5r55e high pressure spikes at WOT

[inh]

5r55e high pressure spikes at WOT (codes P0741 and P0743)

Today my transmission started doing funny things when downshifting or accelerating at WOT. It will spike to 500-600 PSI (estimated, based on the needle pegging on my 0-400 PSI VDO trans pressure gauge) when accelerating at WOT from a stop. Most of the time, when it downshifts to second or third, under WOT the needle will peg as well. It even does it on the highway when downshifting to maintain 70 MPH. It goes well passed the 400 PSI mark and will sit there for a few seconds before dropping back down. My pressure gauge has an electric sender and functions fine otherwise, so I don't think it's a wiring issue.

Background: Installed a sonnax increased ratio boost valve, increased pressure spring and the updated separator plate a couple years ago, along with an external trans cooler and filter, and filled with mobile 1 ATF. Hasn't been changed since (I know, shame on me...)

I planned on flushing the system and changing the external filter here in a couple weeks, but maybe doing that sooner might help un-stick whatever seems to be sticking? I have a feeling I need to drop the valve body though..

 

[inh]

New CVB valve body installed, same issue. Odd, I didn't think anything outside of the valve body would influence the pressure.. Thoughts on this?

Also now getting a flashing OD light after driving for a few miles. This is new as of today... Going to go to a trans shop and have the codes read, since no one I know has a reader that can pull Ford transmission codes.

I'm not opposed to purchasing a code scanner that can do this though, if anyone knows of any that can do it.

 

[wood1]

Does the computer tell the pressure control solenoids what to do I am guessing? Do you have a copy of the ATSG manual? If not I can send you the 5R55N pdf. Maybe the line pressure relief valve assembly in the pump is screwy?

 

[inh]

I do have a copy of the ATSG for this trans. The computer controls the solenoids, but I thought that the EPC solenoid would only affect EPC pressure, not line pressure, which is what I am measuring.

It looks like the Equus 3120 and up can read transmission codes. These are fairly affordable on amazon.com

 

[wood1]

http://www.explorerforum.com/forums/showthread.php?t=310331

 

[wood1]

Where are you tapping the line pressure from?

 

[wood1]

Page 22 says the EPC controls line pressure, isn't it normal for computer controlled transmissions to have a limp-home mode whereby the computer jacks up the line pressure? A bad EPC can also set a false VSS code. Hmmm... Did you replace the EPC with the VB?

 

[inh]

Line pressure is tapped from the line pressure port by the manual shift linkage. I see now that it says the EPC regulates line pressure, hrm.. I was going to take my ATSG with me to work tomorrow and dig through it more deeply. EPC was replaced with the VB.

The pressure is no longer pegging my gauge, it will only go up to about 300 PSI or so. It's also much less sensitive. After a few miles though, it pressure will start spiking and pegging the gauge and then limp mode ensues shortly after. Odd to say the least. This doesn't seem to be fluid temperature dependent either. Shutting the truck off will get the truck out of limp mode and it will behave just like it was when I first started it (though fluid is now at the normal 150-175 degrees.) Then a few miles later, pressure spikes that peg the gauge followed by limp mode.

Going to see if the trans shop is going to charge to pull the codes. If they are I'll buy a reader and have it Tuesday.

Keep the ideas coming

 

[wood1]

Wonder what code has been set. If you didn't have the pressure gauge you probably would have just figured it was a sensor out of spec. Have to wait and see...

 

[BrooklynBay]

Check the line pressure with the electrical harness disconnected. I know that it will cause more codes to appear, but this will help determine if the EPC is causing the boost in pressure. Compare EPC port pressure with the harness connected, then with it disconnected. Check this thread for information on a scanner: http://www.explorerforum.com/forums/showthread.php?t=223600

 

[inh]

I'll have to move my pressure line around to get to the EPC port. I think it's on the right side of the trans?

Got the Innova 3160 and pulled codes, P0741 after a couple miles of driving and P0743 on a KOEO test.

