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Minimum fuel pressure

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  #1  
Old 04-09-2018, 04:16 PM
beau680
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Default Minimum fuel pressure

hello, I was curious on absolute minimum pressure that my 98 2500 5.9 magnum needs to run?
My truck periodically sputters out, I hooked a harbor freight pressure gauge an it read 50 psi then after I revved the engine it read right around 40 psi (also the time when it started to sputter but did not die) the gauge I have has no pressure relief valve itís an odd one.
An as we all know 5 minutes before I hooked up the gauge my truck was doing its thing an died out. But when I hooked up the gauge it wouldnít do it.
The famouse mechanic shop line it worked fine when I drove it. Lol
 
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Old 04-09-2018, 06:44 PM
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Dropping to 40 psi is going to be a problem. Still the original pump?
 
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Old 04-10-2018, 12:13 AM
beau680
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I believe I remember the guy I bought the truck from saying he had just replaced it.
I thought that might be a problem. The book says 35-45
 
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Old 04-10-2018, 07:58 AM
true blue
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Before you start to fire the parts cannon and do what is best described as guessing...do you get a loud hissing noise from around the top of the engine just before the engine dies. If the pick up runs but dies when your foot is off the accelerator pedal, then your problem most likely isn't in the pump, it's more likely the idle air control valve or valve seat is either dirty, bad or has a bad electrical connection. If there's no "hiss of death" just before, well death, then your problem might also be a very dirty air cleaner, a vacuum leak, bad fuel, dirty injectors, spark related problems or even a clogged cat. So many potential problems, but so many potential causes. Invest n a scanner if you don't already have one, but you need one that MUST DISPLAY live data (you can get one for 30-40 bucks at wallyworld or any auto parts store). Hook it up, wait for the beast to go into closed loop (or wait till it's normal operating temp) and what you're looking for is the short and long term fuel trims at idle/1500/2500 RPM (do this in your driveway/ they should hover around or close to "0"), and the O2 sensors. Upstream O2 should move up n down constantly in voltage and the downstream should be steady around .5 volts or move just like the upstream if the cat's gone around the bend. Last, what is the coolant temp and intake air temp read as well.
 
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Old 04-10-2018, 07:59 AM
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Dammit Jim, I did it again...is the check engine lite on?
 
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Old 04-10-2018, 12:31 PM
beau680
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parts cannon went off along time ago with two this truck been tracking em down an moving along. Lol I got about 14k into this truck the last 3 years. It has no cat. Iíve done the non fouler on the rear o2 sensor. An have recently replaced the IAC 3rd time since Iíve had the truck. The last time was with genuine Mopar part. My tank is almost empty vwry well could have dirty injectors.
So the live data thing. I had posted some data awhile back about an issue I was having (I donít recall). I believe it was heyyou who had reviewed the data I posted an came up with the map dropping off significantly even though the engine load never changed. He has recommended that I check out a runner elbow on the vac pump. I have checked all vacuum lines an do not see an obvious damage.
 
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Old 04-10-2018, 02:52 PM
true blue
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By vacuum pump, do you mean ye 'ol smog/air pump that California weighs it's vehicles down with?
 
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Old 04-10-2018, 05:30 PM
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Well I was quoting what someone had told me to look into. I myself did not know what pump he was referring to. I do not have a smog pump on my truck. I have some freeze frame data from a few months back it doesnít like to load in order although they are numbered. Maybe you can give me your input on this info? I can reload somemore when my buddy gets home to use his tool
 
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Old 04-10-2018, 05:52 PM
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Why is O2S11 always at .24?

Long term fuel trim is always 0...... Have you reset the computer recently?

Do you have the ability to do graphing while driving??
 
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Old 04-11-2018, 07:13 AM
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Heyyou is on the right trac here. Hard to tell O2 trends when a snapshot in time is all we have. The main thing about your fuel trims to note here are the short term numbers. Those hi negative numbers mean that your HAL 9000 is leaning you out in a big way and that's why you sputtering. The long term fuel trim at "0" only means that the trims start here. Try unplugging your battery n short the terminals together for 15-30 seconds n try again.Your upstream O2 seems almost lip locked on a lean condition (especially when you see numbers as lean as -29/the engine is being starved of fuel by the ECM) and your ECM isn't correcting for that for some strange reason. did you have an electrical problem recently? The other place to look is into a severe fuel injector problem on 1 of your cylinders. Probably stuck open or ECM is telling it to stay open, however I'm only guessing here. Pull your plugs and look for oil/fuel fouling.
 
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