My EGR on my Datamaster show it opening for one frame at 12.5 then the next frome its at 0 and goes back and forth between 12.5 and 0. This will go on for the entire time it is open. Some times it only shows 6.3 but has the same on one time and off the next. It will never show anything but 12.5 or 6.3 on numerous runs. I am not sure if this means the part is bad, just needs cleaned or is normal. Does anyone know?

 

Most likely its bad, mine was showing all the way to 100% but it wasnt able to hold vacuum which caused me to fail smog

 

The reading you are seeing on the scanner is the pulse width modulation duty cycle percent that is being set by the PCM. Its pulsing the vacuum solenoid to achieve a 6.3%, 12.5%, etc openeing on the valve. The PCM has determined that is the EGR that it wants to flow. There is no feedback (on the LT1) to the PCM on the actual position of the EGR valve, or whether there is actual flow, other than in intermittent diagnostic check using MAP, and only under conditions where the engine is operating under extremely steady-state conditions.

Having a 6.3% or 12.5% EGR duty cycle commanded by the PCM is not a sign of a faulty valve. Its the PCM determining that's the DC % that will provide the EGR flow that the engine requires to control NOx.

 

I've seen similiar things. Seems to be normal.

 

memint, here's a url with some additional info on the $EE definition file for EGR. I'm puzzled because the TC people mentioned MAP (no problem) but then mentioned hi and low vacuum, since there are no vacuum sensors on the '94-'95 LT1 I'm not sure what they meant. ' http://www.monodax.com/forums/tunerc...operation.html '
By the way the only time my EGR duty cycles around 0-12.5% is at low throttle TPS below 7% otherwise the DC cycles between 0-100% almost all the time it is on. It goes to 0% in fuel cell 18 (TPS=0%) and when the RPM hi/low limits are met, but it then cycles up very fast back to 0-100%

 

The PCM measures the barometric (BAR) pressure, and the manifold absolute pressure (MAP). The difference between BAR and MAP = vacuum.

 

I totally deleted my EGR. kept getting EGR valve codes on my car so i took it off.

 

Injuneer, thanks for the insight, BAR is listed in freescan , but down in engine plot items under DataMaster. I never paid much attention to that field.. Bob D.