I need your help guys. My son's 94 F150 is running rough. It's got new sparkplugs, cap, rotor and wires. All plugs looked fine when pulled.

It runs rough. Actually feels like it has a dead cylinder. But wouldn't the plug have looked funny?

And it drinks gas fast. Gets around 10 mpg.

We just bought the truck a few months ago and have tried a few things to get it running better. I'm in need of some new ideas to try.

The cats are gone and the O2 is not hooked up. What do I need to do to bypass it or get it useable again? I suspect that's part of the fuel mileage problem...

Do you think it could have a dead injector causing it to run rough? if so, how do I test for that?

If the rings were bad on one cylinder causing it to run rough you think it'd smoke. Doesn't blow smoke at all.

I plan to do a compression test next weekend. Could it have a blown gasket between two cylinders causing the rough running?

Any ideas or advice you can offer is greatly appreciated...! And BTW the tuck is a mass air truck.

 

Sounds like the same problem I had when o2 sensor went bad.

 

You absolutely need the O2 sensor plugged in. The computer uses it to determine fuel air ratio. Get it working (the best bet is to replace it with a new one as they don't really last all that long, a few years at best) and then pull your codes. That will give you an idea of what to look for and where to look.

I'm not sure about the California trucks but trucks for Canada and the rest of the US were SD in 1994. Someone may have swapped the SD for MAF. If so, you need to check to see if they swapped out the computer for the appropriate one. I think it should be grey but I am not sure. Hopefully others will chime in and correct me if I am mistaken.

 

Think about this: If the O2 sensor is not working, the computer has very limited compensation when it comes to calculating fuel. It can use the MAF sensor to measure incoming air but it cannot adjust fuel trim if it can't get a reading from the O2 sensor. My suggestion: Install the O2 into the exhaust because even if you don't have a catalytic converter, the PCM can at least read the O2 content in the exhaust and the truck should run decent.

 

OK, here's the problem. The previous owner cut out the cat and the O2 bung along with it. Can I just weld it in nearby where it should be in either pipe? Other option would be to buy a new Y pipe with the O2 bung in it.

And I'm pretty sure it's a factory MAF truck. My old 94 I got rid of in 2006 was a factory MAF truck and this one is identical to it except the color...

 

hope this works

 

Not a very good pic,but shows where bung should be.

 

Yes. That helps. Much appreciated. I’ll start figuring out what we need to get the O2 sensor reinstalled.