Well I thought I had my priming issues cleared up, but it only lasted for a day. I replaced the line between the heater and lift pump hoping that would be the culprit, but it wasn't.

The last couple of months I have been having a miss at idle, about once every 2 seconds or so. Once I rev it up a bit past idle it smooths right out. When I'm in gear it is easier to notice, the no load idle is about 750 RPM or so, with it in gear it pulls it down to about 500 RPM. Could this be related to my losing prime issue? When I think back on it, they started happening about the same time. I don't hear any ticking coming from the lift pump (hard to tell though).

I already replaced the supply and return lines, fuel filter has 3K on it, and replaced the rubber line between the heater and lift pump.

Anybody been here before?

 

I had the same problem was my Overflow Valve.check by crimped my return line and problem went away.

http://www.tstproducts.com/index.asp...PROD&ProdID=32

 

pittom nailed it, probably low fuel pressure caused by a bad overflow valve.
you don't have the means check fuel pressure just replace the overflow valve
Replacing the OF valve is a five minute one wrench job if you don't drop the sealing washers, stuff a rag under the valve to catch a falling washer. Remove the old valve and put new one in it's place. Occasionally the notch in the manifold you see to the left of the OF valve in the picture needs to be filed or ground a little to allow the old valve to be removed. Don't bend the line to remove the valve, it will make it very difficult to line up again. New style OF valves don't always have the retainer on top that says not to remove, don't worry it's just a design change.

The object in the lower left corner is the oil fill cap.



You won't find a better price on an overflow valve than here

Precision Diesel Injection and Turbo Inc.
Marty Tompkins
888-734-7349
$40 + $7 shipping and handling.

 

You're idle is also a bit low. Should be about 750 in gear A/C on.

 

I replaced my OF valve 2 years ago, maybe it's already on it's way out. I'm thinking I'm going to pick up a temporary fuel pressure gauge to check it and see. Thanks for the ideas, hopefully I can look into it this weekend (apartment people don't like college kids wrenching in their parking lots )

 

While you are messing around with the fuel system, install a permanent fuel pressure gauge. It can be a real help. 17-22lbs at idle, 25-35 @ 2500 RPM, no load.

 

CrimeDog,

I had the same problem with the miss (loping) at idle. I only had 8 PSI of fuel pressure. Replaced the LP (Carter) and problem solved, for a little while. Started loping again and I checked the pressure again and it was only at 9 PSI. I removed the LP again and found the check valve at the top fitting was loose and would fall out of the fitting. I had to peen the fitting over to keep the check valve in place. Now 26 PSI at Idle). This was about two months ago and I haven't had a problem since.

Hope this helps!

David

 

Have you 12v folks ever watched your fuel pressure when youre under heavy acceleration? Ive seen the gauge dip down under 10psi!
Im thinking those stock fuel lines are next.

 

Even pulling a 25k trailer from a dead stop with engine mods at 350hp plus my FP has never dipped below 18.
Something else is wrong with your truck besides the stock fuel lines.

 

same here. never saw either of my past two 12v trucks dip below 18 never saw below 20 once up in the rpms pulling down the road with heavy loads. even with twins and lenny stage 4s all on stock lines, lift pump and dv's

 

new fuel lift pump, new overflow valve from cummins and new hoses up front. had the heater screen cleaned and did the filter not long ago. Only things left are the lines. Theres all kinds of rust and a couple unions on them so Im surprised if theyre not leaking air. I dont lose prime though. not yet anyhow. At some point Im going to take the starter off and re-check that heater.