CEL still on???

[91CoupeMike]

Is it p0171 and p0174 now?

At any point since the mid pipe swap did you remove the c/a/I?

If so check for sealed grommet after the MAF and on the t/b.

[Cobraman]

never removed the cai. this code had been on before the midpipe swap, i mistook it for the cats. So I assume the o2's are faulty?

[91CoupeMike]

never removed the cai. this code had been on before the midpipe swap, i mistook it for the cats. So I assume the o2's are faulty?

Is it both banks or just 1?

If it's the same code as before and it's not p0420.

Check for exhaust leaks. Most of the time a leak big enough to throw a CEL will be loud enough to hear, also could be a vac leak. Grab a can of carb cleaner while the engine is running and spray around the intake tube, manifold gaskets and hoses. Be on look out for a change In run quality while spraying.

Also, just a friendly thing to do to your car, change the fuel filter and grab a can of Seafoam. Seafoam is good for finding exhaust leaks too.. Haha

If you do all this and it still throws the code, check for fuel pressure.

If all that tests good, check o2 sensor for any damaged wires or connections. If all that checks out then order some motorcraft o2s from late model or see if orielys can get them in.

The aftermarket sensors are "okay" but if your motorcraft lasted over 100k miles, don't expect but about 20-30k miles from a Bosch o2. JMPO.

[noslow5_0]

was there ever a time when your CEL was NOT on? I'd replace the o2's anyway if they have that many miles on them.

[91CoupeMike]

was there ever a time when your CEL was NOT on? I'd replace the o2's anyway if they have that many miles on them.

Replacing the o2s anyways will just add to the cost of repair and won't acually fix the problem.

I'd find and fix the problem first. Worry about the o2s another day.

[Cobraman]

[QUOTE=91CoupeMike;86033]Replacing the o2s anyways will just add to the cost of repair and won't acually fix the problem. could the exhaust leak be past the midpipe and still trigger it? or does it have to be in the manifold bolts?

[91CoupeMike]

The only leak that will trigger this would be anywhere before the first o2 sensors.

The rear set of sensors ONLY measure catalytic effeciancy. Fresh air to those will bring up differant codes.

So, yes the manifold flange bolts, manifold gasket and donut gasket. Or cracked/rusted pipe. All would be easy to hear and see.

Based on your set of circumstances I'd bet it's a vacuum leak, a mass air flow fault, or in the extreme case an o2 sensor wiring damage.

Very simple.

[Diabolic]

What is the code exactly? Or did I mis that part?

[greenbullitt]

I, personally, would ASSUME the wiring and the injectors are okay. Listen for exhaust leaks, check for severe vacuum leaks, and if everything looks good you might just go ahead and replace the o2 sensors. They are a maintenance item anyway.

I would definitely NOT replace an o2 for a lean code. youre setting yourself up for disappointment with that incorrect diagnosis

[Cobraman]

What is the code exactly? Or did I mis that part?

lean on both banks.

[Cobraman]

I dont really see/ hear an exhaust leak. you mentioned a donut gasket. I dont think either of my pipes had them. another thing. the right front o2 sensor was hard to tighten up because of the cat. could it be from a loose o2? will it fail inspection?

[TENGRAM]

I would definitely NOT replace an o2 for a lean code. youre setting yourself up for disappointment with that incorrect diagnosis

1. An educated guess is not a diagnosis.
2. In my experience when o2 sensors go south they most often return a lean/not switching signal. With only 125k miles and hardly any modifications I don't think my assumption regarding the wiring and injectors is extraordinary; then, if there are no exhaust or vacuum leaks, and no other codes, what else could be the cause?

Sure, he could go in and do a few continuity/voltage tests on the o2s, check fuel pressure, and check for injector operation, but with unknown mileage on those o2 sensors it'd be easiest to replace them, especially since they are a maintenance item.

Whatever. I'm just putting in my 2 cents.

[TENGRAM]

the right front o2 sensor was hard to tighten up because of the cat. could it be from a loose o2?

That could explain one of the banks reading lean but not both.

will it fail inspection?

Yes. Even if you somehow passed the sniffer they would fail you because of the CEL.

[Cobraman]

That could explain one of the banks reading lean but not both.

Good point!

[Cobraman]

Since the back two are good, in theory if I were to swap the back 02's ( that I know work) to the front, the lean code would clear and the code for failed cats would appear??