Thread: 99 sl1 egr?
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Old 08-26-2011, 01:21 AM   #5
td1238
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Join Date: Mar 2010
Location: Milwaukee
Posts: 2,164

1999 SL2
Default Re: 99 sl1 egr?

What code did it throw? There are several codes for the EGR valve.

The electronically controlled EGR valve contains a position sensing device. This device is identical in operation to the TPS and to a traditional radio volume control. It is called a potentiometer. A potentiometer is a variable resistor that serves as a variable voltage dividing device. Voltage of opposite polarity is connected to each end of the resistor, and the wiper glides over the resistance material to collect voltage from various points on this resistor.

In the case of the EGR valve, this device can be used to tell the computer how far open the EGR valve is.

The purpose of the EGR valve is to inject inert 'spent' gasses to the combustion chamber, to cool combustion somewhat (dilute the combustion mixture and also absorb heat), because too hot a combustion releases NOx gasses, which are a pollutant. A biproduct of this combustion cooling is that the exhaust valves last significantly longer, so please do not block off the EGR valve. The computer must know how much exhaust gas is being injected to the combustion chamber so that it can adjust fuel mixture properly, since the exhaust gas will displace available oxygen. If the computer doesn't know where the EGR valve is, it can't accurately meter fuel, and so you have a lack of power due to incorrect combustion mixtures, as well as an EGR valve that's open during critical power moments (normally the valve is closed for idle and when power is needed, as it destroys good combustion).

To test the EGR valve potentiometer, connect your ohmmeter (preferrably with alligator clips) to the center terminal and to each adjacent terminal, one at a time. Move the pintle in and out smoothly. Resistance should change smoothly, and should start and stop pretty much in the same place each time. If it jumps around, the potentiometer is faulty, and the entire assembly must be replaced. The jumping around is on par to the scratchiness you hear from a worn volume control.

If the potentiomter is worn, you likely got an 'EGR out-of-range' code.

Replacement of the EGR valve due to this fault on my '99 SL2 greatly improved power, and eliminated the very random characteristics of my car's acceleration. It even made for quite acceptable power with the AC on.
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