More tranmission diagnosis (which pressure ports to test?)

Topic: More tranmission diagnosis (which pressure ports to test?) (Read 4405 times) previous topic - next topic

More tranmission diagnosis (which pressure ports to test?)

January 26, 2015, 12:18:45 PM

Backstory:

So I was attempting to pull my pressure port plugs out this weekend to hook up some hoses for gathering transmission pressures. The "TV"/EPC pressure port plug is stuck - I will need to pull the exhaust and get a torch in there to heat up the casing to break that one free. This is a 4R70W, but pressure diagnosis should be the same as an AODE or AOD.

I've had minor converter issues for a long time, including when this transmission was stock with 13,000 miles, converter and all, so it doesn't seem to be anything new. When commanding lockup at closed throttle and low engine speeds (near downshift), the lockup clutch would fail to remain engaged and the rpms would start to bounce up and down as the lockup would successfully engage, then disengage, and repeat. Giving a small boost to pressure at closed-throttle made that issue go away for years while the car was my daily driver.

Now that I have more stall and higher numerical gears, I don't think the pressure is rising as quickly as it needs to and is now showing up as a major converter-slippage problem (measured as 20-25% loss at 5k rpms according to engine vs tire speed). When I had the transmission apart last year, the clutches looked brand new and the oil looked great, so I don't believe I have pressure problems in that section of the transmission. Idle pressures in the garage also looked correct.

Anyway, I believe that I am getting insufficient line-rise pressure to the torque converter when the fluid is warmed up and I go WOT. Part throttle gives me much more response. WOT works well when the fluid is cold. As the fluid heats up, it gets worse. The engine hits max air charge and coolant temperature by the time the transmission fluid is only 150F, and the car still behaves okay. As the transmission fluid continues to warm up beyond this point, WOT starts to fall on its face. Warm up a bit more and go WOT from a roll, the rpms shoot up to 5500k but very little happens. Tires don't break loose, car barely accelerates. I let off and go back to part throttle, it behaves much better. Engine parameters aren't the issue - air-fuel ratio is good, no misfiring, etc. The issue has to be down the line, slippage in the transmission.

Question:

Would line pressure be enough to go off of, or do I really need to test pressures from every port? Does anyone know what direction I should go for finishing this diagnosis and repair?

More tranmission diagnosis (which pressure ports to test?)

Reply #1 – January 26, 2015, 07:44:51 PM

Spoke with someone that put an interesting thought into my head. It's an aftermarket TCS, so who knows what could be going on, but I have another thought/theory. When I go WOT right now, my tach does some weird things. I'm wondering if the electrical signal to the transmission is also getting dirty, making it have any of many problems I've experienced. Maybe my converter locking/unlocking issue isn't pressure but an inconsistent lockup signal. Maybe the pressure being commanded isn't staying consistent. I'll need to probe the wires, and more than that, narrow down where my weird twitchy tach is coming from. At WOT it may bounce between 3500rpms and redline, but it works fine at part throttle. On cold start I may get a shaky speedometer for a few seconds also, while I'm parked. I don't see any of that being 5v regulator, if it is also affecting the transmission, but I'll have to oscilloscope it all. I could be looking in the wrong area.

I could try unplugging the TCS and letting the transmission stick itself in failsafe 2nd gear/max pressure mode, but 1st gear really is where I'm seeing this issue show up.

More tranmission diagnosis (which pressure ports to test?)

Reply #2 – January 30, 2015, 10:54:29 AM

Sounds more like a electronic issue. It's a electric trans. I do bowties all the time, so can't guide you on that tranny, I'd check the electronics first. Could be a dirty plug or something simple.

More tranmission diagnosis (which pressure ports to test?)

Reply #3 – January 31, 2015, 02:17:34 AM

DSO oscilloscope will be here Tuesday (4 channel, hackable to 100MHz, cheap), so I should be able to better pinpoint what type of noise I'm seeing. I also have some 5V 5A regulators here now so I'm going to get the old IVR replaced in the instrument cluster. I wonder if there's any decent self-contained datalogger that's better than the typical logging multimeter - would be a useful tool to have around also.

I figure fix the obvious issues first, then see what I have left.

More tranmission diagnosis (which pressure ports to test?)

Reply #4 – May 10, 2015, 05:45:17 PM

Quote from: Kitz Kat;443679

Sounds more like a electronic issue. It's a electric trans. I do bowties all the time, so can't guide you on that tranny, I'd check the electronics first. Could be a dirty plug or something simple.

