Cause for running lean ?

What would be causing my 01 with the 5.9 360 to be running lean ? Some where some how it's A not getting enough fuel or b to much air. Could it be the intake plenum gasket ? Also no codes are being thrown. But it does how ever hesitate or act like it's running out of fuel.

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Need more info. When does it act like it's running out of fuel? At idle, under load, coming to a stop?

When my truck gets to temp and I'm under load and coming to a stop it will cut out or act like it's running out of fuel

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Often a function of the 02 or tps. Since you're not getting misfires I'd say it's more likely flooding it. I'd prob start with tps being cheaper and easier

Alright. It's just odd because the code reader did the read out on fuel and it said lean.

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If that's the case I retract my previous statement of likely flooding.

Suggestions remain with the addition of checking fuel rail pressure via the valve on the driverside. Should be 49 +/- about 5

Maybe a vacuum leak which could be the intake plenum gasket. There is a test but I think if block off the the pcv and check the breather. It should be blowing if it's sucking then the gasket. Some report quarts of oil missing too.

A vacuum leak can cause an engine to run lean but it seems to be more of a problem with engines that use a MAF (Mass Air Flow) sensor rather than a MAP (Manifold Absolute Pressure) sensor.

MAP sensors detect and respond to pressure inside the intake manifold. Any kind of vacuum leak, which ultimately leads into the manifold, will be "felt" by a MAP sensor as the increased airflow into the intake manifold will cause a reduction to manifold vacuum which the MAP sensor will "feel." The computer determines that more fuel is required to compensate for what it correctly perceives as increased air flow into the manifold. However, since vacuum leaks will occur under all RPM and load conditions, the computer will indefinitely dump extra fuel into the engine irregardless of whether it needs it or not and this will ultimately result in reduced fuel economy.

Also because leaks weaken manifold vacuum, you may also experience poor throttle response and rough idling.

MAF sensors can't "feel" vacuum leaks that occur downsteam of them as they only detect the volume of air that directly passes through them and the computer won't increase injector pulse (add fuel) as a result of the extra air. The engine will run lean as a result. Although this probably won't affect fuel economy much, a lean running engine tends to run hot which can cause increased wear on pretty much everything and may be more prone to spark knock which has the potential to really mess up your engine.

In the case of our engines which use a MAP sensor, if you truly are running lean, I would guess a vacuum leak which is large enough that the computer can't adjust for (unplugged/blown vacuum hose), poor fuel pressure or plugged injectors, MAYBE an IAC valve that is stuck wide open, faulty upsteam O2 sensor (the ultimate judge of engine fueling) or simply just a faulty MAP sensor.

Lots of things, honestly. Since your scanner is able to determine that your fueling is lean, can it by chance moniter the MAP sensor? I've read around here recently that the MAP sensor on a warm Magnum at idle should read 8-10 inHg. Mine runs at 12 and my long term fuel trim is around -11 (I am running a tune and open-element intake however) so I may need to look at a thing or two myself.

Good info. Thanks