m20 engine failing horribly on NO(x) emissions!

[jlevie]

The plugs (swap them out to NGK ZGR5A plugs) and/or the O2 sensor could easily cause high HC from partial misfires or excessive fuel trim. But I don't see either as being responsible for the high NOx. High NOx in the absence of high HC means higher than normal cylinder temps, a lean condition, or bad catalytic converters.

The first thing I'd do would be to diagnose the engine management system and get it working like it is supposed to. In the process of doing that I'd want to see the A/F curves from the car on a dyno for both a part and full throttle pull. If the engine management system is operating properly, the A/F curve should be right at 14:1 everywhere.

Diagnosing the engine management system would consist of:

1) A smoke test of intake
2) A rail fuel pressure check
2) An electrical check of the AFM, ECT, and IAT

I would pull the injectors and have them cleaned and flow tested. If I haven't found a "smoking gun" at this point and the dyno data shows lean, I'd change the DME.

[JrCamacho]

Smoke test showed no significant leaks,

I need to do a pressure test at the rail, i know everything prior to the rail (lines, pump, tank, and filter) are all new or close to it (everything but the tank)

still in need to check AFM, ECT, and IAT.

the e30 is at a gold shield smog station right now, i went ahead and approved the repairs (plugs and 02 sensor,) i have proof of purchase for the sensor back in MARCH, so if it isnt the o2 sensor, i get a refund from them (nice)


my only concern that everythign else on the smog report shows a great working cat, HC's and CO's are EXCELLENT! just NO(X) are through the roof.

As far as butt-dyno goes, car seems to run fine, not exactly as "peppy" as i would like it to be, but idles at a rock solid 750ish RPM, no hiccups during the powerband.

I would also like to add that i am running a Dinan chip for my 173 ECU. its CARB legal, so i would assume that wouldnt effect me much.

[jlevie]

When I take a Spec E30 to the dyno to tune it we take a half dozen or so DME's so we can pick one or two of the best ones. Since pretty much every 173 DME you get you hands on is 20 years old, and since the analog portions of the DME do age, there are differences in the way the DME's perform. It isn't unusual to find one DME in the bunch that that causes a 15:1 or greater A/F ratio below 5k. That is lean enough to drive NOx through the roof.

[JrCamacho]

When I take a Spec E30 to the dyno to tune it we take a half dozen or so DME's so we can pick one or two of the best ones. Since pretty much every 173 DME you get you hands on is 20 years old, and since the analog portions of the DME do age, there are differences in the way the DME's perform. It isn't unusual to find one DME in the bunch that that causes a 15:1 or greater A/F ratio below 5k. That is lean enough to drive NOx through the roof.

i'll try a new DME if these repairs do nothing as far as change the NO(X) levels.

could the Dinan chip cause my AF ratio to be that high below 5k? or just the "analog portions" from the DME itself cause that? i assume that the chip is just a "program" of parameters that the DME uses to help regulate the ratio.

[jlevie]

The Dinan chip riches the fuel mixture and advances timing, so no it should not be responsibe for the high NOX. Spending a $100-150 for a few runs on a dyno will tell you a lot about what is going one.

[urbancynic]

I believe you have an "i" so I'm not entirely sure where your coolant temp sensor is.

On my eta I think it is near the thermostat housing, but not on it. But I'm guessing from memory. Haven't looked at my engine in ages.

An o2 sensor and/or plugs can make a huge difference.

I was struggling with NOx on my eta when I got it too. Threw many parts at it trying to avoid the inevitable... a cat.

When I replaced the plugs (they were also +4's) with the proper NGK plugs and the coolant temp sensor for good measure my NOx dropped significantly.

Not enough to pass, but dropped it by half!

I did eventually replace the cat and o2 sensor. I went cheap and bought a sensor for a 91 Ford Mustang GT and spliced it on to the original connector.

I did that and I passed with flying colors.

[JrCamacho]

I believe you have an "i" so I'm not entirely sure where your coolant temp sensor is.

On my eta I think it is near the thermostat housing, but not on it. But I'm guessing from memory. Haven't looked at my engine in ages.

An o2 sensor and/or plugs can make a huge difference.

I was struggling with NOx on my eta when I got it too. Threw many parts at it trying to avoid the inevitable... a cat.

When I replaced the plugs (they were also +4's) with the proper NGK plugs and the coolant temp sensor for good measure my NOx dropped significantly.

Not enough to pass, but dropped it by half!

I did eventually replace the cat and o2 sensor. I went cheap and bought a sensor for a 91 Ford Mustang GT and spliced it on to the original connector.

I did that and I passed with flying colors.

Its still in the shop, im having them replace the plugs and the o2 sensor..

i have already replaced those things when i first got the car, but i used those bosch +4 platinum ones, and this oxygen sensor: http://www.amazon.com/Bosch-13231-Ox...ZG64S/ref=pd_2

BOSCH 13231 oxygen sensor, and that was back in april, they said that it is bad.. am i fouling out my oxygen sensors? i will let you guys know the verdict on tuesday when i go to pickup my car.

[JrCamacho]

UPDATE:

just talked to the rep at the smog station thats working with me on this situation. He just went ahead and let me know that my catalytic converter is bad, even though i replaced it 4 months ago. He is saying that i need to get an OEM/Factory catalytic converter to get my car to pass smog.

he was also saying that my AFM could be failing or doing something weird? im sure that it hasnt been tampered with but could be compromised, any takes on that?

[amcink]

So what finally happen? Did you change the Cat?