I've read numerous threads on this error code but I want to understand one aspect of the system.

I posted some questions inadvertently on an old thread on the Bronco Forum.
Pushing aside diagnostics (Solenoids/Vacuum/Tab/Tad/Check Valves/Circuits) I'm trying to understand where the ECM gets its input from that make it set the 44 code and also specifically when the system on my 91 EFI model dumps air.

Relative to the behavior of the TAB on an EEC system The Haynes manual says "Proper dumping of air during periods of heavy load, extended idle or rapid deceleration. Caution:EEC models with fuel injection are much more tolerant to extended idle and deceleration conditions, air is not dumped unless the engine coolant temperature exceeds normal range".

On my vehicle ('91 5.8 EFI) when it's warmed up and idling the air is coming full blast out of the exhaust port just above the Folgers can and keeps "dumping" which seems to be in contradiction to what the Haynes manual suggests should be happening. Does this suggest TAB (Bypass valve) is not switching to enable air to be then moved either to the cat or the engine cross pipe via the diverter valve (TAD)? i.e check TAB Solenoid, vacuum etc.

I do have to fix a lower intake leaking gasket (small leak) and I'm thinking that is what is causing my slightly high idle. I'd like to diagnose code 44 before I do that if possible although it looks like access to the check valves and TAD is only possible when the intakes are off, although I can certainly get to the TAB valve by removing the fender guard.

Comments/Suggestions?

 

Looking at the wiring diagrams the solenoids return ground via the ECM - 190 from TAB and 200 from TAD. At the ECM they are described as follows:
190 - Thermactor Dump Valve Feed
200 - Thermactor Diverter Valve Feed.

I see the following codes defined in the Ford Code reader Book - KOER:
44 Thermactor air system fault
45 Thermactor air upstream
46 Thermactor air is not bypassed

So what is the ECM using to push out this seemingly catchall code?

 

see miesk5 post #9, and 12, in link below
Code 44 - Idling too Rich - Please Help | Bronco Forum - Full Size Ford Bronco Forum

 

Thanks for that link. More interesting reading. I'm going to test the TAB/TAD solenoids first and then look at the vacuum lines & TAB valve. The one thing I have going on that I have not seen referenced in other posts is the continual "dumping" of air through the exhaust. That makes me believe it's TAB related as the default TAB status is closed (vent to atmosphere), which Haynes says only occurs when the engine coolant temperature exceeds the normal range. Of course if something is blocked downstream of the TAB valve from TAD to Intakes or CAT then I guess the air has to go somewhere.

 

The pump is pumping any time it is spinning, but air will only be sent to the engine or exhaust in a few circumstances. Default position = no vacuum applied to any of the solenoids, would be venting to atmosphere. That said, I have never noticed any noise from the system in operation under any circumstance.

The only way for the processor to check operation is to add air and then watch the O2 sensor for an appropriate change.

 

Here's what Haynes says. Pay particular attention to the Caution on EEC models with Fuel Injection:

EEC controlled bypass and diverter valve operation
5. The EEC controlled secondary air injection systems uses the same valves and air pump plumbing as the earlier version. And in fact, in addition to its own unique set of operating conditions, incorporates the same basic operating restraints as the other systems as follows:
a) Proper dumping of air during periods of heavy load, extended idle or rapid deceleration: Caution: EEC models with fuel injection are much more tolerant to extended idle and deceleration conditions, air is not dumped unless the engine coolant temperature exceeds normal range.
b) Proper diverting of air to the exhaust manifold during cold start, warming, and warm cold start conditions or to the converter in all other conditions by the diverter valve. BTW - they must mean intake manifold cross pipe as there is no exhaust manifold piping on '91 5.8 with EFI despite what's shown in the Ford Shop Manual.

Based on the above I would certainly not expect to feel air being dumped at cold start up for sure and it suggests dumping is the exception rather than the default. I would think air to the CAT would be more likely to be the default.

I can certainly force vacuum to the Bypass valve to see if dumping stops, after I get breakfast & it warms up and I do the normal solenoid testing.:-)

 

Sometimes I don't know what I am thinking...

You are correct that that the air is directed to the exhaust under most running conditions... I don't see any way for the processor to see this without the later model after cat O2 sensor.. I would still guess in the absence of any vacuum being applied air would be pumped to atmosphere to protect the CAT from overheating, but I could be wrong on that.

So... I would guess you have a vacuum leak, which you already know.

 

Air bypassing the whole system and simply being vented to atmosphere is the default condition, the whole purpose of air injection is to help the cats heat up after a cold start, once they are heated up continued air injection would cause them to overheat so air must be vented to atmosphere. Also once the EFI system goes into closed loop air injection at the motor would alter the A/F ratio seen at the O2 sensor so it can only be diverted downstream directly to the the cat or returned to atmosphere. There were multiple different plumbing configurations used over the years, some early models used spider manifolds connected to each port on the exhaust manifolds, but most of the cylinder heads were already internally manifolded to accomplish the same thing so a crossover tube connecting ports on the back of the heads was used, and on HD trucks the crossover pipe at the back of the motor connected to the exhaust manifolds instead.

 

Do you mean "During a cold start" rather than "after a cold start"? That would jive with other cars I have where the electric pumps only run briefly during startup pushing air into the exhaust manifolds. If so then I need to ascertain why it's being dumped at cold start. Regarding the mysterious code 44 - the air input at the Cat is after the 02 Sensor. The only other sensors involved are the ECT and IAT I believe. It's been suggested elsewhere that the code is pushed out as a last resort because the ECM is unable to make the necessary corrections. Could it be the A/F ratio which is too low at cold start, with air being dumped instead of some going to the intakes, which also causes high idle?

What is the logic for the Diverter valve? When is air needed in the intakes rather than the Cat which needs it during cold start? i.e. what prompts the ECM to energize the diverter valve?

Also the Haynes comment seems to imply that the ECM on the EFI models is able to manage the A/F ratio better, suggesting that dumping may not occur during extended idle after the engine has warmed up and is in Closed Loop. So timing of dumping after warmup is unclear on EFI models.
Caution: EEC models with fuel injection are much more tolerant to extended idle and deceleration conditions, air is not dumped unless the engine coolant temperature exceeds normal range.

 

I am making some corrections & comments after some research:

During Cold Start the O2 Sensor senses the extra oxygen content in the gases and sends low voltage to the ECM. The ECM ignores any O2 Sensor reading while the Thermactor is diverted to the upstream (Manifold Runner).
The above information is a summary from Ford Fuel Injection and Electronic Engine Control by Charles O. Probst. What a great book!

So - this does not change the diagnostics - Vacuum/Solenoids/Bypass Valve/Diverter Valve/Plumbing/One Way Valves. But it sheds more light on at least one time when you should not feel air being bypassed / expelled, and that's at startup from cold for sure. My current speculation is that because the ECM knows that it should be expecting low voltage from the O2 sensor while the engine is cold (ECT sensor tells it the engine is cold and otherwise it would not know to ignore the low voltage), and because it does not see the low voltage it concludes the Thermactor system is not functioning and throws code 44. When the ECT tells the ECM the engine is warm the Bypass system is opened (de-energized) and air is expelled. Then the ECM will react to O2 sensor readings.

 

I made a number of errors in my last post. As there have been no replies I edited the post to correctly reflect the Thermactor plumbing & behavior.