Diesels and EGR

[UFO]

Originally Posted by Duffman

Pulling the EGR cable throws a code on some vehicles. This puts them into a limp mode which adjusts injection timing, messes with the VGT boost tables etc. Less EGR is better for economy but it may be offset by the computer depending on the vehicle.

But if the computer doesn't know....

[COcyclist]

After much reading and talking to mechanic friends I decided to replace the cracked egr pipe and keep the car egr system stock. When I disassembled the egr system I found that only the lower pipe was broken and I had only a thin coating of soot, no intake or egr cooler clogging at 60,000 miles. The parts cost is about $100 and I did the work myself.

I did find several missing and cross-threaded bolts from the last time the dealership did this job (warranty repair). The egr cooler is designed to be solidly mounted to the intake manifold. Mine was loose and only supported by the two egr pipes. No wonder the pipe fails!

I decided that replacing the pipe myself is the most cost effective repair, reduces Nox emissions and may give me the best mpg in the VW TDI. The tricks done to the car's computer would have to be very carefully worked out to keep injection timing optimal as designed and I wasn't willing to risk losing mileage.