My 2010 E-150 (4.6L engine) speed varies slightly when driving at highway speeds (like someone is lightly tapping and letting off on gas pedal). Happens with or without cruise control. It's so slight that tachometer does not vary, but passenger and I both noticed it and it's annoying. Any help on cause and fix will be appreciated. Thanks JJB

 

Your universal joints are bad. Very Common with my E250/E350.


Jim

 

Thanks Jim-I'll check the drive shaft universal joints.

 

JJB,


If the universal joints look good, you may have a problem with the pinion bearing in the differential.


Jim

 

I have a question, If the engine speed varies slightly and the tach does not show any difference , one of them is not registering correctly. Could you please clarify because depending on which one is faulty could direct us to the possible source of the problem.

 

Thanks Jim, The Universal Joints were fine. I just purchased the van with 47k miles. I tried the easiest/cheapest fix which appears to lessen the problem (Chevron Techtron FI Cleaner). Need to put more miles on it to see if this solves the issue. Thanks for your replies.

 

Thanks Hanky. After further testing, the tach did move slightly, but I had to set the cruise when the needle of the tach was at a line (the 2K line), then I could see it move very very slightly. The speed variance was slight, but obviously not normal (and really annoying). Techtron FI cleaner has lessen the issue so I hope more miles will clean injectors and solve the issue. I appreciate your input, cause it's something that needs to be corrected. Thanks Again.

 

You would need a digital scope to capture the crank and cam profiles to confirm the problem is not beginning there. Since it is present almost all the time it would not be too difficult to capture those waveforms with the right equipment.

 

Update-I just came back from a 350 mile road trip. The Van no longer experiences the speed variation. I can only think of 2 possible causes of the speed variation considering it's riding great presently. 1) dirty fuel injectors which Techton cleaned, or 2) Bad gas fill-up (although I can't recall ever having bad gas (No joke intended!!)). I appreciate everyone's input!

 

Thanks for sharing the solution with us ! Let us know if the problem returns.