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Hesitates. Fuel Pump?

Old March 11th, 2019, 8:29 PM
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Default Hesitates. Fuel Pump?

Been having a random issue. Truck is a 2001 6.0L with 130k. I have dug into this and don't know what else to do. Been having a hesitation on acceleration on moderate to heavy throttle. It starts to buck a little and nothing I've done fixes it. No codes.

Has a new MAF, new MAF harness, New spark plugs. I've checked the intake gaskets, they are fine.

The symptoms include; low idle on occasion (400rpm), dying on occasion when starting, cutting out/bucking with moderate to heavy acceleration. It is completely random, does it cold, does it hot. Sometimes it is fine and has excellent power and torque when accelerating, sometimes it falls on its face for a couple seconds.

Any ideas? I'm starting to think fuel pump. Thanks

Last edited by ChevyB; March 11th, 2019 at 8:32 PM.
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Old March 11th, 2019, 8:37 PM
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Low idle, intermittent. That dosen't act like a fuel pump. I'd suspect fuel pressure regulator.
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Old March 11th, 2019, 8:52 PM
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Thank you. I'll do some research on the regulator.
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Old March 11th, 2019, 9:19 PM
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From what I could derive from the videos I saw, the vacuum line at the top of the regulator should not have any gas in it. If it does, it is definitely bad. I just now checked mine, it is dry, no fuel in the vacuum line. I don't think my fuel pressure regulator is bad based off of that.
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Old March 12th, 2019, 6:25 AM
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Any other ideas? I will say that it is more prominent when warm as opposed to being cold. Cold being less than a mile of driving before acting up.

Iím lost. Could an incorrect thermostat do this? The previous owner had the system converted to green coolant, Iím pretty sure they also had a thermostat done because it runs cool. If itís say 20 or 30 degrees outside and I hop on the highway for an hour, it will never get above 190 degrees. Then when I get into town and idle at some red lights it will cool down to 185 degrees ish. Makes me wonder if it doesnít have a 180 degree thermostat.

if itís about 65+ out, it will warm up to 205 degrees.


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Old March 12th, 2019, 6:55 PM
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check the fuel pressure. my 02 ran with 20psi, would stall on some startups (mainly cold) and if you went to take off it wouldnt go anywhere. the rpms would jump up but the speed wouldnt change. i even had the low rpms. but even after changing the pump the rpms stayed around 400-500 when warm but the performance of the motor was night and day. after the pump change she would scoot even with the 4.8 and 250k miles
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Old March 12th, 2019, 7:13 PM
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We got a game changer folks. MAF code...

The hesitation now triggers a service light. P0102 MAF low output... I thought I fixed that P0102, I had an intake leak that I fixed.

Truck has new MAF, new harness, I had the system smoke tested LITERALLY today to make sure I fixed it. Not one vacume or intake leak on my engine. Checked out good.

So this isn't fuel pump, this is a MAF error. Where do I go next??
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Old March 12th, 2019, 8:03 PM
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unplug the maf see it improves.
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Old March 12th, 2019, 9:04 PM
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Irish_alley:

I will do this tomorrow morning. What will this do? obviously there will be a service engine light for the time being, but if it is better, does that just mean the MAF is bad?

I am going to borrow someones same year 2500 6.0L MAF out of their truck tomorrow. We will see if I have a faulty replacement MAF. I had a brand new one that was defective on a crown vic one time. It is possible.

Then what do I do from there if neither are better? PCM? Exposed wire?

Last edited by ChevyB; March 12th, 2019 at 9:33 PM.
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Old March 12th, 2019, 10:20 PM
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from what i understand it will go into default mode for the maf sensor. yes a cel will come up
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