1996 Grand Cherokee transmission rebuild & on to other stuff

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SirRobyn0

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#1. Battery temp sensor, yes my Jeep has one disconnecting it made no difference other than to set the check engine light off.
#2. Drivers side cylinder head grounds in perfect condition, clean anyway made no difference.
#3. I made an incorrect assumption on the charge wire it does go to the fuse box, and it does have a fusible link it in, but all of that stuff is in perfect condition.

GRRRRR I did not think about this when I was working on it, but the last thing I could try is to put it in gear with all the electrical loads on and field the alternator. If voltage jumps up then it has to be the AVR....
 

SirRobyn0

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Well huh....

Full field alternator test. Multimeter connected to battery for all testing. Battery voltage engine off about 12.20 voltage I full fielded the alternator, and revved the engine to about 1,500 RPM. I chickened out when the multi-meter got up to 16 volts. So that's a good test result, at least at speed the alternator and electrical system is capable of producing and carrying voltage. At idle with a full load and the alternator fielded I'd see about 12.4 volts.

Then I hooked up the AVR and ran the same tests again. At 1,500RPM I got 13.8 volts. At idle fully loaded 12.40. Just for giggles, I shut the Jeep off left the headlights on for 1/2 an hour and ran the tests again. I was really hoping to see 14 - 14.4, but no. I couldn't get better than 13.8 volts.

Ran voltage drop tests on both the positive and negative sides, both we around .02 volts. That's nothing.
Only one last thing to check and that's the wiring to and from the ECM.

One issue I've observed is that my dash gauge seems to read just a little lower than the multi-meter did so there is that.

Unfortunately the ECM is available from module companies but not from any local parts stores. If one of the local places could get it, I'd ask really nice if they'd let me try it to see if it fixes it and I bet they would allow it.

I'm not very happy that the the alternator will only produce 12.4 volts underload at idle - even when full fielded.

Maybe I'm expecting to much but I don't remember the gauge dang near in the red at idle, in the past.

But I have a plan. To set a side gauging issues I'm going to fire up the Dakota tomorrow and compare readings. I might even pull the alternator off it and put it in the Jeep just to eliminate any possibility of 2 defects in a row.

That's enough for now more when I actually know something.....
 

Grit dog

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So I was comparing part numbers to see if by chance the 99 Durango I just got may have a compatible ecm. And doesn’t look like it with a quick review of compatible part numbers between the 2 vehicles.
But it seems this reman ecm may be returned as long as it’s not burnt, modified damaged etc?

If you do find the 2 vehicles are compatible though, you’re welcome to come down and try a swap.
PS I like reading your diagnostic processes. I learn from what you speak.
 

SirRobyn0

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So I was comparing part numbers to see if by chance the 99 Durango I just got may have a compatible ecm. And doesn’t look like it with a quick review of compatible part numbers between the 2 vehicles.
But it seems this reman ecm may be returned as long as it’s not burnt, modified damaged etc?

If you do find the 2 vehicles are compatible though, you’re welcome to come down and try a swap.
PS I like reading your diagnostic processes. I learn from what you speak.

Thanks for that:
I like reading your diagnostic processes. I learn from what you speak.
I'm never sure. When I go on and on about something I'm trying to fix, sometimes I think I'm just boring everyone. Anyhow I appreciate the comment and the offer on the swap however the Durango and GC security systems are different and it's unlikely that the Durango ECM would even start the Jeep and visa versa.

Something I discovered last night at about 1AM, both of the alternators I've installed on the Jeep were 90AMP units. My Jeep calls for a 120amp unit which is available from another source. If I add up, headlights, driving lights, running lights, blower motor, rear defroster and seat heaters well that's right around 90 amps. I think I estimated 85 amps. I don't really think that's the cause of my issue but on Monday I will swap it out with the proper unit.

Flagship does free shipping and they will preprogram the vin. I've used them before and that is who I will use if it comes to it. This morning I ran though doing more resistance tests. Wiring from the PCM to the alternator is just fine. However, the ECM has harness grounds, and also grounds though it's body to the Jeep's body. There was some slightly elevated resistance there, so I pulled the ECM bolts, cleaned everything up and also ran a direct ground wire from the ECM body to the battery. Couldn't hurt.

I needed to clean her up from the trip anyway so figured I'd grab a few pictures to share.


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She's really in pretty good shape for 275K I think, in the long run it would be nice to do something with the headliner as it's pretty rough. I need a new set of seat covers, I'm not a fan of leather and the one that was on the D/S is worn out. I keep hoping Seat Cover Man will open back up again, but I'm loosing hope.....
 

SirRobyn0

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Need to see under the hood too!

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Yes the battery hold down is home made. The story on the air cleaner is the factory air clear tube and housing was in bad shape when I bought the truck and new hose and housing was more than I wanted to pay. The Edelbrock air cleaner was like $25 at the time and will accept a standard wix replacement filter.
 

Grit dog

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Must be a Jeep thang, lol. Looks just like the battery hood down I made for the CJ 5 except yours shows some pride. Mine isn’t painted and I didn’t grind down the edge I torched!
Looks clean man! I like it.
 

