I have a long description of my problem, but need some opinions.
2001 expedition with 240,000 miles. It is my wifes daily driver and we use it to pull our 32 foot travel trailer. trailer weighs in around 9000 pounds fully loaded.
Here is a description of the issue I have been having.
About 2 years ago it started bucking once in a while. My description of what I call bucking, while driving at highway speed with no load it will buck once in a while. It feels like it does when you are pulling a trailer and the trailer wheel drops into a pothole. It will just lurch once maybe twice every 5 or 10 miles or so. It doesn't do it every time we drive. Sometimes it will do it more often, every mile or so. But it doesn't feel like a misfire, it just bucks once then runs fine for a few more minutes. When it does it often I push the tow haul button and kick it out of overdrive, then it runs fine. That is when it is not loaded with a trailer.
It does this bucking more frequently when towing the trailer.
This has been happening for 2 or 2 and a half years. Not getting worse or better. No weather conditions that make it worse or better. Summer, winter, rain it doesn't matter.
Now it gets better. Last weekend we were pulling our camper down the highway. A level highway, no steep hills, no high wind but it started bucking more frequently, like every 20 seconds unless it kept it pushed hard enough to make it down shift. Keeping the rpms above 3000 it ran fine. After about 2 hours of this the OD light started blinking.
By the way, the service engine light has been on for a few months.
When we were loading to head home I pulled the battery cables for 5 minutes, but the lights were still on. The 4 hour drive home was tough fighting a 30 mph cross wind. I had to keep it almost to the floor to keep it running smooth.
This weekend I finally got around to checking the codes. The only code I got was a p0708, transmission range sensor high input.
I am looking for some opinions, what kind of problems will the range sensor cause? By the way, usually I get 12.5 mpg when pulling our camper. This weekend and last weekend I got around 5 mpg pulling the trailer.
And I do not think it is a coil pack. It does not feel like a misfire, it is short in duration with just one hiccup then it smooths out, and in over 2 years a coil would have failed completely. Last weekend after about 3 hours of pulling hard it did develop an engine miss on top of the other issue, but that cleared up after I shut it off for a half hour and cooled things down. I am wondering if the position sensor could be telling the computer it is in a different gear causing another issue? Also, could the EGR be getting hot causing problems after running hard high rpm's? When we pull hard it smells like hot plastic, and the egr pressure sensor gets hot. I have melted one pressure sensor a year ago, and melted a couple of small hoses off of the pressure sensor once about 4 years ago.

 

I think I forgot, the p0708 was the only code stored. There were no other codes. I reset the codes, drove it less than a mile and the same code came back up. Check engine light back on, od light still flashing. No other codes.

 

I would clear up the P0708 code first.
Have you changed the sensor and checked the wiring?
Google search "Expedition P0708", there are lots of hits.

 

I cleared all codes, they all came back right away, less than 10 seconds of driving.

 

I guess I wasn't clear enough - troubleshoot the P0708 code by first making sure the sensor is good and sending correct signals.
Check the wiring and connector for the TRS to ensure wiring/connection are good.
Readjust the linkage connection to the TRS.
Try another sensor - Dorman 511-101 on ebay are $28.
When was the last time the spark plug boots were changed?
Have you checked all the vacuum hoses including the PCV hose for cracks/soft spots?
Is the RPM holding smooth when climbing hills?
What gear is it in when cruising because the sensor might not be letting you get into OD?
An intermittent cut-out in my experience is usually electrical.
Check all your ground connections and try reseating relays.
Check connectors to the computer for corrosion.

