Hello! Just joined today.
Ford 4.0 V6 on my Mazda (94 B4000) and I am experiencing a problem. A little history on the truck before I get to the Problem. I have replaced Coil Pack, Plugs, Wires, DPFE, DPFE Hoses, Transmission, Torque Convertor, Thermosat, Brakes, Master Cylinder, Radiator, and a few minor things here and there over the past year.

Anyways on to the problem. I am sure you have heard of this problem before but I am experiencing a "bucking sensation" at 25% throttle. This happens whether going up hill or straight between 45-55..but Since I know how to create the problem, it can do it whenever i want it to.. Now I know the DPFE is normally the issue. (I have been reading alot this week) but I replaced the DPFE a few months ago and the problem still consisted. Found a vacuum hose disconnected 2 days ago, and that still didnt fix the problem. I am pretty decent at diagnosing problems but im starting to run out of ideas. I need to take a closer look at ALL the vacuum lines, but my senses are telling me I could have a Possible Sticking EGR Valve. I read that the EGR valves usually dont go bad but I have replaced almost everything in the system that I thought could be the problem.
Any helpful thoughts on this issue would be great, I usually work on my truck in my downtime so Im trying to get this last issue resolved with the truck.
Thanks to all in Advance!
Kyle

 

I'd say the throttle position sensor has a flat spot in it.

 

Also check around the intake for any vacuum leaks.

 

Ditto. Check for any air leaks at the air box also. Are the clamps tightened down?

 

I will go over the tightening sequence on the manifold Saturday or sunday. Afterwards, I will look into the TPS and Checking all Vacuum Lines for holes. Thanks again for your thoughts and opinions! I will check back with you guys!

 

I know this sounds lame, but when my 95 4.0 did that after sitting for a couple of weeks, Techron cured it.

 

Mine was jumpy under acceleration, but mine turned out to be bad plugs, even though they were new autolite platinums. I put Motorcraft back in, changed coil pack and wires and it runs fine now.

 

Welcome to R-F!

 

So i checked the manifold bolts today, didnt find any problems there... I was looking at the Vacuum Line under the throttle body that leads around to a black box below the battery, looked ok... (what is this box??).. i didnt have time to pull the hoses off and completely check them but I will tomorrow..I will blow compressed air through as much of the vacuum lines as i can make sure they are all clear.. So ill keep trying to find this problem..I know I have to do the Valve cover gaskets soon so ill eventually end up going through everything. Ill replace the plugs this week as well.
Any other opinions or routes to take, Im open and willing to do so!

 

So I Cleaned MAF throughly, cleaned out Vacuum Tube below throttle body (it was definitely clogged), replaced plugs, and made sure I reinstalled intake correctly. (I noticed the bottom of the intake started sliding out when installing possibly causing a vacuum leak)...I haven't had an problems since i have done the corrections on my truck. Hope this helps.