Off-Idle Acceleration Anomoly
 

1998 Ford 4.0 OHV 4x4 5-speed auto Ranger. Runs fine, but seems to get louder than it should for a second or two off the line if I don't really ease into the throttle. This only happens when the engine is warmed up. I have tested the EGR with a vacuum pump, and the valve is working properly. Also cleaned out the IAC valve and put on a new gasket (the previous owner's mechanic forgot to put a new gasket on); the truck now idles smoother, but this still hasn't fixed the problem. A friend of mine suggested I check the coolant temp sensor. If anyone here has any other ideas, please let me know. Both my friend and I are beginning to run out of them. Thanks in advance for your time.

Try starting off in 1st manually

From your description it reads like transmission is slipping, not an engine issue, engine is REVing up before trans engages

The front pump(main pump) in the transmission needs to generate at least 100psi to hold clutch and bands(brakes) in place
Pump is operated at engine RPMs, so at warm idle RPMs are lower, if there are leaks in the valve body which there always are, then pressure may drop low enough for a delay to engage until engine RPMs get above say 1,100

How is reverse?
Reverse needs even more pressure to engage that forward, slow to engage Reverse is usually one of the first signs of lower than normal pressure

Reverse feels fine. This noise does not occur until around 1500-1600 ish RPMs. If it was a transmission issue, wouldn't this happen regardless of engine temperature? I would think that I'd also be experiencing other driveability issues, but the truck shifts fine.

I forgot to mention two things that you've reminded me of, though. Revving in neutral, it doesn't make a sound. Also shifting manually into first gear does not make any difference.

No, transmission fluid warms up and gets thinner just like engine oil does, so cold warm applies to both

Check the fan clutch
Before starting COLD engine, open the hood and try to spin the fan blades, they should barely move, clutch is locked because fluid inside is cold
When you start a COLD engine you should hear the locked fan clutch, it pulls lots of air thru radiator, that only lasts maybe 10 seconds or less, is that a similar noise?

Checked the fan clutch, it works like it should. I have done some research and learned that the EGR regulator and DPFE can also cause problems, so I will check those when I get the chance. It very well could be the transmission, like you said, but I'm trying to rule out the simple variables first, before I start shelling out cash.

By the way, Ron, I want to thank you for your time and expertise. I really appreciate it.

Nice of you to say, thank you

Hey Ron, I noticed something today while driving. The transmission takes a couple of seconds to shift from D to 1 while the truck is moving. It doesn't have this issue from D to 2. I wonder if it is related to my current issue.

If so, I suspect thay it might be a valve body leak, solenoid issue or if the transmission could need a band adjustment. It only has 85,000 miles on it, so I'm confident that the clutches are still good. Also shifts perfect in D through all the gears. Or, maybe your initial guess is correct, and it is the oil pump.

Really hoping it's not a major transmission problem, and I still have a few other suspects to rule out, but this little test got me thinking.

Transmission is a 5R55e, if it helps.

Update: symptom occurs in both 1st and 2nd gear manual. No losses of power or rpm fluctuations present.

I will be using this thread as a sort of troubleshooting journal from here forward.

Doesn't read like a known issue unless its "flaring" which is a know issue in all automatic transmissions

The EPC(electronic pressure control) solenoid could be the cause but so could a few other things

Good read here on the 5R55E: https://atracom.blob.core.windows.ne.../2003_5_50.pdf

A local transmission guy advised checking the u-joints. I found that they're quite rusty, and I swear, I could see a bit of grease between the cap (for lack of a better word) and the flange on the driveshaft.

​​​​​​Found a problem, even if it isn't the problem.

Troubleshooting update: no play in u-joints. Blew cigar smoke into the manifold, no vacuum leaks from the looks of it. DPFE holds vacuum without power, EVR solenoid was replaced...thats a rant for a different thread. So that exhausts my engine related ideas, so I'll be moving on to transmission related suspects.

