Fixed Idle Problem, But Now Stalling At Abrupt Stops?

All it takes is 5 minutes or so. Turn the lights on while the battery is disconnected to drain down anything that might have a small keep alive voltage in it to preserve settings. Typical things like the clock, radio or XM receiver might use this function.
 
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Timing was set to 10 degrees. I bumped it up to more like 12-13. Forgot to plug the spout back in so it really ran crappy until I remember and plugged it back in. Seems to run good. Almost a little "valve-ish", but I think the recommendation is to run high test with timing advanced?

Also pulled my plugs and put in Autolite 25's. Guy before me put in NGK, but I have no idea how long they've been in there. According to him less than 5K miles. All plugs looked the same which is good. Kinda of a lightish red on the probe. I think this is a sign of running rich which is true.

Going to put a few more miles on it then swap out MAF to see if I can get rid of 41 and 91. I also have an after market larger MAF (not a brand I'm familiar with but it was $300). The diameter is 4" so I'll need to pick up a reducer before I can install.

Do you think the TAD can throw code 41 and 91? I read at least two people cured these codes by replacing the TAD.
 
Let's look at the Thermactor Air System (smog pump) first.

Thermactor Air System
Some review of how it works...

Revised 6 Oct 2014 to add location of TAB & TAD control soelnoids

The Thermactor air pump (smog pump) supplies air to the heads or catalytic converters. This air helps break down the excess HC (hydrocarbons) and CO (carbon monoxide). The air supplied to the catalytic converters helps create the catalytic reaction that changes the HC & CO into CO2 and water vapor. Catalytic converters on 5.0 Mustangs are designed to use the extra air provided by the smog pump. Without the extra air, the catalytic converters will clog and fail.

The Thermactor air pump draws air from an inlet filter in the front of the pump. The smog pump puts air into the heads when the engine is cold and then into the catalytic converters when it is warm. The Thermactor control valves serve to direct the flow. The first valve, TAB (Thermactor Air Bypass) or AM1 valve) either dumps air to the atmosphere or passes it on to the second valve. The second valve, TAD (Thermactor Air Diverter valve or AM2 valve) directs it to the heads or the catalytic converters. Check valves located after the TAB & TAD solenoids prevent hot exhaust gases from damaging the control valves or pump in case of a backfire. The air serves to help consume any unburned hydrocarbons by supplying extra oxygen to the catalytic process. The computer tells the Thermactor Air System to open the Bypass valve at WOT (wide open throttle) minimizing engine drag. This dumps the pump's output to the atmosphere, and reduces the parasitic drag caused by the smog pump to about 2-4 HP at WOT. The Bypass valve also opens during deceleration to reduce or prevent backfires.

Code 44 RH side air not functioning.
Code 94 LH side air not functioning.

The computer uses the change in the O2 sensor readings to detect operation of the Thermactor control valves. When the dump valve opens, it reduces the O2 readings in the exhaust system. Then it closes the dump valve and the O2 readings increase. By toggling the dump valve (TAB), the computer tests for the 44/94 codes.

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.


thermactor-air-system-65-gif.50636



Computer operation & control for the Thermactor Air System
Automobile computers use current sink technology. They do not source power to any relay, solenoid or actuator like the IAC, fuel pump relay, or fuel injectors. Instead the computer provides a ground path for the positive battery voltage to get back to the battery negative terminal. That flow of power from positive to negative is what provides the energy to make the IAC, fuel pump relay, or fuel injectors work. No ground provided by the computer, then the actuators and relays don't operate.

One side of the any relay/actuator/solenoid in the engine compartment will be connected to a red wire that has 12-14 volts anytime the ignition switch is in the run position. The other side will have 12-14 volts when the relay/actuator/solenoid isn't turned on. Once the computer turns on the clamp side, the voltage on the computer side of the wire will drop down to 1 volt or less.

In order to test the TAD/TAB solenoids, you need to ground the white/red wire on the TAB solenoid or the light green/black wire on the TAD solenoid. The TAB and TAD solenoid are located on the passenger side shock strut tower. Uneducated owners sometimes remove them to get more HP. This does not work, it just causes 81 & 82 codes.

For 94-95 cars: the colors are different. The White/Red wire (TAB control) is White/Orange (Pin 31 on the PCM). The Green/Black wire (TAD control) should be Brown (pin 34 at the PCM). Thanks to HISSIN50 for this tip.

