My HC's moved just outside passing when the truck shifted gears and went into 3rd during the loaded dyno emission test at 25mph. I'm wondering whats the easiest way to geta pass? Should I try and lean it a little more in 3rd w/light load? Play with timming? Fuel pressure?

Thanks

Kelvin

http://www.jaybquick.com/_Kelvin_Upload/Smog Test-1.tif

Setup:355,10.1,CNC TF 195's,Ported Edelbrock manifold,46mmT-body,75#inj's,219@.050 .520 HR etc....

 

You said this is in a truck? What is your setup on it? I had a real mild setup when I last had mine on the emissions rollers. Make sure that you have a good cat and it is up to temperature before you test. I have also seen Bosch NB 02 sensors cause emission failures.

Why are you going into 3rd @ 25 MPH, I keep them in 2nd out of personal preference when I inspect them down here. I have an 1,100-2,500 window and have found that alot of them will fail when you run it down near the bottom of the rpm and they become cleaner as the RPMs rise. 25 MPH is pretty early for 3rd, especially if your truck has say 3.08 gears like alot of them do. What ends up happening is the dyno puts more load on your engine than say driving 25 MPH in the city would do and puts you into places on the VE table that your engine would likely rarely see.

 

You're right, it must have been the shift to second. And this is my 1990 K5 with 3.73 gears. The CAT is new OEM piece and it was pretty much up to temp. I heard my electric kick on so 195'ish is my guess. The O2 is AC Delco as well.

I agree with you on the RPM lowering the results. But it's up to the tech I guess to run it on the upper end vs lower. So the normal rpm window is as you indicated? Cause I can see on the printout that it was tested at 1500ish rpm.

KM

 

My suggestion is to ask the tech to let it stay running before he tests it. Take it out for a good 30 mile or so highway drive. Get on it some, blow it out, get everything up to temp. Then take it back for the inspection. You might pull 2-4* of timing out of it. Don't forget that with too much retard and too lean of a mixture you will pick up a lean miss and actually raise the HCs.

 

I ran the Pass or don't pay additive in my fuel before I went. I passed then. Just a thought. Dunno if it will help you though.....