Weather is nice enough to tackle this again. I grounded the solenoids straight to battery and tried disconnecting the EPC wire to force full fluid pressure. Neither change does anything to how the transmission performs (well pressure does make it shift harder at light throttle, but it doesn't change WOT or lockup behavior). Main power and grounds are hooked up to the same ones as the EECIV. None of the other wires have anything to do with fluid pressures.

More tranmission diagnosis (which pressure ports to test?)

Reply #5 – May 10, 2015, 09:27:01 PM

Reviewed logs from transmission temperatures being cold to hot - It didn't seem to change at all during the driving I did, with probably 20 WOT pulls in 1st and 2nd. Transmission temperature of 80F or 200F, no difference.

You'd think this converter looks like some 6000rpm stall unit. It's a PI 3000rpm converter.

4000rpms: 36%
4500rpms: 30%
5000rpms: 23%
5500rpms: 17%
6000rpms: 13%

Below these rpm ranges, I can't tell - it flashes up too quickly.

I'm going to get under the car this week and get some extensions hooked up to all the pressure ports so I can test/datalog each one. Seems the next logical step in finding why I'm seeing so much converter slippage. I was hoping to find that I had electrical problems, not something in the transmission. Could also send the converter off to have them verify they sent the correct stall speed...

More tranmission diagnosis (which pressure ports to test?)

Reply #6 – May 10, 2015, 09:55:28 PM

Went back to some datalogs from years back when I was using the stock 4r70w 12" converter - rated for something like 2200rpm stall on a v6.

3000rpms 26%
3500rpms 17%
4000rpms 14%
4500rpms 12%
5000rpms 10%

I appear to have an ongoing slippage issue with this trans. It may make more sense to just get a different transmission, rather than continue dumping time and money into the current one. I'll get pressure readings if I can, but even those old converter numbers weren't looking good.

More tranmission diagnosis (which pressure ports to test?)

Reply #7 – May 12, 2015, 07:28:25 PM

Man that sucks.

More tranmission diagnosis (which pressure ports to test?)

Reply #8 – May 12, 2015, 09:17:35 PM

Sn-95 3.8 t-5's are a dime a dozen and bolt right up.

More tranmission diagnosis (which pressure ports to test?)

Reply #9 – May 13, 2015, 02:25:50 PM

Quote from: Haystack;448008

Sn-95 3.8 t-5's are a dime a dozen and bolt right up.

I've thought on and off about manuals over the last 10 years. Have a manual in my daily driver. Plan on sticking with automatic in the tbird, especially as I have plans down the road to go more motor/power and it's far easier to manage with an auto. If I was going manual, I'd start with a magnum t56 - it can handle good power, and the 0.50 6th gear option could make my 3.55's return highway rpms similar to stock 2.73s and aod (out of drone range, and returning 34mpg again). Nice, strong, but heavy (similar dry weight as 4r70w) and expensive transmission.

I got the EPC and line pressure hoses hooked up last night and exhaust back on, and just need to make one more wiring harness for my second pressure transducer. I have full plans to put the car back on the ground tonight and get some datalogs of my pressures. This may be as simply as a weak spring in the pressure regulator valve.

I also found some datalog entries that show me 3500rpm slippage - 55% (should be closer to 10% with my converter). Since I have pressures being 20% too low at closed throttle in lockup also ("fixed" years ago by increasing commanded pressure by 20%), it appears to be slightly low pressure across the board and not related to any specific clutches. My guess is I will see 170-180psi instead of 220-230psi at WOT. Pressure regulator valve can do that. It can be a weak spring, or worn bore. If it is this valve, I will probably just get a silverfox valve body and install it, rather than buying new solenoids, valve, and trying to find a transmission shop that will ream out the pressure valve's bore so it can use the oversized aftermarket pressure regulator valve. With all the hidden costs, it could be $150-200 vs $300. Starting over with a new valve body for $300 would be a nice fix, and be setup a little better than a jmodded vb. Once again though, I had these pressure issues pre-jmod and didn't feel the jmod improve much - low pressure would kill the firmness I should be seeing there also.

The pump should be fine - everything looked great in the pump when I had it apart and idle pressure was on the higher end of good.

More tranmission diagnosis (which pressure ports to test?)

Reply #10 – May 14, 2015, 02:46:21 AM

Well this sucks - pressures didn't tell me anything useful. I have 200-205psi line pressure at wot in forward gears, and 290psi in reverse. I'll need to lift the car back up and hook up the other pressures. EPC pegs my 100psi pressure transducer at 100psi whenever going wot.

I tried braking and slowly bringing the rpms up - it got to a bit after 3500rpms before the car began to move. I wasn't putting any excessive force on the brakes, but holding them firm.