2.9 Fuel Issues

[BBoleac]

hey guys,
I have a 1988 ranger 4x4 with a 2.9 in it. just recently it has started running very poorly. it will idle all day, and run at WOT fine. under load anywhere between idle and WOT it sputters and bogs out. no black smoke out the tail pipe. It has yet to fail to start in the mornings and has gottenme to work running like this every day so far but its a pain in the ass to drive. I have got a brand new tank, pump and sending unit in it. the intertia switch was faulty and has been by passed, new fpr and plugs and its still doing it. I have yet to replace the fuel filter, would that make that much of a difference? and this truck has the two pump setup on it so does that mean two filters? any help would be greatly appreciated, i want it running properly again so i can go back out wheelin

 

[Psychopete]

Kind of two filters - one being sock intank, and there's a filter on the driver's side frame rail directly after the external pump. Easy enough to change the filter on the frame rail.

I really can't comment that your fuel system is fine, usually the best way to check is with a fuel pressure gauge so there's no guessing involved. Could have possibly prevented some of the additional parts, but hindsight is 20/20.

Given what you have, I would start with fuel pressure and pulling diagnostic codes. Then I would probably check the TPS sensor and MAP sensor. TPS is input from the gas pedal. MAP because this sends vacuum and barometric pressure measurements to the computer, and vacuum changes as the throttle movement changes. MAP is also used to determine engine load.

To test the MAP, need a meter that can read frequencies, and then plot each frequency per 1"hg of vacuum applied and you should end up with a strait line. Frequency will decrease as vacuum increases.

MAP: http://www.fordfuelinjection.com/?p=27
TPS: http://www.fordfuelinjection.com/?p=30

 

[BBoleac]

tested fuel, its fine even when running like a bag. tried a different MAP sensor that i know is good and it made no difference. i did notice that when the check engine light comes on it runs fine. this would suggest a sensor would it not? could the O2 sensor give these kind of symptoms?