1988 F150 300ci Fuel Injection Questions - Ford Forums

skullcar · 08-04-2009, 11:28

I have an '88 F150 300ci. During the last year or so I haven't driven it very much because of the way gas prices shot up last year. Late last year it started to have some bad driveability issues, stalling and occassionally not re-starting for hours or days, and I eventually reached the conclusion that the high pressure pump was bad, no sound from it, and the truck ran fine after I replaced it.

Last month it needed to do the California Smog Check so I did an ignition tune-up and oil & filters change. With it running as smooth as butter and having as much get-and-go as it ever had I took it in for the check. It passed good on everything but the low-speed hydrocarbons, one more point and it would have failed. It also sucked the gas down pretty hard.

I have checked the Fuel Pressure Regulator for a ruptured diaphram by pulling the vacuum line and checking for gas,,, none found or smelled. I checked the fuel pressure and at idle it has 49 psi, drops 2-3 psi when revved and jumps to 59 when the vacuum line is disconnected.

So my questions are,,, what would cause high hydrocarbons during the low-speed test? Is there a way to test the O2 sensor? What fuel pressure psi should it have?

Thanks in advance for any ideas, Gerald

Steve83 · 08-10-2009, 22:27

The most likely cause of the rich exhaust is a bad cat. They don't last forever, and that one has done its job. Any decent repair shop can test it, but make them prove to you that it needs changing before you buy it. It could also be engine oil making its way into the exhaust, or a leak upstream of the oxygen sensor, or a dirty air filter, worn-out PCV valve, dirty ACT sensor, failing ECT sensor...

Testing the HEGO directly is tricky - it's easier to test everything ELSE and only condemn the HEGO by elimination. Get an old edition of the Haynes manual & a cheapo digital multimeter.

skullcar · 08-12-2009, 10:01

Thanks Steve! It took me awhile to notice the Fuel Pressure Chart link in your reply,,, looks like my pressure is ok. Now I just need to test those sensors and most likely bite the bullet and get a new cat.
Thanks Again, Gerald