Have a 99 f350 7.3 powerstroke. Runs fine when it is cold. After about five minutes of driving, it starts having a rough idle and blue smoke comes out of the exhaust. Smells like raw diesel. Has rough idle for 2-3 minutes--will not take fuel at this time---and then shuts off. Have replaced fuel pump and cam sensor. When first started doing this, could pull fuel line off back of pump, blow back into tank, problem would clear up for a week or two. Over the past month and a half, it has gotten progressively worse. No check engine light and no codes come up on scanner. Have unplugged ICP--no difference. Fuel pump running for 20-30 seconds---book says that it should only run for 5 before start up. Any ideas? Any help greatly appreciated as it is now parked until problem solved.

 

Welcome to the site..

A very common problem with the 7.3 was the 'micro filters/screens' within the fuel tank module,, (not the pick up screen on the inlet) but inside the white plastic body of the module itself. They tend to get overlooked at times,, and usually higher mileage trucks suffer or fuel quality can/will affect screen flow at any mileage. You can check fuel pressure and volume at the test ports (1/8" pipe plug) at the end of either cylinder head. Low volume, low pressure or foamed fuel usually point towards a screen problem.. Fuel filter changed at a regular mileage/inteval? The module case can be opened easily and the screens cleaned but requires the tank be dropped.

The system is a 'return to tank' setup, and if the screens are restricted it will eventually starve the engine for fuel once the available volume and pressure are exhausted.. Usually affects mid/high throttle positions when fuel demand/load is greatest, but depending on how plugged, it can cause starvation down low. Since you've used compressed air to purge the line, with a running improvement, I'd be suspect of the screens..

If the engine starts to bog while driving, drop RPM or a flat throttle with a cackle or rattle/knock at idle, then sounds like fuel delivery issues, more so if no CEL..

 

Have pulled tank,cleaned pic up.Not sure but wanting to think electrical,doesn't seem to happen until gets warm.Could fuel pump running 20 to 30 secs be a problem?Talked to diesel mech he said nothing to worry about.Would like to hear how to test different sensors.Thanks again.

 

Not the pick up screen on the nose of the module,,, there are cylinder type screens 'inside' the modules white plastic body. Did you cleaned those when the tank was down??

Possible another issue, IPR, HPOP etc. but with no codes present and and a repeat pattern failure (?) sometimes your best bet it to eliminate or prove out 'whats its not' first. Diesels DO NOT like aireated fuel, at all,, and a good/spec volume and pressure needs to be checked,,, more so since the engine seems to run fine for some time before the problem occurs..

Quote: (blow back into tank, problem would clear up for a week or two) doesn't seemingly follow an powertrain/engine management failure..

After the driving stall out or idle,, with some key/fuel pump cycling and pump run time will it restart right away and run fine until the next event? During the rough idle about to stall, if it knocks, rattles, misfires,, make sure you have adaquite fuel supply before moving on..

20 sec pump run time is correct with key on, engine off. 30 PSI min fuel pressure..

 

No didn't clean those,wasn't aware they were there until your post.Thanks!After shutoff will not start back without cool off period.Seems to heat up quicker and take longer to cool off each time.Trying to locate pressure gauge.Again,thanks for input.

 

Without a gauge,, and as a quick test only,, you 'could' insert a pipe/hose fitting into the RIGHT cylinder head front/forward test port (you'll see a 1/8 pipe plug there) and attached a hose and either block it off, or install a valve in line.. When it stalls out, have a helper cycle the key and/or a restart attempt.. If the no start is present, cycle/crank and open the valve,, if you have very little/no pressure, low volume, mostly air bubbles, or very aireated fuel, then its a fuel delivery problem.

If it 'jets' out a good steady clear fuel stream (into a container),, then chances are its not fuel related, at least the screens.. You should be able to guess about 30 PSI of pressure, and a good volume is easy to see.. If you get enough fuel to fill a fuel filter sized container within seconds, then probably no restrictions...

You can also try,, wait for the stall, drain any remaining fuel from the fuel filter canister (yellow lever on the back/left of the canister), remove the fuel filter canister top, remove the filter, and have a helper cycle the key. It should fill the canister 'very quickly', so be ready.. Should fill quickly, and not perk with air.. Although testing (gauged PSI check and measure fill) through the head test port is more accurate..

On the stall,, if you continually cycle the key to extend the amount of pump run time, will it start?

After a stall,, (and cool off) does it restart immediately? Does it run smooth once restarted? or misfire, idle/run rough some until it smooths ?

You could check the HPOP reservoir too, make sure the level is within 3/4 or so from the top. Loss of oil would cause a stall as well. But being you were able to use compressed air to the module line, and had a improvement for some time, keeps me thinking fuel screens.. Could be wrong though