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Testing Back Pressure
Car is a 91 Camry, 4 cyl 3SFE, 172K miles. Recently did a upper engine rebuild due to a burnt exhaust valve. Car seems to be running great, no more oil leaks, not burning oil, etc. I have noticed however that my fuel economy doesn't seem real good.
Before my rebuild, I could average 29-32 on the interstate doing 70 with the ac off. On a 200 miles round trip last summer, doing 70 with the ac on I averaged 29.5 MPG last summer, not too bad. Since the rebuild, I'm getting around 25 MPG on each tank. Sometimes lower, lowest has been around 22 MPG.
Car has decent power, but does seem sluggish at lower speeds. Ignition timing is right on spec. Vacuum seems good, no leaks. Plugs, wires, filters, etc have all been changed within the last few thousand miles. A friend recently had a similar issue with a newer Chevy car with a bad rocker arm causing a miss. After fixing the problem they experienced sluggishness at lower speeds and poor fuel economy. Turns out it was a plugged CAT, reading over 9 psi of backpressure at idle.
I removed the o2 sensor and started my engine, exhaust seemed to be blowing real hard out of the hole, and the car was idling slightly higher than it usually does (at 1K instead of 600-700 RPM). Whats a good way to measure the back pressure on this motor? Only way I can think of is to drill a small hole somewhere in the ex manifold and thread a guage in, amnd plug the hole with a bolt when finished.
On the poor MPG issue, anyone have any other good suggestions to track down this problem?
Thanks!
Jeremy
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