dpkelly

Background
My ignition coil failed recently. I replaced that along with plugs, dizzy and rotor. I had the injectors cleaned about 1 month ago. Since then it has run great. Spark plugs had white powder on them prior to this proving the engine was running lean before I changed the plugs and other components.

The smog results show good HC and CO results, except the NOx readings are way above the limit.

More Background: Just after I replaced the exhaust manifold with cat due to it being cracked, my secondary 02 sensor failed. It was an aftermarket version. This was about 4 years ago.
I suspect the cat converter is bad and needs replacing.

I also plan on seafoaming the engine and replacing the fuel filter. The current one is only 2 years old.

Former User

High NOx is produced when the engine runs lean or hot. Have you tried replacing the fuel filter?

The_Todd

Could be a number of things, vacuum leaks can also cause it to run lean. I'd check fuel/air filter, vacuum leaks, timing and egr. Typically a cat won't reduce extremely high nox readings but will help.

Former User

The ECU in conjunction with signals from the O2 sensor would prevent a vacuum leak from making the engine run lean, although the engine would have a high or surging idle.

riZe`

I just had the same problem and I replaced the cat, put 91 octane AND put the timing at 14(16 stock). These 3 things dropped my NOX by 500

dpkelly

Picked up a fuel filter this morning from Honda. I plan on replacing it and checking the timing just to be sure this evening.

The_Todd

Correct, it was an open ended statement as I had no clue what year his vehicle was but due to having a secondary o2 sensor it's obd2. Vacuum leaks can cause issues within emissions testing.

dpkelly

New fuel filter is in and timing is bang on.

I did notice it took about 2-3 sec for engine to rev up to a stable RPM. I suspect a faulty or weak fuel pump. I hope to take to a mechanic to diagnose the fuel pressure since I have no way of testing it. Heck it might even be the fuel pump relay that's faulty.

Can't wait to put this lean running issue behind me once and for all.

Former User

Some auto parts stores off free rentals on fuel pressure gauges.

dpkelly

Haven't had it smogged yet, however it runs way better then prior to the fuel filter change out.

Another question, what if I do an ECU reset prior to the smog test? Will this allow the ECU to dump more fuel in the engine and help it run richer, thereby reducing the NOx even more?

dpkelly

Smog test is tomorrow. They were too booked today. I took the extra day to retard the timing slightly and add octane boost to the tank. Retarding the timing means turning the dizzy assembly clockwise. Resetting the ECU is in fact a BAD idea for emissions testing. Let's hope it passes.

rhymeshark916

Dang I hate smog. Hope you get it to pass. How old/new is your
CAT?

dpkelly

Here's the results for NOx.

First test was 1054 ppm. Second test was 647 ppm after fuel filter change, timing adjustment (retard) and fuel additive. The limit was 576 ppm! Darn close!

Well I discovered this evening a crack in the manifold! The Cat/manifold assembly is about 5yrs old. It was a cheap aftermarket one

I'm thinking of just taking it to Midas and have them weld it shut. I think that should fix it (I hope).

But if there's a manifold leak, shouldn't it run rich? I do have an engine code 67 for faulty catalyst.

beecee18

And this whole time you didnt get a CEL for system to lean with that cracked manifold???

Was the Car getting poor fuel economy during this or no???

dpkelly

No CEL for too lean. Shouldn't it run rich with a crack manifold though?

Anyhow, I took it to a different place and it passed by 1 point on the NOx.
They placed a huge fan in front of the car and they said it makes a difference.
I'll just take it to Midas and have the darn thing welded.

Fuel economy was excellent (6L/100km or 39mpg) on the last tank!

looseOFFboost

I was thinking its obd2 also. And if so Why is he getting tail piped. Or do they do both no matter what in some places?

beecee18

If you Had a crack in an area that can intoduce oxegen rich air from the atmosphere into the exhaust system before O2S1 (primary o2) You would have definitly had a huge reduction in fuel efficiency.
Although obviously this is not your case as if it was you would have def got the system to lean code. And when you do get this code the ECU dumps a ton of fuel to combat the excess o2 introduced into your system as a safety feature.

This code is only thrown when the fueltrims reach a pretty big correction %.
And reach thier max range of correction. At this point the ECU knows something is wrong.

So ill assume that the extra o2 being introduced into your system was either minute, or in an area that does not offset o2 sensor readings that much.
But I will assure you one thing. Even the smallest amount of air will still make the fuel trims jump around making corrections to combat it, they just havent reached thier max cap to net you the lean code.
So this will net you a failed smog test, as when ECU is constantly makng corrections is no time to bring her in for a smog.
They cat effiency code is probably from the cracked exhaust also. But doesnt effect how the car drives, fuels, ect.
I suspect the damage of the manifold to be after O2S1 and before O2S2 netting you the cat code.

You must replace the exhaust manifold with preferably a nice OEM unit.