The truck is a 98 Western Star with a 12.7 liter series 60 Detroit engine (500hp). The problem is that it is loosing prime when sitting overnight and is hard to start. A description of the fuel system is as follows. The fuel tube out of the tank goes under the cab to a rectangular block. It goes into the rectangular block on the side and comes out the bottom. I removed the rectangular block and found a small broken piece of hard plastic tubing inside which I removed. It could have been sucked up from the fuel tank. The fuel level sending unit had been replaced at some time and maybe the plastic came from that. From the exit at the bottom of this rectangular block, the fuel tubing goes to the primary fuel filter. From there it goes to the fuel pump (which is at the rear of the air compressor). Out of the fuel pump it goes to the secondary fuel filter. From there it goes through a manual shut off valve and then up to the back of the engine. At the back of the engine is a y fitting where one leg of the y comes from the shut off valve after the secondary filter and the other leg of the y returns to the tank via another retangular block under the cab. This rectangular block houses the one way pressure overide (spring loaded) valve. I removed this and found it to be clean and functioning. The tail of the y fitting goes into the rear of the engine to the injectors. I checked all fittings and hoses (replaced a few) and replaced both fuel filters. Nothing has fixed the problem. There are no visible signs of leaks anywhere. There are no one/way check valves in the system that I can see. There is a fitting at the top of the secondary fuel filter with 2 wires coming out of it. I assume this monitors fuel pressure. I found if I close the manual shut off (after the second fuel filter) the truck will start right up, but it runs rough for a few seconds and then smooths right out. If I don't close the shut off, it is hard to start. It will take several 20 second cranking intervals before starting, or one 20 second cranking interval with ether. This problem just appeared out of the blue one morning when is was hard to start. Other than this, the truck runs fine, absolutely no rough idle or lack of power and, as I said before, no fuel leaks of any kind. I was hoping someone would have an idea of where my problem lies. Does anyone know if there is a one/way check valve inside the fuel pump? The fuel tank gets warm from the returned fuel, and when it cools overnight I figure that it allows fuel to drain back. The vent in the tank is OK. On a hot day, the truck can sit for 8hrs while I work, and then start without me closing the shut off valve. It will run rough for a few seconds after it starts, but is does start right up. I am stumped at this point. It seems like there should be some sort of one/way valve to hold the pressure, but I can't find one. The only thing similar is the pressure overide for returning fuel to the tank as mentioned already. I would sure appreciate any ideas any of you might have. I don't have a shop manual for this truck and so far have not been able to find one other than through a dealer (they must be gold plated at the dealer as they are quite pricey). Thanks in advance.
Bummer to have a pesky problem like this, Bob. You mentioned the line leaves the primary filter and goes to the pump, then to the secondary filter. Is it going through a lift pump after the primary? If so, lift pumps have backflow check valves. Could that be your problem? Don't have much experience on the 60 series.
ATCOEQUIP, thanks for the reply. I suspected there was probably a check valve in the pump. When I get a chance, I will pull the pump and check it out. The pump has plenty of output because it seems to pump enough to return quite a bit back to the tank as evidenced by the heat build up in the tank.
I hope it turns out to be something this simple. Pesky problems are just that. I just haven't worked on the 60 series, don't know much about them. If it has a lift pump, it's possible for it to push plenty of fuel while running, but a slight leak in the check valves would allow fuel to drain back overnight, making hard starting. Seems I remember we had a member join not long ago that maintained a fleet of trucks out in New Mexico or Arizona, can't remember his name, haven't seen it for a while. And maybe mufflerbearing has worked on these. Come to think of it...seems he's been quite for a while now. Where's everybody at when ya need 'em?
Remove your injectors and replace all the "O" rings , retorque the bolts to specs . It sounds like your losing pressure to the injectors and it is also alowing air in so that the fuel returns to tank . There is also a check valve at the rear of the head you may want to inspect first .
Iron Horse, do these things use something like the HEUI injectors?
Bob, I would also suspect that the lift pump has a some sort of one way valve that has deterioted , cracked , or worn out. Good luck.
The EUI injectors are pressurised by a cam driven pushrod , early engines used steel cam rollers but could not handle the pressures , ceramic rollers where then used . The fuel pressure rises to around 28,000lb by way of the pushrod , the ECU then tells the injector solenoid to open a poppet valve holding the fuel back which then allows the high pressure fuel to overcome the check valve spring . This starts the injection of fuel , the ECU controls how much fuel and for how long it is injected taking into consideration all the inputs from the various sensors , boost pressure , potentiometer position , Turbo vane position etc . Going back over some notes i wrote in my old diary , Engines with the Serial number 6R13060 had a check valve fitted in the secondary filter head , this may need checking also . If the injectors are removed , new hold down bolts should be used . They should be torqued to 37 lbsft , backed off 60* , retorqued to 27 lbsft and then a further 90* . N3 and N4 injectors used different coloured "O" rings , you must make sure wich ones you have .
Bob, Iron Horse has given you some info that I would print out and keep for future reference. I would focus on the check valve/valves. What he said about the check valves is more than likely where you'll find your problem. You mentioned that there was a recent problem with the sending unit in the tank, and that you had already found some sort of plastic tube in line. A good place to start lookng would be the check valves. Take them out, check them closely for debri or damage, and if you suspect a problem, just replace them. I have found over time that is usually the first place to look when the engine looses it's prime. Either that or a loose fitting in the fuel line. Anytime a fuel system is opened up for repairs, it is subject to foreign material being allowed to enter the system. One other culprit would be a fuel line deteriating inside and sending trash thru the system. The check valve has very close tolerances to begin with, and a piece lodged at the sealing point overnight would cause a no start, or start and then shut off due to losing its prime. While the initial culprit may get flushed on thru to the filter the next day, it can cause an imperfection in the sealing surface of the check valve, rendering it defective. Then you have an ongoing problem, daily. Just my 2 cents worth. Rigandig
Thanks for all the replies. I am fortunate enough to be busy right now, so the first chance I'll have to look at it again will probably be this weekend. I'll let you know what I find (or not).
I would say check valves at the rear of the head. Dont know about your particular truck model but their usually a cheep easy thing to change first.
Some good information here, make sure you don't get bit like I have a on Series 60 and troubleshoot for a day replace a few parts and then finally find the fuel line that needed an extra 3/4 turn to be tight.
Not sure what fuel filters you have but i had one with the replaceable cartridge with the plastic cover. Right after having a service done i had the same problems, found that someone hadnt cleaned the cover seats and replaced the o-ring which was causing the system to lose its prime.