I've got a problem with my EGR system that I've been trying to figure out. I live in California so I have to pass the smog test every couple of years. I've got a stock head and cam L98 in my 1988 IROC with full C.A.R.B. legal intake and exhaust bolt on's. My motor is an AC/Delco stock replacement motor with 35,000 miles on it since I put it in my car.

My NOx emissions exceed the limits of the test but, on all the other points of concern on the test it passes.

These are the results of my last emissions test.

15 mph test: 1,398 rpm

%CO2: measured = 13.5

%O2: measured: 1.8

HC (PPM): measured = 13, average = 48, max = 83

CO (%): measured = 0.00, average = 0.12, max = 0.71

NOx (PPM): measured = 1814, average = 227, max = 537



25 mph test: 1,345 rpm

%CO2: measured = 13.4

%O2: measured: 1.9

HC (PPM): measured = 9, average = 35, max = 83

CO (%): measured = 0.00, average = 0.09, max = 0.40

NOx (PPM): measured = 1645, average = 202, max = 494

My car is still running a little lean. It was running hot because the radiator was plugged. I got another stock replacement radiator, switch for the fans to turn them on earlier and a high flow water pump. So far that's fixed the over heating problem that I had.

I've changed a lot of sensors and parts trying to figure things out but, since the NOx values are still so high I've zeroed in on the EGR system. I've got a new cat, new ignition system, new O2 sensor, new IAT, new CTS, EGR swtich installed in the past 8 months.

I bought a replacement EGR and put that in.

They don't make EGR solenoids for TPI motors anymore. A friend told me that an EGR solienoid for an LTI would fit (and they still make them) so I bought on and put it in last week. Does anybody know what the cause of that could be?

I've had friends suggest that I have a build up of carbon in the motor and that I need to take my heads off and clean the EGR passages. What do you guys think I should do next to get the car to run right so that I can pass smog?

 

Did you find a fix for this? Im seeing just about the same thing on my 89 w/lb9/m5.
i have initial timing set to 6 deg.

Measured NO is 995@15mph, 1098@25mph. everything else is low.

Ive replaced the cats, dist, module, ias as well as ecm chip (jet 18904) spark plugs, msd coil + wires etc....

I checked the the website aircare.ca to see what could be that cause of hi NO.

http://www.aircare.ca/repinfo-ere-causes-nox.php

listed are:

Over advanced ignition timing

Inadequate EGR flow

Lean Air/Fuel Ratio

Defective 3-way converters (brand new)

Combustion chamber deposits

And i was about to go get an egr valve until i came across your post. Any update? thanks!

 

Not yet. I replaced the EGR valve though. I got another EGR solenoid from a TPI car to put on and I'll see if that works. With the values so high the egr isn't even running.

 

Thanks for the update! Ill get an EGR and check the solenoid. I'm thinking of using a combustion chamber cleaner to see if that helps. The car had been sitting for a couple years before I rescued it.

 

yeah see if that helps too. They don't make TPI style EGR solenoids any more though. I got one for an LT1 but it dosen't work properly. I got another TPI style EGR solenoid cheap on ebay.

 

Retarding the ignition can also help, but they check that during the test and you have to be within 3 degrees for them to pass it. So you don't have much wiggle room to play with and there's a risk the inspector might not read it exactly the same way as you.

If you're able to make your own chips, you can retard it using a chip, while keeping the physical base timing stock. That way the inspector won't see that it's retarded.

 

Update: I took the car in for diagnosis on high NOX. Technician says that if he puts in about 15lbs of vacuum to the EGR, the nox is reduced from 1098 to under 200! The tech says the EGR should not need 15lbs. So, either the EGR is bad, or the manifold passage is plugged with carbon. So i will be removing the egr valve to check/clean the air passages and swap out the EGR. Will update once all this is done.