Stumble at Startup

[LorenS]

I have searched the prior posts and articles and have not found anything that reflects the situation I have - if one exists, please send me the link!

When I start the truck in the morning, the engine stumbles a bit and acts like it's going to die.  It then idles and runs "smoothly".  This problem happens only if the truck has sat for at least 10 hours, and not every time.

 

On Monday it DID die, and didn't want to restart at all! I don't believe I drove the truck at all on Sunday, so it sat a LONG time before the restart.  I smelled no unburnt fuel in the exhaust after a combined cranking time of 15 seconds, I had my normal 12 PSI of lift pump pressure before cranking (measured at the VP44 inlet).  I disconnected the VP44 wiring to look for issues and found nothing.  Reinstalled and the truck fired up after a couple seconds of cranking it lit off.  Clearly that could just be a coincidence, and if I'd just kept cranking a few more seconds instead of disconnecting the electrical it would start.  No sign of a FUEL leak anywhere, even back of the block.  No idea if it's sucking air somewhere, or if that is even a potential problem at startup.

 

My injectors are stock rebuilds, maybe 15k miles on them.  My EGTs at highway speed seem higher than before the stumble started, but it's also gotten a lot hotter and I dropped my tire pressures around the same time.  I do not have a chip of any kind.  Fuel mileage is about the same as always, hard to judge as I've towed more recently.  16' utility trailer with some deck lumber, nothing heavy like a skid steer, etc.  My OBDLink shows the same type of data as usual, little higher IAT as it's summer.  I buy my fuel at the same places as usual.

Any trouble-shooting advice is appreciated!

[dripley]

It sounds like your loosing prime of the fuel system. Just early signs of it any way. It could easily be the return, back of the head or tee it connects to. It is possibly for it to leak air into the system and not see a leak. Thats how mine started out but a leak did finally show. I went thru this again about a yeaar ago it turned out to be a bad cross over tube O ring letting some air in.

[LorenS]

Thanks, Dripley.  I hope it's not a crossover tube, I changed all the o-rings this winter when I changed the injectors.  Glad no one so far has said "your VP44 is about to die"!

[wil440]

surely with the AD165 bump the starter so the pump runs, turn the ignition off  and then try to start it, if the fuel is running back (air leak into the fuel system) then it will start with no or less cranking, depends how bad the leak is as to how long the transfer pump has to run to build prime, and leak in this instance is a leak of air INTO the fuel lines and as M73M has said on another thread not a leak of fuel out of the lines...... this will only happen when you get to crank for minutes not a few seconds

for me if everything on the outside looked ok and was nice and tight nothing chaffed etc I'd be sending an engine oil sample off to the lab to check for fuel in oil but this is easy for me due to working on Cat heavy plant but anyone can walk into a Cat dealer and buy any amount of sample kits from 1 upwards and get the results. Parts per million is what comes back for any oil as well as coolant