Help!! Thermostat Diagnosis

[Jeff]

First off, I drive a '97 M3 with Dinan SC and headers, as well as assorted other things. My check engine light went off on about 6 months ago. Had the dealer look at it and they said the emissions on my car were a little screwy because of the SC and the headers. They said there was no problem and they reset the light. The light went on again last week. I went out to the dealer and after looking at it for about 2 hours, they finally decided that the thermostat was faulty and was not letting enough air into the engine. This made the car run rich, which is was tripped the check engine light. They said the problem was further complicated becuase that air pump inside the right front fender no longer has the hose connected to the exhaust manifold because there is no port for it in the headers.

Funny thing is, the car does not take an exceptionally long time to warm up (less than 2 minutes yesterday when it was 81 degrees), the car does not get horrible gas mileage (of course the result of running rich), the car has never overheated (even standing in Chicago rush hour traffic) and I have never heard of a thermostat being able to limit the amount of air coming into the engine. I suspected before I got there that the O2 sensor was faulty. A much more likely cause of the check engine light and I am at about 54K miles (I heard O2 sensors fail at about 60K). Before I buy a thermostat from online and bring it to them (I live in a highrise and have zero space to do my own work), has anyone ever had this problem? Could this diagnosis be correct??

Any help or thoughts are appreciated!!!

[Bill]

The Air pump works by pumping more air into the exhaust to lower emissions. Its used to heat the cats up faster during start up. Now if they were testing during warm up it will show a rich condition being you do not have a working air pump.

[Jeff]

That is what I have heard the problem is by not having the air pump hooked up. However, both times the check engine light has come on, it is when I was on the freeway and the car had been running for some time. I have never seen the light come on at startup. As far as I can tell, that air pump only works for about 90 seconds at startup and then never comes on again to regulate anything. I mean, obviously I can't tell if it is running when I am driving, but I have never caught it running when the car is running after the initial startup.

[fourfa]

maybe they're referring to a thermostat for the secondary air pump, not the coolant?

sounds like BS to me though

[Jeff]

Well, he did say the thermostat was not letting air get through the secondary pump, but as far as I know, there is only one thermostat. I even told him that I would order the parts cheaper and bring to the dealer to install...so he knows what I am ordering.

Is the secondary air pump the pump inside the right fender or is there something else? If the secondary air pump is the one inside the right fender that runs when the car is started, the pump blows cold air without a problem, but the hose has been disconnected because there is no port in the headers for it. I thought it sounded like BS too...that is why I am looking for all the info I can get.

[Erik@EDGE]

If the car is running at the right temp (right in the middle of the guage) then the thermo is probably fine. Maybe you want to take the car to a good custom muffler shop and have them install the correct pipe fitting to hook the air pump up.

[UD///M]

I would agree that they are not referring to the water flow thermostat. There are a few thermostats on the engine. The normal one everyone talks about is the one that controls the water flow to cool the engine. There is also one for the guage on the dash and another for the ECU to monitor the engine temp. The last one ilsted is probably the one they (dealer) are referring to. A proper description of the last two are sensors since they are not controlling any temperatures.

The air pump is to provide fresh oxygen to the exhaust so that the cat can more easily "burn" the remainder of the unburnt fuel in the exhaust. I believe it only runs when the engine is cold though (not sure about that).

[Jeff]

I have confirmed with the shop that built the car that the secondary air pump only runs when the car is first started. It's sole purpose is to pump fresh air into the exhaust to fool a sniff test when the car is cold. Since the car runs rich until it is warmed up, the pump mixes fresh air with the exhaust to "thin out" the exhaust until the car is at running temp. The only time it should run is when the car is first started.

It is possible I am confused which thermostat he was referring to (I only knew of one.) But from his description and the conversation we had, I didn't think there was any confusion or misunderstanding regarding which thermostat it was. Again, I confirmed with the shop that built the car that the thermostat is mechanical so it can either be cracked, stuck open, stuck closed, or responding slowly. However, they thought it was strange that the car did not run hot or take too long to warm up. They agreed that the thermostat I assumed he was talking about was probably not at fault.

[Bill]

There is a EGR valve that controls the air from the air pump to the headers and of course this is disconected due to your new headers.

[BMWguy206]

Its not an EGR VALVE!!!

Its a "non-return valve" for the secondary air injection system. Valve is open during operation of the secondary air pump by engine vacuum and is closed when the DME tells it to or when secondary air injection pump is deactivated.

[UD///M]

John C. is right. It is not an EGR. EGR stands for Exhaust Gas Recirculation valve. If it were an EGR valve then there would be a pipe that would run from it to the intake manifold. But you will not find such an animal.

[Hank]

You maybe need to find someone you trust to work on your car. If I'm wrong I apologize in advance. I don't mean to be facitious but this is a minor problem and no engine damage has occured.? Hope you find someone you trust to fix it and you're not driving it day after day hoping for a post you agree with. Get it into the hands of someone you have confidence in.

Hope this helps!

Hank

[Jeff]

Thanks for all the ideas guys. I have decided to abandon the dealer and take it back to the shop that built the car. I would have gone there in the first place, but I have trouble getting there when they are open. Appt. is set for next Tues. so I will know more next week. I am interested to see what is really causing the problem.

Thanks again!

[Bill]

Sorry Jon,

Thanks for the corection on the valve thingy. I just couldnt remeber what it was. egr kept flashing in my head.