Well I've had this problem for about 9 months. I replaced the lift pump (with a PPE 165GPH), put on a big hose kit, put in a FP Gauge, etc... Problem didn't get any better. That was about 5 months ago.

I finally saved enough money (we don't get much work in the winter), bought a new set of injectors, and installed them today. Even pulled the radiator and pressure washed it clean and flushed all the coolant. Well, I installed a set of RV275's got everything back together, fired it up in the driveway (trying to burp the cooling system), and it sounded like a 24V should at idle. Sweet! Buttoned things up, took care of the tools, etc. Got back in to take it for a test drive, ran it good and hard for about 6 miles, and every time I let it idle it was back to its old self, a miss or lope, rough idle, I don't know how else to describe it. Its really only when the engine is warm, cold it seems normal. Now, the old injectors were original at 230K miles, so I am happy I changed them anyways, but I want this thing to run smooth like it oughta!

Sooooo... I don't know whats left besides the pump itself, and I don't have a grand to drop on a new pump if I really don't need it. The thing fires right up every time, and its got plenty of power, so I don't think its really the problem, but I really don't know.

 

Have you checked for codes? tps or apps sensor voltage at idle? overhead set?

 

No codes, APPS hasn't been checked, but I kinda doubt it would be giving me this problem... Possible though.

 

Have you set the overhead? Could be tight cold and when things warm up and grow its holding the valves open a few thousands. Good luck

 

Had a truck with the same problem. Ended up replacing the injection pump and the cured the problem.

 

I'm going to say it's the pump.

When its cold, the fuel is thicker so the pump's leakage doesn't show up. It has no problem making enough flow to pop the injectors open properly and consistently.

But with hot fuel/warm engine, the fuel is much thinner and the pump can't meet the demand. It's running out of capacity and you are having the problem you describe.

There's no fault code for "pump not flowing enough". The ECM on these things has no feedback at all as to whether enough fuel is flowing or how much pressure is in the fuel line and such.

JH

 

I wouldn't get a pump unless you start to see codes. I asked a similar question a while back and never got an answer or explanation. On mine, brand new injection pump, new lift pump, and set of new Bosch stock injectors. Solid 18-19 psi at idle, never below 10 on a hard pull WOT. Using a tuner or not made no difference. Mine has a waving idle ( best way to describe ) when coming off the throttle. No load, just normal everyday commute driving. It doesn't miss or lope like yours, but more of two or three dips in rpm of about 50-100 and then all is fine. It never did this before I went broke replacing all the parts, and the shop I got the pump from had no explanation either.

Question: Did you have this idle problem with your old injectors? I didn't, and mine had over 160k on them. Only reason I replaced was the tech showed me the inconsistencies when they were being pop tested and suggested new ones.

 

Yes, I had the same problem with the old injectors, its honestly one of the biggest reasons I changed them. I'm betting its the pump too at this point. but the truck runs fine, and under load its not a problem. (Although its probably loosing a few ponies because of this). I'll replace it when it dies completely, and not before then...