Ben Feral Selinger

Swapped a 5.3/4l65e from an 05 1500 into my Jeep XJ. Everything wen't pretty smooth.
Trans seems to shift fine, and around town temp stays below 65C. Fuel economy around town is also pretty good at around 20-24mpg.
20 minutes on the highway however, and the trans temp gets up to around 100C before I shut it down, and fuel economy drops at highways speeds to around 17mpg.
I know almost nothing about automatic transmissions, but I did do some research before doing the swap.
My brake switch is hooked up to a relay to provide 12v to the TCC lockup. Brake like switch closed, TCC closed. BLS open, TCC open.

I haven't really delved into it yet because I wasn't super confident I even had a problem until doing some more reading today. From what I understand, I should be able to confirm the TCC lockup by several methods.
1. Trans will feel like it has an extra gear when TCC locks up - I don't feel this.
2. TCC slip speed (reported by OBD) should read 0 when above 35mph, when at a constant speed and not under a massive load. - TCC slip speed occasionally hits 0, but bounces between -10 and +20 or so when I maintain a steady speed.
3. While at a steady cruise, if I tap the brake, the TCC should unlock and I should see the RPM's rise a hundred or so RPM as the TCC is unlocked. - I don't see this either.

The transmission temp was my first hint as it's okay around town but jumps up on the highway. The fuel economy dropping substantially when I get over 75km/h was my second hint.
The temp I thought at first was being caused by poor cooling, but according to the rad manufacturer (Griffin - GRI-CU-28182-TS), I should be good to well over 450HP, in a desert, running the 4l60/5e, while towing a few thousand pound trailer.


So what am I missing? What should I be checking first?
My plan thus far is to start the truck, throw it in gear on axle stands, and give the TCC lockup wire 12v and see if I can stall it by hitting the brake. What's next?


EDIT:
Put the truck back on axle stands and brought it up to 100km/h, and had my buddy disconnect the brake light switch/TCC lockup relay, and TCC slip RPM did increase from (hovering around) 0 to 23 RPM. Starting to wonder if perhaps the clutch is just slipping? Shouldn't I throw a code if that's the case though?

bbond105

It could be that the TCC solenoid is not working. You have a scanner check to see if the PCM is commanding the TCC solenoid on. Also check for trouble codes. It could be an engine or trans sensor problem.

Ben Feral Selinger

Not throwing any codes.
I did throw the Jeep back up on axle stands one more time last night to confirm a few things.

1. With the TCC brake switch relay removed (so TCC can't possibly turn on), I do get 20-30RPM TCC slip speed at 100km/h under low load. With the relay put back in, I get 0RPM TCC slip, so looks like the TCC is at least engaging. From what I understand, the PWM TCC lockup isn't a hard lockup, so a small amount of slip is normal, which seems to be exactly what I'm getting.
2. The problem with this, is that with the TCC power manually engaged, I bring it up to 100km/h and slam on the brake (no TCC brake switch to disable TCC lockup), but I don't stall. Maybe the ECM just responds to the lower wheel speed faster than I can stall it?

Either way, I'm pretty confident at this point that the TCC is engaging. What I really need to know I think, is how much cooling the 4l60e requires with such light duty. I'm only a 3600-3800lbs Jeep. Cruising a flat stretch of highway at 100km/h should barely put any strain on the cooling system.

That said, my t-stat for the engine was a bit sludgy, so I pulled it and cleaned it and tested it (put in boiling water to watch the valve expand). When I re-installed it it seemed to be working, but maybe it's not opening enough? My Rad is rated to 500hp, so I figure a 300hp lm7 driving a light vehicle should have no problem keeping the engine cool, but my electric fan (programmed 94/92C) is coming on pretty often. Has no trouble keeping it below 95C, but I'm wondering if that fan should ever need to come on in the first place? Maybe the built in cooler is just running too hot to cool off the trans?

Edit: Just talked to Griffin Rad. They say the rad I installed should be WAY more than adequate to cool my rig and I shouldn't have to even consider an external trans cooler unless I'm planning on hauling a 5000lbs trailer up a mountain. The guy says in his thousands of support calls, he's talked to heaps of guys with the same swap, using the same or smaller rads, who use the internal cooler all by itself with absolutely no issue. So, I figure he's probably telling the truth as he has an incentive to try to sell me a stand alone cooler.

So, what can I check next?
What temp do most guys run their 5.3 and 4l60e at?

bbond105

If you have the TCC solenoid hard wired to battery voltage and the engine doesn’t stall when you brake to a stop then the TTC solenoid is not working or the TCC clutch is sipping. Try applying the battery voltage at the trans plug.