Transmission (JAPCO) won't shift into 4th Gear
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Thread: Transmission (JAPCO) won't shift into 4th Gear

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    Default Transmission (JAPCO) won't shift into 4th Gear

    Hello Yall,
    I have a 91 Safari Trek 2810 RV with Isuzu 4BDT 3.9L Turbo Diesel engine and a JAPCO 4 speed automatic transmission. . The transmission is no longer shifting into 4th gear and I have no waning lights on the dashboard. This problem started as an on and off issue about 3 months ago, but it has been an "On" issue for the last three weeks. I believe this is an electrical/Computer related issue rather than a bad transmission (it only has 50K). I changed the transmission fluid and filter 5K miles ago (a year ago). The "Economy" light will not light up when I turn it on (whether this light comes on, or not is my indicator whether the transmission is going to shift into final gear). Has anyone experienced this issue before and solved it? I would really appreciate any suggestions.Thanks a lot

    Ollie North
    91 Safari Trek 2810 Isuzu 3.9L Turbo...Austin, TX

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    Have you tried cleaning the grounds for the computer and harness?

    Are both fuses good, and making good contact for that system? (my NPR has 2 fuses for the ATCU, one is constantly hot, the other is switched with the key).

    I haven't had the particular issue you describe, but those two issues have caused me dificulty with how my JATCO JR403E works.

    Are you sure it's 4th, and not the torque converter lockup you are having issues with?

    I'm not nit picking, just asking.
    Erik
    Isuzu Nut
    Deviant that's keeping the NPR (with the engine).
    http://www.4btswaps.com/forum/showthread.php?t=9646
    '94 4BD2-TC, HY35W (early) with 3" exhaust & exhaust brake, 'more power screw' maxed, defuel turned up, pump turned up internally by accident.

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    I did double check both fuses, and they both were good. Where would "the grounds for the computer and harness" be located? I know where the ATCU you is, and I made sure the two plugs were plugged in tight going into it. The RV is devintely not shifting into 4th gear, I can't go faster than 45 mph. The "Economy" light won't come on either. I changed the inhibitor switch a year ago, because the RV was down-shifting on it's own when it was not supposed to...that took care of the problem. How do I know the model # of my transmission...is there an ID plate somewhere?

    Thanks a lot for your reply.

    Ollie North
    91 Safari Trek 2810 Isuzu 3.9L Turbo...Austin, TX .

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    If it's the Jatco (it should be) it will be the JR403E, at least from what I've seen and read.

    Is the chassis under your RV the same as the N series (NPR, NQR, NRR)?

    If it is, that will help locate the grounds, as the harness should be the same.

    If not, I'll see what I can figure out from this end.
    Erik
    Isuzu Nut
    Deviant that's keeping the NPR (with the engine).
    http://www.4btswaps.com/forum/showthread.php?t=9646
    '94 4BD2-TC, HY35W (early) with 3" exhaust & exhaust brake, 'more power screw' maxed, defuel turned up, pump turned up internally by accident.

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    It is based on the NPR truck Chassis. It is a 4BD 1T, 3.9L Turbo diesel. I replaced the ATCU fuses and unplugged the battery for 1hr, still no go. I really feel the issue is a computer/Sensor or vacuum related issue, I do not believe the transmission has gone south.

    Thanks for all your help Erik, I really appreciate it.

    Ollie North
    91 Safari Trek 2810 Isuzu 3.9L Turbo...Austin, TX .

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    Okay, took me a bit, I learned how to upload to photobucket, from my phone. (woohoo )

    So I have pictures.

    First one is the schematic for the ACTU.



    Notice it shows only one constant ground for the harness (lower right hand corner of the pic, on the second trace below the rest of the schematic labled "frame, left front").


    Another is listed as "pressure line duty solenoid", as what appers to be a gang ground at the unit itself (may be internal to the trans, I don't recall).

    In the next diagram, are the grounds that Isuzu fesses up to (I suspect there are a few they forgot).



    It shows several grounds, but one of them is on the left front, it's by the steering box on the frame on mine.

    Best of luck to you.

    FWIW, when I start cleaning grounds on mine, I clean all I can find.

    Do you have a manual?

    In the Isuzu stickies is a link to a free one.

