Egr test

Wondering if my egr is an issue and I see some say to unplug it and see what happens.What am I suppose to look for?

Give us more information year engine size. Are you getting a trouble code symptons etc. Then we might be able to help you.

My 1990 sse has been stalling on me intermittantly.I was getting code 41 cam sensor I cleaned it and made sure magnet was there checked all connections and harness to cam , crankshaft , ICM, cleaned them while I was there cleaned TB , IAC and egr.Now code 41 gone and code 42 appears - EST so I changed ICM AND COIL PACK, still have code 42 so I changed ECM (I had spare).Also cleaned grounds under ICM.It still stalls sometimes bad idle.I feel it is wiring but checked it all and played with wires trying to get it to stall and couldnt.So I also suspect EGR and saw a thread that said unplug it, so I unplugged mine and so far it is running fine and code 26 quad driver circuit shows up intermittant but hasnt stalled yet and idles pretty good.

Each quad driver can control up to four devices. So diagrams will have to be used to find which devices the quad driver at fault is controlling. It's part of the ECM firmware. One of the things a quad driver controls is the EGR valve Ignition module is another.

EGR Valve unplugged so no signal to ecm no control thus fault code 26.
Plug it back in 26 hould disappear probably code 42 will appear.

EST.
This circuit triggers the ignition module. The computer does not know what the actual timing is, what it does know is when it gets a reference signal. It uses this reference signal as a base point and advances or retards the spark from that point. So, if on vehicles where the base timing is adjustable, and the base timing is set incorrectly, the spark curve will be off through its entire range by the amount that the base timing is misadjusted. An open or short to ground in this circuit will set the code and cause the engine to run on ignition module timing.

Why the computer flags this code.
What we have here is a failure to communicate. The ignition module and the computer are in constant communication when the engine is in operation. (Over 400 RPM.)With the computer telling the module the correct timing. If communication is lost or a circuit becomes infected with false signals (bad grounds, short to battery +, Electro Magnetic Interference {spark plug wires to close to circuit wiring}, oil contamination of the circuit connectors and wiring) then the computer will turn timing control back to the ignition module and flag the code. When this occurs engine runs rough but runs. We used to call this limp mode. Because you could limp the vehicle back home or to your mechanic.

Possible causes:
· EST circuit open or grounded.
· Bypass circuit open or grounded.
· Reference Ground circuit open or shorted to battery +.
· A bad computer to engine circuit ground.
· A defective ignition module.
· A defective computer.

Thanks for your reply.I have not been getting any steady code right now that I am able to read,SES light only comes on if it stalls which isnt very often anymore.Yesterday I had 1 stall in 6 trips.I have a feeling it is the harness that leads to ignition module, it is oily at cam and crank sensors.I also suspect grounds, can you tell me all grounds to check.I am really frustrated with this one.Any thing else to check, thanks.

I'll have to see if I have a wiring diagram for your particular model. Without that diagram I would just be guessing.

If I can't find one look at the wires at the ignition module. See what color they are. Example say it's blue with white stripe. You cold do a continuity check of that wire to be sure there's no break.

Sorry for my ignorance but can you explain exactly how to do continuity test.Thank you