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I was having some minor fueling issues and then I noticed that my AFC housing was starting to leak diesel. This usually means that fuel is getting by the o-ring seal on the guide pin that rides on the fuel pin and adds fuel as boost increases. When I pulled it apart I saw that my rubber diaphragm was cracked and leaking boost. I tried to patch it with some sealant to buy me a little time but that really didn't hold up and so I ordered a new one to replace it. It is sandwiched between two cup washers and fits on the top of the fuel pin. Here it is all apart.
Part of my theory of why I was getting diesel into the AFC housing was because boost would hit the top of the diaphragm, go through the crack and exit the vent hole in the chamber below the diaphragm. This created a kind of venturi effect creating negative pressure in the AFC chamber and helped suck fuel passed the o-ring. It only seemed to leak when I was building boost. Due to the crack in the diaphragm I wasn't fueling as hard and lost some overall boost pressure.
The old one on the left with the crack at 6 o'clock. New one on the right upside down from the old one.
While I was there and was going to replace the guide pin o-ring, which requires removing the top of the injection pump, I had read up about different length guide pins and found the following part numbers:
Bosch guide pins
1 463 105 416 (23.8mm long)
1 463 105 363 (24.3mm long)
1 463 105 364 (24.8mm long)
An older thread talked about how the longer pin helped reduce their bottom end fueling and reduced low end smoke. The pins were only 12$ a piece from my local injection shop so I picked up the longest version to see what it would do.
I didn't know what original length I had in my pump and my digital calipers broke so all I could really do until I got another set was to eyeball the difference. The top is the new longest pin and the bottom is my old pin.
The results were that I did reduce some fueling but that I couldn't build into the 50psi range that I was after even with power screw adjustments. It lost a little bit of snappiness on the throttle and the midrange wasn't as strong. I played with the power screw, smoke screw, and AFC spring tension but I didn't see a big difference in low end smoke, it was still more hazy than I'd like. Plus, the AFC housing started to leak again. I decided to try the next size smaller and pull the top off the injection pump again. I bought the 363 guide pin and did another comparison. Original on the left, new in the middle, longest on the right. It looks to me like my original and the new are the same length.
I put the new guide pin in and reused my o-ring. No more leaking. Maybe the longest one is a little skinnier or something but the same o-ring now seems to seal fine. I didn't do anything different on replacing the guide pin either but maybe I botched that somehow. I did get some snappiness back and a stronger midrange returned. I tuned it back for power and 50psi is back. It's still hazing so the next fueling mod will be injector nozzles.
Part of my theory of why I was getting diesel into the AFC housing was because boost would hit the top of the diaphragm, go through the crack and exit the vent hole in the chamber below the diaphragm. This created a kind of venturi effect creating negative pressure in the AFC chamber and helped suck fuel passed the o-ring. It only seemed to leak when I was building boost. Due to the crack in the diaphragm I wasn't fueling as hard and lost some overall boost pressure.
The old one on the left with the crack at 6 o'clock. New one on the right upside down from the old one.
While I was there and was going to replace the guide pin o-ring, which requires removing the top of the injection pump, I had read up about different length guide pins and found the following part numbers:
Bosch guide pins
1 463 105 416 (23.8mm long)
1 463 105 363 (24.3mm long)
1 463 105 364 (24.8mm long)
An older thread talked about how the longer pin helped reduce their bottom end fueling and reduced low end smoke. The pins were only 12$ a piece from my local injection shop so I picked up the longest version to see what it would do.
I didn't know what original length I had in my pump and my digital calipers broke so all I could really do until I got another set was to eyeball the difference. The top is the new longest pin and the bottom is my old pin.
The results were that I did reduce some fueling but that I couldn't build into the 50psi range that I was after even with power screw adjustments. It lost a little bit of snappiness on the throttle and the midrange wasn't as strong. I played with the power screw, smoke screw, and AFC spring tension but I didn't see a big difference in low end smoke, it was still more hazy than I'd like. Plus, the AFC housing started to leak again. I decided to try the next size smaller and pull the top off the injection pump again. I bought the 363 guide pin and did another comparison. Original on the left, new in the middle, longest on the right. It looks to me like my original and the new are the same length.
I put the new guide pin in and reused my o-ring. No more leaking. Maybe the longest one is a little skinnier or something but the same o-ring now seems to seal fine. I didn't do anything different on replacing the guide pin either but maybe I botched that somehow. I did get some snappiness back and a stronger midrange returned. I tuned it back for power and 50psi is back. It's still hazing so the next fueling mod will be injector nozzles.
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