4 speed automatic wO/D in the limp-in mode. Wiring harness?

1991 Dodge Spirit 3.0L V6 with 4 speed automatic transmission bought for $1,000 has 58,000 miles. Car is beautiful inside and out. Want to fix it for high school and college for 16 year old daughter.

The transmission is in limp-in mode only engaging 1st and 2nd gears. Aamco manager, former Chrysler dealership mechanic, says when connected to scan for error codes the scanner will experience loss of signal. Suspects wiring harness issues for transmission or the transmission computer (which has been replaced to most recent new firmware/software by previous owner).

Any known issues for wiring harness or connectors for a 91 with the 4 speed overdrive transmission? Know the transmission was a redesign with new internal parts in 93 or 94 and would rebuild to those new parts if required. First have to solve this electrical problem.

U-Pull-It has a 91 4-door LeBaron which is the same car as Acclaim/Spirit for 91 model year. The under hood wiring harness is $45.

Dealership service dept says there is no information, no repair kits, no new parts. They are basically helpless and hopeless.

Can Aamco tell a transmission needs to be rebuilt from scanning codes? No automatic transmission rebuilding experience.

I would start with a can of contact cleaner (walmart automotive chemicals aisle, CRC brand short red can) and first unplug the solenoid connector and throughly hose out with cleaner and blow out with lots of air both the solenoid half and the harness half. Do the same for the input and output speed sensors, there the two screw in plastic sensors on the front of the unit.

The 4 speed has a feature called CVI or clutch volume index which measures the time/volume required to apply a particular clutch and assigns a numerical value that you compare against what the known new specs range is supposed to be. The more the clutch wears from use the higher the number value. Putting new parts into an original 1991 era unit is a touchy area. Starting with a later core that already has all the improvements to the input clutch's assembly would gain you more in the end.

The dealership isn't going to be of any value here. Whether just stupidity/ignorance or just lazy to open the parts catalog. 98% of that transmission is the same thing as what would have been found in most chrysler FWD's until a couple years ago.

http://www.transmissionpartsusa.com/...-00057389a.htm

If the fluid looks ok and smells ok i don't see any reason to jump to conclusions about internal damage. Limp mode is a result of electrical signals which may or may not correspond correctly to the physical reality inside the trans. Sensor/solenoid/wiring/computer issues can all cause limp mode on an internally perfect transmission.

There are only a few wires between the transmission diagnostic port and the TCM. I would verify the integrity of that wiring before doing anything else.

The early ones were known for speed sensors going bad and it going into limp mode, weren't they? Or is that more of the internet slip-0-4 crap?

Limp-in mode should only be 2nd and reverse, IIRC. Could be bad solenoid pack not allowing it to shift to 3 or 4.

Went to U-Pull-It yesterday and spent 4+ hours under the hood of a 91 4 door LeBaron which for 1991 was the Spirit/Acclaim. There is a separate piece of the harness which goes from the solenoid pack and the four sensors on the transmission up to the Transmission Computer on the pass fender. I took that piece as well as the separate piece that is on the passenger side covering front lights and engine sensors. The rest of the harness is ONE-PIECE from starter, left side lights, computer area and back of engine down to transmission speed sensor and it goes through the firewall. I also got the Transmission Computer from the LeBaron.

I'm going to try the spray cleaning (have CRC Contact Cleaner and 4 ounce can of dielectric grease already) on all of the connectors and check the existing harness for damage.

If necessary to get the rest of the engine bay wiring harness from the LeBaron does anyone know if it all unplugs under the dash if I pull everything loose and remove the dash to get to the wiring?

Aamco said they read the CVI's when they had continuity. Can that alone tell them that the original transmission needs to be rebuilt? Apparently this car was driven on city secondary roads so it didn't have to go too fast after it went into limp-in mode before I bought it.

This U-Pull-It 91 LeBaron looks like it was well taken care of and used for business as it has a mobile telephone installed, new radiator, sealant on the thermostat housing, new alternator, and sealant squeezed out of the transmission pan gasket. It has 85,000 miles. What, maybe? did it in is a four wire connector on the back side of the engine that goes under the metal intake box towards the top center of the motor. This connector has the insulation melted and crumbled off of 3 of the 4 wires. (It's not the O2 sensor)

Anyone familiar with a 1991 3.0L V-6 (single coil and distributor) who knows what this connector goes to from the harness on the back side of the motor under the metal intake box that has the raised 3.0 on it. It connects to something on the center top of the motor.

CVIs along with fluid condition can give a good idea of the health of the trans. Being able to see any metal in the pan would be even better. Have you had ANY reason to even SUSPECT an internal problem? There's no internal problem that causes the TCM to intermittently stop communicating through the diagnostic port.

I know that the first thing to do is to resolve the electrical issue(s). That done, then evaluate the trans for it's working condition. That said, I wrote "Aamco said they read the CVI's when they had continuity. Can that alone tell them that the original transmission needs to be rebuilt? Apparently this car was driven on city secondary roads so it didn't have to go too fast after it went into limp-in mode before I bought it."

So the question still is, can the CVI values alone demonstrate that the transmission needs to be rebuilt?

I could get the sensors and the solenoid pack off of the LeBaron with 85,000 miles or new parts from Transmission Parts USA (thank you 135SOHC). It's cheap enough, but is it worth it if the CVI values reliably indicate excess wear?

Ronnie, Aamco manager, says that the redesigned, stronger internal parts can be used in the 1991 case to do a rebuild up to new standards. If you want to use a later case do you also need a later harness and computer? Can a later transmission computer talk to a 1991 vehicle computer?

Ronnie says fix the electrical problem(s) and then rebuild the existing trans with the redesigned parts.

I just had the '91 trans built for Project LookOwt with all the upgrades, like you're talking about. Cost $1200 and I know the guy.

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So the question still is, can the CVI values alone demonstrate that the transmission needs to be rebuilt?

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Yes.

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If you want to use a later case do you also need a later harness and computer?

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After a certain year, yes. Your case should have what looks like a good old chrysler 3-prong 'neutral safety switch' sticking out the front left corner of the case (as in front left of the car with trans installed). At some point they got rid of that sensor and its hole in the case and replaced it with a transmission range sensor mounted on top of the valve body. If you were to try to use one of those later cases you would have to upgrade to the newer computer as well. There were some connector pinout changes at the TCM as well although the TCM connector itself did not physically change.

I don't know of a reason to go to a newer case.