Engine surges while cruising.

[arco777]

As I'm driving down the road in Overdrive, with steady throttle the engine surges. RPMs rise and fall, see video below.

Video here - http://youtu.be/H4wuoj0nmQA
Video taken at about 70 MPH, cruising with steady throttle on level ground. This occurs at any cruising speed in Overdrive, though the amount of surge varies slightly with the speed.

No KOEO codes, no KOER codes, cylinder balance test results 90.

Swapped PCM, new MAF, and TPS with no change. New spark plugs and wires. Torque converter seems to properly unlock when I tap the brakes at speed, then locks up again as it should.

Any ideas why this is happening? Thanks in advance!

 

[wood1]

I would rig up a wire to feed 12V on a manual switch to the brake switch so you can fool it into thinking you have your foot on the brake. I think your converter is locking and unlocking.

 

[wood1]

I guess you could just hold your left foot on the brake pedal slightly...

PM me for you email address for a copy of the ATSG manual

 

[wood1]

Did some reading in the Ford A4LD reference manual, there are a few sensors that have input but only a failing TPS has a symptom of "Abnormal shift schedule, torque converter clutch does not engage, torque converter clutch cycling."

 

[arco777]

Thanks for the reply!

I tried tapping the brake and the TC unlocks as it should, increasing RPM to ~2900 and then locking back up a few seconds later.

I don't have any problems in Drive, and with the larger tires I can run in Drive at cruising speeds just under 3000 RPM until I fix this issue.

Tried using the TPS off my other Explorer. Same exact problem It did seem slightly smoother at lower speeds, but that could have been my imagination. I did calibrate both TPS sensors to .95-98 volts at idle, in case you were wondering.

I have valve body gaskets on the way, a Transgo shift correction kit and an assortment of Sonnax goodies. Hoping that a valve body rebuild will fix the issue and that I'll find something like a torn valve body gasket.

I still have a bad shudder from 40-45MPH that saps all power unless I force a downshift and power past 45MPH. Wonder if it's related.

 

[wood1]

Did you try holding your foot on the brake to see if the rpm continues cycling up and down? I wouldn't think the engine would be able to increase in rpm like that with a locked converter.

 

[arco777]

No, I just tapped it. I can try driving it with a foot on the brake. Give me 20 minutes.

 

[arco777]

So I took it out on the highway. Got up to speed. Hit the brake gently and held it - RPMs rose and stayed steady, no bounce - just like when tapping the brake. As long as I held the brake the revs stayed steady, converter felt unlocked.

Let off the brake, it relocked and went back to bouncing/surging. Then it got steady. And stayed steady. Rode the brake, RPMs jumped to 2900 and held, let off brake and it dropped to 2600 and stayed steady. No more surging/bouncing! I drove for another 15 minutes and could not get it to do the surging any more!

Now I'm not sure if riding the brake like that fixed something or broke something, but it is no longer surging. I even tried shutting the engine off at a stop sign, restarting and driving some more. No change. Seems fixed? I will next drive the truck tomorrow morning and will report back in the evening about my results.

 

[wood1]

Weird... definitely the converter though.

 

[arco777]

Very weird. It has been surging for over two weeks that I've noticed it, perhaps longer. This trans is supposedly "rebuilt" within the last 5k miles, with a "new converter". I can believe that it was rebuilt but I doubt it was a quality job, probably just a soft parts rebuild. Not the original trans to the truck so I don't know how many miles are on it total.

 

[wood1]

Scratching my head on this one a bit. You could rule out the transmission and converter clutch solenoid by feeding it a ground signal so you don't have to rely on the ECM. It's the p/y wire in the 3 wire connector going to the trans.

I always suggest a VB rebuild to increase the life of these trans'. I thought it was a fun project.

 

[arco777]

Drove it again twice since the last post. Still no surging. I note that at speed, it cruises at a higher RPM than before. TC seems to unlock, even though it's a little lazy about it and only jumps a couple hundred RPM at most.

 

[wood1]

If you drive it when it's cold before it goes into closed loop it won't try to lock the converter. Maybe you don't have OD?

 

[wood1]

Hmmmmmmmm...

Good info

 

[arco777]

I think my overdrive is not engaging at all any more. I notice no difference between Drive and Overdrive shift positions at 60-65MPH. TCC still unlocks when I tap the brake.

Going to be swapping in a rebuilt valve body soon and look into some other possible causes, including the TPS link you posted. Thanks

 

[wood1]

http://www.explorerforum.com/Singleton/web/pages/at3.html

Never know...

 

[arco777]

I'll check on the electrical side of things. Couldn't find the old "wires on the manifold" failure, but haven't traced it down all the way to the trans. Did have that problem already on my 2DR with a burnt up bundle of wires.

No 4th gear / 3-4-3 shift hunting
If you are halfway mechanical I would pull the pan and check the 3-4 shift solenoid. Theres a bulletin (#111, 10/95) about an upgraded 3-4 shift solenoid. details 3-4 shift complaints caused by clogged solenoid screen.
No 3-4 upshift for almost completely clogged screen. Partially clogged screen may cause 3-4-3 shift hunting, no 3-4 upshift after 15 min of operation, or a 3-4 upshift only at high throttle openings(high line pressure)
screen can be removed to restore operation, but better solution is to replace with new part number.
Check for clogged or restricted holes under the screen.Updated part number is E8TZ-7M107A

I would pull the pan and check the valve body and shift solenoids.

I will be rotating valve bodies out between my Explorers, so this should get covered. Have a 97k mile body to go into my 2DR, and the 2DR's body is going into my 4DR. Valve body rebuild of the 97k unit is in progress but the bore plugs are giving me a hard time.