rough running, about to sputter out

The tanks are top draw. The lines run from the tops of the tanks to a junction (T fitting) on the top of the transmission. From the junction, a line runs to the primary filter. Then a line runs from the primary filter to the fuel pump. at the outlet of the fuel pump is the check valve I installed many years ago. From the check valve is a line to the secondary filter. At the back of the secondary filter is a single, small, fuel shut-off valve that I turn off when changing filters. From that fuel shut-off valve runs the last fuel line, up to the rear of the cylinder head, right next to the .8 mm fitting. At the output side of that .8 mm fitting is only a flare fitting to the return line--no check valve. I know there is supposed to be a check valve there, but there is none and never was.

I have stated this several times and I will again. When I bought this truck it was often necessary to crank it for long periods before it would start, so yes, I was losing prime from the beginning. The longer it sat the longer it needed to crank. I don't know what Penske did, or who, but the check valve that was supposed to be there never was. Everybody keeps telling me, "Yeah, there is a check valve or you would be losing prime." All I can say is, "No there is no check valve at the back of the cylinder head and yeah, I was losing prime."

As I stated before, I discovered that if I shut off the fuel valve at the back of the secondary filter every time I shut down the truck, and then turned it back on before trying to start it, then I had no problem losing prime. However, in the wintertime, or in cold rain in the middle of the night, it's tough to have to climb out of a warm bunk, climb into cold clothing, go outside, open the hood, and turn on a valve in order to start the truck. There had to be a better way. There was. As I stated, I bought a universal type check valve from Northern Tool and installed at the back of the head, where it was supposed to be. However, after communicating with Gone Fishen, (Did you know that fellow?) I discovered that if the pressure was too much in the Northern Tool check valve, it would negatively affect the performance of the engine.

I went to Freightliner and explained the situation. (This was all many years ago.) They sold me a check valve that was supposed to have the correct back pressure. When I looked at it, I realized that the fittings, pipe and flare, were much too large for the lines at the back of the cylinder head. However, the thread sizes were perfect for a position at the output of the fuel pump. As I stated before, I reasoned that if shutting off the fuel valve directly at the back of the secondary filter prevented the loss of prime, then placing a check valve directly before the secondary filter should have the same effect. I installed the check valve right there in the parking lot of the Freightliner dealer. About a month later, I got around to removing the Northern Tool check valve I had installed at the back of the cylinder head. I was correct in my reasoning. The check valve I placed between the fuel pump and the secondary filter sufficed to prevent the loss of prime.

I did replace the fuel pump on this engine, years ago. I don't remember the circumstances. I don't think there is much pressure on the fuel pump from the check valve. It is the valve that Freightliner recommends and sells. Whether the valve is located at the back of the head or directly at the output of the pump does not change the fact that the pump has to pump fuel through it. I can't afford to go on too many wild goose chases. I just changed the fuel line going from the secondary filter up to the cylinder head because I suspected, (and had been told) that it was probably clogged and that no fuel was getting to the injectors. It was a difficult job changing that line, and when I got the old line off, I realized it was wide open--not clogged at all. That was a lot of work for nothing, except that now I know the problem must lie elsewhere. In that way, the effort was not futile. However, I hate throwing parts and money at a problem.

I'm still stumped, and time and money are running out.

 

I rethought your suggestion. Yes, I believe I will remove the check valve that I presently have between the fuel pump and the secondary filter.

Maybe my problem is a combination of things that result in low fuel pressure at the injectors.

If the check valve were at the back of the cylinder head rather than before the cylinder head, that could only aid in supplying fuel pressure to the injectors.

Thanks, Rideandrepair.

 

I drilled a small hole in the back of the driver side tank, at the top. On the passenger side, I drilled a hole through the vented cap.

This appears to have solved the problem. When I got home, I bought new caps and plugged the hole in the tank.

It's bad not having a fuel pressure gauge. I just installed one. I believe if I'd had a gauge from the beginning I'd have known my problem was not fuel starvation. I must believe the problem was related to the fuel tanks not venting properly.

Looking back, I realize that the problem disappeared whenever I removed the caps, either to dump in additives or get fuel. I never heard a whoosh of air, in or out, but then again the motor was usually running and I wasn't listening. I don't always tighten the caps. I think the problem occurred when I tightened the caps and then ran for a while. I was assuming that the filters were clogging and starving the engine.