Hard starting after sitting a week or two

Today I removed the "doghouse" cover and inspected the fuel lines connected to the rear of the cylinder head. Here is how it looked when I removed the doghouse:



After scraping some of the gunk off with a screwdriver it looked like this:



I believe this is the check valve; can anyone confirm the chrome-plated-looking thing in the middle is a check valve?



Here is a shot looking up from below the fitting:



According to this image from the Detroit Diesel website, the return to the tank is the upper port, the one with the check valve, and the high-pressure line from the pump is the lower one (hard to see in my image):



Note that my return line goes the other way, to the left, while this diagram shows it going to the right, but that shouldn't mean anything. I am also curious what is the sensor whose cable enters the head just above these fittings, with the black plastic shroud? My supply line, the lower fitting, looks like a very old braided cover fuel line; I'm wondering if I should replace it while I have access to all these fittings. I'm also planning to redress the electrical cable in the loom that is tie-wrapped to the return fitting check valve; I don't think it's a good idea to have electrical wires directly in the path of potential fuel leaks.

The fact all this black crud has built up, and the general oily nature of it, suggests there may be a slow leak at one of these fittings. I plan to clean it all up properly with solvent and rags, then start the engine and see if I can find a leak oozing fuel in this area.

In terms of the effectiveness of the check valve, if it is indeed designed to be in the return line, then the direction of flow through the valve is towards the tank. I don't see how this prevents drain-down when the engine is shut off for a few days. I would have thought it would be in the supply line, to prevent draining back towards the filters and pump. I must be missing something here. Is "GoneFishen" still active on this forum?

Pete

 

Thanks, Arnell. Yeah, that one post was a bit confusing; makes sense now!
Pete

 

Exiled: The check valve I replaced was at the rear of the head in the line that returns unused fuel back to the tanks. If your fuel pump is starved for fuel, it is unlikely that is the culprit. More likely you either have a slight air leak in the suction piping, or a restriction between the tank and the pump. Have you replaced your primary fuel filter yet? That is certainly a prime candidate if it is getting plugged.

I have a bit of an update on my situation. I brought the truck to Rochester Fuel Injection to replace the fuel pump (a reman unit I bought from Highway Heavy Parts online), both fuel filters, and the three flexible braided fuel lines between the pump, filters, and head. After they did all that, I picked up the truck and the next day drove to a nearby fuel station to top up the tanks (which were about 3/4 full already). After fueling the truck wouldn't start. I tried quite a bit of cranking and even a shot of ether, but no good. It clearly wasn't getting fuel. I had to have it towed back to RFI, which was close by, and the next day they found what was wrong. Two of the fittings on the new hoses they made were leaking air, causing the pump to break prime. They re-made those hoses (no charge of course) and it has been fine since then. I've only driven it 1500 miles however, and the longest it has sat is overnight. So now it is parked again, and in a week I will try starting it to see if it is fixed.

One further odd note: during the trip at one point I wanted to drain a bit of fuel and/or water from the primary fuel filter (water separator). This is a Fleetguard FS19513; I do NOT have a Davco unit. But when I opened the drain valve at the bottom of the filter, rather than anything draining out, I heard air hissing in! The engine was stopped, of course, so this implies there is some level of vacuum at the pump input, even hours after the engine has stopped. I'm beginning to wonder whether there may be some restriction at my tank pickup line. I had asked RFI to check my tank lines and replace any that seemed questionable, but that doesn't mean they did any kind of suction or pressure test to see if the lines were clear inside. The Volvo tanks have separate vent lines at the top of each tank, rather than a vented fuel filler cap. I guess I could find a way to make sure the vent is clear, as well as to measure the vacuum at the primary filter while the engine is running. It seems to me the input side of the primary filter, which is connected to the tank via a fairly large line, should have nearly zero vacuum while running, unless the line is partially plugged somewhere.
Pete