EVilMonkeyMR

Background:
Mods: CBRD BBK full, kelford 272 cams, 1000cc injector, walbro fuel pump, open air filter, supertech sping/retainer set, ARP headstuds, Invidia O2 housing

After my shop installed the mods listed above, I got a tune. Car was fast and I was smiling. However, I quickly noticed that there is a fuel smell from the cabin everytime I hit boost. I brought it back to the shop and they told me it was the donut gasket. I decided to wait to fix it until after I pass SMOG since I plan to install a test pipe after.

Problem:
PASS - Idle
FAIL - The 2500 RPM test has a CO (%) measured of 1.55 (Max is 1.00)

The tech told me there is too much fuel going into the engine and not enough air. I read that a leaking donut gasket will cause the O2 sensor to falsely read extra O2 coming into the exhaust, thus, causing more fuel into the engine? Could the donut gasket leak be the cause of the SMOG test failure?

Thanks in advance!

awdordie

iTrader: (1)

I wouldn think so I may be wrong but the rear o2 function is to make sure the cat is doing its job the front o2 from what I've read and been told is the main one that controls fuel.

EVilMonkeyMR

Yes, I was referring to the front o2 sensor(sensor before cat). So if the sensor is sensing more air, the system will try to send more fuel to the engine to match the AFR ratio programmed by the 'tune.' Is this how it works? Sorry, I'm pretty noobz on this subject.

Anyway, I plan to replace the donut gasket (gasket between the O2 housing & dp) and get it retested.

Anyone have ideas why the CO reading is so high?

awdordie

iTrader: (1)

I would check for a leak before that sensor maybe turbo to o2 housing. The dp gasket is still after the front o2 sensor and I doubt it could pull air in and then flow back up to the sensor.

mithrandir7533

iTrader: (1)

I'm calling BS on the donut gasket. The gasket is after the o2 sensor. Find a way to put some smoke around the gasket, rev the car up and see if air comes out. Air can't move back up to the o2 sensor that fast.

I'm never moving to CA!

FedEvo8

Too much gas will cause high HCs. Is your car operating at normal temperature?

Are you using your stock cat?

EVilMonkeyMR

The HC (PPM) actually passed. Measured 51 and Max is 130. Yes, I have stock cat.

EVilMonkeyMR

Ok so it's prolly not the donut gasket causing smog to fail.

Running too rich will cause the CO reading to be high, correct?

awdordie

iTrader: (1)

^yes running rich will cause it to read higher because it looks like the cat is not doing its job.

EVilMonkeyMR

Hi again. Thanks for everyone's inputs so far.

So after doing some homework, i found some common causes of high CO reading are the following:
-defective o2 sensor, cat, thermostat, fuel injectors, and even extended time between oil changes?

1) Could I eliminate the following suspects?
Thermostat - because the engine is running at normal temp
Fuel injectors - recently replaced ~8k miles ago
o2 sensor - engine light not lit

2) Oil - I'm due for an oil change in ~300miles (every 3kmiles). Will change this weekend.
3) Cat - I don't remember the exact words but my tuner did mention my cat looks like it was about to give up.
4) Is it possible my car is tuned to run too 'rich'?

sparky

iTrader: (1)

As long as there are no other problems then your tuner should be able to flash your car to pass emissions by leaning out the fuel tables etc. At least with my Buick we could do it by swapping a specially burned "smog" chip into the ECM.I don't know if with Evo's you could get a special "smog" tune though.

awdordie

iTrader: (1)

Its very possible your car is tuned to run really rich. That's insurance for the tuner and your motor to avoid detonation knock and and blowing your motor

dastallion951

your best bet man is to change the oil which will help because if your car is running overly rich, then theres a chance some of the extra fuel can contaminate the oil. rule of thumb, change the oil, but also prior to draining it, throw in an oil system cleaner to clean all of the oil system galleys etc. Then change the oil. Now if your 02 sensor was reading air from an exhaust leak, it would throw a code usually system to lean bank 1 code. I went to smog mine 2 years ago with my mods and no cat, i was off by 30 ppm hc at 2500. To be honest if your cars running good the cats not a problem, usually a broken or clogged up cat, will cause high egts and cause the NOX to climb on the smog test. check your fuel injector seals for cracks or tears in them. Make sure you have no signs of fuel leakage around your intake manifold. Good luck, you can always do the unhonest thing and get it "passed" haha

golgo13

iTrader: (134)

+1

You may also want to see if your cat is going **** up.

Before your next retest heat up the cat really good by pushing the motor. Cats work best when hot.

BluEVOIX

iTrader: (69)

The primary O2 sensor is behind the donut gasket. You can pretty much remove your downpipe and not affect a/f ratios, meaning leaks after the o2 wont affect the engine.

Do you have a wideband? Is your a/f ratio hovering around 14.7 (during normal driving and off boost) ?

Do you have any types of CEL codes being thrown?

Have you checked for any vacuum leaks? EGR vacuum lines not popped off etc...?

Assuming your a/f ratio is running fine verified with wideband and no CEL's, then most likely it may just be your cat not working well.