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1991 Chevrolet Suburban:
Service Engine Soon, EGR Valve

By
Alex Steele
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seen in Truck Trend

Question:

 

My main problem is with a 1991 Chevrolet Suburban. The service light code said EGR was the problem. I replaced the EGR solenoid and made sure the valve actually moves. While I was at it, I also replaced the vacuum hoses.

 

If I drive slowly around town, the service light is off, likewise if driven hard like getting on the freeway. When I slack off to a steady 55 MPH, the light comes back on. What do you think I should do next?

 

Answer:

 

Let's start with the fundamentals of EGR (Exhaust Gas Recirculation). The system consists of passages from the exhaust to the intake, connected by the EGR valve. This vacuum-operated valve carefully bleeds exhaust gases into the air/fuel mixture entering the engine. This process will lower combustion chamber temperature. Believe it or not, the hot exhaust cools the combustion process and therefore aids in reducing harmful emissions.

 

I have an idea as to the cause of your "code 32" EGR failure. You've said that the valve was moving after installing the new solenoid, which controls the amount of vacuum applied to the valve. I'm assuming it was moving while the engine was under a load. A good way to simulate a normal driving load is to slowly depress the accelerator with the transmission in drive, the parking brake firmly applied, the wheels carefully blocked and no one in front of the vehicle. At this point you should be able to visually see the vacuum diaphragm of the valve move. This would confirm the operation of the EGR valve assembly.

 

With the engine idling in park, reach under the EGR valve and slowly pull up on the diaphragm. At this point you should feel a noticeable rough running or even a stall of the engine. If not, that's the problem, the valve and/or the passages to the valve are clogged with carbon deposits and stopping the exhaust gases from reaching the intake. Remove the valve in order to clean it and the passages in the intake manifold. On rare occasions, the intake must be removed and boiled out in order to clear the deposits.

 

When your computer set the trouble code it was actually seeing improper emissions, via the oxygen sensor and determined the EGR wasn't functioning using this data.

 

If you've followed my instructions correctly and the system checked out OK, then it's an intermittent problem that will require further investigation by a qualified technician, at the scene, with a scanning device and a service manual.

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Comments:

Jerry
28 Nov 2011, 11:22
1991 Chevy truck, service engine soon light comes on and engine shuts down after a minute or so, I have no scanner
Admin
29 Nov 2011, 19:29
You have 2 choices:

Go to an auto parts store (such as AutoZone) where they can hook up a scanner, give you the diagnostic trouble code, which will point you in the right direction.

Or, bring it to a qualified repair shop and pay the fee for an accurate diagnosis of the problem.

Either way, you need to know the DTC before going any further.

 

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