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View Full Version : rebuilt 4l60e - hunting for 3rd and 4th in low.


blistovmhz
August 29th, 2017, 11:47
Yea I know. Not XJ related, but you guys are the only knowledgeable guys on the Intarnet. If it helps, I also have a bunch of 5.3 swapped XJ's with 4l60e's so this is SORT OF applicable.

Had a 4l60e rebuilt by a local shop. I NEVER pay someone to do anything, because it always ends up being shit. This was no exception, but I just didn't have time to do it myself, and the guy said he had a 4l65e for me, and I couldn't find one. Long short, he didn't have a 65e, gave me a 60e, tried to convince me it was a 65... 1-2 shifts are crazy harsh, but that's probably just a simple adjustment in the VB.

The real issue is 3rd and 4th feeling like they're slipping or changing gears constantly when in 4L. Doesn't happen in high gear at all. At relatively low speed and low throttle the trans feels like it's just popping in and out of gear. I don't see a gear change being commanded by the ECU but it could be happening too fast for my machine to update the screen. VSS is reading correctly so the 4L switch is definitely working and the ECU knows we're in low. Everything worked prior to swapping the trans. Manual 3rd or 4th selection does the same thing.
For some reason, it also seems to skip 3rd entirely, when in the 4th position. 1>2>4 every time. Again, didn't do this before. Nothing has been changed on the ECU.

Any brilliant idea's? The shop owner is pretty confident it's not a transmission issue, but rather a control issue. He's got a proper scanner, so he should be able to prove that, but I don't trust him at all at this point. It only went back to him because I told him i'm giving him one more chance to get this right before I demand he take the trans back, and give me all my performance parts back.

I had him install a Sonnax Smart Reaction shell, corvette servo, and Transgo HD2 kit. Told him to use relatively conservative valving. I just don't have enough experience with auto's to know if anything in the trans could be the problem. It's entirely possible the issue also exists in high range, but you just don't feel it or it's not as prevalent.

clydefrog
August 30th, 2017, 22:11
Does it try to go into third then skip it and go straight to fourth? Or does it just skip it entirely? If it tries to go into third (slips, hesitates after second) then it sounds like a worn clutch in third but if it skips it then I think your on the right track with it being a control issue. Meaning something electronic internally in the trans, NOT your ECU. I would give him a chance and see if he can correct.

blistovmhz
August 30th, 2017, 23:05
Does it try to go into third then skip it and go straight to fourth? Or does it just skip it entirely? If it tries to go into third (slips, hesitates after second) then it sounds like a worn clutch in third but if it skips it then I think your on the right track with it being a control issue. Meaning something electronic internally in the trans, NOT your ECU. I would give him a chance and see if he can correct.

I finally got my buddies scanner hooked up and found out some interesting/strange stuff.
Scanner is showing that the Brake TCC switch is constantly closed, even when I hit the brake, or remove the relay entirely. No voltage on pin 33, but ECU says it's closed.
Also looked at the shift points and TCC lockup in low. Definitely found my problem. ECU is commanding 1-2, and then 3 comes in WAY too early, TCC is locked, and then half a second later, 4th is commanded and TCC remains locked. Only under part throttle with load applied. That load is my brakes, which should be disabling the TCC lockup.

So the ECU is definitely sending bad commands. Now I'm just trying to figure out why. The timing is suspicious, given the new trans and all, but I'm almost wondering if I had the same problem before, but didn't notice because perhaps the old trans was just slipping the clutch enough that it didn't wonk out on me.
Other option is a short in the trans or harness is causing the ECU to respond dumbly, or cooked the ECU entirely. I've got a guy bringing a few ECU's over now, but I'll have to double check the entire harness and trans first before plugging it in. Wouldn't it be amazing though, to find out the ECU was just cooked the entire time, and my trans issues weren't actually trans issues ?

blistovmhz
August 31st, 2017, 12:57
It gets weirder.

I was positive my TCC brake switch was wired correctly and works. I am still positive it is wired correctly now (though i think something may be shorted.. but even that doesn't make sense).

I built a test ECU harness. Just powers, grounds, serial data to the obd port, and the TCC brake switch signal. I plugged in my OLD ECU (nothing else is on this harness) and checked the TCC Brake switch status. It says closed, with no voltage applied to the pin. So I checked this on Mouses truck as well, and it says the same thing, so I've figured out that Snap-On's verbage is backwards. The TCC Brake switch is supposed to provide constant 12V+ to pin33, UNLESS the brake is applied, in which case the pin should receive no voltage.
My relay is setup with Pin 30 Batt+, Pin 85 ground, Pin 86 Brake signal +12V, and Pin 87a to the ECU. This should now be a normally closed circuit, providing 12v+ to the ECU pin 33 at all times, unless brake is pressed, in which case the circuit should go open.
But, when I read pin 87a, it is open. No voltage. Try another relay, same issue. Double check all wiring and do continuity tests wth battery disconnected. Pin 30 has continuity to batt+, Pin 85 goes to ground. Pin 87a goes to the ECU, and pin 86 is open until I press the brake, at which time it closes. This is all correct right? Again, I'm dead serious, am I having an aneurism?

