I have a 1996 F-150 with a 300-6. 213xxx miles. Check engine light was on about a month ago, for several months. I have an OBD-II Diag. programmer at work, and I pulled a code that said it was running too lean. I had a new true-dual exhaust system installed about a month ago, since I was replacing my cats anyways (I work at an exhaust distribution warehouse). However, I took the cheap route and bought pre-OBD II catalytic converters. I knew my stock cats were bad from the get-go.

My new setup is basically....

I've had the system for about a month. But I just changed all 3 of my sensors yesterday. Light came on today. I know I'm running lean again. Do I need new cats? Thanks.

 

Yes you need obdii cats not the obdi ones.

 

Yeah I figured, I wasn't aware that the C19xx series wasn't OBD-II, they're a new product for us and they didn't have labels. Should spark plugs be an issue too? I had a tune-up around 6000 miles ago or so. Thanks.

 

Not if you used Motorcraft or Autolite copper core plugs no.

 

Is it that proprietary of plugs? It's not a problem, I'll change them asap. I'm assuming no, since I didn't pay for the tune up. The former owner did. However, I will certainly check first thing tomorrow. Thanks for the help.

 

No you don't need cats. You're getting a lean code which comes from the O2 sensors before the cats. The code for bad cats is different.

 

OBDII reads from all the sensors. You need to know which one is sending the lean code. If you have access to a ford diagnostic computer its an easy thing to check. A lean code after the cat can mean blocked cats or too small, not enough flow. Try a vacuum test. Hook to manifold vacuum, hit wot and let it snap shut. Reading should return to normal quickly. If the needle moves slowly you have an exhaust obstruction.

 

The rear oxygen sensor only measures how efficiently the catalytic converter is working.

 

a lean O2 sensor reading can also be a bad sensor...even new ones can be bad.

Google how to take a reading while its active and check the reference voltage while its live (running)

also a Lean condition reported by the O2 can also be a loose ground or a bad ground. less ground will cause a lower reference voltage which in turn makes the ECM think its lean....Also when you change ANY sensor you need to disconnect the battery and drain all the ECMs memory so it can "Learn" the new sensor...if the old sensor was out of range and the new one is within range then it reports Lean...