EGR carbon build up and coolant bypass?
05-08-2014 | 10:30 PM
#1
EGR carbon build up and coolant bypass?
I Know VW and other diesels have issues with EGR coolers plugging with carbon. Ive seen pics of maximas with blocked EGR tubes near the coolant pipe on the UIM. Ive also seen plugging in small block Chevys in the head and intake manifold where coolant passages are near.
Many say that the coolant in this context is for heating the EGR gasses in cold weather, but I am with the minority that believes the coolant serves to cool the hot exhaust gasses. I believe that the relatively cold coolant causes the exhaust gasses to cool down and solidify over time in the passages.
Can anyone with a coolant bypass and functioning EGR system say the blockages have increased or decreased?
Many say that the coolant in this context is for heating the EGR gasses in cold weather, but I am with the minority that believes the coolant serves to cool the hot exhaust gasses. I believe that the relatively cold coolant causes the exhaust gasses to cool down and solidify over time in the passages.
Can anyone with a coolant bypass and functioning EGR system say the blockages have increased or decreased?
05-08-2014 | 10:37 PM
#2
Here is an alldata TSB that supports my theory.
Jim Grant's Tech Tips
95 GMC Jimmy, EGR Carbon Problems
Q: I recently bought a used '95 GMC Jimmy at a dealer with 78,000 miles with a 30 day warranty. The very next day after the warranty expired the fuel pump also expired. After replacing the fuel pump a code for the EGR pintle out of position occurred. Upon inspection of the EGR it appeared that it had been recently replaced. I personally pulled the unit and found pieces of carbon stuck in it keeping the pintle from closing all the way. I removed the carbon and reinstalled the EGR. The problem caused a serious idling effect. The very next day the same thing happened. I cleared the EGR again and the Jimmy ran fine. My question is where does the carbon come from and will this continue to happen? Is this a problem unique to Central Multi-Port Fuel Injection systems or is there some special maintenance that I need to perform to prevent it from happening again. Any info would be appreciated...........Don
A: The valve that you are referring to is GM's Linear Exhaust Gas Recirculation (LEGR) valve which is common to GM vehicles equipped with a 4.3 liter engine. The LEGR valve has been prone to carbon problems that cause the valve to stick open. When carbon deposits get caught in the valve it can turn the Check Engine Light on and the driver of the vehicle may experience problems such as engine surge, stalling, rough idle, and/or hard starting. Where does the carbon come from? The exhaust system. The LEGR valve introduces metered amounts of exhaust gases back to the engine. As the hot exhaust gases travel through the cooler passage, leading to the LEGR valve, the gases will cool and form deposits. Over time the deposits can build up and break off. If the deposits get caught in the valve, it will stick open and cause driveability problems. ALLDATA Information Systems shows GM Technical Service Bulletin # 96067 addressing problems caused by deposits of foreign material affecting the LEGR valve. The fix was a revised program for the computer that would increase the movement of the valve, reducing the chance of debris being caught in the valve.
95 GMC Jimmy, EGR Carbon Problems
Q: I recently bought a used '95 GMC Jimmy at a dealer with 78,000 miles with a 30 day warranty. The very next day after the warranty expired the fuel pump also expired. After replacing the fuel pump a code for the EGR pintle out of position occurred. Upon inspection of the EGR it appeared that it had been recently replaced. I personally pulled the unit and found pieces of carbon stuck in it keeping the pintle from closing all the way. I removed the carbon and reinstalled the EGR. The problem caused a serious idling effect. The very next day the same thing happened. I cleared the EGR again and the Jimmy ran fine. My question is where does the carbon come from and will this continue to happen? Is this a problem unique to Central Multi-Port Fuel Injection systems or is there some special maintenance that I need to perform to prevent it from happening again. Any info would be appreciated...........Don
A: The valve that you are referring to is GM's Linear Exhaust Gas Recirculation (LEGR) valve which is common to GM vehicles equipped with a 4.3 liter engine. The LEGR valve has been prone to carbon problems that cause the valve to stick open. When carbon deposits get caught in the valve it can turn the Check Engine Light on and the driver of the vehicle may experience problems such as engine surge, stalling, rough idle, and/or hard starting. Where does the carbon come from? The exhaust system. The LEGR valve introduces metered amounts of exhaust gases back to the engine. As the hot exhaust gases travel through the cooler passage, leading to the LEGR valve, the gases will cool and form deposits. Over time the deposits can build up and break off. If the deposits get caught in the valve, it will stick open and cause driveability problems. ALLDATA Information Systems shows GM Technical Service Bulletin # 96067 addressing problems caused by deposits of foreign material affecting the LEGR valve. The fix was a revised program for the computer that would increase the movement of the valve, reducing the chance of debris being caught in the valve.
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