Failed Emission Testing - Thoughts?
 

My 1992 5.0 Mustang failed emissions today for the first time since I have had it. Where I live we have to do it every 2 years.

It runs well and still has the factory h-pipe and catalytic converters. Based on these results what do you guys/gals think?

Thank you!

OK, I have tired to upload the picture a number of times...

how far off and for what measurent?

We have emission checks annually. My ‘95 911 failed the first two years, spent $1000 each year for my mechanic to get the numbers barely above passing. A Mech that works on older cars (356s) said to run a full tank of 91 ethanol-free gas through it. Refill again with the same and then make sure it is nice and hot and then get it checked. Passed with flying colors for the last 4 years. I know, completely different engines, but it’s the cheapest thing to try for a Pre-ethanol car. YMMV, I know mine does.

Tune-up

Running too rich or incomplete burning of fuel if I'm reading that right.
Start by checking the plugs for evidence of ignition or injector issues.
If the plugs all look decent and all the same, without any more info I'd suspect the O2 sensor.

Maybe not. New plugs would not hurt.

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Thanks for the advice so far. I will start with plugs, wires, cap and rotor. It is running well and I cleaned the mass air flow not long ago.

There is also a place near by that sells ethanol free gas, I will also run some fuel system cleaner through it and put the ethanol free gas in.

yes, do that & start with a tune up - may be needed anyway

then pull the plugs (again) and look at them

see if you can test the O2 sensor or just replace; hopefully you don't need new cat(s)

I am temped to try that to a couple of my cars even if there's no check engine light.

Yes fuel injector cleaner...

Have you had a look under the car? there may be one or two pedestrians jammed under there and that's messing up the air fuel ratio.


You're most welcome, I'm pleased to be able to help.

Oh, I have been under the car plenty. One of the main joys of old fox body Mustangs is adjusting the clutch fairly often. I have the fancy Steeda adjuster, just need to install it.

I put a bottle of Techron in it today and will run the tank low then add another.

My 1993 van barely passed emissions 4 years ago. This year I changed the plugs and air filter and it passed with flying colors.

fify

Change the oil too, that makes a surprisingly large difference, especially on hydrocarbons

Does it sit a lot? If it is just used for runs to the Piggly Wiggly, or to cars and coffee deals hunting pedestrians, but at low speeds, it will tend to gum Take it out on the freeway, or run it in a lower gear to get the cat hot. My understanding it that burns stuff off the catalyst. Italian tune up in the vernacular.


I like that soap and water wash it out thing Scotty does in that video.

Bad oxygen sensor can make it throw a cat code too

Porsche 356 Guru "The Maestro" The Late Harry Pellow once wrote about his trials and tribulations with the early California smog tests. He'd put a set of fouled plugs and dirty air filter in his old Mercedes and take it in for the test to intentionally flunk it. They'd give him the opportunity to make repairs and re-test, and if the re-test was marginally better they'd pass him. So he'd put a new set of plugs and a new air filter and pass with flying colors the next time. :D

It does not sit much, used to be my airport car (120 mile round trip all interstate) but now my daughter drives it in town and typically short distances. Once I get the plugs etc. I will take her (Farrah the Fox Body) out for a nice long drive. Cabelas is about an hour away on the interstate so I will get it nice and hot.

This isn't a cars and coffee mustang by any means. I prefer to scare all the pedestrians in my '78 VW Westfalia with its whopping 70 hp.

It is a bit more sporting using the bus, you have lot more room for disposing of victims, double bonus.

All of the above: complete tune up, change oil, plugs, and coil, and if you have the test values for O2 sensor, check it for resistance with multimeter, or just change the O2 sensor.

In my experience, it is 90% caused by faulty O2 sensor. Connect OBD1 reader or measure if O2 cycles as it should.

(WAG here)

The high CO = Way too rich of a mixture, or oil is present.
There is too little oxygen to turn the burn the mix into pure H20+CO2. A bad head temperature sensor or O2 sensor might be keeping the fuel trim in Open Loop (the startup rich mode where the computer doesn't pay attention to the O2 to lean it out).

The high HC = A dirty burn.
Raw gas or oil vapors are being pumped out the exhaust and even the CAT can't burn it all up. That can become too much for even the long-term fuel trim to compensate for. The tailpipe after the CAT should be 50-150deg hotter if it's doing its job. They do get contaminated with silicone from sealants, get gummed up from oil, or just wear out.
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I'd first suspect very high fuel rail line pressure or a leaking injector(s) on the fuel side. A bad plug might also be sending raw air downstream, then the O2 'sees' this and richens up the mixture, making the entire system worse. An EGR not closing can do the same thing somewhat. Or a gunked up MAP/MAF could be telling the computer to pour in the gas.
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I'd suspect leaking valve guides/seals or sticking oil rings on the oil side. You are still getting good performance so the compression rings and ignition system are mostly doing their job.
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To be sure of what the computer is seeing , it might be best to drive it around with a https://www.bing.com/search?form=MOZTSB&pc=MOZI&q=obd2+scanner hooked up to the 16 pin OBD2 port which is probably located under the left dash. This will help tell you what the computer inputs are saying, especially for open/closed loop function, MAP/MAF ranges during operation, and the O2 readings which are either dead or off the charts. Just remember a thrown code is only what the computer sees and is not necessarily the true source of the problem.

A stuck-open injector might show up as a bleeding-down of line pressure at the fuel rail a little while after shutdown. If it's just worn out and dumping fuel like an open hose-end instead of spraying in a droplet cone pattern, comparing the plug conditions will show which cylinder is getting carboned-up.

Oil treatments such as https://seafoamsales.com/knowledge-base/how-to-add-sea-foam-motor-treatment-to-crankcase-oil/ need to done carefully with an oil change afterwards, and may gunk up an already borderline CAT, but will clean out carbon deposits and un-stick rings and valves. This may create a dense smokey fog throughout the entire neighborhood as a caveate. Higher consistent revs on the freeway will also give it that "Italian Tuneup" and should done once in a while anyways.

Be sure to run it for at least 30 minutes at freeway speed before testing it. And don't let it sit waiting to be tested either, keep it running so the cat doesn't cool down.
Fresh plugs, air filter, oil change should do it.

do the cheapest stuff first...

Cheapest would be to check the voltage coming from the O2 sensor after the engine is warmed up, and check the operating fuel pressure. Both would affect rich running. Could be bad O2 sensor or bad fuel pressure regulator. More likely the former.

I will check the O2 sensors as well.

Thank you guys!

These also have air pumps on them. Make sure the air is going where its supposed to.

Just to update this thread, I replaced the plugs, wires, cap and rotor and put two new Ford O2 sensor in it. It is running really well right now. The gap on the plugs was crazy big, .054 surprised me.

And the emissions place is closed, so I have not had a chance to get it checked yet.

I’m going to bet it passes now. New plugs make a big difference. Good luck.

Thanks!