I have a 1997 4.0 Ford Ranger that hesitates when you reach speeds between 40 and 45. What could be the problem with this?
This is not nearly enough information.
Does it ONLY happen in that speed range (40-45mph) Is it gone at lower speeds? higher speeds?
Is it dependent on throttle position, or only speed? In other words if you hit 40-45mph via slow acceleration, is the hesitation the same as if you floor it? Have you tried various steady rates of acceleration, (ie, at different throttle positions). Is it even present when accelerating, or only under steady "cruise" conditions? Again, at what throttle position/engine load? Is the problem present/the same whether you are on flat ground, or going up, or even down, a hill?
Is it RPM related/dependent? Try maintaining all the same other conditions that will cause the issue, but in a different gear, so that engine rpm is different,but you are at the same speed. Obviously, this is easier with a manual trans, but you should still be able to do it with an automatic.
If you just want to try some stuff first, I would clean the MAFS, throttle body, and IAC motor, with the appropriate spray cleaners/chemicals for each. Changing the fuel filter can't hurt, but I don't think that will be it, if the problem is restricted to just that narrow speed range. If you cna get a scan tool on it, I would monitor the voltage of the TPS while smoothly running the throttle through it's range, from idle to WOT (with the key on, engine OFF). If the problem seems to be related to, or changes with throttle position/engine load, yuo may have a bad sensor.
