2003 H.O, 5.9, 3500 Dually, 6spd Manual

On a recent trip towing my 8000 pound RV, I lost considerable power on an uphill section to where I only topped the hill in 1st gear (6spd manual) at 2900rpm w/ the pedal to the floor. VERY scary since there was a cliff on one side, and a 1000ft drop-off on the other on the very narrow rural mountainous Utah road.

We just plugged the Snap-On DRB Scanner into the truck, and found that regardless of throttle position beyond about 1/2 throttle, the MOST fuel pressure commanded was 18,000psi rather than the 24,000psi the tech said we should have seen. Actual Rail pressure followed commanded perfectly, so the problem is not downstream leakage.

I replaced filters in the AirDog pump system in case we had a input fuel restriction, with no change.

We then unplugged the connector to the Fuel Control Actuator (FCA) on the injection pump, the tech saying that this should drive the system to MAX fuel pressure of 24,000psi + regardless of the actual throttle pedal position or engine rpm.

Commanded fuel pressure only went to 19,000psi, and rail pressure also went to 19,000psi. This was w/ the engine idling. The rpm didn't change, but the engine sounded more like a 2nd gen 5.9 engine (loud clatter) with the higher fuel pressure applied.

He recommended replacing the FCA and TPS (throttle position sensor), and if that didn't work, we were likely looking at anew ECU (master computer) unit.

Anyone offer any other ideas?

The rail pressure DOES rise to exactly match the "Commanded" fuel pressure, so I would think so far, we can't suspect the injection pump.

Does anything else affect the COMMANDED fuel pressure?

Bob

 

I'd start with the tps. It's cheap and easy. I got mine from tstproducts.com. Mine went at 60k with absolutely no previous warning or codes. The codes after it quit weren't really conclusive that it was the tps but I got lucky and the new one fixed everything. Craig

 

Funny you should suggest that...

I got a TPS and an FCA from the tech to try today (I'll order new ones to replace his) and on advice of my tech replaced them both.

The engine "feels" like it has more grunt and the exhaust "sounds" more robust (but that could be wishful thinking on my part and the fact I had the windows open rather than the A/C on w/ closed windows).

In the upper gears at relatively low rpm (1600-2200) anything more than 1/2 throttle has little effect. In fact, going full throttle, then reducing it half throttle brings on MORE power than at full throttle (Hmmm...).

At sea level, not towing, the truck didn't "feel" like the slug. It was at 6000ft on a 10% grade w/ 8000 pounds in tow where it was frighteningly obvious.

In the lower gears, however, full throttle seems to be a better kick in the seat-of-the-pants than before-again subjective.

I don't have the DRB Scanner at home (it's at my tech's shop), so I'll have to go back, plug it in, and SEE what the command and rail pressures actually are to really see if anything's changed.

I went to tstproducts.com and didn't see the TPS (link?). Mine came from Genos Garage and wasn't that cheap ($170), unfortunately. If it's cheaper at TST I'll buy one there to replace the one I installed.

I had no codes at all-just a vague power loss (mostly at altitude on steep terrain while towing) confirmed today by the inability of the ECU to "command" more than 18,000psi (which the injection pump happily made).

Tomorrow I'll plug in the scanner and see if these parts really did anything meaningful I guess.

Bob

 

Double check and make sure your rail pressure sensor isn't faulty and then check your crossover tubes and make sure none of them have loosened in the head.

 

Do you have an auxillary tank in the bed? If so, make sure that no trash got caught up in the filter heads of your AD. A friend of mine just had that happen to him and it took 2 weeks to finally figure out why the truck couldn't get out of it's own way after about 50 miles or so. It would literally run itself out of fuel because of insufficient supply.