Failed Smog 3rd Time - What's Wrong?

[iso_hi]

So today my new 1992 325iC failed smog for the second time. In both tests there was no CO% at 25mph and my NO% was also too high on both tests. I've replaced all basic items besides my O2 sensor. Would that be my problem?

[Todd Black 88]

You are lean. Hot combustion temps.
Run a smoke test on the intake for air leaks. Also measure your fuel pressure while running, possibly low fuel pressure/dirty fuel filter/ dirty injectors.

[Todd Black 88]

Just saw the mileage on the car. If the head has never been off, you could have carbon build up in the combustion chamber causing hot spots.
Google high nox and there are quite a few things to check. (Coolant temp sensor/o2 also)

[iso_hi]

As far as I know the head hasn't been off. Just got the car a few weeks ago. Ive changed the coolant sensor and fuel filter before the second test. I also changed the thermostat because the temp gauge would only reach 1/4, now it reached 1/2 as it should.

Could I do a smoke test through the FPR?

[jlevie]

Those numbers represent an engine running lean. Since the fail is at speed, the rail fuel pressure, injectors, or AFM are all suspects. Intake leaks would cause a failure at idle. You can check the rail pressure by tee'ing in a pressure gauge, zip tying it to a wiper and see what the pressure is at 25mph or higher. It should be about 40psi. Low rail pressure could be weak pump or bad FPR.

If the rail pressure is okay I'd send the injectors to RC Engineering for rebuilding and flow checks. If the car still fails at 25mph I'd swap in a known good AFM. If, at that point the CO level is within bounds and the NOX is out of bounds, new catalytic converters are called for.

It would be a good idea to have a shop run a smoke test just due to the age of the car.

[iso_hi]

Would an O2 sensor change anything? I did a stomp test and received a 1222 code, which from my research could be anything from an O2 sensor to running lean/rich. I ordered one on Amazon for $30.

The car itself seems to run perfectly fine other than terrible gas mileage. No hesitation at any time and doesn't stutter if I blip the throttle.

[jlevie]

A bad O2 sensor tends to make the engine run lean. So that could be part of the problem.

[iso_hi]

I get the sensor tomorrow so gonna try that and drive around and hopefully mileage increases. If not I'll start rebuilding my injectors and check fuel pressure as you suggested.

[iso_hi]

Failed again after replacing the O2 sensor. The 1222 stomp code went away and showed a 1444 code so I thought I was good to go.



Should I pull and clean the injectors or get a new cat? Or I'll consider any ideas at this point. I do have a free retest (test 4).

[Todd Black 88]

Those numbers represent an engine running lean. Since the fail is at speed, the rail fuel pressure, injectors, or AFM are all suspects. Intake leaks would cause a failure at idle. You can check the rail pressure by tee'ing in a pressure gauge, zip tying it to a wiper and see what the pressure is at 25mph or higher. It should be about 40psi. Low rail pressure could be weak pump or bad FPR.

If the rail pressure is okay I'd send the injectors to RC Engineering for rebuilding and flow checks. If the car still fails at 25mph I'd swap in a known good AFM. If, at that point the CO level is within bounds and the NOX is out of bounds, new catalytic converters are called for.

It would be a good idea to have a shop run a smoke test just due to the age of the car.

It's still running lean at idle, just not to the point of failure. Nox is still well above normal at idle, and CO is 0.03

Have you smoke tested it yet, or checked the fuel rail pressure at speed?

No sense throwing parts at it, your O2 sensor change made no difference except make your wallet lighter.

[Sean S.]

Do you know anyone with whom you could borrow the entire exhaust system out of their car? Especially someone who has recently passed smog? If you swap out the cats and it passes, there's your problem.

[dnguyen1963]

You can check the condition of the cat with a IR thermometer. Measure the temp of the front and back of the cat after the engine has been running for about 20 min.

https://www.youtube.com/watch?v=psIFUZaLLaM

[siggy]

Here is what a virtually new OEM BMW catalytic converter can yield for smog numbers, todays test:

[iso_hi]

Here is what a virtually new OEM BMW catalytic converter can yield for smog numbers, todays test:

Yeah had my brother smog my old E30 which his girl has now and it passed with similar results. I got an new aftermarket cat for it last year so going to swap the system into my car and try again.

Do I need any new gaskets when changing exhausts?