1994 Ford Explorer RPM problem at high speeds

1994 FORD EXPLORER
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JHERRERA
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Engine Mechanical problem
1994 Ford Explorer 6 cyl Two Wheel Drive Automatic

When im driving on the highway ive noticed at 55mph or so the rpms dont wont go any higher than about 2k unless i punch it. I can tell its not as peppy but i still am able to speed up the without any problems but after i let off the gas the rpms will shoot up a few hundred then drop right back down. It also seems sometimes when im goin fast the rpms will go up a little then right back dowm. I got the truck from an older woman who didnt drive very much it only has 80k miles. So I recently went to do a tune up but everything looked clean so i just flushed the raditator, changed the thermostat, pcv valve, tranny fluid... I thought the problem could be from the fuel filter and i havent changed than yet because i havent had a chance to get the tool. If also noticed every now and then for some reason when i crank it it will shake a little and then when i give it gas it will die down after about 30 seconds or so. So sorry about the long message but i was wondering if you guys would know of any reason why it would do these things.... Thanks
Nov 6, 2009 at 6:35 AM
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JACOBANDNICKOLAS
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I'm not sure I understand the concern about the RPM's at 2K at 55MPH. The only way they will go up is if it downshifts. Does everything seem normal when that happens? Also, has the check engine light ever come on? Have you checked fuel pump pressure? Finally, why didn't you do the tune up?

Let me know so I can better guide you.

Joe
Nov 10, 2009 at 9:57 PM
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JHERRERA
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At 55 mph or faster the rpms wont go much higher then 2k... Then it boggs down to about 1500. When i give it gas it there rpms will sit where they are at and the motor will hesitate then after a second or so the rpms will go up and the power will be there. I doesnt down shift. I did a tune up and didnt get a chance to do the plugs or wires because of the weather here. I changed every fluid, air filter, fuel filter, pcv valve, new thermostat, pcv valve, belt, and cleaned the throttle body, iac valve, and checked the mas... (None of this made any difference) I am going to check the fuel pressure because i was told its either the plugs or the fuel pump but it seems to me like if it were the plugs it would do it all the time rather than just highway speeds. Maybe the fuel pump is having trouble keeping up with the amount of gas the motor needs????
Nov 11, 2009 at 6:24 AM
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JACOBANDNICKOLAS
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You ae exactly right. If you had bad plugs, it would have a miss all of the time. What you have described does sound like the fuel pump.

Here is a "How To" for checking fuel pump pressure. It is both written directions and there is a video. It also shows how to check the fuel pressure regulator. Make sure to do that.

https://www.2carpros.com/how_to/how_to_check_fuel_pressure.htm

The video is very helpful if you have never done it before. You will, however, need a fuel pressure gauge. Most nationally recognized parts stores will lend or rent the tool you need. If you can't find one, they are not expensive. You can get one from the "Test Equipment Store" site on this page.

Let me know if you have questions, problems, or concerns.

Joe
Nov 11, 2009 at 9:29 PM
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.