Komatsu FG25ST-16:
No Start

Machine came in with a bad ECU and other problems after some one either tried to incorrectly jumpstart or crank with low voltage.
ordered new ECU from Local Dealer and installed. It now cycles the throttle and turns the fuel on as well as the relays. However when i try to start it fires 1 time then shuts down. Tests show the the trigger from ecu to coils is cutting off after first fire. Oddly though when I was testing to see if it was fuel or spark if I gave it a little extra LPG fuel through the PCV hose (yes i have a way to allow low pressure vapor into the engine since old school methods mess with sensors these days) while cranking it would fire then not fire for a moment then catch and run very well until shut down. Then i would get the one round of fire just enough to kick the starter out.
New parts already are ECU, Vaporizer, Crank and Cam sensors,
Parts swapped with Known good unit Injector, Assist Injector neither of them changed situation and other machine worked fine with this machines parts. When I have it running no check engine light. I have the schematic and all inputs test ok to the ECU.
Not sure which way to go next.
  • Posted 7 Nov 2014 08:25
  • Discussion started by Lifter8tor
  • Washington, United States
Showing items 1 - 11 of 11 results.
I am working in a komatsu FG 150 15. It is fueled by LP. I have checked the fuses and the light shows on the dash. A coworker told me that in order to start it you have to wiggle the forward and reverse gear shifter. To no avail does it start for me nor does it even fire or TICK. I'm lost and need help please
  • Posted 16 Jun 2021 07:58
  • Reply by levin_Ray
  • Missouri, United States
Levin
a very odd one......without a code this ones going to give you headaches it sounds.....if you had a labscope/meter to see the waveform of the cam and crank signals to see if there is a issue with them or the wiring.....one thing im thinking to check is to check your 5 volt refrence voltage to your sensors while cranking and running and see if your losing it,can check it at the coils as well as at the TPS one and two and at the MAF sensor,maybe is a bad sensor pulling tour refrence voltage down....just a wild guess but worth looking at

One other thing....what condition is the battery in? Is the charging voltage ok? Wondering if maybe there is a bad diode in the alternator causing to much AC voltage into the system......can put your meter on the alternator post at the alternator and set meter to measure AC and should be less that.5 v i believe.....might be less than.3 is the prefered cnat remeber off hand..
Posted 7 Nov
I am having the same issue with my Komatsu 40 with 4.5 propane does not want to start if I remove fuel feed line, as the fuel bleeds off, acts as though it wants to start. I have put a regulator and both injectors on it from another exact forklift, that runs and it still does the exact same thing. can you email me the pdf to sales at forkliftusa.com. i will appreciate anything you can send me please help
  • Posted 14 Jun 2018 05:52
  • Modified 14 Jun 2018 05:53 by poster
  • Reply by HydroForklift
  • Georgia, United States
Romat
yes I need them to please
  • Posted 12 Sep 2017 02:56
  • Reply by elverglrga
  • Oklahoma, United States
Hello, I saw your post on forklift action about having some diagnostic schematics for a FG25? We have a 2007 FG25t16 K21 LPG that is a no start, it has spark, but has no power to the main injector when cranking, all fuses appear ok, have had no luck getting info from dealer, which happens to be 2,000km's away, we are automotive techs by trade, had no luck finding wiring diagrams or diagnostic/troubleshooting manuals on line. Would you be interested in sharing some of the info you might have?
Regards
Mark
  • Posted 26 Jan 2016 15:28
  • Reply by LostNorthof60
  • Yukon Territory, Canada
Is a very odd one......without a code this ones going to give you headaches it sounds.....if you had a labscope/meter to see the waveform of the cam and crank signals to see if there is a issue with them or the wiring.....one thing im thinking to check is to check your 5 volt refrence voltage to your sensors while cranking and running and see if your losing it,can check it at the coils as well as at the TPS one and two and at the MAF sensor,maybe is a bad sensor pulling tour refrence voltage down....just a wild guess but worth looking at

One other thing....what condition is the battery in? Is the charging voltage ok? Wondering if maybe there is a bad diode in the alternator causing to much AC voltage into the system......can put your meter on the alternator post at the alternator and set meter to measure AC and should be less that.5 v i believe.....might be less than.3 is the prefered cnat remeber off hand..
  • Posted 7 Nov 2014 10:25
  • Modified 7 Nov 2014 10:30 by poster
  • Reply by kevin_t
  • Pennsylvania, United States
Sent you the Schematics.
No injector driver.
Fuel pressure 4.5psi key on then stays 4.5 while cranking and running. tested at injector holder t into fuel pressure sensor port.
Last chance clean.
According to my meter the trigger for the ignition coils drops off after it fires and then comes back if it spins enough from the first firing.?
  • Posted 7 Nov 2014 10:03
  • Reply by Lifter8tor
  • Washington, United States
Also you said "other problems" what were these problems?? Does this truck have a seperate injector driver controller for the injector? This might be just on the older tier one and six cylinder trucks just wondered if this truck had one? Did you match up the old ecm numbers with the new one to make sure you received the right one?
What is your fuel pressure running at the vaporizor while its cranking? Did you check the last chance screen in the mixer...this is where the vapor hose comes into the mixer,is a small screen about the size if a nickel....
  • Posted 7 Nov 2014 09:56
  • Modified 7 Nov 2014 09:57 by poster
  • Reply by kevin_t
  • Pennsylvania, United States
You say you have the schematic...is this a paper or PDF copy? If PDF can i get a copy of it to look at,i hqve the ones for CAT NISSAN and MITSU but heat that the komatsu is set up a little diffrent? EMAIL,is in my profile...
  • Posted 7 Nov 2014 09:37
  • Reply by kevin_t
  • Pennsylvania, United States
Yes K21 engine 2010 tier 2
fuel solenoid stays on and I have a gauge in the low pressure fuel line it holds steady.
  • Posted 7 Nov 2014 09:02
  • Reply by Lifter8tor
  • Washington, United States
Fresh Set of Eyes always helps!
Does this have the Nissan K21/25 engine?......how does the power to the fuel lockoff look is it staying energized with the key on? Might be a relay issue either the egi 1 or 2 relay or the ignition relay in the other relay box....somthing to check out...also check the main c relay believe this is the one that energizes the lockoff.....
  • Posted 7 Nov 2014 08:33
  • Reply by kevin_t
  • Pennsylvania, United States

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