Hello all, I am new to your site. The forum looks great with lots of good feedback. I hope someone can give me some good feedback on this one, too. I have an '88 Bronco, 351, and installed a rebuilt long block. The manufacturer said that he had a high torque cam that he could install that would work fine with the EFI. The problem is that I get a check engine light, after about 10 minutes of driving, and the only error code is 41, system lean, no O2 switching. I installed a new O2 sensor, searched for vacuum leaks, made sure that the thermactor switching was working, and can't get the error code to go away. It clears with each engine start, but returns after a few minutes of driving. I would try anything that might help, even if it includes garlic and dead chickens...

Thanks for the help.
Bill

 

First off, welcome to FTE and the Big Bronco Forum.

If you have replaced the O2 sensor, have you "cleared the codes" from the computer by disconnecting the battery for at least 7-10 minutes? The computer's keep-alive power source will allow the codes to remain and confuse the ECA even if the problem has been rectified. If the codes have indeed been cleared you can test the O2 sensor but its a slightly involved process. Personally, I'd check the fuel rail for the proper pressure. KOEO pressure should be between 35-45 psi and should only drop 5 psi at most when the engine is running. You can check the pressure at the schrader valve on the driver's side of the fuel rail. If the pressure checks out ok then you may want to make sure the "spark" portion of the system is in good working order (plugs, cap, rotor, etc).

If the Code remains an issue, the test for a faulty O2 sensor requires a voltmeter and an unlit propane torch. Drop me a line if you decide you want the details. Its a rather involved process.

 

I had a code 41 on my 89. I tested the output from the O2 sensor and it indicated that it was running rich. It turned out to be the ground for the O2 sensor was loose. The ground is an orange wire on the firewall right behing the intake plenuim. I would check that first. if you want more information on how I found it, let me know.

 

Thanks for the info. I have cleared the trouble codes, but this one always comes back. I have a pressure gauge on the fuel rail that shows between 35 and 40 psi. I have grounded everything I can think of, including jumpercables from the O2 sensor to the battery without luck. The plugs, wires, cap and rotor are all new. The timing is at 15 degrees, but I have reset it to 10 and still get the error. The truck runs great. The plugs are really clean, almost new looking when I pulled them to check. Has anyone modified their air density systems, after adding a high torque cam, to get better performance? I wish there was a quick way to crank more fuel into it and see if the error clears. At least this would tell me that the problem is real. If it doesn't clear and the exhaust gas is burning you eyes, then the EEC is having problems. What do ya think?

 

You CAN dump more fuel into the the system by fooling the computer into thnking the engine is still not quite warmed up. Pull the conector off of the ECT (engine coolant temperature) sensor and put a 5,500 ohm resistor across the terminals. This is actually a racer's trick to dump more fuel into the system even after the engine has warmed up. Since fuel/air ratios are determined by the ECA based on readings from the ECT and other sensors you can "fool" the ECA this way.

Could be that you have a faulty ECT sensor too but the ECA doesn't "know" it because the resistance value that its stuck at is still within "acceptable parameters". If this is tha case, the ECA will not trigger any fault codes but simply adjust fuel/air ratios accordingly regardless of engine temp.

ECT resistance value as it corresponds to the coolant temp is as follows.

Degrees Farenheit/Resistance
50/58,750
100/16,150
150/5,250
200/2,550
250/1,150

These numbers are approximates and may fluctuate slightly.