Power down alittle grey to black smoke rear tanks?
I took a trip (2200 mile with toy box) last week and a few things started to happen. First off the engine started to act like it was running out of fuel on the rear tank at 1/4. I would switch tanks and it would run fine. Then my son mentioned that there was quite a bit of grey to black exhaust. Since I was on the road I added sea foam and fuel drier to the rear tank but the it keptrun funny at 1/4 tank and yes the smoke was still there. Mid way though the trip I changed the fuel filter with no improvement.
When I got home I drained the rear fuel tank add some more sea foam and drier. I then refilled the rear tank to 1/3 and when I got to 1/4 tank same thing happened. I changed the fuel filter again noticed that the bowl was 1/4 full when I open it up (Don't remember if htat is normal) Yes the smoke is still there. The truck starts are seems to run fine just a slight lose of power?????
Does the fuel level in the bowl come up to full when you install the new filter? Sounds like a venting problem in the rear tank to me, if it's not venting properly you'll get a vacuum which would starve the engine of fuel. Does it do it on the front tank?
The extra smoke happens with both tanks. Front tanks runs all the way to the the red below E. Is there a vent for each tanks? Where is it? Could this be causing the extra smoke?
Each tank is vented through the filler neck for that specific tank, that's what makes me think that is what is making it seem like it is running out of gas only on the rear tank. I don't think the smoking is related to that problem, especially if it does that on both tanks. When it runs rough on the rear tank have you checked your fuel press at the schrader valve on the fpr? Pretty sure the fuel bowl should always be full. Others with more experience should chime in soon.
In the morning I'll blow out the vent lines. Should I do it from the line as it comes off the filter? I have not checked the press. at the schrader valve. Still wondering about the bowl level too. I read that air could be getting in the system via a leak in the supply line because fuel is drawn to the engine (vac) instead to pos pressure from a fuel tank pump. Not sure why extra air in the fuel would cause smoke?? Thanks for your inputs
There is also a small (1/8" inner dia.) rubber vent hose on the top of each tank. It clips to the frame and has a little mushroom shaped cap to keep dirt out. This cap can also get filled with crud and keep it from venting properly. On the rear tank the vent line should be clipped to a crossmember just above the rear axle, near where the fuel gauge sender connects to the chassis wiring harness.
Additionally, there is a rubber pickup foot in the tank with a screen on the bottom. If this screen gets clogged then fuel can be pulled through a rubber bypass valve on the side of the foot. The result there is that the pickup will start sucking air at about 1/4 tank. (Note, this can also happen if the bypass valve falls out of the rubber foot). There should be some pictures of it in the webshots link in my signature.
Unfortunately, the only way to get to the pickup is to drop the tank (or remove the bed). Fortunately, it's not that tough of a job. It should only take a couple of hours, and the only specialty tool you'll need is the fuel line quick-disconnect tool (less than $10). There were two such tools at AutoZone when I got mine, and you need the one that works for the two sizes "E" and "F".
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1997 F350 CC DRW E4OD POS webshots
Maybe you you could prove out the vent theory by loosening the fuel cap the next time the engine does it. If the symptoms don't go away then it's not a plugged vent. I would suspect a cracked fuel pickup tube and the fuel is aerating.
I try keeping the filler cap loose tonight on the way home tonight. Still wondering about the grey smoke with little load and filter bowl not being full when I changed it
Dont feel bad about taking your truck in. They can be daunting to work on. I am fortunate to have holes in my wallet so I was pretty much forced to work on it myself when I first started with trucks. Much more knowledge and experience later, but still a holey wallet, I have adopted the attitude that I wanna fix it and no one else can touch it. Obsessive huh?
97 F350XLT, CC, SRW ,LB 4x4, 4.10LS, E40D, genuine Tymar intake, Diamond Eye 3" DP- 4" back to 5"tip, Stage 1 inj, IDM mod, gutted EBPV, modded pedestal, TW 6 pos chip, 1.0 turbo, shimmed FPR, Dipricol Optix pyro, boost & tranny temp on A-pillar, Pioneer CD, SIRIUS Sat. 
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