My truck is very hard to start and stumbles for a long time after starting when cold. Runs fine when warm. There is a lot of white smoke on start up. It acts like an air leak or an over flow valve is bad. I have replaced all the fuel and return lines from tank to engine with new marine rated diesel hose. The hose between the fuel heater and filter is new. I put a new over flow valve on and replaced the fuel filter. I removed my fuel heater to eliminate the possible leak where the wire connections go into the heater. I have a fuel pressure gauge . Before I replaced the filter and over flow valve it would idel at 20 lbs and drop to about 5 at full aceleration. Now it idels at 20 lbs and at cruesing speed it is at 30 lbs but at full acceleration it drops to about 18-20 lbs. Before I was having trouble the fuel pressure would hold 30 lbs at full acceleration with no problem. I am out of ideas on where else there could be a fuel leak that would make it start so hard. I also wonder if my lift pump is getting weak since the truck will not hold 30 lbs at full acceleration any more. I have 142k on the truck.
Are there any other leak prone areas in the fuel system that I have not covered.

 

is this w a full tank of fuel or partially empty? if partially empty you cud have a crack in the pickup of the fuel sender assembly

 

Its sounds like your timing might be off

 

I have seen a few lift pumps go bad around that mileage or earlier. I've also read on here about new overflow valves (especially Ebay ones) that didn't keep the pressure up. As mentioned, pump timing plays a big role in the stumbling and white smoke during warmup too.

 

Have you checked your grid heaters and verified operation? Those failing to come on will cause hard starts and stumbling when cold.

 

It does not matter if the tank is full or empty. I got the Overflow valve from Larry B so I am confident that it is good. I have not checked the grid heaters for a while but in the cold I can see my volt meter rise and fall as they cycle so I think they are ok.
I was reading another thread here on the site and they were talking about a fuel line that goes behind the fuel filter and goes to the back of the engine. I think this is one I have replaced but I am not sure , I was wondering if this is a metal line and if so do they crack? If it is a metal line then I know I did not replace it.
I have not driven my truck much since last June and the truck was doing this in the summer also just not as bad. As the weather got colder it is more prominent.

 

Its possible that the timing could slip. I have not checkeed it since I set it at 15 1/2 degrees and that was several years ago. The truck runs like a scalded dog when it is warmed up though so I would think I would see a performance diference if the timing did slip.
I forgot to say also that I adjusted the vaves about 2 weeks ago also. So in case someone was thinking the valves might be the problem, there not. The intakes were down to about .006 and the exhausts were about .021. I set the intakes back to .010 and the exhaust at .020 . Truck runs the same as it did before I set them.

 

If the timing did slip, the quick test is to free rev a warm engine up to redline. If the timing is late, you will get stumbling and white smoke in the upper RPM range. This is somewhat true for low fuel pressure too though.

 

I will have to check the timing. Now that you mentioned the high rpm stumble when warm I have noticed that the truck stumbles at higher revs even after the truck has been running for 10 or 15 min. and it never did that before. I have also noticed that the temp gauge never even reaches the first line on the gauge even after driving the truck for an hour. I was thinking the thermastat might be stuck open but if the timing sliped the cylinder pressures would be very low and it could make the truck not warm up in the cold weather we are having right now.

 

Well I went out to start the truck this morning after siting since saturday night and it fired right up like it used to with no white smoke and no stumbling. It was 31 degrees . I wonder if it just took a few starts to get all the air out of the fuel system. I also took it for a drive and on the way home I did a full acceleration run and was able to hit 36 psi on my boost gauge, I have only been able to get it to about 32 or 33 for quite a while. It used to hit 36 all the time a year or 2 ago. When I got back home I reved it up to 3K and there was no stumbling at all. Im going to drive it for a few days and see if it continues to start good, if it does not then I will check the timing.

 

To check the LP, while the engine is idling, pinch off the 5/16" return line up by the fuel filter ( it is the one running behind the FF ). Pressure should spike up to at least 60 PSI. If it does, LP is still good.

 

Well I found the problem. I took the truck for a drive and the puled it into the garage and started looking for wet spots. I ran my hand under the banjo bolt where the fuel line connects to the injector pump and my fingers were covered with fuel so I replacing the washers on both sides of the bolt to stop the leak.