So anyhow, the OTHER issue.
If the ECU is never receiving a 12v+ signal on pin 33, it should assume the brake is pressed, in which case the TCC should never lock. But I'm having the opposite problem. Since swapping the transmission, the TCC applies constantly. ECM commands gears normally in high, but in Low range, the 1-2 shift is normal, and the time when it SHOULD shift to 3rd, it does, but then also locks the TCC even though it's not getting 12v to pin33, and then jumps straight to 4th and tcc lockup again. At no time does pin 33 receive 12v.

Unless...... No. I can't think of anything. Pin 33 definitely never receives 12v. I keep thinking that a short in the trans harness could cause some feedback to the ECU, so the ECU thinks it's getting 12V at pin33, and that perhaps whatever circuits go closed to engage 3rd and 4th (only in low) and one of them is shorted to something that feeds back to the ECU. It's either that or the ECU is just ****ed, but every test I've run on it shows that it works correctly. It's just commanding TCC lockup 1. Way too early, and 2. In the absence of 12v at pin 33. Neither of these should be possible.

clydefrog
August 31st, 2017, 22:50
Pin 30 has continuity to batt+, Pin 85 goes to ground. Pin 87a goes to the ECU, and pin 86 is open until I press the brake, at which time it closes. This is all correct right? Again, I'm dead serious, am I having an aneurism?


Pin 30 is ground I believe and pin 85 should be bat +. I don't think it would matter though if you had them swapped. I had my relay backwards on my swap and TCC would always be on and I didn't have your symptoms so i don't think that's your prob. I'm going to think on this and see if anything pops out. All the detailed info helps. I will get back to you tomorrow.

blistovmhz
September 1st, 2017, 09:42
Pin 30 is ground I believe and pin 85 should be bat +. I don't think it would matter though if you had them swapped. I had my relay backwards on my swap and TCC would always be on and I didn't have your symptoms so i don't think that's your prob. I'm going to think on this and see if anything pops out. All the detailed info helps. I will get back to you tomorrow.

Yea, the TCC brake switch relay never makes sense to me (too dumb). I was looking at it all day yesterday though and finally figured out why it didn't make sense. There was a short somewhere, which was causing me to see continuity (but not voltage) from several grounds to the positive battery terminal. Not reliably, but I kept seeing it and it was making me mental.
I ended up just unplugging things until the mysterious continuity went away. It was the transmission connector. Unplugged it and all the gremlins ran away. I double checked all my harness wiring for a 12th time, no issues, so there is a short inside the transmission, and it must have been shorting the TCC solenoids during the 3 and 4 applies. This explains SO MUCH!

But, I'm not yet sure how it explains the trans skipping 3rd gear (or just blowing past it) and moving on to 4th in low. I originally thought one of the shift solenoids was shorted to the ground on the TCC, because that would mean 3rd could not be reliably commanded as both sols have to be off. But I had my solendoids backwards so that theory doesn't work.

Disconnecting the TCC signal grounds from the ECU did prevent the TCC from locking, but didn't solve the skipping 3rd gear. Nor would it explain why we'd ever get a TCC lockup without the ECU seeing pin33 high. Something has to be shorting the TCC solenoids to ground.

At any rate, I wiggled the shit out of the transmission plug (transmission side) and plugged it back in, and voila! Mysterious continuity gone, and TCC no longer locks up for no reason. We're still skipping 3rd gear in low range, but it's at least driveable for now. At this point I'm pretty confident there is a short inside the transmission, as well as a valvebody issue. Short explains the TCC lockup without an ECM command, and VB explains the harsh shifting and possibly the lack of 3rd gear (3rd works if I manually command it, just skips it if i'm in D and low range).

Sending the trans rebuilder an email with my logs. I'll post'm here as well on the off chance someone else has the snap-on software (free to download).

Log: https://www.dropbox.com/s/e5w6nctue07rqnv/trans.pdf?dl=0
ShopStream software: https://www1.snapon.com/diagnostics/us/SSC/DownloadForm.htm

Bear in mind that not even Snap-On techs can tell me which data points are ECU commands, vs a reflection of the REALITY inside the trans. EG: PWM Duty% could be what we're actually SEEING happen in the trans, or it could be what the ECU is commanding. Their documentation is at odds with itself as well. It might be that i'm on a slightly older version of the firmware. I've no idea. But there are several inconsistencies. EG: TCC Brake switch status says "Closed" when pin 33 is OPEN, which makes no sense. and OPEN when the switch is actually closed. Snap-On support told me that "Closed" means there is 12v on pin 33, but they're just wrong. Verified on several working vortec swaps. I almost think the scanner set me back further than if I'd just not used it at all. Damnit.