Transmission/Transfer Case Need Advice…

[OGFlo54]

03 Expedition XLT 4wd Triton 5.4
4R70W with a BW4416 TC.
So here’s the issue…

My speedo upon acceleration in 2H, AWD4 and 4H, maxes out at 100mph- I’ve clocked the actual speed around 25mph. When reaching 100 power is reduced and a clunking noise can be heard from the transfer case. It sounds as if the TC is engaging and disengaging and with each clunk the truck lurches or lunges. (If going up a hill the TC will actually engage for a moment or two depending on how long the hill is)

In 4L the speedo stops at 60mph with an approximate speed around 35mph no clunking or lurching. The truck will not shift into 3rd gear regardless of selector position. I’ve checked and verified that 4wd is engaging in all TOD settings and disengaging as well. I’ve also verified that the TCM is working using a multi meter and by the audible clicks moving from 4L to 4H.

I’ve replaced the VSS but as of yet have not replaced the wheel speed sensors. I’ve never had a check engine light or a blinking O/D light ,ABS light or a blinking or solid 4H/4L light. I’ve reset the PCM. I’ve checked the 4wd solenoid and check valves and it’s working properly. Vacuum appears ok as I’ve not heard any vacuum leaks and the fact that 4wd is engaging and disengaging. I drained the TC to check for a possible stretched chain thru drain plug but it appears to be fairly tight.

I do need to do a trans flush. All fuses are good and relays as well. There’s no grinding noise from either the transmission or TC. The TC shift motor is working but it’s old and I could probably use a new one. I’ve never had a 4wd till now so I wanted to do my research before bringing the issue to the forum.

Is there anything I’ve missed or not listed? Any advice or solutions will be welcomed and appreciated. Thanks for reading!!

 

[mhg1]

Speed limiter in the ECM. Shutting down the engine and then back on as the speed drops below the cut off.
Mike

 

[OGFlo54]

I will give it a try see if that works and get back at you. Thanks Mike

 

[Hamfisted]

Most aftermarket performance tuners remove the speed limiter. You might try that if you really need to go that fast.



.

 

[OGFlo54]

I’m not trying to eliminate the speed limiter. Whenever I’m parked or at a stop light or stop sign the moment I accelerate the needle quickly moves up the speedo and at 100mph power is reduced. Like I said I’ve replaced the vehicle speed sensor. Could it be the wheel sensors?

 

[Hamfisted]

I’m not trying to eliminate the speed limiter. Whenever I’m parked or at a stop light or stop sign the moment I accelerate the needle quickly moves up the speedo and at 100mph power is reduced. Like I said I’ve replaced the vehicle speed sensor. Could it be the wheel sensors?

Oh ok. I miss-understood your issue. Sounds like a wiring issue and signal to the PCM. But something is telling your PCM you're at 100 mph and it's killing the ignition signal to "slow you down". How'd the harness and plug to the speed sensor look ? The harness could be grounding out with the torque twist of the motor upon acceleration. Has any work been done in the area of the harness path ? It's not contacting the exhaust system at all right ? If you have the hood open, and put the Expy in gear, and your foot on the brake, and give it a little gas like you're accelerating, do you see the motor lift up much? Like a bad motor or tranny mount ? I'm thinking some kind of stress on the speed sensor harness that's allowing it to ground out, sending a bad signal to the PCM.

 

[OGFlo54]

The connection at the speed sensor looks good but I haven’t traced the harness back to the engine compartment. I will do so and report back on what I find. I thank you for that information, I hadn’t thought of that.