gt500pwr

OK, i apologize up front but this is going to be a long winded post. I've been trying desperately to pass emissions over the last couple of months without success. I finally got a "conditional pass" but I'd really like to resolve the issue. 1991 Camaro, L03 stock, open element, edelbrock tbi intake. No AIR but functioning pcv and egr, JET stage II performance chip.

First test taken results May 5th:
hc ppm limit 57, read 56 PASS limit 200, read 253 FAIL
CO% limit .32, read .04 PASS limit 1, read 1.13 FAIL
NO ppm limit 632, read 613 PASS

Second test taken results May 26th:
Changed the o2 sensor(delco replacement) and used some guaranteed to pass in the fuel. Also burned stock chip and replaced the JET chip
hc ppm limit 57, read 62 FAIL limit 200, read 356 FAIL
CO% limit .32, read .01 PASS limit 1, read 1.74 FAIL
NO ppm limit 632, read 1455 FAIL

Third test taken results Aug 3rd:
Installed heddman hedders and y-pipe, goerlich 3" ss cat, and magnaflow 3" ss catback system
hc ppm limit 57, read 54 PASS limit 200, read 24 PASS
CO% limit .32, read .02 PASS limit 1, read .03 PASS
NO ppm limit 632, read 1966 FAIL

OK, from here we didn't know where to go. From what we gathered it was the EGR system that was creating high NOX readings. I read lots, made posts and got some good responses but without success.

My mechanic figures the EGR system which requires backpressure to operate properly but the high flow exhaust now doesn't allow the EGR to operate properly. We can't find a non-backpressure type EGR to fit this application which he figures will solve the problem.

One suggestion I got was to drill out the EGR vacuum orifice to .025-.038. I drilled it out to .0292 and these were the results Aug 15th:
HC ppm limit 57, read 96 FAIL limit 200, read 58 PASS
CO% limit .32, read .09 PASS limit 1, read .01 PASS
NO ppm limit 632, read 1735 FAIL

I can burn my own chips however I'm still new so I'm not entirely familiar with "tuning".

If anyone can suggest some kind of resolution... I'm stumped!

//<86TA>\\

iTrader: (14)

dont know that much about this but looking at your #'s your ppm limit passed origonaly with the jet chip, then after you changed it to you new burnt "stock" chip the readings went through the roof, maybe try with the jet chip again

gt500pwr

Please, if anyone can chime in here, I could really use your help.

cgtms

You were passing with the JET Chip burn, so try that. New new cat fixed the HC and CO.

When working correctly, the EGR will keep your combustion temperatures down and thus keep your PPM in check. You can check the voltage going to your EGR solenoid once the car is warmed up or better yet, place a vacuum gauge in-line with the vacuum line going to your EGR valve. You should see vacuum cycle if your system is working. If you don’t have a voltmeter or a vacuum gauge, you can also use a “spare” EGR value that is not installed in the car and plug it into the EGR vacuum line to watch if the plunger moved up and down as the car is running.

All these checks will help you verify if the EGR valve is opening and letting the exhaust cycle back into the intake. The vacuum of the intake and pressure from the exhaust will do the rest if the EGR valve is opening as the VCM calls for it to cycle.

Let us know what you find.....

D's89IROCZ

Get an oil change ....and really take it out for a run . With regular gas. Make sure the car is still hot when you pull it in . make an appointment to show up at a certain time ...so you can keep it running . Worked for me after numerous failed attemps by previous owner .

gt500pwr

That's great, i'll check the vacuum but I'm quite sure the mechanic said the egr was functioning properly. It had the correct vacuum but the loss of backpressure is keeping the egr from recycling the exhaust?

DENN_SHAH

iTrader: (1)

looking at those numbers, jet may have actually gotten your chip right.

i believe if you get a EGR valve without a N or P at the end of the part number it will be what you need.

you can check it before you buy it, take a piece of vacuum hose with you, first push up on the diaphragm & then put your finger over the nipple where the vacuum hose goes, if the valve stays open then put the hose on the EGR valve & suck on the hose while watching the diaphragm, if the valve opens then that valve should work.

1991L98G92

That's the way negative back pressure valves work. Once the engine creates negative back pressure, the valve closes. Positive back pressure valves need back pressure to open. After reading the first test, it looked to be running rich on the second readings. The second test wasn't much of a change. The third test, seemed to fix the rich problem, but created higher cylinder temps. The only way driving the car first will help, will be if the machine is set up and ready to test when you pull your car in. After a couple minutes the cat will have lost all that heat. And seeing that the car is being ran on a dyno, it is basically being driven under load. Sounds like back pressure is the most likely culprit. Coolant temps above 200 degrees will reduce NOX. Lower timing should also lower NOX, but can increase exhaust system temps from the manifolds back (usually the cause of glowing). Reducing the amount of fuel into the cylinder will lower temps (which is what the EGR system does). If the NOX reading is failing at Low Speed the EGR may not be funtioning yet. If the NOX reading is failing at cruise, suspect the EGR.

gt500pwr

In Canada we have 40km/h cruise and idle, the data above reflects that, therefore the nox reading is at 40km/h cruise. I've checked with Delco and we they can't seem to find an direct fit EGR requiring NO backpressure. Does anyone know if there is one? I'll have to check with the prom guys to see if I can turn the EGR on sooner.

Thanks for all the info so far...

gt500pwr

I noticed in my winaldl logs that the HIGH MAP flag is on. High MAP means low manifold vacuum, therefore not necessarily enough for the EGR. I'll have to test the map i guess, maybe there's an issue there?