Here is the truck:

88 F-150, I-6, multiport EFI, M5OD 5 spd. with 90,000 miles, all stock except for maintenance materials.

Here are the symptoms:

* "Smells" rich, both closed loop or open loop fueling. Check plugs, they look normal.
* No hesitation when revved under no load. While moving, it hesitates/stutters momentarily when rolling off throttle lower than 2500 rpm. Hesitation under gentle/gradual acceleration to 3000 rpm. Cruising @ steady RPM, no hesitation. On hard acceleration, there is momentary hesitation when you floor it, then it "clears up", though not 100%. It does rev more easily after that.
* very poor gas mileage...tends to be near 10 miles/gallon or slightly above regardless of type of driving.

In the last few months I have replaced:
* plugs
* plug wires
* cap/rotor
* O2 sensor
* TB gasket (due to a previous fueling-related problem)
* air filter
* PCV (last year)

I have not had access to an ECM scanner, I might tonight, to see if there is something that may be assessed. Since there is so much rust and resultant rotted out nuts, bolts, etc. around the engine, I would prefer not to disturb anything that does not need to be messed with...

 

[font size="1" color="#FF0000"]LAST EDITED ON 11-Dec-00 AT 01:30 PM (EST)[/font][p]Check your exhaust system, especialy the catalic converter. If the exhaust is plugged up you will experience problems.

One way to test is idle the truck engine and get out and hold or block off the tail pipe exhaust. If the block is blown off quickly you have no problem. If the exhaust is not strong enough to blow your hand or foot away from the tail pipe then you have an exhaust restriction somewhere. Probably the converter or rusted muffler. It needs to breath freely.

Also check your fuel filter under the frame. That to will cause the problems.

 

OK, as per recommendations on this site, I let the truck warm up and idle, then placed my hand over the tailpipe. My hand is pressed on with enough pressure to move the pipe a few inches (rubber mounts flexing) and there is enough gas pressure developed to push out from around my hand in a few spots around the diameter of the pipe but not push it off the pipe completely. Additionally it drops RPM, then gains it back, then drops again, in a cycle, while idling. I have located the EEC Test block but there is no provision for a "2" and "4" pin as displayed on this website: http://www.dalidesign.com/hbook/eectest.html

So I assume I cannot test it as recommended.

 

Normaly you should not be able to hold your hand over the exhaust at all. You can take it to a mechanic and ask them to perform a exhaust pressure test. They will know how. It shouldnt cost much.

Also dont forget to check or replace the fuel filter.

 

Have your fuel pressure regulator checked. If it smells rich, and the mouth of the tailpipe is sooty black, and mpg is way down, your fuel pressure regulator is probably shot. Mine was, and it drank gas like a drunk drinks whiskey. Cost me $15 to have it checked and less than $100 (including test) to have it replaced. Also, go to a muffler shop and let them check both cats for exhaust restriction. Good luck.

 

I am having the same problem with a 87 E-150 since I changed the O2 sensor with a Bosch instead of the Motorcraft. I just don't want to take the new part out without been sure if that is really the problem. Computer test gives message of "Running too rich" Please let me know if you could solve that problem.

Dax