Chevy Colorado, dissapointing first tank

[OL'55]

Thanks JR, I'll check it on my way home tonight

[aerohead]

Since you have the ScanGauge you might consider testing on a calm day,fully-warmed up.Drive at a constant,steady speed,record your mpg,then change by 5-mph,and repeat,maybe from 45-70-mph.
You'll be able to construct a mpg curve based upon driving speed,and if you have a 'sweet-spot' it'll show.
My T-100 seems to like 60-mph the best.Any faster or slower and mpg falls off.
And steady-state driving is your only hope for meaningful data,or else you'll be lost inside the other variables.You'll never sort it out.

[OL'55]

Looks like I have found a possible culprit. The exhaust manifold is cracked in half at the Y between cyl 2 and 3. Guess I am off to the junkyard!

[user removed]

That will drive the 02 sensor crazy.

regards
Mech

[OL'55]

So apparently junk yards cant sell used catalytic converters unless they are approved to do so, and the Colorado manifold has the converter built in. Nobody in my neck of the woods has one and they are $5-600 new.

JTR sells a header that will work if I move the O2 sensor, its $320

[OL'55]

Ok, I'm cheap! I found a guy to weld up the manifold and I've been at 25 mpg the past couple tanks. Yay! Not good enough though. According to JR my timing should be around 45 deg at 7lbs MAP but I'm right around 35 degrees. 22 degrees at 10lbs MAP.

Picked up a new knock sensor today and just installed it, I'll let you know how it goes


Edit: No effect on timing, exactly the same