Fuel starved in low gear descents?

[denvermaxd]

My 2000 T4R SR5 5-speed has long exhibited a strange trait when I'm in 4wd low using the engine to slow a descent.

Oftentimes you have to maintain a little pressure on the gas pedal in this situation to just keep going downhill. What I've noticed is, if there is a long period of consistent RPMs in this state, the engine will occasionally start to "die" like it's starved for gas when I do this. If is punch/tap the gas a little it revs right back up and continues as if nothing happened.

Anyone have any ideas what could cause this? It feels like vapor lock, but I don't know if that's even possible with this engine?

 

[Hopeless Diamond]

maybe the fuel pressure regulator is on it's way out

 

[phattyduck]

What RPM are we talking about?

There may be some ECU 'smarts' that are working against you here. Above a certain RPM, fuel will be cut completely (maybe 1200 or 1500?). Below that there will be some fuel injected as the engine would normally be coming back down to idle and it needs to 'catch' it before it dies. There might be some interaction with the amount of time you are off the throttle and engine RPM that confuses the ECU into doing odd things.

-Charlie

 

[St Runner]

There is stuff going on in the ecu under this circumstances. On my Ultaguage I run one of the window on engine load, as soon as the engine goes above 1400 rpm downhill with no throttle, the ecu goes into open loop and engine load drops from 14% to 7%. Essentially half the fuel as with idle. You might be getting even less. As soon as you hit the throttle it goes back to closed loop and runs normal. I have never had your symptoms but at least part of what is happening is normal

 

[denvermaxd]

Great tips... thanks.

Maybe I'll adjust my Scangauge to show engine load if that's possible.

I'm mostly nervous it's a fuel system issue, as it only occurs when I'm off-roading, which by it's nature is a bad place to have fuel delivery failure.

Any tips on a Scangauge setting that would help me pinpoint the issue?