Chasing A Power Loss Issue

Yeah guys, I'll try the MSD because it was the first on you guys list! I don't know maybe she is drunk! I was wondering if anybody would catch that. Its not a 6btm but do really think I do not need my MSD @Onefine88 ?

Finally got around checking the codes. Twin newborns have been suckling the life out of me but here are my codes.
Key on running
41
Key on not running
15
114
41
91
I haven't taken off the May Suddenly Die but what do you think my next testing step should be?

That would definitely explain a lot of the problems I am Having... I will test that sensor and see where that lands me @a5literma

ECT changed to known good unit
Fuel pressure 40 psi
Smoke vacuum test
Stock ignition wired in and it runs worse. Breaking up at wot 5k. Check engine light wit same codes. Anything else should I check?

Extensive testing done today. Cylinder balance test done and it saw a problem in number 8 cylinder, pulled the plug and found a cracked porcelain. Replace it and I no longer have a code 91. Got her up to temperature again and it saw a problem with number 4 and 7. Checked those plugs and saw no issues. I've been reading a lot about an orange wire that is a ground for the o2 sensor. From what I'm reading, it's supposed to be grounded on either the head or intake manifold. Mine is grounded through one of the bell housing bolts to the block. Really can't see that being an issue but maybe I'll move it. With my still existing code 41, it's bringing me to my passenger side o2. I will follow O2 Sensor Codes 41/42/91/92 Troubleshooting instructions and go from there. Any more advise?
@A5literMan it's on my list next and @MY 85 GT distributor is slaughterzone new and I'll double check my maf. I did clean it but saw no change

@jrichker that checklist is priceless! I'll get to the bottom of it, it's just a matter of time. Speaking of which, please give me a class on how oNE would check the resistance of my o2 sensors. I have a multimeter but I'm no electrician! Here's some of your old info pulled from another thread I will be using.
Code 41 or 91. Or 43 Three digit code 172 or 176 - O2 sensor indicates system lean. Look for a vacuum leak or failing O2 sensor.

Revised 6-Oct-2014 to improve code 41 description due to clogged Thermactor air crossover tube

Code 41 is a RH side sensor, as viewed from the driver's seat.
Code 91 is the LH side sensor, as viewed from the driver's seat.

Code 172 is the RH side sensor, as viewed from the driver's seat.
Code 176 is the LH side sensor, as viewed from the driver's seat.

Code 43 is not side specific according to the Probst Ford Fuel injection book.

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

Testing the O2 sensors 87-93 5.0 Mustangs
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.

Disconnect the O2 sensor from the harness and use the body side O2 sensor harness as the starting point for testing. Do not measure the resistance of the O2 sensor , you may damage it. Resistance measurements for the O2 sensor harness are made with one meter lead on the O2 sensor harness and the other meter lead on the computer wire or pin for the O2 sensor.

Backside view of the computer wiring connector:


87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
The computer pins are 29 (L\RH O2 with a dark green/pink wire) and 43 (LH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
The computer pins are 29 (LH O2 with a Gray/Lt blue wire) and 43 (RH O2 with a Red/Black wire). Use the ground next to the computer to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


Testing the O2 sensors 94-95 5.0 Mustangs
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 red/black wire) and 27 (RH O2 with a gray/lt blue wire). Use pin 32 (gray/red wire) to ground the voltmeter. The O2 sensor voltage should switch between .2-.9 volt at idle.


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.

Testing the O2 sensor wiring harness
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. Using theLow Ohms range (usually 200 Ohms) you should see less than 1.5 Ohms.

87-90 5.0 Mustangs:
Computer pin 43 Dark blue/Lt green – LH O2 sensor
Computer pin 29 Dark Green/Pink – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Dark blue/Lt green wire in the LH O2 sensor harness and the Dark blue/Lt green wire on the computer pin 43
From the Dark Green/Pink wire on the RH Os sensor harness and the Dark Green/Pink wire on the computer pin 29

91-93 5.0 Mustangs:
Computer pin 43 Red/Black – LH O2 sensor
Computer pin 29 Gray/Lt blue – RH O2 sensor
Disconnect the connector from the O2 sensor and measure the resistance:
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 43
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wire on the computer pin 29

94-95 5.0 Mustangs:
Computer pin 29 Red/Black – LH O2 sensor
Computer pin 27 Gray/Lt blue – RH O2 sensor
From the Red/Black wire in the LH O2 sensor harness and the Red/Black wire on the computer pin 29
From the Dark Green/Pink Gray/Lt blue wire on the RH Os sensor harness and the Gray/Lt blue wireon the computer pin 27

There is a connector between the body harness and the O2 sensor harness. Make sure the connectors are mated together, the contacts and wiring are not damaged and the contacts are clean and not coated with oil.

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

Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness.

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

Code 41 can also be due to carbon plugging the driver’s side Thermactor air crossover tube on the back of the engine. The tube fills up with carbon and does not pass air to the driver’s side head ports. This puts an excess amount of air in the passenger side exhaust and can set the code 41. Remove the tube and clean it out so that both sides get good airflow: this may be more difficult than it sounds. You need something like a mini rotor-rooter to do the job because of the curves in the tube. Something like the outer spiral jacket of a flexible push-pull cable may be the thing that does the trick.

If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true if you are having idle problems. The small plastic tubing is very brittle after many years of the heating it receives. Replace the tubing and check the PVC and the hoses connected to it.

Thanks in advance @jrichker

@MFE92 do you think k my aeromotive 340 is dying. It's new replaced last year in preparation for v3. I will be testing today

My my my! Well after 2 days of testing everything then finally going to the o2 sensors I found my problem. I had a low resistance from passenger side o2. I swapped it out for a known working unit and voila, no more cell and she runs like a bat outta hell! Sucks that I had to check everything twice but now I know everything works as it should. Once again @jrichker that checklist is priceless and gave me all the tools I needed to figure things out. I can now put it away for the winter knowing everything works. Thanks all again and happy motoring!