98 Ranger 4x4, 3.0, 142K miles, auto;
Problem- when the vehicle is placed in any gear the engine loses power and runs rough until it gets to about 35 MPH.

Engine idles great
Engine starts great
When put to the floor at high RPMs runs great

What i have done:
Replaced: wires, plugs (gapped at .045), fuel filter, EGR Valve, air filter
Cleaned a ton of gunk out of the throttle body
Sea Foamed the Fuel system two tanks of fuel (not the bottom end)

Any help will assit me at this time!

thanks
BION
Believe it or Not

 

Have a look at the CPS(cam position sensor) it is at the back top of the engine where distributor used to be.
The CPS and the synchronizer it sits on are good for 80-100k miles and should then be changed.

CPS helps computer with spark advance and fuel injector timing.
A problem here would usually cause CEL(check engine light) to come on.

Does your CEL come on when key is first turned on and then go out after a few seconds?
That is the computer doing a self test.
If it does then all is well, if not then bulb could be bad and you do have codes that need to be checked.

Also remove EGR valves vacuum hose and plug it, then drive truck and see if it works better.
And you should get a CEL for this after engine warms up, and EGR valve isn't opening(EGR valve isn't used when engine is cold).
This tests the EGR vacuum solenoid, computer opens this solenoid to send vacuum to EGR valve
And also the DPFE sensor, this sensor tells computer if EGR valve is opening and by how much.

 

Was none of the above,
Did a compression test on it this weekend; seems the number 6 cyl is low on compression (120 PSI when the rest are at 150). Put a few squirts of oil in the hole and tested again read 150; shows its the rings. Going to run it till it blows or find a 3.0 that is good.

If any one has a GOODd 3.0 in the KC area give me a shout!

Thanks
BION

 

low power and partial misfire on one cylinder would sure cause a vibration.

Thanks for posting the update

3.0l Vulcan engines also came in Taurus and Sables up to '07 for Taurus and '05 in Sables, they were transverse mounted but block and heads are the same, cam has more HP but less torque, most who have used car 3.0l said they couldn't tell a difference.
In '98 taurus and sable got 3.0l Duratec DOHC engine as a upgrade option, so if looking make sure you are seeing Vulcan 3.0l, Duratec won't work

Vulcan 3.0l was used in Rangers and B3000 until '08 and '07 repectively

 

you might try the ATF fluid flush trick

the #6 cylinder piston rings might just be stuck in the compressed position from sludge build up