rdurh
10-10-2007, 11:05
I recently installed an injection pump for my younger sister on her 1984 Blazer (6.2L na). Being the frugal (re: cheap) person that she is, and on a limited budget, I found her an NOS GM rebuilt pump from a dealer close out. The IP is a DB2 4723 and the application is for a heavy duty 1988-89 Chevrolet trucks from what I can tell. I also had to replace the TPS as one of the wires was broken off.
The first time I tried to install the pump, after I had threaded in the first IP gear bolt, I could not turn the engine over by hand to get to the other two IP gear bolts installed. Also, the indexing pin is in the slotted hole in the IP gear, not the round hole. The crankshaft would turn about an inch and bind up. I removed the IP and reinstalled and the crankshaft would then turn without any problem. However, about half way into to tightening down the bolts on the IP gear the gear moved into the IP and all the bolts became finger tight. I finished tightening them down without any issues. After I got everything back together I used my Snap On MT480 timing/tach meter to set the timing. RPM was 675 and steady but timing was 7 degrees after top dead center. I can retard the timing until it is off the scale of the MT480. When retarded that much I get a lot of white, diesel smelling smoke out the tailpipes, hard starting and really rough running engine. Advancing the timing I can only get to 1.5 degrees after top dead center. I was shooting for at least 2 degrees before top dead center. At 1.5 degrees the engine would idle OK but driving the acceleration was weak and the truck would blow out clouds of black smoke from both tail pipes. I originally retarded the timing just by splitting the difference between the static mark on the engine and where the timing mark on the IP was set for 1.5 degrees ATDC. Power was better but I was still getting a good deal of black smoke out the tail pipes, less than before but still too much. I continued retarding the timing a little bit at a time and the smoke seemed to diminish, but that is just seat of the pants feel. However, no matter what timing setting I put the pump at I am still getting black smoke under acceleration, or white smoke once it is retarded too much. At anything above approximately 10 degrees ATDC the idle is nice and smooth and it starts a lot easier than it did with the old pump. No smoke at idle and no EGR (CUCV J code engine). Not sure how much wear there is in the chain. This engine had 12,000+ miles on it when my sister got the engine, and the mileage was documented with the military service records that were with the truck when it was scrapped.
Based on the suggestion of a friend, who's been a diesel mechanic for 20+ years, I presently have set the timing to 7 degrees ATDC at 1200 RPM. At idle, 675 RPM, the timing is 10 degrees ATDC. According to my friend "the (timing) reading has to be taken at the LLadvance setpoint which is probably about 1,200 rpm or so" and timing should be set at 7 degrees ATDC at 1200 RPM. The truck still has a good amount of black smoke under load, but significantly less than at 1.5 degrees ATDC. I understand that for the injection pump for these engines that you can turn up the fuel volume. Could it be that I need to turn down the fuel volume for this particular pump?
The truck idles fine with no smoke at idle or cruise. Even under acceleration/load it is much better than it ever was with the original pump. I just need to get the smoke to go away so it will pass emissions this year. However, on the plus side, no one tailgates me. :-)
The first time I tried to install the pump, after I had threaded in the first IP gear bolt, I could not turn the engine over by hand to get to the other two IP gear bolts installed. Also, the indexing pin is in the slotted hole in the IP gear, not the round hole. The crankshaft would turn about an inch and bind up. I removed the IP and reinstalled and the crankshaft would then turn without any problem. However, about half way into to tightening down the bolts on the IP gear the gear moved into the IP and all the bolts became finger tight. I finished tightening them down without any issues. After I got everything back together I used my Snap On MT480 timing/tach meter to set the timing. RPM was 675 and steady but timing was 7 degrees after top dead center. I can retard the timing until it is off the scale of the MT480. When retarded that much I get a lot of white, diesel smelling smoke out the tailpipes, hard starting and really rough running engine. Advancing the timing I can only get to 1.5 degrees after top dead center. I was shooting for at least 2 degrees before top dead center. At 1.5 degrees the engine would idle OK but driving the acceleration was weak and the truck would blow out clouds of black smoke from both tail pipes. I originally retarded the timing just by splitting the difference between the static mark on the engine and where the timing mark on the IP was set for 1.5 degrees ATDC. Power was better but I was still getting a good deal of black smoke out the tail pipes, less than before but still too much. I continued retarding the timing a little bit at a time and the smoke seemed to diminish, but that is just seat of the pants feel. However, no matter what timing setting I put the pump at I am still getting black smoke under acceleration, or white smoke once it is retarded too much. At anything above approximately 10 degrees ATDC the idle is nice and smooth and it starts a lot easier than it did with the old pump. No smoke at idle and no EGR (CUCV J code engine). Not sure how much wear there is in the chain. This engine had 12,000+ miles on it when my sister got the engine, and the mileage was documented with the military service records that were with the truck when it was scrapped.
Based on the suggestion of a friend, who's been a diesel mechanic for 20+ years, I presently have set the timing to 7 degrees ATDC at 1200 RPM. At idle, 675 RPM, the timing is 10 degrees ATDC. According to my friend "the (timing) reading has to be taken at the LLadvance setpoint which is probably about 1,200 rpm or so" and timing should be set at 7 degrees ATDC at 1200 RPM. The truck still has a good amount of black smoke under load, but significantly less than at 1.5 degrees ATDC. I understand that for the injection pump for these engines that you can turn up the fuel volume. Could it be that I need to turn down the fuel volume for this particular pump?
The truck idles fine with no smoke at idle or cruise. Even under acceleration/load it is much better than it ever was with the original pump. I just need to get the smoke to go away so it will pass emissions this year. However, on the plus side, no one tailgates me. :-)