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Old 07-31-2013
TxLodge TxLodge is offline
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Default 3208 Fuel Filter Assembly Sucking Air Through Mystery Line??

Hopefully a simple newbie question... I am tracking an air leak in the fuel supply system and I have it narrowed to the fuel filer / hand primer pump assembly. You can see in the photo that I have bypassed the assembly and have no problems, but when I route the fuel through the filter I get air in the lines that I cannot bleed out (probably $15 in diesel on the pavement so far...). I have replaced the primer pump since the photo as I understand they are a common culprit, so now I'm left with the supply lines and the mystery line. So here is the question: what is the mystery line (blue arrow in the photo)? It routes down through the tunnel, past the batteries in the driver side fender well, back up though the driver's foot well and up into the dash, where I lose it. Seems that it's headed for a gauge or idiot light, but which one?? Just the routing makes me suspicious that this is the work of a PO, not the factory.
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Old 07-31-2013
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Racor Gauge?
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Old 07-31-2013
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yep,it goes to the Racor filter gauge.
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Old 07-31-2013
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I had a problem with sucking air in that area a while back and it turned out to be one of the short rubber lines. Look for drying and or cracking around the ends of those lines or just replace them It only takes a couple feet of fuel tubing and isn't hard to do.
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Old 07-31-2013
TxLodge TxLodge is offline
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Ok, this makes some sense to me. The gauge measures pressure, and mine is inop which further points to a leak in the line. Here's a follow up question though: what is teh gauge telling me about the Racor? Isn't it just giving me general info about fuel pressure? Not enough pressure equals clogged Racor filter?
BTW, I had previously assumed that the gauge was inop bc a PO had removed the Racor, which I have recently replaced though I haven't hooked up any of the wires yet as mine didn't come with the heater or water sensor.
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Old 07-31-2013
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It measures restriction not pressure.
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Old 07-31-2013
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FYI, a few years ago when we ran Cat's in our truck fleet we would keep stock on the hand primer pumps as they would fail regularly
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Old 07-31-2013
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The Racor Gauge is actually a Vacuum Gauge. The injection pump is pulling the fuel from the Racor filter. If the filter is plugged it pulls harder, hence a greater vacuum on the line. If the gauge is not reading you either have a bad gauge or a big enough air leak that it is not pulling anything. When I had my problem I could pump the hand pump then hear it sucking air.
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Old 07-31-2013
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remove & plug that line for now, then check for air leak, Remove from racor gage & blow low pressure air to clear the line. Still need to fine the air leak, that little fuel filter on the right side in the picture looks owner installed & suspicious
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Old 07-31-2013
TxLodge TxLodge is offline
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Thanks for the guidance. I'm going to start by taking the Racor gauge out of the loop and working from there. Bill, the suspicious fuel filter I added while bypassing the primer pump and screw-on filter. It's coming back out once I find the leak and route the fuel properly back through the screw-on filter.
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