Quote:
Originally Posted by Boydness
Back pressure could definitely be the issue here!
What would be the long term effect of not having the proper back pressure?
Steven
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Well, the DTC 32 is an indicator that ECM failed to verify EGR system function test sequence. Before jumping to any conclusions you'll have to verify component level operation - EGR solenoid, EGR valve, harness, etc. Not having EGR functional increases exhaust NoX levels and your gas mileage may drop. Otherwise, engine performance should be more less the same.
Depending on exhaust system and emission system requirements different EGR valves may be employed, for example Positive, Negative, Neutral or linear.
The positive back pressure EGR valve can be readily identified by the letter "P" stamped next to the part number and date code. A 'P' EGR valve is easy to spot because its pintle shaft is much thicker than the single diaphragm type. This is so because the shaft is hollow. The hollow design allows exhaust gases to flow into the shaft and push up on it. When positive back pressure in the exhaust system is sufficient, the shaft raises up and seals the built-in control valve. Once the control valve is closed, it allows applied vacuum to pull up on the diaphragm. Without back pressure to lift the hollow shaft and close the control valve opening, the EGR valve will not hold vacuum. It is bled off to the atmosphere. This design thus modulates EGR flow by modulating the applied vacuum. As engine load increases, so does engine back pressure, which causes the control valve inside the EGR to trap vacuum and open up. To test this valve, bring the engine up to 2,000 rpms to create back pressure, then apply vacuum. EGR should open and cause a 100 rpm drop or more. Exhaust leaks or a modified exhaust system can create problems. Adding dual exhaust or headers on a truck designed for a single exhaust will reduce back pressure and set a Code 32. Positive back pressure EGR valves are used in simple vacuum controlled systems, as well as more complex pulse width modulated (PWM) applications - 1227747 ECM.
Code 32 problem has been around since CCC days and can be caused by a number of reasons. Every so often GM engineers altered ECM strategy for this code and depending on sophistication of the algorithm employed in the ECM causing enough grief and misinformation about Code 32. Unfortunately, Code 32 strategy has been inconsistently applied across different drivetrains over the years. The most common strategy entails the ECM monitoring fuel integrator counts to decrease momentarily when the EGR is commanded open. Since there is little or no oxygen in exhaust gases the integrator subtracts (causes a lean condition) fuel to compensate. This process relies on having a good working oxygen (O2) sensor. O2 sensor functional checks usually are not noted in the Code 32 troubleshooting flow chart, so be aware. Later BCC codes implementations look for a change in manifold absolute pressure (MAP) when EGR is flowing, which tends to be a more reliable method.
Negative back pressure may be best for modified exhaust systems. In this case as back pressure increases the valve will close. A positive back pressure valve needs back pressure to open. With headers and a decent exhaust there may not be enough back pressure to open it.
//RF