1990Redcoupe

I have been getting an occasional EGR fault on my 90 L98. Turns out the diaphram on the EGR valve had a leak and the valve was not opening.

I have a replacement on the way but how does the ECM sense whether the EGR system is functioning ? There is no direct feedback to the ECM for the valve position and as far as I know the ECM cannot measure the combustion temperature.

Does anyone know ?

Thanks

C4boy

Gonna change my name to EGRboy

The ECM doesn't actually know if the system is functioning correctly. The only 2 components that can set a fault (at least on L98s as I understand them) are a bad EGR solenoid or bad EGR temp. sensor. That's assuming there's no problem with the wiring circuit to the ECM.

The solenoid is an electro-mechanical part so only the electrical portion can send a fault. If the solenoid doesn't hold vacuum (the mechanical portion), it can be faulty but you won't know it w/o manually testing it.

Most people don't know their EGR is bad until they go for an emissions inspection.

You might want to check this thread too

Aggravated4life

I forget exactly how but a FSM(Factory service manual) will tell you.If certain parameters arent met,a EGR code will light up the service light on the dash.

C4boy

The ECM takes input from other sensors like the MAT & TPS to determine when to cycle EGR. But those sensors won't trigger a code 32.

Maybe an easier way of explaining it is, all the EGR/code 32 circuit does is cycle the EGR solenoid off and on.

coupeguy2001

the computer cycles the solenoid on, and in a certain time frame, I think it's 25 seconds, the temp sensor resistance change tells the computer that it's working.
1. The computer sees the resistance of the solenoid coil, and that translates into load current. that tells the computer :
A. the solenoid is connected, and
B.the coil is good.
That load current has parameters programmed in to the computer. if the load is out of tolerances, it triggers a fault.
2. the resistance of the sensor works the same way. there is a small circuit that monitors the temp rise, and the total load. The computer knows
A. the vacuum lines are connected, and
B.the valve is opening abd closing.
It is an if-then logic.
if the parameters are withn, then no fault. if the resistances are out of tolerance, then log a fault code.

BigLee

on my 86E, when i disabled the EGR it set the code for a few ign. cycles, then the code simply disappered....
any time i disconnected the battery, the code would return again for a few ign. cycles, the go away again, and not return...

anybody has this happen on theirs?

byebyeL98

From the FSM for my '87:

"Code 32 means that the EGR diagnostic switch was closed during start up or that the switch was not detected closed under the following conditions:
*Coolant temp greater than 176F
*EGR duty cycle commanded by the ECM is greater than 75%
*TPS less than 1/2 throttle, but not at idle
*Codes 21,22,33,34 not present
*All conditions above must be met for about 4 minutes"

AGENT 86

http://members.shaw.ca/corvette86/EGR%20System.pdf