My 1993 is showing low fuel pressure measured after the filter. Low like it wont showup on a gauge, or 1-2 psi. I have a new piston low pressure pump, that I benched tested and it is still pumping 15psi. I rigged a line for the lift pump to pull fuel out of a jug, and that made no difference. I plugged off the return line, and the pressure went up to 15 psi, but with everything hooked up normaly it shows just slight positive pressure. I pull the return banjo bolt out of the pump and everything looks good.
No fuel leaking past either pump seal. new filter just to be sure. Truck runs fine, some problems starting, but that went away once I plugged off the return line. so the only place that I can think the fuel is going is returning past the injectors.
I have also had the truck not want to turn off 3 times, once this week when the fuel was reading low/ zero, and twice as I had been working with it yesterday and today. I know that this is probubly the FSS, but just throwing it in to be thorough.
So I am wonding if anyone had any clue on where the fuel is going, or just info on how fuel returns around the injectors.
Thanks for the help.

 

I am not real familier with the 1st gens but I believe that there is an overflow valve on your injector pump. It will be in the banjo bolt that holds the return line on your injection pump. There should be a spring loaded ball in the banjo bolt. The second gens have more trouble with this part than the first gen but they do still go bad. If the ball is stuck, spring too weak, or the seat worn it will not let the fuel system hold pressure. This will usually make the engine hard to start and stuble and smoke bad on start up. I think normal fuel pressure on the rotory pump engines is 3-5lbs.

 

Thanks for the reply,
I pulled that banjo out yeaterday and didnt see a spring or ball, all it had was a 1/32 or so hole in it to regulate pressure, and I cant see 15 psi of fuel moving throught this one very small hole, but I will see what I can find on that topic, thanks.

 

It seems that I may have fixed the problem, but I am not sure I found the true cause. I found an injector that had a slow leak between the injector and the lock bushing. I also tightened the fitting at the inlet of the pump, that I am not sure if it was pre-existing or I caused the leaks in my investigations.
I also found that my autometer fuel gauge sender was toasted. So I hooked up a oil pressure gauge using the small plastic tubing. It seemed the pressure gauge was slamming from 0 to 15psi at idle and evening out at 12-15 at higher RPMs. After I tightened the injector and pump inlet fitting I notice the gauge was jumping between 5 and 15 at idle, and would hold a couple psi with the engine off. I let some air into the line at the pressure gauge and it slowed the pulsing to about 10-15.
But since I never had a mechanical gauge on my truck I do not know if this is normal or not? What do you guys think? Could the leaking injector cause the low/no pressure going into the lift pump? and does the pressure gauge seem to be working as other's with mechanical gauges?
FYI lift pump is the low pressure piston pump that was shimmed to max at 15psi.
Thanks.

 

You need to put a needle valve in the line to your fuel pressure gauge. The pulsing will destroy your gauge in short order. Install a needle valve and just barly crack the valve open, you will know when you have it right when your gauge calms down to a steady pressure.

 

Thanks,
The mechanical gauge is just to get me by till I get a new sender from autometer. My main questions was if this type of pulsation is normal.

Has anyone else had problems with an autometer electric fuel pressure sender. Autometer assured me that the sender/gauge would be fine for my application. I had my gauge for 2-3 years.

Thanks for the help.

 

I'd run a needle valve on the electric sender too. Good chance that's what did it in...

 

The pulsing is normal. It comes from the mechanical fuel pump action every time the pump is sroked it makes the pulse raise. The needle valve will save your electric sender also.

 

Thanks for verifying.
I have fuel pressure now, but the truck will still not start consistantly. I have a Fuel shutoff solenoid on the way, but am pretty much out of Ideas. the lift pump to injection pump is holding pressure, but I am missing something, any Ideas?

 

The number one problem on these trucks is air leaks into the fuel delivery system. You could have a leak anywhere from the pickup tube in the tank all the way to the engine. You might get lucky and find it by modifying an extra gas cap by drilling and installing an air fitting, then pressurize the system to no more than 10lbs. Then get a strong flashlight and start crawling around looking for any wet spots where fuel might be leaking from the fuel system. I am having the same problem now on my 2 gen. It can be very frustrating and time consuming if it is not an obvious leak. The problem is that the system can draw air even though there is not fuel leaking out. By pressurizing the system it forces it to leak fuel. Good luck and do a lot of searches on this forum to find where many common leak point have been found. You will find that this can be expensive even doing this yourself. Good diesel fuel line is very expensive. Do not cheap out and buy cheap fuel line or other parts or you will just be doing this again down the line.

 

That's very good advice lifer!
t_oad01, in order to avoid the hassle of trying to find leaks on my truck, and to avoid future problems, I just went ahead and changed all my fuel lines. I ordered Marine Grade Diesel Hose from Larry B's and it cost me over two hundred bucks and an afternoon to change it all over. (plus a couple fittings) It was worth it. No issues now, and no issues in the future as I plan to keep this truck for a long loooooooong time!
Just another thing to consider...

 

Thanks for the help guys.
I seem to have found the problem to be a combo of a loose injector nut and a bad fuel shutoff solenoid. tightening the injector nut solved the fuel pressure problem, then I had a shutoff solenoid that wouldnt let the truck start all the time, and didnt always shut the truck down.
When I removed the old solenoid the plunger was half stuck and after swaping the solenoid everything has been working correctly for the last couple days. Solenoid from Genos $35.
Thanks again for the help.