SirRobyn0

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Must be a Jeep thang, lol. Looks just like the battery hood down I made for the CJ 5 except yours shows some pride. Mine isn’t painted and I didn’t grind down the edge I torched!
Looks clean man! I like it.
Hey that CJ of yours is pretty nice! I think at this point I'd home make any over the top style of battery hold down, all the ones I've seen at the auto parts stores in the last decade or more have just been so flimsy.
 

Grit dog

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Hey that CJ of yours is pretty nice! I think at this point I'd home make any over the top style of battery hold down, all the ones I've seen at the auto parts stores in the last decade or more have just been so flimsy.
Thanks! One of AMCs finest, lol.
Actually just took it for a rip yesterday. Hasn’t been started in the last 3-4 months. Lit right off and down the road she went.
I really do need to find a set of wiper blade inserts for the 50 year old windshield wiper frames. They’re too shiny and chrom-ey to stick a set of disposable plastic wiper blades on!
 

SirRobyn0

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Thanks! One of AMCs finest, lol.
Actually just took it for a rip yesterday. Hasn’t been started in the last 3-4 months. Lit right off and down the road she went.
I really do need to find a set of wiper blade inserts for the 50 year old windshield wiper frames. They’re too shiny and chrom-ey to stick a set of disposable plastic wiper blades on!
If you need help finding part numbers or something that might work with those frames let me know. And I'll see what I can lookup for you. Ya you need good wipers around here!
 

SirRobyn0

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Ok, so we had the sales guy at the shop call out again today.... So my time was limited, but I did get and install a 120 amp alternator. I did not have time to hook a multi-meter to it or the load tester. Really all I got was enough time to install the thing, shut the hood and drive home. My observations, watching the voltage on the way home was improvement, but not what I recall as normal.

The gauge:
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So that's a picture from previously so ignore where the needle is and look at the colored bands I added. The green is what I recall being normal. The red is what I was seeing, and the yellow is what I seeing tonight.

We all know gauge readings aren't always accurate so I'll check it with a meter tomorrow and see if it's more normal now, but it's definitely improved. I wonder if part of it is how the AVR "talks" to the alternator. IDK if the AVR is calibrated differently for the 90 amp alternator than it is for the 120amp. I don't know. I'm counting my eggs just yet. Need to meter it and go from there.
 

SirRobyn0

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Ok I think we are done.

I checked just about everything I could today at lunch. First load testing the system.

This alternator is able to produce 90 amps - get this at IDLE! and 13.5 volts.
This alternator can achieve it's peak amp rating of 120amps @ 1,200RPM. Voltage peaked out at 13.8.

Voltage fully loaded all vehicle electronics on at idle never falls below 13.0 volts.

So all of that looks good except one thing. I'd like to see the voltage a little higher when there is a current draw, so I hooked up the scanner so I could monitor the AVR, well the ECM never commands the AVR over 13.8 volts. Fine I guess that's just the way it's programmed and I've never noticed it before.....

THE only vague concern is that at idle with all the electronics on the PCM is asking the AVR for 13.5 volts and the system voltage is 13.0. Off idle the system voltage never gets further than .1 volts from the AVR command, so that's very good.

One thing for sure the AVR is functioning, I really don't know if it not getting to 14 - 14.4 is because there is some impairment with the AVR or if it's just simply programming. I don't see any abnormalities other than the 1/2 volt drop at idle, below the AVR demand. Without another GC here to compare it, I'm kind of guessing, but I "think" it's functioning as it should. At the very least I now feel like the charging system is doing much better, and I'm just going to drive the Jeep and monitor it for now.

I think that in the end one issue was some dirty connections, but the biggest issue was the accidental installation of an alternator rated for lower amperage than the Jeep needs. I suspect because I installed 2 different 90 amp alternators and they both behaved the same way, either the 90 amp units aren't capable of putting out much at idle (the one I tested wouldn't do more than about 35 amps), and I'd get right down to 12 volts, at 1,500 RPM I'd get better but I never saw more than about 60amps. So makes me wonder if the AVR is different and the AVR designed for the 120 alternator can't make a 90 amp alternator produce even 90 amps. Looks like I'm good now.

Next project on the Jeep. Need to replace the evaporator. This is a dash tear off. Will do the heat core at the same time. Need seat covers as well.
 

SirRobyn0

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Bextreme04

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Thats not a horrible price. To rebuild a 700r4 is 1700 to 2500 bucks. A 4L80E is 4200 bucks plus.

Buddy and I bought a dodge Dakota with a bad transmission on the spot thinking it would be easy to find a used one. Yeah good luck and was 2300 bucks for a rebuild. 46re I think it was.
That's an insane price for a 4L80. You can get a Stage 2 or Stage 3 Jakes rebuilt trans rated for a hard 1000+ HP for that price. http://www.jakesperformance.com/4l80/

I got a complete rebuild kit with all new pistons, bearings, solenoids, wiring harness, BW high energy clutches, new steels, new bands, no walk bushing and roller output, trans-go shift kit, sonnex boost valve, etc.. for about $750. Rebuild stock 454 converter was another $250. Took me about a week of piddling around to rebuild the whole thing while doing my own dual feed mod.
 

rusted nuts

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Could be a battery on the way out too.
 

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