mazda_b2000_driver
+1y
Hi Guys, I bought a Mazda B2000 1987 and I invested alot of time diagnosing the fuel economy issues. It now gets 28-32 MPG on the highway at 70-75 mph. I have 425,000 miles on the rig currently - the engine has 275k on it since new (it is a Japanese takeout engine - Magnum).
I am a computer programmer and very familiar with the electronics on the b-series truck, O2 sensor and computer. To improve the mileage, I connected oscilloscope up to the O2 sensor and monitored the waveform generated as a function of speed driven, throttle position and such as I drove the truck and could tell immediately what modifications resulted in an improvement. What I found was my truck was always running full 100% rich above 60 mph and was running somewhat normal below, so I set out to determine why and fix it so I could cruise and 75 and still bag 30 mpg.
Everything is 100% stock on the truck.
What I did to improve the mileage was:
1) replaced the mixture control solenoid - these go bad and will cause a truck to get 20 mpg when it should be getting 30 mpg.
2) disconnected the altitude compensator hoses (this helped a couple mpg)
3) replaced many hoses in the engine to fix vacuum leaks (THIS IS VERY IMPORTANT)
What I did which had only a slight effect on mileage was:
1) took the carb apart and cleaned it and replaced all the seals.
2) adjusted timing
3) new air filter
4) High end spark plug wires from Napa (not the base OEM quality)
5) leaned out the idle mixture
6) replaced the cat converter (these can get plugged up with age)
The things that have no effect on fuel economy :
1) Exhaust back pressure - it has no coupling to mileage as long as cat is not plugged
2) O2 sensor replacement - these seem to last forever despite the guys selling them claims, Mine was working fine with 200k miles on it.
3) Spark plugs - I tried platinum and OEM and both resulted in equal performance and efficiency and mpg
4) disconnecting the EGR - despite everyone complaining about all the emissions overhead I found no significant emissions related issues to fuel economy.
Just a tid bit of info - the computer controls many solenoids on the carb and if it detects any kind of problem (such as a vacuum leak) will cause the mixture to be full rich = 20mpg. Also until the engine gets above about 175 degrees, the computer runs the engine in full rich mode.
My advice - if you have a stock rig, and it is getting less than 28-30, you should be able to fix it for low $ and I see no valid reason to ever go to a Weber carb setup. I would not buy a truck with the Weber.