Testing the system:

To test the computer, you can use a test light across the TAB or TAD wiring connectors and dump the codes. When you dump the codes, the computer does a self test that toggles every relay/actuator/solenoid on and off. When this happens, the test light will flicker.

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 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. Starting the engine 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.

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. 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.

Theory of operation:
Catalytic converters consist of two different types of catalysts: Reduction and Oxidation.
The Reduction catalyst is the first converter in a 5.0 Mustang, and the Oxidation converter is the second converter. The Oxidation converter uses the extra air from the smog pump to burn the excess HC. Aftermarket converters that use the smog pump often combine both types of catalysts in one housing. Since all catalytic reactions depend on heat to happen, catalytic converters do not work as efficiently with long tube headers. The extra length of the long tubes reduces the heat available to operate the O2 sensors and the catalytic converters. That will cause emissions problems, and reduce the chances of passing an actual smog test.


Now for the Chemistry...
"The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2. For example:

2NO => N2 + O2 or 2NO2 => N2 + 2O2

The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. For example:

2CO + O2 => 2CO2

There are two main types of structures used in catalytic converters -- honeycomb and ceramic beads. Most cars today use a honeycomb structure." Quote courtesy of How Stuff Works (HowStuffWorks "Catalysts")

What happens when there is no extra air from the smog pump...
As engines age, the quality of tune decreases and wear causes them to burn oil. We have all seem cars that go down the road puffing blue or black smoke from the tailpipe. Oil consumption and poor tune increase the amount of HC the oxidation catalyst has to deal with. The excess HC that the converters cannot oxidize due to lack of extra air becomes a crusty coating inside the honeycomb structure. This effectively reduces the size of the honeycomb passageways and builds up thicker over time and mileage. Continuous usage under such conditions will cause the converter to fail and clog. The extra air provided by the Thermactor Air System (smog pump) is essential for the oxidation process. It oxidizes the added HC from oil consumption and poor tune and keeps the HC levels within acceptable limits.

Newer catalytic converters do not use the Thermactor Air System (smog pump) because they are designed to work with an improved computer system that runs leaner and cleaner
Newer catalytic converters do not use the Thermactor Air System (smog pump) because they are designed to work with an improved computer system that runs leaner and cleaner
They add an extra set of O2 sensors after the catalytic converters to monitor the oxygen and HC levels. Using this additional information, the improved computer system monitors the health and efficiency of the catalytic converters. If the computer cannot compensate for the added load of emissions due to wear and poor tune, the catalytic converters will eventually fail and clog. The periodic checks (smog inspections) are supposed to help owners keep track of problems and get them repaired. Use them on an 86-95 Mustang and you will slowly kill them with the pollutants that they are not designed to deal with.
 
Grrr, trying to fix one this resulted in creating another probably.

Drove car today post installing new plugs and I'm getting an exhaust leak sound from the motor. I did advance the timing slightly to around 12 the day prior. Drove it and it ran pretty good. That night I swapped out plugs. Properly gaped and I always hand thread them all the way in, then tighten. I will say I had to squeeze my arm in when replaying #3 and #4 and my arm was definitely pressing against the metal tube that goes around the back of the engine. That's the only thing that I can think it could possibly be. Maybe I tweaked one of the seams???

Symptom- can't hear leak idling, but can if you bring RPMs up slightly. Sounds like rear passenger side of the engine. I'm also getting my surging/hanging idle probably again, but worse than I remember my initial problem. Now I have to focus on fixing this before I can do anything else.

I did put the timing back to 10 degree just to rule that out. No change.

I got some JB weld just to see if the leak is coming from one of the seams. The tube that goes around the back of the engine seems pretty solid, but definitely has surface rust.

What else could this be? Only change was plugs and timing???
 
Check plug wire order and that's fine. Can't imagine this is something random.

How bad is it to drive without the SPOUT? I'm sure I'm not the only one that has forgotten. I seem to even recall someone saying they run there car without one. I only drove down the street and back. Then once I plugged in I put 2-3 miles on it and it ran fine, no ping or exhaust sound. I really don't want to swap plugs out again, but that would at least take me back to the beginning. I'm running 25s gaped at .054. I double checked gap, but I guess it was late and I might have not gaped one correctly. This started as soon as I swapped plugs. So it's either that, I disturbed something or this is completely unrelated.
 
