Hey guys, I have an E4OD problem that I haven't heard of before. I have a 1994 F250 4x4 extended cab 7.5 auto with 86,000 miles on it. Normally it runs and drives perfectly, smooth shifts everything is good. The other day I took a load of grass clippings over to a friends house for their garden. The land is a little steep and was wet so I put her in low 4. When I got back on the road I went back to 2wd and was greeted by harsh shifting and code 628. I reset the code and everything went back to wonderfulness. Sunday I took another load over to my friend. This time it was dry and I didn't need 4 wheel drive so I drove in, unloaded and drove out. All this is at 10 mph and under. When I got back on the road same harsh shifts and code. Reset the codes and back to normal. I drive this truck daily and have never experienced this before. The only other symptom is sometimes I get a slight (2mph maybe) variation in speedometer at 65-75 mph, but no bad shifts and no codes. I would think if it was the torque converter the problem wouldn't go away for weeks at a time and only return at low speed, but ..... Any ideas would be greatly appreciated. Thanks.

 

Check your VSS.

 

Yeah, I have a new sensor sitting on my bench right now. Can't figure out why it only sets the code at low speed though.

 

Everything I have read about code 628 points to torque converter slippage.... .Most times it indicates the TC needs to be replaced, though there can be other causes. Solenoid pack,etc What does the tranny fluid look like? Still might be worth it to check the wire for the VSS and make sure the are not causing erratic behavior.

 

Tranny fluid looks and smells fine. The problem only showed up after slow speed operation. once in 4wd and once on the same road in 2wd. I cleared the codes and the truck has run fine since, including a 200 mile run at 70 to 80 mph and about 10 miles of stop and go behind an accident on the interstate. No codes.

 

All your tail lights and brake lights work? In cab light as well?

 

Please forgive my ignorance on F-250s, I am only familiar with the F-150s with the 8.8" rear end and light duty trans (auto and manual). Is your VSS in the rear-end or the trans? There is a reason why I ask this. I am also leaning towards the VSS personally. Aggravated at low speed is typical on this type of rotational feedback circuit. I have seen it numerous times, just not on a truck. Any type of electrical noise, or obtuse signal spikes will cause a form of confusion to the computer tracking the sensor. It is more likely to be aggravated at low speeds because the computer will actually see the irregularities in the signal more prominently when the shaft rotation is slower. At higher speeds, it is switching so fast that random spikes are more likely to go unnoticed.

My 95 shortbox F-150 has the VSS on the pumpkin on the rear-end. It is an inductive sensor that reads rotation of the diff carrier. Other trucks typically have the VSS on the trans output shaft. Ford did both in the ranger over the years. So, what I suggest IF the VSS is mounted in the rear axle is to not only check the sensor and related wiring, but perhaps pop off the rear cover and inspect/service your diff. If you are starting to get metallic particulate in the fluid then that could mess up the sensor reading. This is just a theory not a fact. It just wouldn't hurt.

One more thing... I am perplexed about the fact that this seems to be isolated to a particular location that you visit. This might sound "out there" to some, but hear me out. Is there any high-power radio transmitters or electrical substations in close proximity to that location? As I said, electrical noise can wreak havoc with the signal. That is a long run of wire running front to back of the vehicle, and it carries electrical pulses from the sensor to the PCM. If there is any serious interference electrically affecting that signal, then I can see that happening as well.


Sorry for the long-winded post, please keep us posted. I have never seen a code like that in my years driving these rigs. It is definitely an odd-ball.