Bypass And Diverter Valve Questions

7991LXnSHO · Sep 2, 2012

Time for a new link with specific questions. I am looking at jrichker's and tmoss's emission diagrams at this link.
http://www.stangnet.com/mustang-forums/threads/high-idle-rough-start.860113/page-3

1. Do the air diverter valve and air bypass valves have any electrical connections to them? I only see power to the solenoids in the diagrams.

2. My computer puts out code 94 and 44. My Tad and Tab have power and vacuum. I have the lines to the bypass valves blocked off since the air pump and valves are missing.
How does the computer know the valves are missing, or do I have bad tad and tab solenoids?

Question #3, When I get replacement parts for the missing ones, will the valves and hoses clear and work with my headers? I do not want a melted mess.
Thanks!

jrichker · Sep 2, 2012

The TAD & TAB solenoid are the only thing that has power to them. The computer provides a ground that turns each solenoid off one at a time.

The 44/94 codes are usually due to a blocked crossover tube, check valve stuck closed or insufficient smog pump output. Remove the crossover tube and see if it is filled with carbon or sludge. You may need to devise some sort of Roto-Rooter gadget to check and clean the crossover tube. While you are at it play around with the crossover tube outlet to make sure that it is getting output from the smog pump.

7991LXnSHO · Sep 2, 2012

Oops, I must not have been clear. Except for TAD TAB ,wires and vac lines, the rest of the smog pump system is MIA. I hope the air pump, valves, hoses, head cross over tube, and cats are in a box in a previous owner's garage. They are not in my posession. I hooked up the solenoids to vac and power and hoped it would satisfy the computer for now. The vac lines are capped off where they should hook up to the valves. Do the solenoids have the ability to tell something is missing?
Also will I have clearance issues with the headers when I get the parts replaced?

jrichker · Sep 3, 2012

The TAD solenoid/TAD diverter valve direct 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 converters.

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 direct air through the crossover tube, it detects the lower O2 level and sets the code.

7991LXnSHO · Sep 4, 2012

So until I replace all the missing parts, I will get the code, right? I should have subtracted the from the purchase price of the car. At least I have a picture of what is missing to give the salvage yard folks. I have seen some of these parts in catalogs.

7991LXnSHO · Sep 4, 2012

Oh, is this hurting my performance by messing up my rich/lean mixture?

jrichker · Sep 4, 2012

7991LXnSHO said:
Oh, is this hurting my performance by messing up my rich/lean mixture?

No.

The test only runs when the the engine is first started. A cold start causes the computer to richen up the mixture to make the engine run smoother until it warms up. With a cold start, it diverts air through the crossover tube to the exhaust ports. The excess air consumes the extra fuel. Within 60-180 seconds, the computer goes into closed loop and directs air to the tube that feeds air to the converters downstream of the O2 sensors. It has no effect on driving unless you are racing with a stone cold engine. I wouldn't recommend racing with a cold engine, so it's a non issue.

7991LXnSHO · Sep 10, 2012

I was just told due to EPA regulations a bigger salvage yard can not sell exhaust parts. I explained I was ordering a new cat x pipe elsewhere. The rest of the parts I want are emission controls. It did not help. Is this for real? I do not live in CA.

Blucifer99 · Mar 28, 2019

jrichker said:
No.

The test only runs when the the engine is first started. A cold start causes the computer to richen up the mixture to make the engine run smoother until it warms up. With a cold start, it diverts air through the crossover tube to the exhaust ports. The excess air consumes the extra fuel. Within 60-180 seconds, the computer goes into closed loop and directs air to the tube that feeds air to the converters downstream of the O2 sensors. It has no effect on driving unless you are racing with a stone cold engine. I wouldn't recommend racing with a cold engine, so it's a non issue.

what position does the diverter valve go in when it fails to recieve vacuum? does it feed the heads or does it dump to the cats? Im running megasquirt and would like to keep the air flowing to the cats.. thats why im asking if the valve directs air to the heads with no vacuum or does it direct to the cats without vacuum?

jrichker · Mar 29, 2019

Blucifer99 said:
what position does the diverter valve go in when it fails to recieve vacuum? does it feed the heads or does it dump to the cats? Im running megasquirt and would like to keep the air flowing to the cats.. thats why im asking if the valve directs air to the heads with no vacuum or does it direct to the cats without vacuum?

The default should be to direct the air to the cats.

To confirm this fact, do the following test:
Disconnect the vacuum line to the TAD diverter valve and disconnect the plumbing that feeds air to the cats. Start the engine and see if you feel air coming out of the plumbing that feeds air to the cats.

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