stock car, stock chip - failure

[UNGN]

Great idea for a Fourm

I took my '86 GN today to get tested. I put on a fresh cat and fixed the numerous exhaust leaks and thought it would pass easily. I guess I was over confident.

The Failing numbers were at the low speed (15 mph) 1622 RPM

HC were 193 ppm with passing 152 ppm.
CO was 1.40% while passing is .86%

At the higher speed reading I was just within the limits (148 ppm on a 148 std)

Nox standard was 1146 ppm and I smoked that with a 52.

The two bad things that could have caused the failure was my fuel pressure was 45 psi line off and I had some very small amount of leaded race gas in the tank.

I've turned back the FP to 33 line on (40 line off) and have and I'm going to fill the tank up with gas.

What will help me pass?

 

[gofstbuick]

Since the HC and CO is high and the NOx is on the floor. I'd say that your running rich. When you lean out the mixture, the NOx will rise a little. Probably to the 250-400 ppm range. But the CO and HC will fall. If you lean it out too much, there may not be enough fuel to fire the mixture, and then you may encounter lean misfire. The HC will rise, the CO will fall to the floor and NOx will go through the roof. If you go leaner still, the same would happen for the HC and CO, but now since the mixture is just barely fireing, the NOx will fall (no heat created because there is not enough fire). So, just lean it out a little, but not too much. If you can view the CO2 reading, they are probably low and so is O2. Co2 should be around 14.5% to 15.5% and O2 should be 0.03 or less. CO2 is a product of combution, so as the engine runs more efficiently, the CO2 will rise. Hope this helps

 

[TurboJim]

I would get rid of the race gas. You wont get that stuff thru. It takes too long to burn. Thats one reason for HC. Your CO is kinda high as well. What is your BLM value at that engine load. I wond if you have a failing O2 sensor from the leaded fuel. Not a dead sensor, but starting to get lazy. .8 is kinda high for CO IMHO, and is most likely the cause of the VERY low NOx.

So, get rid of the race gas, possibly throw in a new O2 sensor (or at least check the one you have, as far as activity). Your fuel pressure setting wont make diddly squat of a diff, assuming your BLM is not maxed in either direction. If you wind up with lower CO and the same or higher HC, try goin to the stock heat range plug and gapping it at spec. I personally run R43TS gapped at .035 and never had a problem getting thru emissions. See a leaner mixture is harder to light and sometimes opening the gap a bit helps as the flame kernal is a bit larger/longer. If you notice, back when the cars were carb'd in the 80's, seeing plug gaps up to .080 wasnt unusual, this was to aid in lean misfire.

If gofast has nothing to add, See what you got and get back to us.

 

[TurboJim]

Wow, both of us musta been replying at the same time!! hahaha

 

[UNGN]

Turned Fuel pressure down to 33 psi line on.
Changed 5 spark plugs to Autolite 25's .
Pumped out 4.5 gallons of race gas mix, filled the tank with 93 Octane.

In the low speed test, Nox went up to 93, CO to .60 on a .86 Scale, HC's were on the bubble 152 out of 152.

High speed it had tons of room to spare.

Next year my goal will be to try to get the HC's lower. What are the Strategies for this?

Thanks for everyone's Help!

 

[gofstbuick]

What did the CO2 and O2 end up being? If the O2 is high, you still may have some more room to play. Try keeping a fresh cat in storage.