This is a long post, even by my standards, but I want to try and include as much detail in the presentation as possible instead of waiting for respondents to ask a lot of questions, and then have to add details one at a time.
I will outline the problem in the order of occurrence that led me to the present problem.
During the first week of 2013 the truck was sent to our shop from another facility for us to fix a problem indicated by the MIL being lit continuously.
The DTC at that time was 0031, "HEGO sensor heater circuit open".
Testing the O2 sensor heater circuit (in the sensor itself) showed the HEGO to be in good order so I then checked for continuity on the BLUE/black tracer wire from the HEGO chassis connector to pin # 24 of the ECU chassis connector. That showed there was continuity present, so the wire was sound.
My conclusion was that the ECU itself was defective.
I ordered a new ECU from our local Komatsu dealer. I obtained the ECU part number from the Komatsu Parts manual we have on hand. I ordered ECU part # 37B-1DT-3210.
When the new ECU arrived, I was told the part number had been superseded to 23710-FT860.
I installed the new ECU and immediately got an MIL and DTC 1245 described as "LPG FUEL PRESSURE SENSOR HIGH, INPUT FAILURE". But the 0031 HEGO DTC was gone.
Subsequent investigation and conference with the local Komatsu dealer revealed that the ECU I had ordered was configured for the early version K-21 which has the LPG pressure sensor mounted atop the injector body with two 5mm screws. But the ailing K-21 I'm working with has the later version of LPG pressure sensor which threads directly into the front of the injector body. I learned that the ECUs do not interchange so I had no choice but to let my local dealer select the correct ECU by VIN and the Nissan part # from the original ECU (23710-FT81B). We will retain the "wrong ECU" in our stock because we actually have quite a few of the early versions in our fleet.
OK, if you are still reading, we are now going to get to the present problem, and I have not had but about 1 hour to devote to it so far at work, but I am trying hard to cipher it out here at home this weekend.
Friday I got the latest ECU and the old Nissan part number has been superseded to 23710-GU21A.
I installed this ECU and as soon as the engine started, the MIL came on, a few seconds later the engine stopped running. An immediate attempt to restart was futile but after waiting a minute or so it restarted.........and died again after running about 30 seconds. This could be repeated with consistent results.
Connecting the Hitachi diagnostic reader tool revealed the DTC as 1241 "LPG_F/INJ 1 FAILURE (NO INJ MEDIUM ZONE)", further described as "LPG injector signal circuit is open" in our Komatsu SM 300 manual.
Thinking perhaps there might be a compatibility issue with yet the newest ECU I decided to re-install the original ECU and see what happened.
With the original ECU in place, the engine started and immediately lit the MIL, after about 30 seconds the engine died.
Checking the reader revealed DTC 0031 (as expected) and DTC 1241 (same as with the new ECU).
When we received this truck DTC 1241 never came up and we ran the ran the engine for long periods and it never shut down.
I only got as far last evening as determining that the engine is shutting down because the ECU (both of them) is interrupting power to the LPG Interception Valve (fuel inlet solenoid valve). I interpret this action as part of the safety interlocks incorporated into the LPG system design to prevent leakage of LPG through the engine should some parameter (injection signal?) be absent while the key switch is ON.
With the Hitachi reader I was able to watch the indicated LPG pressure drop rapidly from 23 kpa to 1 kpa at which point the engine died. A physical check of the vapor hose at that time showed no fuel pressure present, so I was able to deduce that the engine is consuming the quantity of fuel between the Interception Valve and the Injector, resulting in "fuel out".
Has anyone out there ever had a problem similar to this?
I am suspecting that there might now be a broken wire in the big chassis connector at the ECU and I plan to do continuity testing when I return to work Monday but I wanted to run this issue past the forum community in hopes I might get some helpful feed back.
If you are tired of reading this, imagine how weary I am becoming of this truck.
Showing items 16 - 16 of 16 results.
I think you are absolutely correct in that the engine control computer is shutting off fuel at what most of us call the lpg lock-off, that Nissan engineers refer to as the 'interceptor valve', in the books, due to the ECU not seeing an important input from something in the vehicle's can bus.
While I would never suggest anyone tamper with any parts that are specified as "tamper proof" or "tamper resistant",,,
I think if someone were to open up the ecu wire plug connectors on the wire side they may well find a broken wire, and/or replace the wire harness, depending on the age of the truck. A newer truck still under the government mandated extended warranty for items related to the emissions controls may get a new harness at the factories expense so the factory engineers can look at the failure and try to figure out how to avoid it in the future, where a 10 year old truck may get the soldering pencil and a drip of super glue taken to the spot the wire pulled off the connector plug.
The legality of doing repairs to an item specified by government mandate to be 'tamper proof' and that the factory says requires replacement rather than repair is not something I would be wanting to be on the wrong end of telling someone to do, for someone else to profit from. and I do not know what Komatsu suggests as the proper way to repair a wire that has pulled loose from the pin.
I do know that in the past the factory has suggested a dab of Dielectric (spark plug boot) grease in each of the plugs during reassembly as a way to reduce moisture and related corrosion in those pins and sockets on the ECU.
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