Heading up to the NHRDA race in Gainsville with the race truck in tow, truck was running great at about 80-85mph. Stoped in Ocala for some BBQ and let the truck idle while we ate (~20minutes). Hopped back into the truck and got on the interstated and it ran great up to 75mph, but it would not pass 75mph though. I had it floored and once it hit 75, it would de-fuel. All guages looked normal, pulled over and shut it down and restarted with the same result, so I just kept driving and a couple minutes later it was fine. Plugged the Smarty in and no codes were thrown. Drove completely fine on the way home.

Any ideas what could have caused this?

Thanks,
Tobin

 

Have you P.O.'ed any witch doctors lately?......Ben

 

I am sure more than one.

Tobin

 

I've had this happen before and it was my fuel filter.

 

Was it clogged pretty bad?

Tobin

 

I had the same thing happen on my old Suburban, regular throttle it would run fine, but if I gave it more than half throttle or got up to a high enouh speed where the fuel required was more than what could pass through the filter it would fall on it's face.

 

Must have been because as soon as I replaced it the problem was gone. I've had this happen a couple of times. I've had it clogged so bad I couldn't get past 50mph and had to pull over to the shoulder and do a roadside fuel-filter replacement, but in each case its the same. At light load and lower speed everything's fine, and its when you work the engine harder at higher speeds in higher gears that the problem becomes evident. Also I found that if when you hit that "de-fuel" point, if you keep your foot in it for more than 6-8 seconds it will throw the CEL and throw the code for low fuel pressure (I forget the code number off-hand). After you replace the filter, the code and CEL clears itself after a few shutdown/restart cycles.

I always carry 2 spare fuel filters for this reason.

 

this is a perfect example of why a fuel pressure gauge is so important between the filter and injection pump. If you had one, it would've showed a significant pressure drop when you crowded that higher speed.
...
db

 

I am going to swap filters, but I am still sceptical that is what it is. Hasn't happened since and has plenty of power. I could roll 80 mph down a hill and put my foot in it and the engine would not even try to accelerate. Anything under 75mph, it would accelerate fine, just once you hit exactly 75mph, it would de-fuel.

Tobin