Quote:
Originally Posted by chillsworld
Mines a 97, and the code is P0401 (insufficient EGR flow). It's got 288k miles on it, and I think its a safe bet that it's clogged with carbon build up... Haven't had time to really look into it yet. If that's the case I know I will see an increase in FE when I clean it out, do you feel that the increase from deletion is better? I've read a lot of back and forth on this subject... Obviously you have the added benefit from deleting the smog pump, decrease in parasitic losses. And you played with your timing, which I'm assuming also aided in FE? The more I read about it, the more confused I get hahah
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No need to be confused. Deleting the EGR and AIS will improve your fuel mileage. On modern vehicles, the use of EGR is because manufacturers did a cost benefit analysis and would rather use a $25 valve to control NOX instead of a $300 3-way catalyst.
AIS was used long before O2 sensors came to be and is the cheap an easy way to meet EPA rules. AIS is another useless technology where accounting prevailed over engineering. Wideband sensor technology has made AIS obsolete for a long time.
The EGR on your vehicle has a sensor on it that detects the position of the valve. I agree with you that coking of the EGR is the most likely culprit, but there is also the possibility that sensor is bad or an issue with the connector or wiring. There is a way to trick the ECM into thinking the EGR is in place and functioning by chopping off the connector and placing some resistors in its place. I know this trick works on OBDI Fords (pre 1996 EEC-IV) and on some later OBDII (EEC-IV only. Not EEC-V). I'll dig up the diagram and post it later. You would still need to make sure flow through the EGR is blocked completely. If it leaks at all during idle, you'll have issues with idle quality, rpm, hard starting, etc.
I've read a lot about EGR theory and all of the arguments for/against it. I've read a bunch of b.s. about theoretical gains in reduced pumping loss, thermodynamic improvements (?), and improved combustion and I'm pretty sure those theories don't mean anything to 99.9% of the vehicles that have an EGR. (BTW, my wife's 1999 Jeep Cherokee w/4.0 didn't have one from the factory). The truth is, EGR is only used for ONE reason: to reduce NOX (oxides of nitrogen) in the exhaust. NOX emissions are very short lived in the atmosphere and eventually are reduced to N2 and free oxygen. The problem with NOX is its decay product is nitric acid. NOX and nitric acid are also caused by lightning strikes. Nitric acid breaks down quickly in the atmosphere also. The main reason NOX is considered a pollutant is in large enough concentrations in the atmosphere it will cause the reddish brown haze you see in areas that have heavy air pollution because of the presence of nitrogen dioxide (wikipedia(dot)org/wiki/Nitrogen_dioxide). NOX is created in an internal combustion by the presence of oxygen and nitrogen together under high pressure and high temperature. The higher the compression ration and the higher the combustion temperature, the higher the NOX content of the exhaust. NOX, as a percentage of the exhaust gas varies depending on a/f ratio and load and ranges from nearly 0 to about 2500ppm (0.0025%) under peak load at 16:1 a/f ratio. You can read about some of the (b.s.) theoretical gains with EGR here: wikipedia(dot)org/wiki/Exhaust_gas_recirculation.
I don't get the logic of using EGR if it's going to cause my fuel consumption to go up. I'm not against emissions controls on my vehicle but if they are so poorly engineered just to satisfy some disconnected political machine, that opinion changes. EGR almost killed the on-road diesel market because of the technical problems of making it work well enough to satisfy the EPA. Sadly, the 'fix' for EGR's horrible reputation for unreliability and reduced performance was the introduction of 'Diesel Exhaust Fluid' and the burden forced on the consumer of having to periodically fill a tank on your new diesel powered vehicle with piss. I could go on and on about some of the stupidity of some of the garbage you are forced to pay for when you but a car (purposely injecting and burning fuel in the exhaust do 'regenerate' diesel PDF's???) but I would be hijacking my own thread.