or steer functions are being operated the coil on the dump valve should have no power on it and the valve is open allowing fluid flow to the drive pump charge circuit. Once pressure of 300 psi is achieved in charge circuit the charge regulating valve opens and allows excess oil to flow to tank.

When you operate lift or steer function, dump valve coil is energized, closes dump valve and blocks oil going to charge circuit to allow pressure to build for lift and steer functions.

Willie59- is that hinting that I may have a bad coil on the drive coil? My pressure setting are not close to the psi settings you have... Is there a place I may be able to find your service manual?

I downloaded the manual from the JLG website, you should be able to do the same, although typical of JLG, their manuals have never been all that great. There should be ports on the pump to test the charge pressure and the drive stall pressure.

But from what you describe, drive won't work until it's warmed up, then works fine the rest of the day. I'm wondering if the system has a grade of hyd oil that's too thick in viscosity. The JLG book recommends Mobilube 424. I don't know what the equivalent would be, but 424 has a viscosity of Cst @40C of 55, ISO 46 has a CST @40C that's close to that spec. Being in Wisconsin, you might consider using an AW32 hyd oil.

Perfect I will give it a shot! Hopefully it will resolve my issue.