After reading the article, a sticky shift solenoid 1 seems like a logical guess, since both first and second gear rely on it and they both have issues off the line. However, I think that the pressure control solenoid is also a possibility. Any tips on how to troubleshoot them, and is it possible to do so without dropping the pan?

I have finally remembered to video record what is happening. Here is the video. Link cuts past all the stuff that's not important, but also a few other details that I talk about. I've already posted those on here, though.

Just as a heads up
There is no 2nd gear in these 5R55Es(or 5R44Es), these are EXACTLY the same transmissions as the 4R55E/4R44E
Ford engineers added faux 2nd gear using software in the PCM(engine computer), it turns on OD when in 1st, which gives you the faux 2nd.

This came from off-roaders using A4LD transmissions that has just the 2 solenoids, one for OD on/off
They found you could manual engage OD in 1st or 2nd gears to get you a sort of gear splitter
A4LD is same transmission as 4R or 5R, the 4R and 5R just have more solenoids

Now the PCM decides when to use 2nd and when NOT TO, it has a choice, so can skip OD on and go directly to 3rd
Its a parameter choice, meaning PCM is monitoring engine load, throttle position and RPM to make its decision to use 2nd gear, not a clue as to what the software guys used for that choice

4R uses these ratios
1st: 2.47...................2nd: 1.47, 3rd: 1.00, 4th: 0.75

5R uses these
1st: 2.47, 2nd: 1.86, 3rd: 1.47, 4th: 1.00, 5th: 0.75

1st: 2.47 X 5th: 0.75 = 1.8525 ratio, so 2nd gear = 1st + OD

Troubleshooting update:
The following sensors/ units have been checked for voltage, and/ or resistance, and are good:

TPS, MAF, ECT, DPFE, IAT. Additionally, the evap purge solenoid checks out on the resistance, but it doesn't hold vacuum when the engine is off. Not sure if this is supposed to be the case or not. If it is supposed to hold vacuum when the engine is off, then I have found a possible suspect.

Still need to check transmission solenoids, but I'm pretty sure I need to take the pan off for that.

Also discovered that the condition is load dependent, not just off-idle alone.

EVAP purge solenoid is normally closed, so unplug its 2 wire connector and see if it holds vacuum, it should, if not replace it
This solenoid gets 12v, on red wire, with key on, PCM controls the ground wire to open it, so if this control Ground wire gets shorted to ground............then Purge solenoid would be open with key on

EVAP Vent solenoid is normally open, it should close and hold vacuum with key on

I double checked the purge solenoid this morning. Disconnected the two wires, made sure there was no key in the ignition. Will not hold vacuum. Confirmed that the line going to it is good. I think we may have found our gremlin, but it's an expensive part, so I won't do it unless your final verdict approves of it.

Valve is bad

Its just a 12v solenoid valve, get it from wrecking yard, used for 30+ years on all sorts of vehicles, but Ford vehicle will be more likely to have same connector type
Blow into it to make sure its closed, and you can take a 9volt battery with you to make sure it opens, they have no polarity, no specific + and - terminal
Cut the wires on the junk yard solenoid, and hoses, so you can test it with battery but also so you have the connector in case its not an exact match to yours

The purge valve hoses were often heat sealed, meaning they were smaller hoses and then heated up so they would stretch out to fit on the nipple then allowed to cool so you get a tight connection
Use heat gun to soften hoses for easy removal

Car makers used these 12v valves on EGR and EVP systems, same type, closed with no voltage open with voltage, the computer Pulsed voltage(usually the ground) to open it a little or alot

Ron, I'd like to once again thank you for not only your expertise, but for following along with me on my journey to find this issue. It has been an interesting and rich learning experience that really taught me the importance of not only knowing how systems work, but also how to troubleshoot them.

Your wisdom and experience are invaluable. Wish I knew a few guys like you in person, haha!

Nice of you to say, just paying it forward