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Old 06-09-2013, 03:37 PM   #1 (permalink)
t vago
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EGR experiment (Increase EGR flow for fuel economy)

Reference: Increasing EGR flow for better mileage

Today, I modified my EGR system - hopefully for better fuel economy.

First, I took some measurements of my EGR valve. I had a spare EGR valve assembly from a very similar Chrysler engine, so I partially dissected it. The valve controls consist of a solenoid, and a plunger-style potentiometer to measure the solenoid position. The engine computer reads the position of the EGR solenoid (thus, the position of the valve itself), then sends a variable width 128 Hz pulse to the solenoid to open or close the valve to a desired percentage. It goes without saying the the engine computer completely shuts the valve when the engine is idling, at full deceleration, or at moderate (or above) acceleration.

The potentiometer varies along a 2.7k ohm value, and there appears to be a 490 ohm resistance in line with the wiper. Not too concerned about that, though.

Once I got the values, I spliced in a 1 kohm resistor, along with about 3 feet of extra wire, into the EGR sensor supply wire. This willl have the effect of reducing the voltage that the potentiometer sees, thus also reducing the apparent position of the EGR solenoid. The engine computer should then increase the EGR position to compensate.

Looking at the FSM, there does not appear to be any rationality testing for the EGR system. Basically, the EGR valve can pop a code for "No voltage to potentimeter," "Potentiometer shorted to ground," "Potentiometer shorted to supply voltage," or the generic "EGR system not responding." In other words, splicing in the 1 kohm resistor should not pop any codes.

I tested the EGR system with my trusty Snap-on MT2500, and it still responds normally. It's amusing to cause the car engine to start idling horribly when the EGR system is commanded to kick in... Heh. I will take a test drive shortly, and will report my initial feedback here, at some point in the near future.

Last edited by t vago; 06-11-2013 at 06:16 PM.. Reason: change title
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