Bumping when in overdrive-downshifting

[pookapa]

I have a 97 XLT and when I am driving highway speeds about 60+ and I am in overdrive, if I try accelerating somewhat quickly there is a very noticable bumping feeling and sound in the rear of the explorer and seems to have a problem downshifting. If i turn overdrive off it seems to be better and not have this problem, occasionally I may feel a bump or two when accelerating or driving up a hill at highway speeds. what could this be?

 

[Green68]

Tps

I had a similar problem on a Grand Marquis. The problem was the Throttle Position Sensor. It did not throw and codes at all. I found it by measuring the voltage output of the sensor while moving the throttle, I could see a slight blip in the voltage at certain positions.
HTH
Mike

 

[pookapa]

so changing the sensor would solve this problem?

 

[BrooklynBay]

You could verify the same results with a digital multimeter to see if it's defective.

 

[pookapa]

I checked out the TPS with a voltmeter, the connection plug read 5.0V when unplugged. With the plugged attached to the sensor I backprobed the plug and got 1.0V at no throttle and 4.44V at full throttle. should I reach a full 5.0V at full throttle?

 

[pookapa]

bump

 

[Green68]

pookapa, sorry I didn't reply sooner. I checked my wiring diagrams (1999) but they don't show a voltage value. I think the values you are reading are within range. The issue is an intermittant problem that will likely show up as "noise" on the dc voltage due to a worn potentiometer in the TPS. If that's the problem it would be easier to see it with an analog meter or if you have access to an o'scope that would be even better. I could see it on my analog meter, the needle would "jiggle" a little bit when moving the throttle.

My experience with the TPS may not be your problem, but it sure sounds like the symptoms you've described. It is an easy part to replace and not terribly expensive. A Motorcraft brand at O'Reilly is $43.99. Cheaper than one hour labor at most shops.

HTH
Mike

 

[pookapa]

Thanks Green68, I will give the TPS a shot. Another symptom I experience that may be related is when I am in overdrive and release the throttle I feel a bump foward kind of like the way there is backlash on a pair of gears. I will feel this same bumping when I quickly depress the throttle to accelerate.

 

[kenora]

I posted a similar problem with my 99 XLT 4X4 a while ago and haven't resolved it yet either. At 70 - 100 kph I occasionally (sometimes a single event, sometimes a dozen about 1 minute apart) get a single "bump" in the driveline. I have watched the4 tach and there is no corresponding increase or decrease in rpm when this occurs.
I thought it might be the 4wd auto detecting a slip and "momentarily bumping it into 4wd high" on a slippery road but eliminated that as a possibility when I selected 4wd high (now it can't jump into or out of 4wd) and it still does it.
I checked my driveshafts for play or binding...none.
It is a single moderate bump like driving over a 2 x 4 on the road, except that there is no seconadry bump when first the front then the rear axle goes over the 2 x 4.
It is worse when I am using cruise control for some reason.
Any ideas?

 

[pookapa]

changed the sensor today, took it for a quick drive and didnt get any bumping, so it seems good. tomorrow will be the real test as i will be driving on the highway

 

[pookapa]

drving about 3hrs round trip, it seemed pretty good, but i still felt one or two bumps