I believe this is called a Thermac Switch.
Well I found out that the Thermac switch in the photo is staying in an open state allowing a major amount of air into the throttle body and IMO could be called a vacuum leak.
I put the stock assembly on and hooked up the Thermac switch hose like I always do and then set minimum idles speed.
.Is it really supposed to allow that much air into the throttle body at all times or is that a leak. I'm struggling with SMOG so really need to know.
Thanks

.

How hot is it?

Thermac supplies vacuum to the door motor on the air cleaner. Thermac is typically set at 100--120 degrees F.

When air in air cleaner housing is less than the thermac temp threshold, it will close or partially-close the air cleaner door. This brings heated air from the stove around the exhaust manifold into the air cleaner to prevent throttle icing and to help vaporize fuel.

When the air in the air cleaner is at or above the thermac threshold, the air door opens to allow cold air in for better performance.

So, yeah, it could be leaking air into the port on the throttle body when engine compartment or air cleaner temperature is high enough. Not a problem.

What are you failing for at emissions? NOx?

Yes, very high NOx.
Since this test I have had a new CAT installed but if it fails again I'm tempted to block off the air being drawn through the Thermac Switch in a way that is not obvious to the testing personal . Then reset IACV and Minimum Idle Speed and try it again.

High NOx, high HC.

First Guess: Defective cat, defective EGR. Do you have an air pump, and does it work including the upstream/downstream valving?

Second Guess: You can deliberately screw-up the Thermac, but it won't accomplish anything useful.

When NOx is too high your combustion temp is very high. To fix that you need to retard the timing. All you need to do is disconnect the spark advance wire, like when you set base timing. I think the single black wire has a pink stripe on it? The connector is located near the master cylinder or the heater box. Can't remember which side. I've moved my harness around so my car is not a good example anymore. Anyways, I always failed for NOx and then would just pull the plug and go for a retest. Passed every time.

I appreciate that but unhooking the EST wire sets a engine light with my car and timing has to be stock 6* BTDC or it fails.
I'm just praying the new CAT does it. With the Thermac Switch creating such an unbridled amount of air flow its possible the ECM is compensating with a richer fuel mixture and causing trouble. If I could find a new Thermac Switch I would replace it.
The EGR valve and EGR Sensor are both brand new. So are the plugs , plug wires ,Coolant Temp. sensor, O2 sensor , Canister Purge valve and hoses, oil and filter are all brand new.
The smog pump is about 3 years old .
I really appreciate your help because if I cant find the problem the SMOG guys that CA trusts to find the problem start charging for the diagnoses at $260.00 for the first to hours and then $100.00 for every hour after that. One So called SMOG Repair shop said it has taken him up to 10 hours to find the problem. I all most laughed in his face telling him he would have to stop after 3 hours because that all I could afford.
I'm just so sick of all this.
Like I said thanks for all the help.

Ron. Try setting it to 4 degrees next time. That is within allowed variations.
It will help with the nox levels but I think you have other issues.

I'd expect the cat to have an effect on the high HC; especially if the air pump and diverter system works properly; and the rest of the feedback fuel system is within range. High HC is often be the result of misfire; but I don't see other signs of misfire in your test results. Let us hope that in this case, high HC is the result of a poisoned/overheated catalyst.

Compare the amount of air going through the Thermac to a disconected vacuum hose at the inlet to the Thermac. First Guess: The Thermac is not that big of a vacuum leak. If it's somehow defective in a way I don't understand...that's another story. Pull the vacuum supply hose off of the Thermac, and plug the vacuum hose. Does the high NOx go away???

Second Guess: If the thermac is a vacuum leak leaning the engine, the feedback fuel injection would richen the mixture, then close down the IAC to maintain idle speed. There'd be no difference in NOx, but the scan tool would indicate your fuel trim numbers are high, the ECM was in rich-command, and the IAC was more-closed than expected. As said, NOx is a product of high combustion temperature, and EGR was specifically designed to combat NOx. It makes sense to verify the EGR system, INCLUDING the exhaust passages in the cylinder head and intake manifold (they can plug with carbon so they don't pass exhaust gas) so even if the EGR valve works, there's no exhaust gas getting to the fuel/air mixture. Have you tested for vacuum at the valve at fast-idle? Have you seen the valve move in response to vacuum? If the EGR valve can be manually moved at idle, does idle quality suffer? (It should, EGR at idle makes for engine shake--which is why EGR is not activated at idle.)

The emissions test does not care how new the parts are. The emissions test passes or fails based on HOW THEY WORK. I get the sense that you have not tested these components.

A scan tool is your friend.

Can't imagine the Thermac having much of an effect on emissions.

Ron, the stock TBI base timing is 0* BTDC. I'm surprised that the Cali smog tech didn't pick up on that as they are supposed to check it.

Note that the higher base timing will increase HC and NOX.

RBob.

