Questions and Answers

Jeep Comanche EGR System Disabled Q. I just purchased a used 4.0 liter 1990 Jeep Comanche manual transmission. It failed emissions for Oxygen of Nitrates. To fix the problem I began by checking all vacuum lines. I found an intentional block in the EGR line going from the intake to the EGR solenoid. When I removed the block, the idle didn't change. The drivability did however.

It began stumbling, internal back firing, stalling, etc... I'd come to a stop sign it would stall. It passed emissions running while running so badly. I put the block back in just so I could drive it. Now it runs fine. What would cause this?

Thanks,
Nicholas

A. Nitrogen Oxides (NOx) is caused by high combustion chamber temperatures. The EGR routes some exhaust gas back into the intake to lower combustion temperatures thus lower NOx emissions.

The block may have been put there because the EGR solenoid is bad and instead of replacing it, they disabled the whole EGR system by cutting off vacuum to it.