engine fault codes

[bluewolf]

I've got a 92 mustang gt with a check engine light. big surprise. I havent done much to the car yet. I am running a stock 5.0 HO motor with magnaflow x-pipe w/ cats and matching exhaust. I installed new O2 sensors when I put the x-pipe in. I also have electric fan, pulleys, 130amp alternator, new msd blaster tfi coil, frpp 9mm wires, and CAI w/ a pro-m 75 for 19lb injectors. 3.73' in the back with stock tranny. Now for the codes:

during the KOEO test I get 67 (something about a neutral/park switch or sensor?) with continuous memory codes 41 and 91 (lean conditions).

during the KOER test I get codes 41 and 91.

I havent checked the timing as yet. I have done a rather careful inspection of all the wires, vacuum tubes and hoses that I can see and/or reach. Everything looks okay. Will anyone give me some info to help put me on track to get the codes resolved, especially the 67. I have no idea what might be causing that one. Thanks

 

[HISSIN50]

Jrichker has tech synopses of both codes.

Seems to me that 67 happens if you had the car in gear or had the A/C selector on.

See his 41/91 write up for more (it's much better than my off-the-top inarticulate ramblings).

Good luck.

 

[squeeeg]

67 will pop up if you don't have the clutch in or you aren't in park

41 and 91 both are saying that you are running lean.

 

[jrichker]

Code 41 or 91 - O2 indicates system lean. Look for a vacuum leak or failing O2 sensor.

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter.

Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts


Code 67 - clutch not depressed (5 speed) or car not in neutral or park (auto) or A/C in On position when codes where dumped. Possible neutral safety switch or wiring problem. This code may prevent you from running the Key On Engine On tests. You can generally ignore this code, since it has no effect on engine performance.

 

[bluewolf]

found the O2 sensor problem

Thanks for the excellent write-up JRichter. In my case I believe it was the orange ground wire. I reinspected my motor with a mirror when it was fully cool and managed to locate an orange ground wire behind the intake manifold coming out of a larger wire bundle. It was hanging loose. After regrounding it, the check engine light stopped coming on. I will pull the codes again after I check the timing to make sure everything is cool.

 

[troyGT03]

http://www.troublecodes.net/Ford/