68shortfleet

Ok, I have a 68 C10 with a LS1/4l60e swap that I have about 4k miles on.

Motor and transmission donor vehicle was a 98 Camaro. Transmission condition was completely unknown upon purchase for swap. I installed the used trans to see if it's condition was good/bad. It was immediatly apparent that it was slipping bad in the 3/4 gears.

Trans was pulled and completely rebuilt. And worked absolutely great with no signs of slipping for 3.5k miles. Then it started slipping in 4th gear. Took it to the tranny shop that did the rebuild(they did not get the whole truck when they rebuilt it) and had them check it out. They verified the slipping 4th gear and pulled the trans to find that every clutch in the trans was burnt and the 3-4 clutches were extremely burnt. They rebuilt it again and reinstalled it.

They put a pressure guage on it to monitor pressures and it has 80psi at idle, and that's all that it ever gets when controlled by the GM computer. No increase when put into gear or throttle position changes.

When they control the trans with their stand alone controller, they say that everything works fine, and that the line pressures do everything they are supposed to do. Shop says that it must have an electrical input issue and say that they cannot see what gear(R-Od, D, L2, L1) it is in on the scanner. Says it only ever reads "D" on the scanner. I think this is what it is supposed to read since the Park/Neutral position switch in the camaro only has one output to the ECU. They also said it could be a computer output problem.

Shop didn't seem terribly interested in diagnosing the electrical inputs of the swap(done by me) and I am not very excited to pay that bill for a tech that doesn't want to do the work.

So, I drove the truck home today and I will drive my other vehicle until I get it sorted out.

So, what could be causing this? I believe that the wiring to the ECU is all correct and can explain it or diagram it if needed. Driving the truck, nothing feels weird about the trans and no codes in the ECU.
Could it be a failed ECU? Did something get tuned wrong in HPtuners? Is this a ECU input issue?

I do have intermittent access to a Snap-On Modis scanner for data if necessary, but I don't really want to drive the truck until a problem is found.

Any and all help greatly appreciated.

Jason

tigertales

I'd put a vacuum modulator on it. That way the computer does not control the line pressure.

clinebarger

Monitor the "Commanded" EPC Amps on the Scanner & Compare to the "Actual" Current applied to the EPC Solenoid with a Volt-Ohm meter set to the DC Amp scale.

Hook the Amp lead of the meter to the "high" EPC wire, And the Common lead to the "Low" EPC wire.

If the Snap-On scanner supports it...You can go into Functional Test & Control the EPC current up & down & Compare to your Meter.

Do Not drive your truck with no Line Pressure Rise! It will burn Frictions!

68shortfleet

Cline, the truck is sitting in my garage until I can get this sorted out, I have another gas guzzler to drive, but that cheaper than another transmission.

For the EPC test.. Would this maybe be called the Pressure Control Solenoid Valve? Just making sure I am testing the right thing. Transmissions and Electrical are not really my forte.
Am I testing at the main connector on the side of the trans(unplugged), or does the pan need to come off and test internally?

Also, is there any chance that this is a function that could have turned "off" in HPtuners inadvertently?

Thanks for your reply/help.
Jason

Also, I don't like the idea of the vacuum modulator. Millions of these transmissions out there that function fine without them.

clinebarger

EPC, PCS...One in the same.

I'm not a Tuner, But Tuners have been known to do dumb **** too transmission tables/functions.

joecar

With pressure gauge coonected to line tap on side of case, use scantool to control PCS/TFM/EPS current... as commanded current goes down line presssure should go up.

For 1.0A downto 0.1A you should see line pressure go from something like 50 psi to 230 psi.

Also, with electrical connector disconnected, line pressure should go to 230 psi.

Also:
- scantool shows gear range/lever selector position (P, R, N, D4, D3, D2, D1);
- scantool shows current gear (1st, 2nd, 3rd, 4th);
- scantool shows P/N switch input.

PCM needs all of those signals to select various calibration tables internally.

PCM calibration has shift pressure tables which modify the pressure during a shift, but the base pressure has no tables that I can see... base pressure is calculated from PCM's calculated engjne torque output which is calculated from cylinder airmass (load) which depends on VE and/or MAF tables correctly modelling the cylinder air fill.

If VE and MAF tables are way wrong/low the base pressure will be wrong/low.

mrvedit

As mentioned, the scan tool should show the shifter position. This is not performed by the Park/Neutral/Safety switch on the outside of the trans, but by the Manifold Pressure Switch (MPS or PMS) inside the trans and there are 3 signal wires for it in the trans connector harness. The MPS can go bad, but the trans typically will not shift properly then.

Clinebarger and joecar have given excellent detailed descriptions on how to test the PCS.

The key to most transmission diagnosis is a pressure gauge. Search "ATD 5550"; it is about $34 on Amazon and $40 on ebay.

68shortfleet

Thanks for the starting direction on this. I have a pressure guage ordered, should be here tomorrow(Monday).

I have one of the bluetooth OBDII diagnostic scanners also that I have had good luck with in the past. It is giving me an Amp reading for the pressure control solenoid. It reads 1.1A in park and every gear except reverse which reads 0.9A. I hope to get my buddies Snap-On scanner on it tomorrow along with the pressure guage.