    You may have to pay to use the reader to convert it though, as the last time I tried it, it wasn't a PDF.
    Erik
    Isuzu Nut
    Deviant that's keeping the NPR (with the engine).
    http://www.4btswaps.com/forum/showthread.php?t=9646
    '94 4BD2-TC, HY35W (early) with 3" exhaust & exhaust brake, 'more power screw' maxed, defuel turned up, pump turned up internally by accident.

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    Thumbs up

    Thanks a million Erik, I'll start with that and hope that will do the trick. I also plan on changing the transmission fluid and filter. I read on the forum that I can unscrew one of the transmission lines going to the cooler and flush more transmission fluid that way...do you have any tips on how to do it safely?

    Thanks again for all your help

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    I did that on mine like the "hoot" method from Dieselplace.

    The line on the left side of the trans is the return.

    Make sure you don't run the trans dry.

    I'm running an aux cooler and an aux filter (crosses to an allison, amongst other things).

    Seems to help, if you still need it by that point.
    Erik
    Isuzu Nut
    Deviant that's keeping the NPR (with the engine).
    http://www.4btswaps.com/forum/showthread.php?t=9646
    '94 4BD2-TC, HY35W (early) with 3" exhaust & exhaust brake, 'more power screw' maxed, defuel turned up, pump turned up internally by accident.

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    Thanks a lot Erik...I'll get-r-done this Friday...by the way where is the manual, do I need to search in a particular forum?

    Ollie North
    91 Safari Trek 2810 Isuzu 3.9L Turbo...Austin, TX .

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    You may find some useful troubleshooting help in the ATSG rebuild manual for the JR403E. The manual goes into detail with how the electronics work and how to troubleshoot all of it in and out of the tranny.

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    Thanks a lot for the tip...where do I find the "ATSG rebuild manual for the JR403E"?

    Ollie North
    91 Safari Trek 2810 Isuzu 3.9L Turbo...Austin, TX .

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    I bought it online for $25. I tried posting a link to the company I purchased mine through, but couldn't get it to work.

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    Rambler, pm me the link, I'll see if I can get it to work.

    Ollie, sorry for the late reply, there is a link in the Isuzu forum, "reference" stickey, follow it down to "factory service manuals."

    In here:

    http://www.4btswaps.com/forum/showth...BD2T-Reference
    Erik
    Isuzu Nut
    Deviant that's keeping the NPR (with the engine).
    http://www.4btswaps.com/forum/showthread.php?t=9646
    '94 4BD2-TC, HY35W (early) with 3" exhaust & exhaust brake, 'more power screw' maxed, defuel turned up, pump turned up internally by accident.

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    No problem Erik, I did find it...Thanks so much. You know I just drove back from town (without transmission oil...because no one had the gallon size from Valvoline). On the way, I started thinking about the exact symptoms. When i take off, it seems that I have to give the RV more fuel to get it rolling...it feels like I am not starting in first gear...it feels more like I'm starting in second gear. Another thing I noticed is the fact the "Economy" light does not come on when the RV does not go in 4th gear. My understanding is the Economy switch tells the Transmission not to shift in OD. if that is correct, then is it possible that I have a faulty "Economy" switch? Is there a way to test it?
    A couple of questions on flushing the transmission fluid:
    1- Is it best to drain before it goes into the cooler, or after it exits the cooler (return line)?
    2- Do I need to have the RV in gear while I flush the transmission fluid?
    3- I've been using Valvoline, is that what you would recommend?

    Thanks again for all the hel from you and all the other good people on this forum.

    Ollie North
    91 Safari Trek 2810 Isuzu 3.9L Turbo...Austin, TX .

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    I'm using synthetic ATF (Mobil 1, I get it by the 5 gallon pail) as it tends to lubricate better and tollerate more heat.

    I took mine out of the return line.

    I don't know if the economy switch could do that, it doesn't seem to work that way on my NPR, but there's no telling if mine is working right.
    Erik
    Isuzu Nut
    Deviant that's keeping the NPR (with the engine).
    http://www.4btswaps.com/forum/showthread.php?t=9646
    '94 4BD2-TC, HY35W (early) with 3" exhaust & exhaust brake, 'more power screw' maxed, defuel turned up, pump turned up internally by accident.

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    Still won't **** into 4th gear/ I think it is what's know as "Fail Safe Mode"...I just don't know how I got there in the first place and how to get out of that mode, everything I've tried so far did notsolve the issue.

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    Issue Resolved...it was a bad TCM

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