Everybody's favorite variety of thread, failed emissions.

1990 Civic Si converted to obd1, running a D16z6, connected to a P28. AEM air intake. DC header. New distributor, plugs and wires. No check engine light. Magnaflow California approved CAT. Fuel pressure set to 35psi.

 

High NOx is a product of high engine temperatures.

My fan kicks on. And I have a new radiator. The bottom hose starts out cold and warms up as the engine reaches operating temperatures, which tells me the thermostat is working properly.

Timing is at 16 TDC.

 

fuel helps to cool the engine
35 psi is mighty low for a d16z6
d16a6 oe spec is 39 psi
d16y8/d16z6 oe spec is 43 psi

I had this problem before: on your dc header, the o2 sensor should go right before the catalytic converter.

check your wiring harness for any damaged wires, especially near the o2 sensor and ecu temperature sensor.
you can switch your coolant out for pure distilled water. Or just drain the radiator and replace that with distilled water.

Water cools better so it should help a lot, bleed the coolant system and make sure you have no leaks that is introducing air pockets. Check your reservoir too for any leaks or cracks, and the radiator cap

Right before smog fill up with 91 octane and pour two bottles of heet(red bottle) in your tank. Heet is basically just alcahol. Alcahol burns cooler than gasoline so it should also help. Move the heater **** to hot so the heater core can help with cooling

Check your ground wires:
thermostat wire harness
head to rad support
battery to chassis
transmission bracket to chassis

Also, make sure the tech put the industrial fan in the grill of your car. Some of them don't.

 

16 btdc +- 2 is the timing for your engine.
I reccomend setting it to 14. It will let more fuel to enter your engine before ignition.

 

Thanks for your in-put. This crap always stresses me out. But each time I go through it I learn something.

Attack Plan:

Retard timing to 14
Increase fuel pressure to 40, just to be conservative
91 octane with Heet additive (Red bottle)
Drain radiator and use distilled water only
Check o2 and temp sensor wiring, clean connections
Check and clean grounds

From what I understand about NOx production, excess oxygen allows it to form. Is my O2 level too high? Does my exhaust describe a mixture so lean that it's interfering with the converters ability to clean NOx?

 

yea, your carbon is too low. but the NOx is high so I believe you're not getting enough fuel

Set it to 43 psi. Look on napa autoparts website for your fuel pressure regulator. It's supposed to be 43.

Also, the catalytic converter does not really effect Nox

I forgot to mention, check for vacuum leaks as well. If you have one, you might have un-metered air coming in that's causing your high nox lean mixture
Grab some brake cleaner(same as carb TB cleaner, just cheaper) and with the car warmed up and idling, spray around the vacuum lines and manifold
If the idle has a sudden surge , there a is a vacuum leak in that area.
Also look for exhaust leaks too.

And make sure your car is warmed up well before you go smog it. Leave it idling if you have to, the cat will be all hot and functioning and the exhaust seals will swell to full seal.
Dont disconnect the battery, if you did, make sure you drive around long enough for the ecu to calibrate itself

One last thing, do you have an AEM fuel regulator? They come set at 42 psi. I have mine set at 41, 2 psi more than oe d16a6 spec. I dont think you'll have any issue setting it at 42.

 

Dont forget to bleed the air.

 

Thank you, sir. I'll be sure to report back.

 

Still failing... New NGK ZFR6F plugs, gapped to .44. I adjusted Fuel pressure to 40. Set timing to 16 btdc. Drained radiator, refilled with distilled water, bled system. I also went over all of my sensors and grounds and everything is cool.

After failing I happened to notice that my clutch fork was very loose. Could that have added to my problem?

 

I had a '92 CX where the timing had been set accidentally 1 tooth advanced. This made it fail inspection because emissions was extremely high, similar to what you are experiencing. On the upside, it ran with a lot of power
Make sure the timing is set correctly.

 

Fuel pressure should be 43 psi
You passed one of them and the other improved

What's the timing spec for your engine? Set it as far back as allowed.

If it's 16 btd +- 2 set it to 14.
And tru adding heet(red bottle)
Make sure your car is nice and hot when you go.

 

I know you have a california cat, BUT IS IT BRAND NEW? Based off what I see the motor is running excellent and the cat is not performing well.

 

right there!! NOx is EGT related, not engine temp, but exhaust gas temp related. yes, you COULD see improvement with a cooler thermostat, but you shouldn't need it. You are doing it right running the correct engine with the correct ECU.

try a ZFR7 plug. the colder plug should drop combustion chamber temps significantly. With the improvements you've already made, it might be what you need.

HOWEVER, you should still find out why you are in need of 2 step colder plugs over the recommended ZFR5-J for that engine.

IIRC 40 psi under vacuum (idle) and 43 psi no vacuum (line disconnected and plugged or WOT) is where fuel pressure ought to be. but that's from memory, service manual should have specs.

Lastly, are they the correct injectors for a P28? In terms of CCs? I don't know about 5th gens, but in 6th gens the non-vtec cars had smaller injectors than the VTEC counterparts. So are you sure your injectors are the correct ones or is there a chance someone swapped them at some point? If someone put in a smaller injector, you would be running lean and therefore causing NOx.

