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post #1 of (permalink) Old 12-14-2000, 12:49 AM
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4L60E Problem-Rocket Scientist Needed

I'm having a local shop do an engine/transmission swap, and they are stumped. They have installed a 1998 5.7L OBD-II engine and 4L60E tranny that came out of a donor vehicle (Suburban) as a pair.

Here's the problem. With the vehicle stationary, the engine runs fine, with no error codes, and all sensors showing normal activity on the scanner. The transmission is fully functional with the vehicle on jack stands and connected to an independent transmission test device. Butů.when the ECM is connected to the transmission, all signals, controls, and status are present, but the transmission defaults to a "limp" mode, second gear only. There are no error codes present for either the engine or the transmission! If they put the transmission in gear, the torque converter locks up and stalls the engine.

They're baffled. I'm baffled. Does anybody have an idea what might be going on here?

Steve




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post #2 of (permalink) Old 12-14-2000, 05:38 AM
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Re: 4L60E Problem-Rocket Scientist Needed

Time to grab you manual and see what trips the lock up. The rpm sounds a little too low to trip. Have you moved around the wiring harness? Often spurious signals can be emitted by other parts of the vehicle and enter into the wiring to, or from, the transmision harnss and cause lots of unusuall stuff. You may want to try shielding the harness.

Happy Holidays and Safe Jeepin'

Larry
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post #3 of (permalink) Old 12-14-2000, 11:27 AM
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Re: 4L60E Problem-Rocket Scientist Needed

Larry,

Hummm (thinking), that could be. They are using a Howell wiring harness to adapt the 1998 5.7L OBD-II engine / 4L60E tranny to the 1986 CJ-7 harness. They claim to have traced every wire that connects to the tranny to verify the correct routing. I'm not sure how much they have messed with the harness. Looking at the manual (I bought the whole 1 ft tall stack of factory manuals), lots of stuff will command "limp" mode, and several conditions will erroneously lock up the torque converter, but they all throw an error code when they do it. They're not seeing any error codes, which makes your idea sound plausible. Extra, erroneous signals commanding limp mode and causing the torque converter to lock, without a error condition being present, and no error code is thrown.

>>You may want to try shielding the harness.

What would work good for this, some of that foil backed heat resistant wrap? I shouldn't have to shield the individual wires in the tranny harness, right?

Thanks for the suggestion, Larry


Happy Holidays to you and yours,

Steve

(originally from Marshfield, WI., now living in northern CA. Yes, I remember rust<G>)



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post #4 of (permalink) Old 12-14-2000, 02:14 PM
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Re: 4L60E Problem-Rocket Scientist Needed

Sheilding the harness down to the transmission, and back, will prevent any radiated signals from entering the harness. Try wrapping it in Aluminum Foil the whole lenght. It'll look kinda stupid, but will provide good shielding. If the problem persists, the problem is in the harness itself, or truly the trnasmission is being told to lock up higher up in the food chain.

Try unhooking one wire at a time that could be responsible for lock up and then seeing if the problem persists, or changes. If it persists, it ain't the one, if the problem goes away... that's probably the cause.

However, you said it works normally on the tester? If so, what's different about the testers "ECM" than the one you have. There could be an EPROM difference or a step difference that's masking problems.

Just start elimnating the posibilities one by one, and pretty soon you'll have the problem to where you can handle it.

Happy Holidays and Safe Jeepin'

Larry
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post #5 of (permalink) Old 12-14-2000, 08:53 PM
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Re: 4L60E Problem-Rocket Scientist Needed

Thanks for the advice Larry. It gives me a couple of avenues to explore that I hadn't considered.

Steve


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