Quote:
Originally Posted by midnight rumbler
I am noticing that at idle my truck runs at 20 on the vacuum gauge and under load depending on what I am doing and how I am driving it averages about 8-12.
At 60 km/h, I am running at about 2200 rpm and at idel 800-900.
This is a cube van with a 14' box and has a 350 5.7 liter with a 3spd tranny. Before these two installs, I was averaging 27 liters per 100/km or 11MPG. I have just installed these two pieces and switched out the old fuel filter and cleaned the TBI. I will advise on what sort of fuel savings I am getting into within the next couple of fill ups.
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800-900 idle rpm might be a smidgen high. If you've got AC, check again with heater control set to off. If that reduces idle rpms a bit, it's fine; you're done. If not, double check manufacturer's specifications.
Engines differ, but if traffic allows 55 km/h @ ~2,000 rpm may give significantly better FE. A bsfc map/chart would be ideal for an initial guess at best speed/rpm for FE, but they are harder to find than hen's teeth. If you can find a dyno chart of torque, power & rpm for a stock 1989 GM 3.7L TBI, that would also be useful
Is 800-900 rpm just an approximation for a steady idle at 8xx +-5 rpm or does it lope? Loping idle indicates a vacuum leak or some other problem.
FWIW
Reading a vacuum gauge give a pretty good summary of various other things a vacuum gauge can tell you.