 

Oh, I see now what you were saying!
I checked the wiring as best I could, connectors are tight and clean. Wires all look good. I have not messed with the linkage connection.
Another symptom to add, once in a while (like once every 3 or 4 weeks) it won't start unless I pull the gear shifter lever harder into park.
Plug boots were changed not too long ago, less than 30,000 miles.
Checked all vacuum hoses, they all look good. No soft spots, no broken or worn spots, and the ends all appear tight.
The RPM's do hold smooth. Even when it hiccups and bucks it doesn't change the rpm's, but the bucking is so short lived it is hard to see a jump. It just feels like I hit a bump in the road.
It does go into overdrive at highway speeds.
Finally, I have a new sensor ordered, it should be here in a day or two.
I will re-check the connector at the computer. I checked it with a flashlight, so might not have been able to get a good look at it.

 

Found this article - P0708 - OBD II Trouble Code

 

Thanks for the link. That is what I was looking for. It sounds like my problems may be all linked to the sensor. The CEL is on, the OD is flashing, I am getting very poor fuel mileage, I can smell that the engine is not burning efficiently from the smell of the exhaust, and I have poor performance. It is also shifting different than usual.
It may or may not be a solution to the bucking issue, but I suspect it is related. Before it only bucked once in a while, once the light started blinking it bucks much more frequently.
This winter will be 3 years since I replaced the engine. At 177,000 miles I dropped a cylinder for some reason. I found a good deal on a rebuild so I went ahead and spent the $2000 and replaced the engine. In 3 years and 65000 miles I should still have a lot of miles left on this engine.

 

Well I changed the position sensor tonight. When I re-connected the battery and started the expedition, the OD light and check engine light stayed off for a minute. Then the OD light started flashing again and the check engine light came on again.
I pulled the transmission dipstick again to re-check the fluid. This time I had my glasses on, before I did not have them with me. The fluid is a nice pink / red color. It smells like clean fresh oil, not burned. However, it is low. The car was warmed up good, the fluid level was showing it was in the middle of the cold section of the dipstick. It should be in the middle of the hot section of the stick, so I am guessing a quart or two low.
All wire connections look good, tight and clean. The wiring has no sign of wear, no pinched or broken places can be seen.
The only visible things I can see is the low fluid, and the PCV valve was whining. It was a little loose in the valve cover, but that should not effect the operation of the transmission? I pulled it out, cleaned it off and re-seated it in the valve cover and the noise stopped. When I shook it the check valve inside rattled. and there was suction on the end of the valve.
What else should I be checking to locate the source of the Po708 code? Would low fluid give that code, or is my tranny about to go bad?

 

What code(s) are you NOW getting?

 

Same, po708.

 

"Look good" won't get it. I'm guessing you have the 4R70 transmission? I suspect you have high resistance in the light blue/yellow wire running from the DTR up to the PCM.


Disconnect the DTR sensor connector and inspect both the male and female ends of the connector for pins that have green crude on them or pins that are pushed back or spread so that they don't make good contact.


Do the same for the connector at the PCM.


Then ohm out the light blue/yellow wire from pin #3 at the DTR connector to pin #64 at the PCM connector. It should not have more than a few ohms resistance.

 

OK, I will do that as soon as I have time to get back to the shop.

 

I found the pin #3 on the DTR and the #64 connector at the PCM. The resistance on that wire showed 0 ohms, so it is good. Another good look at the connectors on all sides they are shiny and good.
After I put it back together and connected the battery, I started the car again. All warning lights were off for about 30 seconds of the engine idling, then the OD light started flashing again, still the same code. The CEL is not on yet, but I am sure once we drive a mile or two it too will come back on.

 

The PCM monitors the voltage at pin 64 in the PCM connector. When you change the gear shift lever, the DTR sensor changes the voltage available at pin 64. That's how the PCM figures out what gear position you have selected.


You could back probe pin 64 with your DVM and go for a short test drive. The voltage should be between 2.6 volts and 5 volts depending on which gear position you have selected. The voltage should remain steady.


If the voltage jumps around the PCM thinks you are changing gear positions and tries to shift the tranny accordingly. If the voltage goes over 5 volts you get a P0708. Either the DTR is defective or you have a wiring issue. (An out of adjustment DTR will not cause a P0708).