Well my business partner borrowed the saturn to view a property out of state. I thought this would be a good time to see how the saturn would do with a "normal" driver.
Tanks are as follows
456.5 10.2 44.75mpg (EGR disabled)
395 9.33 42.33mpg (The EGR valve was enabled at 5/8ths tank)
237 5.87 40.37mpg
Its interesting to not that the average cruise speed, on interstate, was 79mph or above. He shifts late 3k rpms+. He stated that he ran the car hard the last tank. He also said that he ran the car very hard for 1.5hours on country roads late for an appointment.
I was experimenting with the EGR before he left. So I let him run a tank and then had him plug it back up. I will be testing this further.
02 Saturn SL
for pics click the link below
I thought a correctly working EGR valve will give you better mileage?
I cleaned out my EGR valve and passageway at the intake for smog testing (failed NOx). I noticed
better mileage, but that could be due to several factors since I did
alot of work getting my car back together (new tranny bearings, new
plugs, air filter, tranny fluid, colder plugs, etc).
I might just plug my egr intake port just to see if I get an overall increase or
decrease in FE.
EGR does a few things, first it dilutes the incoming mixture and reduces the amount of oxygen in and which lowers peak combustion temps to reduce NOx emissions. Second, it also slows flame speed and reduces tendency to knock making it tolerate lower octane fuel a bit better. The "problem" is that these both tend to reduce engine efficiency (power and MPG). BTW, EGR is not applied at WOT or at idle and speeds just above idle nor at high vacuum at higher RPMs. (very low manifold pressure) As to how important it is depends on how you drive and the fuel you use since its absence while cause the PCM to retard spark even more at times with low octane fuel and it could have some effect on MPG and performance. Being that it is getting cooler outside this time of year, octane needs drop and it may not be a issue for you. Personally, if you do not have a E-check to pass I would not worry about it much and I would just drive it until you have the desire or funds to fix it.
The Exhaust Gas Recirculation (EGR) valve is used to allow a controlled amount of exhaust gas to be recirculated into the intake system. This limits peak flame temperature in the combustion chamber so the engine produces less NOx (oxides of nitrogen).
A negative backpressure EGR valve is used to control the amount of exhaust gas which is recirculated. Intake manifold vacuum is supplied directly to the top of the diaphragm to pull open the normally closed valve. Exhaust backpressure pushing against the valve keeps the diaphragm pushed against the bleed hole. When the rpm is high but the throttle is closed, exhaust backpressure becomes negative and the diaphragm is pulled down just enough to uncover the bleed hole. The vacuum on top of the diaphragm leaks off and the valve slowly closes.
The EGR vacuum is controlled by the PCM through a solenoid valve. The PCM energizes or de-energizes the solenoid by providing or withholding ground at the appropriate times. When the solenoid is energized, it prevents vacuum from reaching the EGR valve by venting it to the atmosphere. Once the proper conditions have been met, the PCM removes the ground, thus de-energizing the solenoid and allowing vacuum to open the EGR valve. The valve is open only when the throttle is open more than 4 percent and coolant temperature is above 104?F (40?C) for the DOHC engine with automatic transaxle, or 122?F (50?C) for all others.