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Bad mpg and have replaced many components.

598 Views 5 Replies 4 Participants Last post by  palladin
This started back in Sep when my 83 failed emissions. It also had showed a drop in gas mileage for about a year. Logs are kept at every fillup since 1983. And for you naysayers, even though every single data might not be exactly correct, the trend will be. i.e., if one fill up underfilled to show high mileage, you will notice low mipg the next.

Recently: replaced all 6 FI with new Borg Warner OEM. Cat was just replaced
NEW: wires, NGK plugs, cap, EGR, O2 sensor
Repaired: Throttle switch, FI pigtails were replaced, Distributor was rebuilt with new magnet and coil, bearing plate and vacuum advance
Inspected, tested but OK: Cyl temp sensor, AFM, Vac leaks, Fuel Injectors connectors, timing, valves set properly, coil tested a bit weak so was replaced with one from donor car

The "miss" or stumble smoothed out as it warmed up. It is still present just above idle but after that she has smoothed out and you cannot feel it once underway like you could.

Trip to Knoxville was 129 miles on 6.7 gal or 19.25 mpg. Now we have established the speedometer is running 5 mph slow which boosts this to 20.5. Problem is what used to be normal was 23.5-25.5 on a freeway trip.


This is a post from Nov 2 to listen to the eng running http://www.youtube.com/watch?v=M6vDx1oO3dU

This was made just last night. http://www.youtube.com/watch?v=ujM6bjVco08
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What if the cylinder temp tested good but wasn't as good as it should be?
Ethanol and/or winter formula gasoline...

Check initial lead, vacuum and centrifugal advance.

You'll get a more accurate MPG average reading after 3/4 to 7/8 of a tank used.
Dragging calipers, different tires, wrong viscosity tranny and diff lube, 180deg t'stat instead of 195? Just playing devils advocate.
Powerglide got it, the ethanol mixes give noticably lower fuel economy and it's especially noticable in 'older' vehicles with first generation EFI and carburetors. They simply can compensate for the loss of fuel BTU's.
PG & Tony: I would buy that if it suddenly now in the winter dropped the mpg or when we switched to ethashit. Sep 09 it tested extremely well at emissions. I'll check when the mpg drop hit but I think it was around the same time. It has to be something else. The compression ratio and leak down is good down the line. Changing the FI really smoothed it out. There is just a hint of a stumble every now and then. If detectable at all it is at the tail pipe.
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