Rough idle?

[albinobob]

My 6.9 N/A started running rough this week (just fine before that) and has died at a stop once or twice. At first I thought it was bad diesel, but it's still doing it on the new tank. It is not constant, it'll be running rough for a while then all of the sudden it'll take off with out further pressing the pedal. Feels like turbo lag but I don't have a turbo. Is it time for a new fuel pump? Anything else I should be looking at? Thanks for any insight.

 

[79jasper]

I would start with a new fuel filter, even if you just changed it a few weeks ago.
Next do a fuel pressure test.

How many miles are on the injector pump and injectors?

 

[albinobob]

Fuel filter is about 9 months old. I'll put a new one on this weekend. Anybody know what the fuel pressure spec is? The IP and injectors are factory as far as I know (They look it). I bought it off a guy who inherited it from his brother, so I didn't get any history with it. I was hoping the IP would last until the end of the year so I could do Moose IP/Injectors and turbo all at the same time. Thanks for the input, I would of probably skipped the fuel filter since it's not that old.

 

[79jasper]

4-7 psi, IIRC.
Definitely time for a new fuel system.
But right now your problem seems to be fuel delivery related, instead of fuel injection related.
And filters are cheap enough to just throw a new one on.

Oh the factory injectors should have grey paint.

 

[albinobob]

Thanks for all the info. Hopefully I'll have time to dig into it this weekend.

 

[oregon96psd]

Fuel filter is about 9 months old............... Thanks for the input, I would of probably skipped the fuel filter since it's not that old.

Coming from a heavy equipment background that's a LONG time to run a fuel filter. Not sure what everyone else changes them at but I do mine every other oil change. We do machine's at work every 250 hrs.

 

[albinobob]

It probably is a long time and hopefully that's the problem. I'm a decent mechanic but this is my first experience with anything diesel. I wouldn't know anything if it wasn't for this forum.

 

[79jasper]

Coming from a heavy equipment background that's a LONG time to run a fuel filter. Not sure what everyone else changes them at but I do mine every other oil change. We do machine's at work every 250 hrs.

Especially if the fuel tanks are ran low quite often.
Something which I'm bad about, but I drain the water separator religiously.

 

[icanfixall]

In general terms... The fuel filter lite on the dash will come on when the filter is dirty or the lift pump goes bad. That lite depends on seeing a vacuum on the fuel system and it depends of the filter senser to be working. I really have never seen a post where that dash lite was burned out either. My filter has been in service for probably 4 to 5 years now. I may have to look into the switch and dash lite to be in working order. I believe all the lites are supposed to lite up when the ignition switch is first turned on...

 

[albinobob]

I change the filter and she runs a little better. Still rough though. Next is the fuel pressure test, but I got a lot of stuff going on right now. I don't see a fuel filter light on my dash. She's an '85 and all I can see is the 2 blinkers, brake light and high-beam light.

 

[gatorman21218]

sounds like an air problem. when the engine races like that it means that its passing an air bubble.

 

[stumiister]

There is no filter light on our trucks the light is for water in the fuel which is installed in the water seperator on the far left corner of the cab under the hood to the left of the brake booster.
If your water seperator has been bypassed like mine it will not work.
There are three lights on the dash for our trucks they are no specific order, glow plug, water in fuel and engine temp.
The only light that comes on when you turn the key on is the GP light unless your GP system is on a push button.
The engine temp light comes on when the engine over heats.
The water in the fuel light comes on when the sensor has deteced too much water in the fuel but if the water sperator has been bypassed it will not work.