1998 F-150 XLT Supercab 2WD, 4.6 Windsor, 4R70W, 3.55 ls rear, 230K miles. Original owner, always maintained & garage kept.

A couple months ago this truck began stuttering at the low end of the power band in 4th gear only (O/D). Highway entrance ramps on long shallow uphill grades, that type of thing. Since it began, I had an episode that I thought was a failed fuel pump (crank/no start), but which turned out to be the crank position sensor. Replaced that with the hopes that would also resolve the stutter. The truck is back to starting & running fine, but it did nothing for the stutter. Then, I discovered it had a P0500 code (there has never been a MIL light, O/D flashing, etc.; I just happened to run a scan and discovered it). So I replaced the vehicle speed sensor (this one is transmission mounted), hoping that might help the stutter. It didn't. The plastic gear on the sensor (orange, 20 teeth) seemed to be in pristine condition so I reused it.

My question is, does the ECU need to re-learn anything on these trucks after replacing these parts? I haven't disconnected the battery throughout all this and have only driven it maybe 15 miles since the speed sensor was done. The P0500 has not returned after those miles, so I have reason to believe I got a good part. Are there any other non-transmission components that could cause mistaking this stutter for an actual transmission problem?

Thanks for reading this and giving me your thoughts!

Mike

 

No, the PCM doesn't need to relearn anything after replacing those parts.

There are no transmission parts that could cause this problem. The problem is a slight misfire, and that's an engine issue, not a transmission issue. It is either a worn spark plug or a weak ignition coil.

 

But why only 4th gear? And why no misfire codes?

 

Because the RPM is low and the load is high in fourth gear. The misfire testing is notoriously unreliable.

If you use a scan tool you may be able to see the misfire counter rising, but not to the level of setting a code.

 

OK, thanks! I’ll start with two new coils since those are still original.

 

230,000 miles on original coil packs? This might be worth watching.

 

Thanks for that! It’s interesting to me that Brian had never seen one of the old style 4.6 coils do that though. I have coils on the way but am not very hopeful that they’re the problem.

 

By the way I did look it up today and my plugs & wires only have about 35,000 miles on them.

 

With that many miles I'd check cylinder pressures. A weak cylinder might be fine until it's under load. If you get a low cylinder or two, then a leakdown test. Both inexpensive tests. Might just be valves. Good luck.

 

Well, it’s not coils.

Good thought on cylinder pressures. This truck has had 100% synthetic every 3K miles since the first change at 100 miles, but I know that guarantees nothing.

 

When was the last time you tuned it up (new plugs and wires)?
Might want to do that now
One test is the "lightning test" at night
Spray those plug wires and the coils with water out of a squirt bottle (cold engine, spray the plug boots, wires and coils good)
Then
Watch for lightning
It might have to miss for weeks to set a code if it is subtle
It's easy to get those plug wires messed up on a 4.2 so grab a book

 

35,000 miles ago. I just did the coils since they were still original.

 

Back in the older days of these trucks, they did develop torque converter shudder that did nearly mirror the low RPM ignition issues that had been suggested.

How old is that transmission fluid?

 

5,224 miles and 1.5 years (I work from home). Last changed by a Ford dealer.

Looking at the ticket I see they charged me for 12 quarts of fluid; is that an indication that they flushed it instead of drain & fill? They didn’t change the filter.

 

Does it say what type of fluid they used?