IHADAV8.com - Turbo Buick Tech, and Nonsense
Tech Area => General Buick Tech => Topic started by: Scoobum on September 15 2013, 08:12:09 PM
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Got a call from a GN owner this morning. He has an in car fuel pressure gauge and it dropped to 20 lbs last nite while he was driving home with the engine under no load/boost. This morning it was back up to 38 with no load/boost. New Racetronix SS hanger and pump. AFPR is a used unit I gave him back in the spring...so it could be suspect. Also...he hasn't swapped out to a new fuel filter as of yet...and injectors are new 60's. Same thing happened to me when my AFPR went south. Open to suggestions as to what's wrong. I swear this guys car is possessed...it's been giving me fits the entire year.
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or a pump that is beginning to die when it gets hot
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or a pump that is beginning to die when it gets hot
Thanks Steve...hope you're wrong. That pump only has a couple passes on it and maybe a couple hundred miles of normal driving.
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I assume the car ran like crap? Surprised it actually kept running with pressure that low
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I assume the car ran like crap? Surprised it actually kept running with pressure that low
He never said. I'll take your word for it tho. His car has been down all year. It's one thing after another.
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Ask him. If it did not, then it was not the pump or fpr
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Ask him. If it did not, then it was not the pump or fpr
Will do. If it isn't the FPR or pump...what else could it be? Alternator and battery are both new.
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Steve...got a text back from him and he said it ran fine at 20 PSI of pressure.
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That ain't possible so that should tell us something. bet the blms and O2 were normal
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Even at 20psi the car will run fine. The ECM will compensate and up the injector duty cycle/pulse width.
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When my car idled at a of 28lbs, it wanted to die. Then I got a good gauge and realized that the gauge was WAY off.
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So with the first guage I had on there, it was showing my car idling at 42 lbs or so. Then Steve sent me an Ashcroft that verified that my FP gauge was shot.
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So with the first guage I had on there, it was showing my car idling at 42 lbs or so. Then Steve sent me an Ashcroft that verified that my FP gauge was shot.
Which gauge did he send you? I ordered one like a dummy that wasn't liquid filled and it is a POS... I KNOW I KNOW!!
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Even at 20psi the car will run fine. The ECM will compensate and up the injector duty cycle/pulse width.
far as i know and what do i know... minimum operating pressure is 26 below that iys a dribbler and at 1/2 the recommended fp the output will be so low compared to what it needs and the ecm cant compensate that much... it will run like ass
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The one I sent him was not liquid filled and it was not a POS.
I have seen more than one liquid filled gauge that was no good.
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liquid filled gauges are inherently screwy based on temperature.
When the front of the face is sealed it can't be referenced to atmosphere and the pressure in the sealed compartment can cause the gauge to read low based on thermal expansion.
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The one I sent him was not liquid filled and it was not a POS.
I have seen more than one liquid filled gauge that was no good.
Gotta part # :) I was saying mine is a piece
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i run a three foot braided -4 hose and use autometer liquid filled fuel gauges (2 5/8) mounted in a cup mount like you would mount on the hood , but i ziptie them to the cruise bracket by the air cleaner , if need arises the gauge could be swung up to the windshield
no way i would ever run one of those rail mounted gauges for something as important as fuel pressure is to these motors
and a pressure sensor logged on the PL means nothing if the calibration isnt checked or was baselined to a bad gauge .. for clibrating the sensor you need a good gauge that hasnt been shook to shit , ive seen those railmount POS gauges off more than 20psi
for calibrating i use a compressor regulator with a calibrated gauge that uses shop air , i also use that regulator setup to verify boost gauges (fyi vdo 30psi 2 1/16 boost gauge that is probably the most common used gauge are by far the most inaccurate boost gauges ive ever tested , how about being off 7psi at 20psi!!!)
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It was an Ashcroft 3" 2% accuracy unit. Last I looked, it cost somewhere over a $100. Everything Paul said is right. Rail mounted gauges are useless
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Steve the latest update I got from him is the fuel pressure climbed to 46 line on. The fuel pressure gauge is an electric in car, I'm dropping him off a spare AFPR to his mechanic today to install. I'll report back.
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That explains it
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If you have a source to check the calibration Ebay has lots of used industrial grade gauges.Otherwi se I posted a Mcmaster Carr number for something decent a while back.
I suspect if you put enough rubber hose on a non dampened gauge it would become quite usable- just a guess tho.
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Definatly want to buy a good used gauge and verify the calibration. Large faced quality industrial gauges cost a WAD (giggity) when bought new.
When I started pricing 4" temp gauges for my still I almost passed out!
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It was an Ashcroft 3" 2% accuracy unit. Last I looked, it cost somewhere over a $100. Everything Paul said is right. Rail mounted gauges are useless
I take it that is 2% of full scale and not reading? I've seen real cheapo gauges that had accuracy of reading, needless to say they were POS.
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actually, I was wrong, it is an 0.5% accuracy gauge +/- 0.5 of the range
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How bad could this gauge be?
http://www.northerntool.com/shop/tools/product_357793_357793 (http://www.northerntool.com/shop/tools/product_357793_357793)
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Gauges are the most accurate at the 50% reading. Notice this one lists 2-1-2 for accuracy? Only way to say how good it is for sure is to test it with some good calibration equipment. Most the places I've worked if we are reading 100psi pressure on a process, the gauge will have a 0 to 200psi scale.
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Gauges are the most accurate at the 50% reading. Notice this one lists 2-1-2 for accuracy? Only way to say how good it is for sure is to test it with some good calibration equipment. Most the places I've worked if we are reading 100psi pressure on a process, the gauge will have a 0 to 200psi scale.
Interesting..
So a ~140psi gauge would be perfect, not sure if that scale is available.
I noticed it says it has a temperature compensating window..
I saw a whole shelf unit of various pressure gauges last time I was there. I may give one of these a shot - not rail mounted though.
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How bad could this gauge be?
http://www.northerntool.com/shop/tools/product_357793_357793 (http://www.northerntool.com/shop/tools/product_357793_357793)
It's liquid filled so it'll be affected by temperature swings.
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How bad could this gauge be?
http://www.northerntool.com/shop/tools/product_357793_357793 (http://www.northerntool.com/shop/tools/product_357793_357793)
It's liquid filled so it'll be affected by temperature swings.
The one I just got isn't liquid filled but the reading is bouncing around...that's not normal right? My liquid one I pulled of wasn't doing that.
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Now you know what the liquid does :)
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In the end, it does not matter exactly how precise the gauge is. It is more important that it reads exactly the same each time
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Accuracy is the closest to the true value while precision is the repeatability. Up scale and down scale will vary with the gauge because it inherently suffers from hysterisis. Given accuracy of a gauge means nothing unless you know if it is for full scale, every half scale or of reading.
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you missed my point...but that is okay :)
Not disagreeing with what you said as it is part of my point....
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I always stumble over using those two term correctly.
( my $22.00 used ebay Ashcroft is in the mail :) )