This has me stumped! truck will run fine until 1/2 tank of fuel, starts missing and blowing black smoke, throttle pedal gets very hard chugs and dies. pull over to the side of the road wait a few minutes and restarts and runs like a top for about 5 miles ,does the same thing starts missing , throttle pedal gets hard then stalls out. let set a few minuts and restarts and runs fine. it ran for 130 miles before acting up, i changed the fuel filter thinking it was water in the fuel, ran good for about 10 miles started acting up again. was able to coast down the mountain for about 40 miles, no problem, got back on the interstate and ran another 130 miles without an issue. i replaced the fuel lines, and pickup pump before this all started happening, but it seems after you get below 1/2 tank it will not stall and runs just fine. If it was an injector or main p-pump wouldn't it do it all the time? anyone have any suggestions. Thanks for looking.

 

You say it's fine above and noticeably below the half-tank level? It's only troublesome around the half-tank level? Was this a one-time occurrence (so far), or repeating?

If it is troublesome from the half-tank level and below, I have a couple of possibilities. But if it clears up below half-tank, then one or both possibilities probably won't apply. If it acts up below half-tank, the two possibilities that come to mind off-hand are:1) Cracked pickup tube in the tank around the half-tank level - once the fuel level is below the crack, air gets pulled in. I kind of doubt this one since you were able to run a fair number of miles (130) after the problem started one point, but you didn't mention if you filled up before the 130 miles. I assume you didn't. 2) Gunk covering the screen on the tank module below the half-tank level. Again, this probably doesn't apply if the truck behaves again after the fuel level drops below half-tank. But I throw these out there to get other ideas going.

The black smoke and stiff throttle pedal make me think lack/loss of boost. I suggest looking at wastegate/AFC/boost-reference line - really everything boost-related. Those don't have any connection to the fuel level, so maybe the fuel level is a coincidence. Do you have a boost gauge?

 

i don't think it is boost, i have a boost gauge and it will still produce boost when it acts up. after the secound time and below 1/2 tank it ran over 80 miles with an average of 17 to 25 lbs of boost. I drained the fuel filter i pulled off before the 80 mile trip and no water was in it? i am wondering if i have a p-pump problem. i have a number 2 fuel plate with the afe spring kit on the govener. 225,000 miles on pump and never had any work ever done on it. i drove it a little today and can not get it to duplicate the problem, i am at 1/4 of a tank off fuel. thanks for any info!

 

I read on "another forum" (check your PM's) that there is at least one brand of GSK (governor spring kit) that perceived to be troublesome - I don't remember the name, though. I'm not sure of the symptoms of a problem GSK (especially as I've never run one myself) - I don't want to mislead you as to possible symptoms.

 

OK i think we may have figured it out, i have been running low sulfer fuel and #1 fuel alot, and with no addative in the fuel whitch makes the pump run a little on the dry side, we filled up with fuel and added a bottle of fuel treatment and drove a full tank with no isses. Hopefully i did not damage my pump. The guy at the diesel pump shop said that the old p-pumps need lubrication and the new low sulfer fuel does not provide that in the old 12 valves. So i will use addative every fuel up and see what happens.

 

Sucking air when it gets to that level

 

Half tank fuel die out is a problem I had for years. Just fixed mine as the orings in the fuel reservoir were shot. No issues since

 

Sounds like sucking air when you get on it- had that problem when I bought my 94. Had a tiny hole in the fuel line coming out of the tank right where the cab & bed meet