98 5.0 RPM Surge while coasting

[Mbrooks420]

Like the title says, my Mounty will surge in RPM if I am coasting down a hill under no throttle. If I have my foot on the gas at all it doesn’t do it. Surges almost 1,000 RPMs at times.

Otherwise it’s shifts well, and doesn’t miss. Transmission fluid color is good (about 40k on it though). I do need to recheck the level correctly.

Any thoughts?

 

[Turdle]

Stock tune and engine or are there some mods?

Reason I ask is our black 347 cammed mounty did this until James fixed it during tuning. I do not know the term he used but it had to do with the injector pulses turning off when coasting, and coming back on.

 

[974X4BLACKSPORT]

De accell fuel cut off?

 

[fastpakr]

Isn't there an ECU strategy to cut the injectors when in gear and engine speed is above a set point with TPS signal below a certain threshold? I'm wondering if that's not occurring, so it's continuing to inject when it should otherwise be allowed to shut them down. I'm wondering if there's an issue with the range sensor?

Edit: It's called DFSO, deceleration fuel shut off. A bit of generalized discussion here:
Turning off Fuel Injectors on decel

Not that it really answers your question, I'm just hazarding a guess that it's related to what you're experiencing.

 

[Mbrooks420]

Motorwise it’s 100% stock.

Interesting. I always assumed it never fully cut the injectors while running.