41-lean
Lead Driver
Joined: May 2011
Posts: 5,798
Likes: 453
Unplug the regulator, drive again....do a long heavy throttle pull in 3rd while watching the gauge, if the fuel pressure never drops then your pumps are strong and it's time to begin troubleshooting other possible causes.
Lead Driver
Joined: May 2011
Posts: 5,798
Likes: 453
Do you have a tach? It dropped from ~39 to 34? It's important to recognize the starting fuel pressure (basically the idle fuel pressure, then pressure at the start of the pull) then how it drops as rpm and throttle increase.
Lead Driver
Joined: May 2011
Posts: 5,798
Likes: 453
The goal of the test is to determine whether or not, as the computer demands more fuel (meaning more rpm and throttle position), the pumps can keep up and maintain the rail pressure. If the fuel pumps can't keep up the injectors will eat the pressure faster than it can be supplied and it will result in a drop in pressure and lean condition.
The reason I am stressing this, is that you cannot diagnose anything else until you know you have an adequate fuel system. Troubleshooting further without doing this "101" step means you'll be pissing on the electric fence and hoping it's not energized.
The reason I am stressing this, is that you cannot diagnose anything else until you know you have an adequate fuel system. Troubleshooting further without doing this "101" step means you'll be pissing on the electric fence and hoping it's not energized.
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Cargo Master
Joined: Mar 2010
Posts: 3,342
Likes: 294
From: Laramie, WY
I'm seeing 30-45psi. Seems to me, if it's 39 with no load (no vacuum to regulator) but then drops when under load, the pump is weak. I just tested my mildly built 351, 39 psi at idle with no vacuum to regulaton, 39psi at WOT up to 80mph. Stock pump, regulator, and fresh filter, much higher fuel demand but the pump keeps up. If the OP runs the tank down a bit, air temp is up, the pump typically performs worse, and could easily be dropping below 30psi. I've run into this with a Tundra. Mid day, high load (pass outside Leadville CO) , 1/4 tank, thought I was going to be stranded because this thing fell on its face. Limped it to town at 15mph. Checked codes, lean. Waited a few hours, put ten gallons fuel in. Air temp dropped. Drove 150 miles home with no issue, even with more passes. Checked fuel pressure at home, it was fine. Drove it, all was good under most conditions. Step into it hard, fuel pressure dropped out to ~20psi as I bounced my face off the steering wheel and AFR hit 18:1. Weak pump! But it was in spec the way many will test them. If it can't hold its nominal idle pressure under load it can't keep up and its junk.
Cargo Master
Joined: Jun 2013
Posts: 3,182
Likes: 15
From: Somewhere n North America
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Mountain Pass
Joined: Oct 2016
Posts: 172
Likes: 1
From: georgia
I'm at work for a few more hours. I'll build a longer line for the pressure test so I can see better. The overheating was solved and it came back added an overflow tank hoping that helps. I reconnected he regulator for work and it was missing real hard in od but so much better with it unplugged. Think it can be fuel injectors? Just curious until I can get home and make a longer line for a more comprehensive fuel test
Lead Driver
Joined: May 2011
Posts: 5,798
Likes: 453
Faulty injector could indeed be a possible cause, but it's unlikely in your situation because if one injector wasn't working, the computer would try to compensate resulting in a rich condition on the functioning cylinders, and it'd be much easier to detect the lean cylinder via spark plug analysis.
I think you have a lean condition across the board, the proper fuel pressure test will confirm.
I think you have a lean condition across the board, the proper fuel pressure test will confirm.
Thread Starter
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Mountain Pass
Joined: Oct 2016
Posts: 172
Likes: 1
From: georgia
i tried to get a longer line built today but that didnt happen no one had the right fittings home depot, napa, oreileys. so im gonna order one from summit and ill test further once it comes in. gonna swing by harbor freight and see if their kit comes with a longer line and if so ill grab it.