I'm Stumped, Need Help!

[Bill wahler]

First a little about my car. It's a 1991 5.0 gt convertible 5 speed. Only upgrades is the explorer intake, explorer injectors, equal length headers, catless h pipe, and 3G alternator, all else is stock.
I have ran this configuration for years with no issues, but now I have a problem I can't seem to fix.
It started to run rough one day, idled fine, no backfire, between 2k-3500 rpm it misses. I did a tune up, all motorcraft parts, changed the fuel filter. Checked timing, still no change. What is odd is that if you unplug the alternator regulator it runs like a top.also the power accessories i.e. Top, windows and headlights make the problem worse. Once i plug it back in it goes right back to the miss. Alternator is putting out 14.5 volts. I had it checked by my local rebuilder and it tested good. I even swapped in a new one and same issue. I checked all wiring to the alternator and everything looks ok. I have literally been through this car. I have changed the tfi and distributor. Fuel pressure is good, stock regulator. I have traced wires looking for shorts. And have come up with nothing. I pulled the ecm, the caps were leaking a bit but since there was no board damage I replaced them and put it back in. I swapped in a good known maf, tps, and idle air with no change. Also there is no stereo equipment, msd, or other add ons that could be Causing this problem. Battery is good as well. I have cleaned all the grounds.
Any ideas would be greatly appreciated. I have owned this car for 18+ years, and this is the first time it has stumped me. Sorry if this is long winded. Thanks in advance!!!!

 

[FoxMustangLvr]

Stop blindly replacing parts. You should try pulling codes. Please tell me how you wired your 3G alternator. How long have you been driving the car with your 3g upgrade before this issue began?

 

[Bill wahler]

Codes are 11,44,94. 3G was installed about 3 years ago. 4ga. From alt post to solenoid. 4ga. Ground from alt. Case to core support. Wht/blk from d plug to stator. Original power wires were heatshrinked out of way.

 

[jrichker]

Codes are 11,44,94. 3G was installed about 3 years ago. 4ga. From alt post to solenoid. 4ga. Ground from alt. Case to core support. Wht/blk from d plug to stator. Original power wires were heatshrinked out of way.

Pull the alternator and have it tested. Most auto parts stores will doe this for free. You may have a shorted diode allowing the AC voltage that the alternator creates to get into the car's electrical system. Usually this runs the battery down after a while.

Did you dump bot the engine running codes and the engine not running codes?
The code 44 is not likely to cause the problem you describe.

Codes 44 & 94 - AIR system inoperative - Air Injection. Check vacuum lines for leaks, & cracks. Check for a clogged air crossover tube, where one or both sides of the tube clog with carbon.

Revised 21 Sep 2012 to correct the description of the process that sets the code and include Thermactor Air System diagram.

If you have a catalytic converter H pipe, you need to fix these codes. If you don't, then don't worry about them.

Code 44 passenger side air not functioning.
Code 94 driver side air not functioning.

The TAD solenoid/TAD diverter valve directs smog pump output to either the crossover tube attached to the cylinder heads or to the catalytic converters.

The O2 sensors are placed before the catalytic converters, so they do not see the extra O2 when the smog pump's output is directed to the converters or the input just before the converter.

The 44/94 code uses the O2 sensors to detect a shift in the O2 level in the exhaust. The smog pump provides extra air to the exhaust which raises the O2 level in the exhaust when the smog pump output is directed through the crossover tube.

When there is an absence of increase in the O2 levels when the TAD solenoid/TAD diverter valve directs air through the crossover tube, it detects the lower O2 level and sets the code.

Failure mode is usually due to a clogged air crossover tube, where one or both sides of the tube clog with carbon. The air crossover tube mounts on the back of the cylinder heads and supplies air to each of the Thermactor air passages cast into the cylinder heads. When the heads do not get the proper air delivery, they set codes 44 & 94, depending on which passage is clogged. It is possible to get both 44 & 94, which would suggest that the air pump or control valves are not working correctly, or the crossover tube is full of carbon or missing.

Testing the system:
Note that the engine must be running to do the tests unless stated otherwise. For safety’s sake, do test preparation like loosening clamps, disconnecting hoses and connecting things to a vacuum source with the engine off.

Disconnect the big hose from smog pump: with the engine running you should feel air output. Reconnect the smog pump hose & apply vacuum to the first vacuum controlled valve: Its purpose is to either dump the pump's output to the atmosphere or pass it to the next valve.

The next vacuum controlled valve directs the air to either the cylinder heads when the engine is cold or to the catalytic converter when the engine is warm. Disconnect the big hoses from the back side of the vacuum controlled valve and start the engine. Apply vacuum to the valve and see if the airflow changes from one hose to the next.

The two electrical controlled vacuum valves mounted on the rear of the passenger side wheel well turn the vacuum on & off under computer control. Check to see that both valves have +12 volts on the red wire. Then ground the white/red wire and the first solenoid should open and pass vacuum. Do the same thing to the light green/black wire on the second solenoid and it should open and pass vacuum.

Remember that the computer does not source power for any actuator or relay, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

The following computer tests are done with the engine not running.
The computer provides the ground to complete the circuit to power the solenoid valve that turns the
vacuum on or off. The computer is located under the passenger side kick panel. Remove the kick panel & the cover over the computer wiring connector pins. Check Pin 38 Solenoid valve #1 that provides vacuum to the first Thermactor control valve for a switch from 12-14 volts to 1 volt or less. Do the same with pin 32 solenoid valve #2 that provides vacuum to the second Thermactor control valve. Turning the ignition to Run with the computer jumpered to self-test mode will cause all the actuators to toggle on and off. If after doing this and you see no switching of the voltage on and off, you can start testing the wiring for shorts to ground and broken wiring. An Ohm check to ground with the computer connector disconnected & the solenoid valves disconnected should show open circuit between the pin 32 and ground and again on pin 38 and ground. In like manner, there should be less than 1 ohm between pin 32 and solenoid valve #2 and pin 38 & Solenoid valve #1.

The following computer tests are done with the engine running.
If after checking the resistance of the wiring & you are sure that there are no wiring faults, start looking at the solenoid valves. If you disconnect them, you can jumper power & ground to them to verify operation with the engine running. Power & ground supplied should turn on the vacuum flow, remove either one and the vacuum should stop flowing.

Typical resistance of the solenoid valves is in the range of 20-70 Ohms.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

If you have a catalytic converter H pipe, you need to fix these codes. If you don't, then don't worry about them

 

[Bill wahler]

I did have the alternator checked, both on and off the car, it checked fine. I replaced it with another to rule it out, and had no change. The smog pump and crossover pipe are long gone, and the h-pipe is catless.
When I dumped the codes, it was key on engine off, I disregarded the 44/94 as they have been there for years after the smog equipment was deleted. At the time I had plugged the 5/8 holes in the back of the stock e7 heads where the tubes has been with plugs.
I will redo the test with engine running and report back with the findings. Thanks for the replies guys, I really appreciate it.