Stupid Checking Myself After A Tuneup (codes Related, Long)


GTFO you fat, heavy bastard
10 Year Member
Oct 21, 2005
st. louis, mo
so ive been noticing my car not really running right for a while, and since i had to put my cats back on a couple weeks ago for inspection, i decided when i put my o/r h-pipe back on i would dig into things, and now i just want to make sure of things that i think i know the answers to. i tend to over think things sometimes, so i want to check myself and maybe dumb this down some.

i was getting a 41/91 as my only codes before, and while redoing my exhaust, i did the following:
new fuel filter
cleaned/flushed injectors (used 24's, and one was clogged up pretty good)
new plugs and wires
swapped my kirban fpr for a stock-replacement i had laying around
new 02's (i had checked voltages about a month before and they didnt seem to fluctuate like they should)
new pcv and filter (the filter was missing before, dunno how that happened, but no more oil in the upper intake now)
air pump delete

after doing all that (and cleaning the injectors a second time cause i was still getting a 41 but not a 91), and reseting the idle and tps (which the one i had apparently took a crap, so new one of those), it runs waaaay better, but now i got different codes: 12, 44, and 94 (the 41/91 are gone, which is what i was really trying to fix). the last two i guess are because the air pump is gone, which is odd since i used to get those when i routed the air pump directly to the cats a couple years ago, but i didnt get them with the 41/91 showing up, so im guessing the lean codes covered up the 94/44?

the 12 i still gotta mess with, i know its iac related and its probably clogged up somewhere. the thing whistles like a sob when its unplugged, and there is a slight idle surge (and it whistles when it closes and the idle drops), so ill take it off tomorrow and see if i cant clean it out, not too worried with this one, been down this path before.

the last "problem" i have is with the fpr, the stock replacement i had sitting around would be at about 40psi with vacuum at idle, but without the vac it would shoot up to 50(!). i just put a brand new one on it, and its 40 with vac and 45 without. i know its supposed to be in the 38-40 range unplugged, so is this one fubar too, or do i have something else going on? i had my kirban adjusted right (~39 vac off, i forget what it was when vac was on), the only real reason i swapped it is because it makes slight contact with the egr valve even with a 3/8's intake spacer, doesnt keep things from sealing up, but i figured while i was in there i would make things simpler. i guess ill just put the kirban back on? other than the slight idle surge, which i think is an iac problem, it seems to run fine?
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SN Certified Technician
Mar 10, 2000
Dublin GA
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 RH side air not functioning.
Code 94 LH 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)

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


GTFO you fat, heavy bastard
10 Year Member
Oct 21, 2005
st. louis, mo
well after messing with cleaning the iac yesterday (wasnt much if anything to clean out), im still getting a code 12, and now im back to getting a 91 (which must cover up the 44/94, cause theyre gone). running a balance test (which im not sure im doing right with the scanner i have because i can only get it to do one level) shows cylinder 4 out of whack. it also wants to stall every so often coming to a stop, and when it doesn't it surges, so ill have to go on the hunt for that one (either iac or tps im guessing, ill go through the checklist)
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