Engine Gremlin

96Br0nc0Guy · Feb 10, 2026

96 E.B. with 351.
Throwing Codes 171/174 (Bank 1/2 Lean).
Took it to shop, they smoke tested and fixed vacuum leaks.
Have replaced the following:
PCV, EGR, MAF, temp sensor, air filter, all three O2 sensors.
The shop guys and I are stumped...
All thoughts or suggestions greatly appreciated.

Tiha · Feb 11, 2026

Weak fuel pump?

There used to be a flow test to do on the pump and it was much more telling than just a pressure test.

It can provide enough pressure but if there is a restriction like a plugged filter it can still be starving for fuel.

L\Bronco · Feb 14, 2026

Good call Tiha!
Pump volume spec is 1quart in 30 sec minimum.
They had an issue with O2 sensor ground issues as well

96Br0nc0Guy · Jun 29, 2026

Finally upgraded injectors. So far no codes and performance is good. Fingers crossed.
Thanks for all the help!

goffprof · Jun 29, 2026

I had similar codes on my ‘96 EB Bronco. Replaced the original fuel tank, fuel pump and problem solved. Also replaced the skid plate, upper fuel tank hanger straps, gas tank breather valve, and rubber valve seal with new exact replacement parts from Bronco Graveyard.

Engine Gremlin

96Br0nc0Guy

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