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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: 1979C20 on June 19, 2014, 04:39:25 am
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Trying to get my suburban to pass.
Test number one:
Gas cap - pass
Pcv - pass
HC loaded 154ppm, 300ppm allowed - pass
HC idle. 427ppm, 300ppm allowed - fail
CO loaded 0.90, 3.00 allowed - pass
CO idle. 1.30, 3.00 allowed - pass
So I went home, checked for vacuum leaks, tried to read the voltage in the o2 sensor with no luck, checked tps voltage, checked timing, and adjusted the throttle blade set screw. Everything checked out fine, and I opened up the throttle blades a bit to let in a little more air at idle.
Test number two:
HC loaded 130ppm, 300ppm allowed - pass
HC idle. 605ppm, 300ppm allowed - fail
CO loaded 0.87, 3.00 allowed - pass
CO idle. 1.20, 3.00 allowed - pass
From these result. Would it be safe to say that problem is caused by the engine running lean? Ive done the Ultimate TBI Mod, spaced the injector pod, took the ridges off the top of the bores, and made my fuel pressure reg adjustable. From the factory, the adjustment table in the reg was all the way out, no pressure. I brought it up to a little over half. I dont have a way to test psi currently. I just changed the oil, spark plugs, plug wires, and ocv valve. The coil and fuel pump is 2 months old. I did the tbi mod 3 months ago. The old spark plugs were kind of a red-ish brown, but were a little chalky. Is it safe to assume high HC and low CO is a lean burn?
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Between the 2 test, if the only thing you did was "allow more air at idle", and the ppm went from 427 to 605. What you need to do is decrease the air, or add more fuel at idle to bring down the ppm to below 300 ppm, which is what is allowed.
I use a fuel gas analyzer (http://www.testersandtools.com/TPI-708-Combustion-Analyzer.php), like this one, but ours has more options, at work. I have used it on my 74 playing around with it, and got it dialed in pretty good surprisingly. If you could find one to rent you could get it dialed in before taking it back to the smog station. They are easy to use also.
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Okay, I will bump the fpr up some more and back the throttle blade screw out a bit.
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I got it to pass! After changing the spark plugs, plug wires, oil and filter, pcv valve, and dropping the throttle blade set screw back down, I passed with flying colors, with no catalytic converter. I will post the results tomorrow sometime.
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A tune up can make miracles some times. Congrats on getting it to pass.