loosing fuel pressure up top?
10-19-2007, 02:06 PM
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loosing fuel pressure up top? well, I finally got the t/a tuned, and afterwards the guy told me that I was loosing fuel pressure around 5k, and it shows on the dyno results. peak power is right around 4.5 k, then it starts to drop. before the tune i was making max power at 5.3k, and with the tune it makes the same power at 5.3. the fuel pump is 15xxx miles old, as well as the filter. i replaced it when it ran out of gas. the car has 75xxx miles. what should I check first? any of you guys run into this problem? my mods are in the sig, just bolt ons, so i shouldnt need bigger injectors.
10-19-2007, 07:18 PM
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You could replace the fuel filter with a good one just for luck
(think a lot of people like Wix), and inspect the entire length
of the forward fuel line for crimps / dents / hose kinks in the soft
runs etc. Also you might hook test leads up the fuel pump power
wires, aft of the last connector, and run them to a voltmeter
up in the cabin so you can see if this is an electrical supply
problem (as happens to some). Flow*pressure = current*voltage
more or less, you just need to see that the voltage is hanging
tough under load.
(think a lot of people like Wix), and inspect the entire length
of the forward fuel line for crimps / dents / hose kinks in the soft
runs etc. Also you might hook test leads up the fuel pump power
wires, aft of the last connector, and run them to a voltmeter
up in the cabin so you can see if this is an electrical supply
problem (as happens to some). Flow*pressure = current*voltage
more or less, you just need to see that the voltage is hanging
tough under load.
10-20-2007, 07:21 AM
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im guessing the pump should have a constant 12 volts? and im ordering a wix filter as soon as first call opens today... I'm using our matco determinator scanner at work to read my fuel pressure (on the highway lol - since the dyno run was in 4th gear wot), then I'm going to put the filter on and see if there is any difference. what should the pressure be at the high rpms?
10-20-2007, 11:54 AM
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You're looking for a minimal pressure fade w/ airflow (MAP*RPM).
If you have 58PSI at idle you want to not fall below maybe 53PSI
at the top end. The more you drop the more fueling error you get
because the injector flow rate model doesn't know from volts.
Same with the power, you're looking more for it to be steady than
any particular value; expect to see about 13.5 running. Voltage
makes rotor speed which equates to flow. Get an idea of voltage
across the pump and then measure the battery terminal-terminal
voltage and you'll see how much it could be improved (like by a
"hot wire" kit or just cleaning connections maybe).
If you have 58PSI at idle you want to not fall below maybe 53PSI
at the top end. The more you drop the more fueling error you get
because the injector flow rate model doesn't know from volts.
Same with the power, you're looking more for it to be steady than
any particular value; expect to see about 13.5 running. Voltage
makes rotor speed which equates to flow. Get an idea of voltage
across the pump and then measure the battery terminal-terminal
voltage and you'll see how much it could be improved (like by a
"hot wire" kit or just cleaning connections maybe).