I just learned something there. I'm more familiar with TPI. 6 degrees BTDC is the stock base timing set up for a TPI car.

yaj15

Took a quick look at your test results. The exhaust is showing lean condition condition by the presence of excess O2 in the exhaust stream (1.1 to 1.3%) The high HC numbers indicate misfire or bad combustion in one or more cylinders. The O2 Sensor will detect extra O2 in the exhaust stream and additional fuel is added by ECM - making HC problem even worst.
As mentioned previously verify that base timing is set correctly - TBI cars are 0 deg - CAL spec allow +/-2 deg variance. Over advancing timing and non functional EGR will drive NOx numbers. High combustion temperatures due to advanced timing and carbon build up will result in high levels. A CAT replacement is last resort - make sure that engine is running at its best. AIR system is only active during cold and WOT so it is out of this picture during 15/25 mph test.

Do not worry about thermac - it is only used when inlet airstream is cold to activate diverter flapper. During the test air is almost always hot. Just make sure that all vacuum tubes are connected to satisfy visual inspection rules.

Good luck with it.
//RF

The man running the test is the same guy for the last 8 years. He is adamant about the 6* and has checked it at two different sources. I was still in doubt but finally took a look carefully at my Chiltons and sure enough = 6* at 700 rpm. I preform the IACV reset then set minimum idle speed with EST wire disconnected to 700 rpm.
Timing at 6* and the stock components installed including the Thermac switch.
Tomorrow I will perform a few tests and get back to you guys. Thanks tremendously for all the help.
But the way where can I buy a different Thermac switch. Cant seem to find one.

Ron

Thermac switches have been discontinued and only a few generic later models are still available. Expect to pay top dollar!! Standard motor parts SMP has a universal replacement: STANDARD MOTOR PRODUCTS Part # ATS3 {#213112, 213114, 6484244, 6484587, E3241, E32414, E3243} - Check Rock Auto

Your friend and Chilton manual are wrong - if you have TBI (throttle body injection) car base timing per factory manual is 0 deg with EST plug open. The 6 deg is for TPI (tuned port injection) equipped engines.

Photo is from GM FSM

//RF

Thank you
I went on line and looked at the "89 5.0 E AUTOMATIC & MANUAL TRANS EMISSIONS DECAL (DCA)"
for my car. Here's what I found everywhere. I made a copy of it and have a shop or two to visit tomorrow. I'm just trying to gather some physical proof and then order the decal for the one missing on my car.
My vin is E so this is a match.

Turns out the photo above is correct for a Federal vehicle.


The new SMOG shop I went to today also has the car put at 6* BTDC.
He said to go to GM Dealer and see if I could get the sticker there . They said is no longer produced.
I'm taking a trip to Pick n Pull tomorrow.


I also talked to the SMOG technician about the Thermac switch and he said it is fine and working the way it should.


I know I'm making a big deal out of this but for me it is.

Up date
I finally found a CA legal emissions label for my exact car at Classic Industries . It was not in the online catalog. Its part # DT719 = http://www.classicindustries.com/pro...rts/dt719.html
I'm still going to pick n pull because the deadline is the July 5th.
Now I need a photo of its exact location for a car with A/C.

Up date,
I touched the Thermac switch moving the lever a bit and it closed. No more airflow gushing into the intake from that port.
Replaced the CAT and broke it in for a while. Took it into SMOG set at 4* and passed.

I also have the Emissions sticker to put on the car that says 0* is the stock setting.
He will honor it starting 2 years from now when I do this again.


Thanks everyone for there help.

I know this is an old thread but I was doing some vacuum system checks and found that on my THERMAC air temperature sensor leaks vacuum in all positions. After plugging it off my little stutter and occasionally and embarrassingly stall at a stop light quit. I did find online a replacement: I havent ordered it yet but plan too at some point.

As read from the GM User's manual, here is how it should function:

Hot Air Delivery Mode: When the temperature is below 86º F, the sensor allows vacuum to the motor and the damper door will be up, shutting off outside air and allowing only heated air from the exhaust manifold to enter the air cleaner.

Outside Air Delivery Mode: When the temperature is above 131ºF, the damper door drops down and only outside air enters the air cleaner.

Regulating Mode: Between 86ºF and 131ºF the damper door allows both heated and outside air to enter the air cleaner.

I did apply some soap and bubbles and applied positive pressure to the inlet. I found what appears to be a little pin hole on top of the small vacuum vessel on the THERMAC (see attached photo). Sorry for the focus issue and the bubbles formed on the part which distorts it further but right on top of the plate there is the smallest hole. I believe this is an intended pressure relief that allows the damper to drop once the THERMAC reached 131ºF (to prevent hot exhaust air and switch completely to Outside 'cold' air.

Assuming my theories are correct regarding the pressure relief opening? I did cycle the bi metal plunger up and down with a screw driver and at all positions, I was able to pull vacuum through. Based on my positive results of plugging it off it only leads to replacement.

Thoughts?

Thanks for looking.

-Chris