Take care with the Delta-P sensor on the E.G.R. System
By Christopher W. Ferrone
As everyone knows, diesel engines now come with an Exhaust Gas Recirculation System (EGR) to help with pollution through the reduction of NOx. It does this first by adding exhaust gases to the air intake side of the engine to lower the combustion temperature. Adding CO2 to the intake increases the heat capacity and lowers the combustion temperature. It also reduces the oxygen content of the intake air due to the addition of the CO2 from the exhaust gases. Both EGR actions reduce the production of NOx.
What also now comes with the new engines are more difficult electronics to manage. The two most typical EGR failure modes are the EGR valve itself and the differential pressure Delta-P switch.
So far at American Sightseeing we have only had to change one complete EGR valve. We have changed quite a few Delta-P sensors on both the Detroit and Cummins engines.
Recently, I spent a good deal of time diagnosing an EGR problem that created an overall engine performance problem. The bus would not reach its maximum programmed road speed and it would buck violently just at the onset of acceleration to reach maximum road speed. This produced the typical E.G.R. fault codes.
However when tested, the EGR itself and the Delta-P sensor checked out fine.
Removing the Delta-P sensor for a closer look (photo 1), I found the plastic adaptor plate that directs the flow of exhaust to the Delta-P sensor had a broken pipe (photo 2a & b). This, of course, led to a leak in the system that the ECM could monitor. We installed a new part and the engine ran fine, allowing the bus to reach maximum road speed without the bucking and black smoke.
One key point to remember: when you change out this part with a new one, make sure you clean out the two small hoses connected to the adaptor plate to eliminate any remaining broken debris remaining in the hoses. Otherwise the hoses will clog and result in a consequent code and problem with the engine. For your reference, DDC upgraded the old part and gave it a new part number. For DDC S-60 engines, the old part number is 23535850. The new part number is 23536986. Remember, when ordering parts, always use the engine serial number. They are only $17, so buy a few extras. I am sure you will use them just as we do in our shop.