Mike,
I had this post on the Engines Forum for a few weeks, but only got 1 hit which called my engine a "slush box". Then his comment after that was not accurate to the problem I was having. I am looking for a serious response. Maybe you can help. I have a 4.6.

"WOT hesitating question
Has anyone else notice their trucks hesitating under WOT? My truck has always done this since I bought it with only 7500 miles on it. An example of what I am talking about is this morning on my way to work. I turned in to the office park where I work then made the right to go down the 1/4 mile strecth to the building I work in. After making the turn I nailed it. I watched the tach today when I did it. It jumped up to 3000 real quick then it dropped to 2800 for a second and begin to accerate again. I did not notice how fast I was going when I nailed it. I would say 15 to 20MPH. I thought the Superchips Micro Tuner would correct the problem, but it didn't. Any ideas or suggestions?"

I was in first gear when I nailed it and it didn't shift until around 4500 when I let out of it. The one response I got in the engine forum thought it was the transmission. I don't think so. Thanks in advance.

 

Hi Johnson505,

Without having the vehicle here there's really no way we can tell you what's going on, we'd have to do some testing.

We're strictly about performance, what we do is make vehicles accelerate quicker and go faster, and with some of our performance modifications, also get better fuel mileage. We're not a vehicle repair facility or a diagnostic shop, nor do we attempt to diagnose vehicles on the Internet or in email.

In general, there are a couple of normal things that are going to reduce rpms at full-throttle in an automatic transmission, and those are an upshift or the TQ (torque converter) locking up. A TQ lockup is going to cause a drop in rpms of about 400 rpm in these vehicles, and an actual gear change even more, 600-1500 rpm. And it's possible to see only about a 200 rpm drop from a TQ lockup at full-throttle in 1st gear, where torque multiplication is at it's highest & the engine gains rpms the quickest.

Not upshifting until you let off of it at 4500 rpm is perfectly normal, it's going to do that when you're at full-throttle. Had you kept your foot into it, it would have upshifted anywhere from a low of about 4800 rpm to a high of about 5400 rpm (assuming this vehicle has an accurate tach, which doesn't happen often), that varies depending on vehicle configuration, computer code, etc.

This may very well just have been the torque converter locking up, which is perfectly normal a little after doing a downshift like that. Without having the vehicle here to test, there's just no way to know what's really going on. If you think you actually have a problem, then pull the chip and take it into your local Ford dealership for them to take a look at it.

I would also try nailing it from a standstill, and see if the same thing happens at about 3000 rpm, just to identify if this is something that happens *only* after the downshift scenario as you've described, or if this also happens when accelerating at full-throttle from a standstill as well.

 

Thanks for the info Mike.

 

Johnson505 is not alone with this anomaly. My truck does it too on occasion. It happens after driving in 'granny' mode for a week or two. During hard acceleration the rpms will dip down 200 around the 3000 rpm mark. If you do several hard runs the hesitation is gone like when passing several cars in a row. So maybe the computer learns the shift/rpm pattern from everyday driving and has to reset for harder use. After a few good runs, the rpm dip is gone for a few weeks. Oh, mine did it stock, with a Superchip and now with the tuner. It just means I have to have kick the fires once in a while.

Fritz

 

Hi Fritz,

What you're describing sounds like adaptive strategy is affecting that function, which is possible, as the Superchips tuning is *not* going to defeat adaptive strategy, nor should that be tried of course, adaptive strategy needs to be present.

The more a vehicle is driven conservatively, as we've discussed here for years, the more you'll see various aspects of adaptive strategy reduce certain aspects of performance. That is reversed once the vehicle is driven harder, or if the PCM is cleared and the vehicle isn't driven as conservatively.

In practical terms, there isn't any getting around adaptive strategy having these effects, especially in daily drivers which are used to go back and forth to work, and which for most people means a significant amount of relatively conservative driving the vehicle sees as a result. And this is exactly why many people will clear the PCM when they go to the drag strip in their daily drivers, as that can get them anywhere from 1 to maybe 3 more more tenths of a second off the acceleration times.

None of the F-150's we have here that have automatic transmissions exhibit this characteristic of dropping 200 rpms at 3000 rpm @ WOT in 1st gear, and all are using the Superchips tuning. Can't say if either do that on the stock program. Both the F-150's that have automatics here are 2001 models, and both have 5.4's.

Interesting that you've noticed this same thing, but that it goes away after a few good WOT bursts, that's a good clue & means obviously adaptive strategy is at work in this area.

Thanks for your post!

 

Hi Johnson505,

Fritz gave some good info in his post, as he's noticed this as well, but it goes away once he starts driving it harder, clearly indicating adaptive strategy at work.

It would be interesting to see if your truck does this from a standstill in addition to when you do a downshift. I would also check to see if it does this after clearing the PCM and then doing an immediate full-throttle run up thru the gears.

Both of you have 4.6's I noticed, and after reading your post I checked to see if either of our 5.4 automatic F-150's does that, and they don't.

It really sounds like adaptive strategy at work at this point, so I wouldn't worry about it, but I *would* try the things I've mentioned in this post just to see if there is any change in that.

Good luck!

 

Mike,
It doesn't do it all the time. I nailed it this morning a few times and it didn't it at all today. It may be the adaptive strategy you were talking about. I was hoping that it might have been the clutch fan or something else that I could change to eliminate this.
Thanks for the info.

 

Hi Johnson505,

OK, thanks for your response.

Sounds like it's just normal adaptive strategy at work, in which case there are 2 things you can do to influence (not cure) that behavior:

1.) Drive it doing that same thing a bit more frequently. The more often you do this, the more the PCM sees you requesting full power and a WOT downshift, and the less that adaptive strategy will lock up the TQ under those WOT downshift conditions.

2.) Disconnect the battery to clear the PCM - this is strictly a short-term thing, like guys will do sometimes when they go to the drag strip with their daily driver to wipe out adaptive strategy adjustments from conservative back & forth to work trips, etc. In a vehicle that sees conservative driving, this can get you 1-3 tenths off the 1/4 mile times at the track. This is not a cure by any means, just a very effective short-term "treatment."

Have fun,