If the Amp readings that I currently have are correct, it seems to me that the Solenoid is not even being commanded by the ECU. So that leads me to the question of what inputs is the computer looking for before it commands anything to the pressure solenoid?

joecar

Either that, or PCM has failed.

68shortfleet

Failed PCM would kinda suck. Means paying to register another PCM with HP tuners.

joecar

You have to first diagnose it (work thru the diagnstic chart for trans low line pressure in the Service Manual)...

and look at the calibration: are VE/MAF tables scaled down (for any reason)...?

68shortfleet

OK, this thing is really making me question what the shop told me.

I now have a pressure guage on the trans that I can monitor while driving. Thanks MRVEDIT for the tip on purchasing the guage.
I also now have a Snap-On MT2500(brick) scanner on the truck. Didn't borrow the Modis, cause I can keep the brick on the truck for weeks if needed.

The line pressure readings are definitely changing, where-as the shop said they were not. I can command the EPC solenoid and alter the pressures from 1.1A down to 0.1A.

At 1500rpm
Amps, Pressure
1.05, 65
.96, 65
.84, 110
.74, 140
.63, 160
.53, 180
.41, 190
.31, 200
.21, 210
.10, 215

Quick drive cycle. Start truck and I get 65psi pressure in all gears except reverse at idle. Reverse has 90psi at idle. At a 9% TPS reading the numbers jump to 125psi and 175psi respectively. With a little more throttle(estimated 25%, I can't seem to watch the scanner and guage for this one), the pressure numbers climb to 150psi+ and 300psi respectively. I suspect that this pressure change is actually based off of the MAP sensor data though, not the TPS%

When looking in the Snap-On scanner troubleshooter, it list pressure specs at idle. And mine fell exactly into the spec range listed.

I can watch the TCC command function properly going in and out of overdrive when I touch the brake.

And I can watch the commanded gear on the scanner change each time it shifts to the next gear when driving. Shown on scanner 1,2,3,4. I haven't found anything on the scanner(yet) showing P,R,N,D,D2,D1.

Sooo, is the trans shop screwing with me? I am starting to question why they would warranty a complete rebuild and tell me that it failed due to something they didn't do. Blaming a ECU command issue of line pressure.

joecar

The PCM commands line pressure based on calculated torque which is roughly proportional to TP which influences MAP...

i.e. as you drive, line pressure should approximately follow TP and/or MAP.

joecar

If line pressure is working properly, then 3/4 clutch slippage is being caused by internal leakage or too much clearance in clutch pack.

68shortfleet

The line pressure changes are not linear at all. They are sudden changes as if switched on.

I took a video of the guage through first gear. Can't seem to get it uploaded to photobucket so I can post it.

clinebarger

Good Job on proving out you have line pressure rise!!! Take it to the trans shop & show them you have pressure rise.

(I'm slow, Responded to the 6:42pm post)

joecar

Can you upload it to youtube...?

68shortfleet

Joe- I think that I got it figured out, but as I was trying to, I watched the video and it was useless garbage.

I'm off to work for the next three days. 12.5 hours shifts with an hour commute each way. The truck will be sitting until Saturday at this point before I get another chance to take a video. I think it might help your thoughts on this.

Maybe I will try to get a passenger to video and see if we can get the scanner view in it also. Scanner is a pretty small screen for that though.

And thanks for the help so far too..

mrvedit

Your Amps and Line Pressure look perfect.
However, you should have much more pressure in Reverse, even in idle.
Reverse fluid should be moving the boost valve and increasing line pressure.
If you think the line pressure changes are erratic, I would suspect a leaking or stuck boost valve. I would suggest installing the Sonnax 4L60e-LB1 boost valve which has o-rings to reduce leakage.
(If you have a 2006+ 4L60E with ISS (Input Speed Sensor), you need the 4L60E-LB2 boost valve.

http://www.sonnax.com/parts/2168-lin...re-booster-kit

You could easily install this yourself - you only need to drop the pan and use snap ring pliers to swap the boost valve. No guarantee this will fix your problem, but you might see a more linear pressure on your gauge.

BTW - Glad you are finding the gauge so useful. I doubted what your trans shop told you and therefore thought you should check things yourself.

68shortfleet

Sorry for the lack of updates on this one. I kinda got sidetracked with other stuff, and I was pretty discouraged with the truck.

So, basically I gave up. I took it to a shop today that was recommended by my tuner. He drove the truck with me as passenger with my line pressure guage routed into the cab so it could be watched at all times.
He says that the trans is working as it is supposed to and that the PCM is controlling it properly, and he was happy with the line pressures.
So, all good news for me today.

He understood and had knowledgeable answers for every question I was able to throw at him, was happy to BS about transmissions and LS swaps with me as he has done several. So all-in-all I think he is much more knowledgeable than the shop that did the rebuild. Unfortunately he is about a two hour drive each way for me.

After all the chit chat and test driving, he was more than happy to write me an invoice about line pressures being in spec and wasn't interested in charging me anything for his time. Pretty much cleaned out my wallet making sure he had an acceptable tip before I left. I would be happy to do business with him if I need a rebuild in the future(I'm sure I will one of the five cars).

Pretty sure forum rules prohibit me from naming businesses, but I would be happy to if allowed.

I will keep the line pressure guage on it for a while so I can keep an eye on it.