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Author : MTVR
Posted 12/27/2023 07:47
Subject: RE: Cat C12 fuel system diagnosis
I picked up the new fuel return check valve and spring yesterday afternoon from the Cat dealer. Again, this is NOT the cartridge style fuel return check valve that screws into the top of the "BLEED" boss on top of the secondary fuel filter base, it's a valve and spring that fits inside the hole in the secondary fuel filter base that the fuel return line AN fitting screws into.
The new valve doesn't look materially different than the old valve.
The new spring doesn't look materially different than the old spring. The free length is identical. When putting the two springs end to end and compressing them with my fingers, the new spring compresses a little less, indicating that it's a little stiffer than the old spring.
I installed the new valve and spring, but the condition remains.
I did notice that the fuel pressure test gauge now bounces back and forth between 40 and 70 pounds when cranking. Before replacing the fuel return check valve and spring, it was bouncing back and forth from 30 to 60 pounds when cranking.
And the fuel pressure still bleeds back to zero, but it takes longer- about a minute or so.
When using the hand pump, I still heard a "click" and the sound of fuel moving, inside the secondary fuel filter base, and then I could hear fuel dribbling back into the tank through the return line, and the fuel pressure gauge never rises off zero. I'm interpreting that as the fuel return check valve opening, because that's the only thing that can send fuel back down the return line. If the hand pump itself was bypassing fuel, it wouldn't be heading back down the return line into the tank.
I can't see very well inside the bore that the fuel return check valve fits into, so I removed the secondary fuel filter base to inspect it on the bench. I took photos, but I can't get my phone to focus inside the bore, so the photos aren't great. I could see inside the bore with my eyes and a flashlight just fine, and I'm not seeing anything that causes me concern. I'll post the pics if anyone wants to see them.
I put it back together with a new Cat 1R-0749 secondary fuel filter, dry. The Cat 1R-0749 filter that I removed, may very well be the original filter, 16 years and 5,000 miles old.
I used the hand pump to prime the fuel system, and then did several 30-second cranking cycles with two minute waiting periods in between each cranking cycle. On the very first crank, it sounded like one cylinder fired once, but other than that, the no start condition remains.
I am once again stuck.
This afternoon, I'm planning to disconnect the fuel return line at the tank and then crank, so that I can visually confirm that fuel is being bypassed back to the tank. I'll report back on that. | |
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Cat C12 fuel system diagnosis
