Need help on Nox #s

[TurboD1987]

I just had my GN e-tested and it failed big on no ppm, limit was 1164 and mine was 1915. I have a Houston 3" cat. so I'm thinking EGR problems. Any ideas out there? What is the best test for this? I think there are only two parts the egr valve and the modual. Thanks
Dave

 

[gofstbuick]

What chip are you running? Also, the cat that accompanies the the THDP is a two way cat. Means it only controls HC and CO and NOT NOx.

 

[TurboD1987]

I am running a smog chip for 009 injectors from Scott. Were all the cats Houston sold 2 ways? I thought mine was a 3 way but I could be wrong, any way of visually telling what it is?
Thanks
Dave

 

[gofstbuick]

The reason I purchased an ATR DP instead of a THDP is that the cat supplied with the ATR DP is a TWC. I talked to someone at Ramchargers prior to making the purchase (from ATR) and verified that the cat supplied with the THDP is a two way (or OC) cat and that I could purchase a TWC to go with the THDP for an additional $199. Since the ATR DP with cat was the same price as the THDP with cat, I chose the one with the TWC.

 

[TurboD1987]

I bought my Houston cat a few years ago but I actually have the ATR downpipe now. I might just try getting a cat from ATR then.
Dave

 

[TurboD1987]

Well I went for a retest and I first changed spark plugs, pcv valve, O2 sensor, put in some fresh gas and also put the mass airflow and egr modual from my T on the GN. The car past the dyno test but not the curb idle test, so I'm hoping just some fuel pressure adjustments are in order. For the test the pressure was 38 lbs with line off. The curb idle test has a limit for the HC ppm at 300 mine was 417, every thing else it passed. Any other ideas out there? Thanks
Dave

 

[gofstbuick]

What are the CO readings at idle? If you take too much fuel out, the HC may go higher, due to lean misfire.

 

[TurboD1987]

Here are all the readings:
40km/h or 25mp/h test

HC limit 104 reading 75
CO limit .58 reading .03
NO limit 1126 reading 1886

Curb idle test
HC limit 300 reading 292
CO limit 1.5 reading .01

I have now bought a 3way Magnaflow cat and just need to have a flange welded on!
Thanks for your help.
Dave

 

[wlaukaitis]

Does your EGR work? When the car is running stick you finger (use a rag on you finger becasue it is HOT) underneath and push up the diaphram (spelling?) The car should stumble and run like poo-poo. i had to replace the upper plenum gasket and I cleaned out the EGR passages while I was there. There was a lot of chunks in the passages in the intake. I also removed the EGR valve itself and blew 90 psi air through it (Both ways, egr to intake and intake to egr) I also had to hack away a few more stubborn pieces.

Needless to say, my NOx went from 1.21 to .56 just about 1/2 what the first reading/test was.

If you do decide to take off the plemun, you will have to get the gasket from gmpartsdirect.com. gnttype has a part number listed but even Fel-Pro says it is no good.

Check my post on the forum.

 

[TurboD1987]

Sorry guys I forgot all about this thread and didn't post back my results. Well after installing the Magnaflow cat. the GN passed with flying colors.
Here are the readings.

25mph test

HC ppm limit 104,actual 23
CO% limit 0.58, actual 0.00
NO ppm limit 1126, actual 374

idle test

HC ppm limit 300, actual 18
CO% limit 1.5, actual 0.01

Dave