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  #1  
Old 09-16-2007, 11:19 PM
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Transmission shifts from OD to 3rd when I let off the gas...

2001 Ford 5.4L w/ 4R70w, 66k miles

Just as the title says, when driving at highway speeds, when I let off of the gas, and the trans will downshift to 3rd then shift back up to 4th. While cruising around 45mph, with the gas pedal between 0%-5% open, it just jumps between 3rd and OD. If I give it say 50%-75% throttle, and accelerate to 80-85 mph, all of the upshifts are perfect, in fact if I am crusing in 4th, then give it 75% throttle to pass, the 4-3 downshift is perfect.

That leads me to believe it's a vacuum or electrical problem, maybe a sensor or controller issue, but not a mechanical failure... but then again, I don't have much experience with these.

Any help is appreciated!!
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  #2  
Old 09-17-2007, 07:10 AM
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I guess we are to assume this is a new behavior that just started...

Only two things come to mind.

Perhaps a dead spot in the TPS is causing the signal to the PCM to be erratic. Other thing is a dirty or mis-reading MAF sensor. Either fault condition would be likely to set an SES, though, if severe enough.

Have you had a check engine/SES or O/D light turn on while driving?

Steve
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  #3  
Old 09-17-2007, 08:03 AM
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Yes, it just now started happening.

I have no check engine light and when it kicks down to 3rd, the 'OD off' light does not come on.

Also thought I'd add this, I can turn off the OD and run in just 3rd gear, and it runs fine (and the 'OD off' light comes on haha)

I'll try blowing out the maf and swapping out the TPS sensor. If you can think of anything else, let me know.

Last edited by lee_eldridge; 09-17-2007 at 09:07 AM.
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  #4  
Old 09-17-2007, 09:51 AM
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On the side of the transmission there is a sensor called the MLPS that detects the position of the lever. This is the one that attaches around the shift lever as it goes into the transmission. If this is going bad it will cause troubles with 3-4 shifting. Most parts stores call it a neutral safety switch.

To install it you have to have the transmission itself in neutral and line up the marks on the sensor and bolt it down tight. Misalignment can cause the same problems.

Good luck with it and let us know what you find.

Darrin
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  #5  
Old 09-17-2007, 10:19 AM
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Darrin, I'll crawl under there today and see if I can just remount it into it's proper position before I go get a new one... It may be self-explanatory once I get under there, but what lines up to the marks on the sensor? Thanks!
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  #6  
Old 09-17-2007, 11:15 AM
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Quote:
Originally Posted by lee_eldridge
Darrin, I'll crawl under there today and see if I can just remount it into it's proper position before I go get a new one... It may be self-explanatory once I get under there, but what lines up to the marks on the sensor? Thanks!
I'll bet it's the throttle position sensor causing the problem.

If it was the TRS (Transmission Range Sensor) it would go to neutral not shift from 4th to 3rd. The TRS can't cause this to happen.

If I'm wrong and the TRS *IS* the problem, realigning it won't help. It would have an internal failure, not a alignment problem. The lines that must be aligned are on the part of the sensor that touches the shaft and on the outer part of the sensor.
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  #7  
Old 09-17-2007, 11:44 AM
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Ok, TPS and MLPS/TRS it is. I'll get those swapped out today and see if that doesn't fix it. Thanks again!!
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  #8  
Old 09-17-2007, 11:27 PM
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I swapped out the TPS sensor, started it up, and within 30 seconds the same problem happened.

I drove it home parked it for an hour, went back out, turned the key to the 'on' position, and ran the throttle through the entire range (I read somewhere that will help, not sure if it did), then tried it again. I drove it for half an hour, ZERO problems, in fact the truck is now running significantly better than when I bought it 4 weeks ago. Shifts are much smoother and softer, and it doesn't 'lock' into gear at ridiculously low rpm.

So it appears that the TPS sensor swap fixed the problem (and other smaller issues that weren't too noticeable). I'll keep it updated if the problem returns, but something tells me it's gone for good.

Thanks again!

Now if I can figure out what the small clunk/bump from the rear is whenever I come to a complete stop...
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  #9  
Old 09-18-2007, 07:54 AM
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Quote:
Originally Posted by Mark Kovalsky
If it was the TRS (Transmission Range Sensor) it would go to neutral not shift from 4th to 3rd. The TRS can't cause this to happen.
You were right on with the diagnosis and honestly thats what I thought it was too. For some reason I thought that he had already done the TPS and it didn't cure his problem. I talk to so many people with this stuff I must have gotten cornfused. LOL

But, the MLPS can cause shift problems both going into and coming out of overdrive. I have seen it many, many times.

Darrin
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  #10  
Old 09-18-2007, 08:55 AM
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I may replace the MLPS sensor anyway. Are there any other problematic sensors that I should replace or watch out for?
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  #11  
Old 09-18-2007, 08:57 AM
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If it's working properly then I wouldnt replace it. The newer units like you have on your truck are a lot less trouble than the older ones.

Darrin
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  #12  
Old 09-18-2007, 09:39 AM
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Alright... thanks again.
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  #13  
Old 09-19-2007, 02:49 PM
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:/ The problem came back again...

One thing I notice now is that it will upshift at significantly lower rpm, and 4th gear will 'lock' into gear at 37-40mph, and it takes a significant amount of throttle to get it to downshift back into 3rd. Once it 'locks' into gear, as soon as I let off of the gas, it will harshly jump back into 3rd, then shift back up to 4th.

I also checked the tranny fluid, and it's overfilled to the point where it reaches the metal part of the stick, well over the plastic gauge on the end. Not sure if that has anything to do with it, but just thought I'd throw that out there.
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  #14  
Old 09-19-2007, 05:25 PM
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The next thing I'd do is suck the excess fluid out of it till it's sitting no higher than the "full" line.
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  #15  
Old 09-20-2007, 08:08 AM
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Hopefully you were checking the fluid level as prescribed: Hot, level, idling in Park. Otherwise, it will read VERY high.

Steve
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1995 Mustang GT Convertible, only 68K miles.
1998 Ford Contour Wifey's old daily driver, now mine.
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Old 09-20-2007, 08:08 AM


 
 
 
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