Truck Bucking Under Load

[beetle boy]

Hi,
I have a '99 F350 short box supercab 7.3 litre with K&N cold air intake, 4 inch magna flow exhaust, and superchip programmer. Tranny is fresh with triple disk torqueconverter.

Lately when driving empty, with the truck under load it is bucking and feels like it is running out of fuel. I have changed the fuel filter and have had the lift pump pressure tested and it is okay. Pressure was 55 lbs but it did fluxuate on test drive with guages attached. It never went below 50 lbs when it fluxuated. To me fluxuation doesn't seem okay, but the mechanic says it is. Your opinions?

Thanks in advance : )

 

[dpantazis]

how much fuel in your tank? you could be sucking air. fill it up and see how it does.

get rid of the K&N POS. look at the $50 DIY in the wiki.

 

[beetle boy]

Have driven it at all different levels of fuel, still does it. I just got back from a road trip of 800 km, did it the whole time regardless of fuel level whenever the truck was under load, pulling a hill or passing.

 

[MBRPCrazyford]

Pressuer fluxuation is normal by some degree. How much was is bouncin around??

 

[JLDickmon]

I hafta agree with Dennis.. sounds like it's sucking air.. check the fuel lines anywhere there's a connector

 

[beetle boy]

thanks for the help will check it out tomorrow need to tow travel trailer on the weekend