Line pressure test results: Low in Reverse and neutral (it pretty much sits at about 75 PSI) and high at WOT stall in all ranges. Like always over 350 PSI, usually up around 400 PSI.

Stall speed test is good, 2400-2408 RPM on the nose in all ranges. Technically a pass, but perhaps a bit low considering that is the BOTTOM of the pass range...

EDIT: I dont THINK it would be the EPC or TCC solenoid, as those were all replaced with the CVB VB install.. Perhaps bad wiring though...

EDIT 2: re ran the KOEO test a couple times to verify, it throws code P0743 consistently. I THINK my TC is locking up but maybe I'm just imagining it. Any way to test?

 

[inh]

I'm now thinking the solenoid wiring inside the pan. It would explain the symptom staying even after the VB swap.

Pulled the connector off the trans and did a resistance check on the TCC solenoid pins. 0.2 ohms. Should be 9-16. EPC checked out fine. Checked the TCC solenoid in my old VB, checked in at 10.something ohms.

I noticed while driving it that it's fine for awhile. Then pressures started to get higher, then limp mode. It seems as if the trans is modulating the pressure higher hoping to get the TC to engage. After it goes so high and it still isnt engaging, it sets the trans in to limp mode..

Going to drop the pan and check out the harness. After looking through the ATSG manual, swapping out that harness doesn't look like fun..

 

[wood1]

Bummer... oh well, you must be getting good at dropping that pan.

If you are driving at a constant highway speed holding your right foot on the gas pedal (engine warmed up etc), and tap the brake pedal with your left foot your engine RPM should flare a couple hundred then return as the converter unlocks and locks again.

 

[inh]

Bummer... oh well, you must be getting good at dropping that pan.

If you are driving at a constant highway speed holding your right foot on the gas pedal (engine warmed up etc), and tap the brake pedal with your left foot your engine RPM should flare a couple hundred then return as the converter unlocks and locks again.

Dropping the pan is easy. The first time I did it I had a nut brazed in for a drain plug The first VB work I did on it I must have pulled and replaced the VB 4 times before it worked right. That was a fun day...

I tried the brake tap trick on the highway earlier, TC is definitely not locking. Highway RPMs are about 3000 at 70 mph with OD on.. I remember them being much lower.

 

[wood1]

Yeah, I agree, can't be locking. You're going to drop the pan and check out the wiring then? Sounds like it must be the harness if your old solenoid is different than the new one, same issues with both VBs. Wish I could help more but I don't know much about these new fangled computerized transmissions...

 

[inh]

Dropped the pan. Wiring was good. TCC solenoid was 0.2 ohms... Pretty far out of spec for a supposedly 'tested' one from central valve body. Checked my old TCC and it was 10.6 ohms. Swapped it in, filled her back up, cleared the codes, and it's good as ever.

Pressures look higher. Under high load it gets up around 300 psi (line) but cruising it's down around 150. Idle is a hair above 100.

No more pressure spikes or anything like that, so I am quite pleased I'll report back if anything else is still amiss but as of now it's good to go!

 

[BrooklynBay]

Thanks for the update! It looks like the solenoid might have an internal short. Crack it open, and see if any of the coil wires blew, and shorted against the metal casing.

 

[wood1]

Great, nice to hear it's working well now. It would be nice to know if it had an internal failure...

 

[inh]

Thanks for the update! It looks like the solenoid might have an internal short. Crack it open, and see if any of the coil wires blew, and shorted against the metal casing.

There's no continuity from either terminal to the case, but judging from the low resistance it looks like the coil shorted on itself.

Drove the truck some more last night and all still seems normal. This pleases me Headed to SMORR this weekend, we'll see how well that thermo bypass is working out.

 

[BrooklynBay]

You're lucky that the shorted coil didn't ruin a section of the computer. I'm surprised that it didn't blow the PCM fuse.