Questions about EGR

[carcrossy]

1. What route does the exhaust gas travel once the egr valve sends it into the intake. Someone mentioned that there are 4 separate channels that take the exhaust to each cylinder. Supposedly these narrow channels can clog with carbon?

2. Leaks in the exhaust before the cat converter are supposed to introduce O2 which drives up nitrogen emissions. I have a pin hole in my egr tube. Would this be enough to cause my nitrogen emissions to go way up?

3. Will a hole in the muffler cause driveability issues. For example, will it cause back pressure to vary and make it hard for ecu to manage egr system?

4. How do you clean the filters on the BPT valve? Just spray them with carb cleaner?

5. Thanks.

Mechanical failures
In closing, I'll leave you with a pattern failure seen in '85-'92 Nissans, models 240 SX and Stanza, and some Hondas about the same vintage. They have individual EGR passages running to each cylinder. Eventually, some of these passages (one or two) will plug up with carbon while others stay open. The remaining passages receive 4-runner EGR volume, which is far too much and causes a misfire on the affected cylinders. It happens above idle and under load. Sometimes you can unscrew Allen head access plugs to clean out the passages, other times you must remove the upper intake plenum chamber to do the repair.