 

Brand new cat needs to be broken in before it lights up properly.
also, when you go to test, drive around for a good 20min before the test to get the cat nice and hot.
then, when you drive up, leave the engine to idle until they test.
If they are busy, drive some more and come back.
dont want to let the cat cool down and don't want to idle too long

what octane gas are you testing on? Got for the lowest octane you engine runs happy on. 87 or 89
are you trying to test on gas only or do you have bottles of any additives in the tank? Don't add anything don't use cheap gas either.
do you have a stock header to use for the test instead of a header?

looks like the box is a lot better. Is you have raw fuel issues.
last time you did cap and rotor?
also.... that header.... make it go away

 

Drove on highway for twenty minutes in 4th at 4k rpm's before test and I was able to get straight onto the dyno. I would say the CAT has two thousand miles on it. I guess I could go to an exhaust shop and have them measure temps before and after CAT.

As far as the DC header, are they just a stupid "fake" mod? I have the stock one, what the hell I'll put it back on. It will probably make the o2 sensor happier, which, by the way is newish.

For fuel I used 87 without additives.

Injectors came with engine from HMO. And I sent them out to get cleaned and balanced, like 2 years ago.

I checked mechanical timing again today and it was dead on. I thought about retarding to 14 btdc but I'm glad that I did not. It is my understanding that retarding the ignition enriches AFR's. Based on my current numbers it seems that advancing the timing would help. Advanced timing leans out mixture.

As far as NOx goes, I thought high temps in the combustion chamber are responsible??? That's why I changed my plugs from 5 to 6 and increased my fuel pressure. Clearly NOW I am running rich, but look at my NOx at 15mph, it's almost failing, and it shouldn't be based on my HC readings. That raw fuel should have kept the chambers cool, as was done during the 25mph test.

 

ohhhh I just took a closer look at your second test, I didn't see that now you are failing on HC and passing NOx. It was a good thought to go with colder plugs, that was a good move on your part. So now maybe just dial back the fuel pressure just a touch and hope you find a sweet spot. There doesn't appear to be any reason why this car would be failing emissions. My near-stock cars pass tailpipe emissions without any issue at all. I used to have trouble with one car on NOx, but that was specific to how the ECU was factory programmed and the test conditions. Once we figured out that the EGR is commanded open at 39 km/hr, then we knew to run the test at 40 km/hr and the car would pass without issue. We ran the dyno in diagnostic mode and varied speed and which gear we ran the test in, then we figured out EGR opening was speed-specific. But prior to that, I tried everything... so many new parts, even ran the car with 1/2 bottle of water in the tank to cool the cylinders... took about 8 tests to figure it all out.

you are forgetting that HCs can come from burning oil as well, not just gas. So your theory on cooling cylinders with raw fuel is a valid one, but HCs aren't necessarily just fuel.

here is a good site that helped me in the past Understanding Engine Exhaust Emissions

are you able to connect a scanner to the P28 and get some live readouts of what TPS, ECTS, IAT, O2, and MAP readings are??

I would love to know what your intake air temp and engine coolant temp says. Have you used a vacuum gauge to see if by chance you have a vacuum leak somewhere? Is there any indication of a misfire? If you think about it, high HC and high NOx COULD mean one cyl is misfiring while the others are running lean and creating the NOx. Pull the plugs and verify you have really nice strong blue spark on all 4. READ THE PLUGS. Let the plugs tell you if you are rich or lean, and if the condition is on one cylinder or all four. At this point, we need to go back to old-school diagnostics. Or post pics of plugs, let us read the plugs for you if you aren't sure.

 

Thinking that you ignition system might need a look into and going back to stock plugs and using 89 octane might work.

 

Thanks guys for your help!!!!

I don't have a vacuum gauge, but I sprayed over all possibilities with break cleaner in search of leaks and found none.

I did however record the resistance of the IAT and ECT. The readings were taken with engine hot, just after fan kicked on.
IAT was 1.40 -- cold reading 2.8
ECT was .19 -- cold reading 2.72

And here are my low mile plugs.

 

those are pretty much plugs out of a perfectly running engine

the IAT and ECT look to be in line also, assuming the scale is kOhm.

WTF are we missing here!??! ok time for a stupid question since 49 state emissions Civics of that vintage don't have it.... but does YOURS have an EGR? Did California Civics come with an EGR?

 

Don't be mislead by the title of this home movie. Yes, it's called Bubbles, but there's nothing happy happening here. The bubbles seem to describe a leaking head gasket.

While watching this video please assume that my coolant system has been bled. I am not overheating but I am loosing coolant, in this case distilled water. It seems to be escaping from my cap, but the cap is not the issue. The radiator is new.

Also, there seems to be no exchange occurring between the overflow tank and the radiator. I checked for blockage, etc. and there seems to be no problem with the tank. However... The radiator does not draw fluid back in, nor does the tank seem to receive fluid.

Based on this video and info. would you say that my head gasket is on the way out?? Keep in mind, if it is the head gasket that might be why my Nox is high.

​​​​​​​Thanks Guys.

 

i didn't watch the vid, but 100% of the time large bubbles in coolant are a head gasket. If it doesn't seem bad, it might make sense to try to retorque your head bolts.

 

Block tester can check the fluid in the radiator for the presents of any traces of anything leaching into it from combustion chamber (failed headgasket).