My 2003 F150 (custom ordered from Ford by me originally) has generally been pretty danged reliable. The only big incident was at around 55k miles the transmission went out almost completely. The shop that fixed it said the sun shell completely disintegrated.

Anyhow, I'm now almost at 170k miles, and have been preparing to do some maintenance work when it got a little warmer (namely, replacing the timing chain).

Last week though, it started hunting gears really bad, and having the torque convert lock and unlock, really odd. It was fine when I would accelerate heavily, and get it under load, but when I was just mildly accelerating, it would exhibit the behavior. Additionally, under a light-mid-load during acceleration, it would occasionally make a sound that appeared to come from the engine area, almost like a hiss, which I took as a possible vacuum leak.

I did some research, and felt that the problem I was seeing, along with the transmission having been clunking into gear pretty heavily recently, that the MLP (transmission range sensor) was faulty. I did a look around the engine, and none of the vacuum lines seemed obviously distressed.

I replaced that, and immediately the truck was shifting right, took it for a 5 mile trip, and didn't sense any problems. Over the next week, I saw a few signs that troubled me, including that hiss sound (I'm not describing it right, but I have yet to reproduce it reliably enough to get it on a recording, and it won't do it except while driving.) Since I installed the AutoZone MLP, I read a couple of forum posts claiming that they are pieces of crap compared to Ford OEM (I was working on the truck on a Sunday and figured OtterZone was just fine), so it has me slightly worried that the new sensor could still be contributing.

This last weekend, I went out of town to pick up my trailer from my parents. It acted generally OK on the way to their place, and while I was tooling around town (picking up parts, working on my dad's 76 F100 with a 360, partially through an engine refresh).

However, on the way home, perhaps due to having the additional load of the trailer, the truck finally threw some codes (SES light came on and I have a programmer installed that I also use to display engine statistics, which also can read the codes off to me.) The overdrive light started flashing part of the way home, which if memory serves from when I last had transmission trouble, puts the thing into protect mode, and it stayed out of OD.

I stopped at a gas station for a bit, and then when took off, the OD light was off, and it was going into OD again.

I decided to take it to work today to see the behavior without the trailer, and it is driving ok minus it feeling funny. However, it threw one less code today (it did eventually start the OD light flashing again though).

• P1000
  • OBD Systems Readiness Test Not Complete
• P0741
  • Torque Converter Clutch Mechanical System
• P0171
  • System Too Lean Bank 1
• P0315
  • Crankshaft Position (CKP) System Variation Not Learned)
  • This error doesn't show up today though.

Based on past experiences with bad coil packs, having a loss of torque can cause the transmission to get very finicky about maintaining overdrive/locked TC. The engine feels like it could be running a lot better, combined with the P0171 code make me jump back to the vacuum leak idea.

I do want to replace the timing chain (and I think that the CKP sensor is in the same location), but I am not going to be home any of the next two weekends. I also hate taking vehicles in to the shop to diagnose these sorts of things. However, if it's a matter of having it done by this weekend, I may have to bite that bullet.

Any recommendations on approaches for me to take diagnosing this?

 

Hmm, with a bit more research, this code may have been thrown because I reverted back to the stock programming (previously, I kept it on program #1, transmission only). I have one of the edge programmers, doesn't look like they sell it anymore, I probably have had it installed for 7-8 years at least.

I'll probably take it back to the transmission only mode. The shop who rebuilt my transmission said it should improve the longevity of the transmission, rather than being harmful, especially since I tow occasionally.

 

Took it to a transmission shop, and they said that it basically didn't have 3rd gear at this point.

When I can afford to get it rebuilt, it will be the second time in 175k miles, dang.

 

Yea, A 4R100 trans is much better if you tow ocasinoally, - as far as logevitity, but even with a 4R100 you still need to know how to tow correctly... Or you'll burn them right up.

Have you seen this in Transmission Forum on this site, -

https://www.f150online.com/forums/tr...fluid-tcs.html

Yea, the 4r70w is even weaker. If you get it rebuilt, - make sure the builder knows how you want it built. I mean, there's definitely more than just one way to do that... Different component types, - really cheap and HD grades.

That can be a competitive business, so to know what your getting is best. And trust who's doing it is important as well.