LLY Rough Idle

[Roy W]

The truck has 122, 000 miles. After the truck is warmed up it has a fairly consistent rough idle, miss, or hiccough while idling. Six months ago it was very inconsistent and only did it once every couple of weeks. A month ago it quit entirely, but now it's back again. It runs smooth out on the road and even at low speeds. It just does it at idle. When it is occuring there is no smoke, either white or black. I've never had a check engine light come on. I've run a fuel conditioner in every tank since new. I've even tried tripling the normal treatment, but it did not help. The fuel filter is changed every 10,000 miles and was just recently changed. (Baldwin filter). I've never had the injector harness kit for #2 and 7 installed and wonder if that is the place to start?......Fuel pressure regulator?......Any other thoughts??

[rapidoxidationman]

Given that you've just changed the fuel filter, I wonder if there's air leaking past the filter gasket. Maybe check the gasket or put another fresh filter on it, bleed the air, prime, and see what happens?

Start with the simple stuff...

[Mark Rinker]

IF NOT FUEL FILTER / SEAL then
FPR
<endif>

[Roy W]

It was doing it long before this filter change, and the water in fuel sending unit on the filter is new.

[rapidoxidationman]

IIRC it would be pretty easy to splice in a clear section of fuel line from the output of the fuel filter and see if there's any air bubbles - unless you've got a lift pump installed there's a chance the vacuum in the fuel system is pulling in air from a small leak that's getting bigger. A cheap test, then follow up on what Mark said if there's no sign of air.

[More Power]

60 gallon RDS toolbox/tank combo, Kennedy Headlight Booster, Isspro pyrometer and boost gauges, Edge EZ, Boost Stick, EGR Blocker, PCV Kit,

Aux tanks have occasionally been the source for engine running problems. Make sure the fuel is clean, make sure there isn't an air entry problem into the fuel supply, and make sure there isn't a vacuum problem created by an improperly vented/plumbed aux tank.

It's usually best to remove/disable any performance product that could affect how the engine runs - as a first step in troubleshooting.

Jim

[Roy W]

The aux tank is plumbed into the OEM tank filler pipe and fed by a electric pump, so that rules that out, but I'll disconnect the Edge EZ and try that.

[Roy W]

I disconnected the Edge EZ and still have the occasional rough idle/hiccough. I guess that points to the FPR. Would a lift pump be a "band aid" fix??

[Mark Rinker]

I disconnected the Edge EZ and still have the occasional rough idle/hiccough. I guess that points to the FPR. Would a lift pump be a "band aid" fix??

Not in my experience, with a 2002 LB7. I never did replace the FPR, the cost outweighed the rough idle.

[Roy W]

Mark,

Are you saying that the surging, rough idle and hiccough won't get any worse as long as I can live with it ??

[Roy W]

Getting worse. While sitting at a traffic light it feels like a gasser with a spark plug miss.

[rapidoxidationman]

Any codes?
Is there air getting into the fuel? A length of clear tubing in line with the fuel filter output line will answer that question...