Stale fuel or bigger issue?

Ciulster

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So recently I've been having some hesitation issues with my 6.9 and I just want some opinions on what the likely culprit is. Back when I first got my truck it ran a tad rough. Almost like it has a slight misfire. Every 5-15 seconds the engine rolls around enough to shake the entire cab once. And the exhaust sounds like its spitting like a misfire when it happens when standing next to it. Not to mention usually pretty heavy blueish white smoke upon revving after idling for more than 15 seconds.

However that all changed when I replaced the injector line clamps (as it was missing two) and the truck now idles quite smoothly without any rumbling shaking or spitting, and the smoke is nowhere to be seen unless at WOT for a bit and even then it's minimal.

But here's the thing. The truck now heasitates pretty bad if I let it idle for more than a few seconds. But once it gets over the 2 second hesitation it has decent power. I even managed to capture a video of me snapping the throttle wide open. 1.5 second hesitation, and as soon as the engine started to rev I snapped the throttle closed and it stalled. It only did that once though.

The last time I fueled up was mid August last year. (So 7 month old summer fuel) It sat over the winter and there were many points where it was probably 30-35 degrees below freezing, but when I started it during a warm spell in December the throttle response was as good as usual still rough as the line clamps were still missing. Come February (currently just above freezing now) I change out the line clamps and start it. Very hard start. I had to crank for like 20 seconds as it slowly gained cylinders and with my foot to the floor it eventually ran on like 6 and gained the rest shortly after and I could take my foot off it. Surging idle when cold. When warm it had that hesitation I mentioned. I did dump like half a bottle of fuel conditioner before the winter though. Return lines were done in summer and arent leaking now... and when it stalled it started back up instantly no problem so not a heatsoak type deal.

So my question is is this probably just really stale gummy fuel with moisture in it. Or is this a larger issue like air intrusion or failing IP/injectors?
 

DaveBen

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More likely air intrusion. Diesel fuel will with stand a long time in storage, like years.
 

chris142

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My peterbilt sat 20+ years un-ran. 2 good batteries and I drove it home on the 20+ yr old fuel.
 

Ciulster

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I have just seen elsewhere that sometimes diesel when not kept in a full tank can have issues with moisture or algae and bacteria growing in the fuel causing issues. Even with additives I guess leaving summer fuel to sit for months below freezing didn't help either. Maybe it just needs to be run and is being grumpy.

Everytime I've taken the fuel filter off its been full so it's not seeping back through return lines and probably not a leaky lift pump or lines. So maybe my best bet is to just try a bunch of fresh fuel when I get it back on the road and drive it and hope it clears up. I guess if it doesn't clear up I could always try running some ATF through the pump and cleaning out the tanks and inspecting the pickup tubes. I just really dread the idea of replacing the injection pump and injectors. Parts like that aren't cheap in Canada anymore unfortunately.
 

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