I drove my car around for a week with the SPOUT out while I was trying to figure out an issue (remote start tach signal wire was grounding out the coil before the TFI could causing a horrible misfire) All it did was keep the PCM from advancing or retarding the timing. You ran it at 12 degrees regardless of driving condition. No harm.
 
Thanks!

Pulled the drivers side plugs and checked gap again. At least on one side- plug wires, gap and tightness all good.

I'll do the harder side tomorrow. My hands hurt.

Worse case I'll have to put the NGKs back in- they seem to be gaped more than .054 and the electrode is pointy which I'm assuming they are supposed to be.
 
Just so you know there is a box in the fuel tank that's around the fuel pump. This box has been known to separate from its fix position around the fuel pump. When this happens you will experience problems like stalling during sustained abrupt stops and hard turns at low and high speeds. Typically you can hear the displaced part moving around in the tank as the fuel sloshes around. The lower the fuel level, the more likely you will have the issue especially around the quarter tank range. Parking on a steep down hill slope with quarter tank level can prevent starting if that condition is present. I hope that it's not your problem but if it is a new fuel tank will solve it.
 
Just so you know there is a box in the fuel tank that's around the fuel pump. This box has been known to separate from its fix position around the fuel pump. When this happens you will experience problems like stalling during sustained abrupt stops and hard turns at low and high speeds. Typically you can hear the displaced part moving around in the tank as the fuel sloshes around. The lower the fuel level, the more likely you will have the issue especially around the quarter tank range. Parking on a steep down hill slope with quarter tank level can prevent starting if that condition is present. I hope that it's not your problem but if it is a new fuel tank will solve it.

Thanks, I'll keep that in mind.
 
I drove my car around for a week with the SPOUT out while I was trying to figure out an issue (remote start tach signal wire was grounding out the coil before the TFI could causing a horrible misfire) All it did was keep the PCM from advancing or retarding the timing. You ran it at 12 degrees regardless of driving condition. No harm.

When I drove my car without the SPOUT the engine definitely sounded like crap. Valves seemed to ping quite a bit. When I plugged it back in, everything sounded good. Is that normal with SPOUT disconnected?
 
Using a mechanics stethoscope, I'm 90% sure I have a header leak next the passenger's side and firewall. I've always suspected a slight exhaust leak but never really spent time chasing it. I'm going to fix this before getting back to chasing my idle/stall issue. I'm hoping fixing this cures my code 41 and 91 (although I wouldn't think a leak at one header would throw both codes) as well as my remaining idle problem. Definitely got side tracked chasing my plugs thinking that's what caused the ticking. Stupid luck.
 
Was a header gasket leak. New gasket in and also replaced the plugs and wires. Runs good (at least in my garage). I'll take it out for a ride later and get back to chasing my original problem where the car wanted to stall at abrupt stops and would struggle hard to stay running. I doubt a new header gasket and plugs and wires cured this.

Very strange my problem starts after I've been driving for 10 or 15 mins and the idle literally bounces up and down (quickly) to the absolute point of stalling then climbs back up.

I'll report back later this week.
 
Check fuel pressure, the fuel pump could be going bad. I have one that went bad I could drive it for about five minutes then it would quit, I would let it cool for about 30 minutes then I could drive it for about another five minutes. Is it the original fuel pump?
 
I drove the car last night for about 15 minutes to get nice and warm. Now car wants to stall at every stop (not just abrupt braking anymore or putting a load on car like when you turn wheel at low speed).

- checked TPS again- .94
- pulled IAC, started car and idle was at 900ish which is strange it was so high since I set this weeks ago. I backed it down to 600ish, shut car off and plugged in IAC. Started back up and seemed to be around 800-900ish. After a few minutes it seemed to drop down to 700ish. Normal?
- Ran codes off- clean
- Ran codes running- 41 and 91 again!

I haven't taken out again for a test run since tweaking the idle, but it seems odd car wants to stall at a stop, then I back off idle screw probably 3/4 of a turn to bring idle back down to 600ish with IAC unplugged. I would think the opposite that I should have increased the idle to help solve my stall problem?

Any ideas? Car runs great except at a stop. Is it the IAC or TPS that regulates idle at a stop? My IAC and TPS are brand new.

I'm probably going to swap out MAFs and see if that changes anything.
 
VSS only if you have cruise?
All the Mass Air computers have VSS as a factory installed sensor. If it is missing or non-functional, it sets code 27 or 29.

Mass Air conversions may or may not have the extra wires run depending on how well the conversion was done.