Which is the fuel feed line?
08-04-2006, 04:24 PM
#1
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Which is the fuel feed line?
I'm running the BEGi AFPR and just installed my new 190hp fuel pump as well as tee'd in a new fuel pressure gauge.
The thing is, it reads 0psi at idle or if I rev it. Can't read it under load because it's mounted in the engine bay and sadly I don't have a dyno at my disposal.
A/F gauge reads 14.7 under normal driving and around 12.0 under full boost, so it seems my fuel pressure is safe.
My dad thinks I tee'd the AFPR into the fuel return line instead of the fuel feed line which would explain the 0psi and the Haynes manuel says the forward fuel line is fuel return, however my instructions that came with the AFPR from FM indicates the forwardmost fuel line is the one to tee into.
Can anyone offer some insight into this?
Thanks in advance,
SamS
The thing is, it reads 0psi at idle or if I rev it. Can't read it under load because it's mounted in the engine bay and sadly I don't have a dyno at my disposal.
A/F gauge reads 14.7 under normal driving and around 12.0 under full boost, so it seems my fuel pressure is safe.
My dad thinks I tee'd the AFPR into the fuel return line instead of the fuel feed line which would explain the 0psi and the Haynes manuel says the forward fuel line is fuel return, however my instructions that came with the AFPR from FM indicates the forwardmost fuel line is the one to tee into.
Can anyone offer some insight into this?
Thanks in advance,
SamS
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08-05-2006, 04:45 PM
#7
Wouldn't you want it in the return line? The regulator opens when you reach a certain pressure on the fuel rail (or am I insane) and then sends any extra pressure back to the tank. If you put it on the feed line it will keep a certain pressure between the pump and the AFPR and bleed any extra to your injectors. AFAIK, your stock FPR is between the fuel rail and the return to the tank.
It's been a while since I have played with AFPR so I may be off base.
It's been a while since I have played with AFPR so I may be off base.
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08-05-2006, 05:39 PM
#9
Originally Posted by magnamx-5
you are correct Ron put the gauge on the feed line. your current setup is measuring your return pressure wich doesnt help at a
ll the feed pressure is important though.
ll the feed pressure is important though.
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08-05-2006, 09:42 PM
#10
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If my AFPR is in the feed line to the fuel rail, shouldn't my gauge be reading the pressure that is getting to the injectors a few inches away? Or am I mising some big point one of you has made?
Isn't fuel pressure on the feed line to the stock FPR going to remain fairly constant, or does it change with different input from the motor?
Are you saying I should put the gauge between the stock FPR and the AFPR?
Isn't fuel pressure on the feed line to the stock FPR going to remain fairly constant, or does it change with different input from the motor?
Are you saying I should put the gauge between the stock FPR and the AFPR?
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08-05-2006, 10:05 PM
#11
If my AFPR is in the feed line to the fuel rail, shouldn't my gauge be reading the pressure that is getting to the injectors a few inches away? Or am I mising some big point one of you has made?
Isn't fuel pressure on the feed line to the stock FPR going to remain fairly constant, or does it change with different input from the motor?
Are you saying I should put the gauge between the stock FPR and the AFPR?
Currently, your AFPR is in the return line along with the gauge. Your AFPR is working correctly because it is in the right place. Your gauge is not doing what you want because it is in the right place. You should be:
fuel pump, feed line, gauge, fuel rail, FPR, return line, AFPR, tank
Isn't fuel pressure on the feed line to the stock FPR going to remain fairly constant, or does it change with different input from the motor?
The fuel pressure to the feed line to the stock FPR is going to remain constant UNTIL you added the AFPR. It has, in a sence, removed your FPR from the equation due to its higher pressure that changes with input from the vacuum/PSI tubing. Imagine a 6" exhaust pipe, lots of flow (i.e. low pressure) going into a 0.0005" exhaust pipe (very high pressure). The low pressure (FPR) has little effect on the higher pressure (AFPR) pipe.
My explaination may be confusing but if you follow the flow path that I detailed above (only requiring you to move your pressure gauge) you should be fine.
See my webpage (defunct sebring miata mirror) for info on how much pressure you need:
http://www.lightweightmiata.com/sebr...ta/page38.html
Isn't fuel pressure on the feed line to the stock FPR going to remain fairly constant, or does it change with different input from the motor?
Are you saying I should put the gauge between the stock FPR and the AFPR?
Currently, your AFPR is in the return line along with the gauge. Your AFPR is working correctly because it is in the right place. Your gauge is not doing what you want because it is in the right place. You should be:
fuel pump, feed line, gauge, fuel rail, FPR, return line, AFPR, tank
Isn't fuel pressure on the feed line to the stock FPR going to remain fairly constant, or does it change with different input from the motor?
The fuel pressure to the feed line to the stock FPR is going to remain constant UNTIL you added the AFPR. It has, in a sence, removed your FPR from the equation due to its higher pressure that changes with input from the vacuum/PSI tubing. Imagine a 6" exhaust pipe, lots of flow (i.e. low pressure) going into a 0.0005" exhaust pipe (very high pressure). The low pressure (FPR) has little effect on the higher pressure (AFPR) pipe.
My explaination may be confusing but if you follow the flow path that I detailed above (only requiring you to move your pressure gauge) you should be fine.
See my webpage (defunct sebring miata mirror) for info on how much pressure you need:
http://www.lightweightmiata.com/sebr...ta/page38.html
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08-06-2006, 05:34 AM
#14
Originally Posted by magnamx-5
that is exactly what i said why did you assum i meant put hte fpr on the feed line i told him it was no good to put the gauge on the return.
you are correct Ron put the gauge on the feed line.
"Ron put the gauge on the feed line" is not the same as "Ron, put the gauge on the feed line". Sorry, I just misread what you were trying to say. That tends to happen after a 12 hour shift at work.
("I see that Ron has put the gauge on the feed line" vs "Ron should move the gauge to the feed line")
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:gay: 
08-06-2006, 12:34 PM
#16
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You can rev the car from under the hood and look at the FPG. Do you see the throttle cable going to the throttle body?
The yellow circle is what you need to pull to rev the car from under the hood. The blue dot is where my FPG is now.
The yellow circle is what you need to pull to rev the car from under the hood. The blue dot is where my FPG is now.
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08-06-2006, 06:56 PM
#17
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yeah, I'm aware of the throttle cable being attached to the throttle body.
I was just saying I couldn't rev it under load because the car would have to be moving or on a dyno.
SamS
I was just saying I couldn't rev it under load because the car would have to be moving or on a dyno.
SamS
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08-11-2006, 03:52 PM
#18
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The AFPR (FMU) installs in the fuel return line. If it is installed in the fuel feed line, it will shut off fuel to the injectors.
The gauge is reading 0 (at idle) because the it has not received a boost signal to kick on. You need to add 4 feet of hose between the line and the gauge. Route the gauge to the windshield, stick it under the windshield wiper and read it under boost.
The gauge needs to install between the pump and the fuel rail to read the fuel pressure at idle and under boost.
Stephanie
The gauge is reading 0 (at idle) because the it has not received a boost signal to kick on. You need to add 4 feet of hose between the line and the gauge. Route the gauge to the windshield, stick it under the windshield wiper and read it under boost.
The gauge needs to install between the pump and the fuel rail to read the fuel pressure at idle and under boost.
Stephanie
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