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'84 Daytona 2.5T
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Discussion Starter · #1 ·
Wondering if my fuel pump is on its way out. I can hear the pump prime itself when the key is on however the car will sometimes die, a/f will go lean. After car is warmed up it will idle fine and so will my a/f. When accelerating sometimes, i can hear a high pitched humming noise inside the cabin and it'll go away. This is an on and off issue, sometimes it'll happen sometimes it wont. Sound like the fuel pump is on its way out? Thanks
 

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The only way you are going to know is to actually check fuel pressure when the problem is occurring.

You will need to connect a fuel pressure gauge and vacuum/pressure gauge, tape them to the windshield and with the aid of a helper go for a ride.

Remember...
1)First you need to establish a baseline and be sure "static rail pressure" (max regulated pressure) is in specs.
The static rail pressure reading (total fuel pressure) is the PSI that will be maintained across the tip of the injector under ALL operating conditions, not in the fuel rail.
Since the injectors are exposed to engine vacuum total fuel pressure is a combination of push (rail pressure) and pull (engine vacuum).
Due to this rail pressure will constantly change as engine vacuum/pressure changes.
2" HG (inches of mercury, a measurement of vacuum) = 1 PSI.
If your static rail pressure is 55 PSI, you start the engine and have 18" HG, rail pressure on the gauge will now read 46 PSI, 46 PSI + 18" HG (= 9 PSI) = 55 PSI at the injector tip.
If you disconnect the vacuum line at the FPR you will read Static Rail Pressure on the gauge.

 

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'84 Daytona 2.5T
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49 Posts
Discussion Starter · #3 ·
Fuel pressure is normal and increases/decreases with vacuum and boost. I recently changed out my ffv injectors back to the stock 2.5 injectors because I was reading pig rich when wot @ 10psi (10.0 was flashing and kept on flashing regardless of how far down I went with the accufab ((also talked to accufab and the guy said my accufab is working normally so i threw it back in))), so I figured my injectors were way too big. Right now it have it set at 50 psi static but is a little lean during idle and sometimes stalls during initail startup, after 10 mins it will adjust to 14.7 again and idle normally however I'm still rich at wot (10.4).
 

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Static Rail Pressure should be 53-57 PSI.
(Rail pressure drops 1 PSI from static for every 2" HG, rail pressure increases 1 PSI over static for every 1 lb. of boost)
14.7/1 is what the controller will attempt to keep the AF at during idle and no load cruise (O2 feedback closed loop operation)
Acceleration/WOT/Deceleration are fixed programs based on Controller Programming, MAP/TPS/CTS/ACT/VSS/RPM readings.
The MAP sensor is the dominant fuel control sensor, the others are minor players in fuel/spark advance control.
Everything is based on the basics being correct (Static Rail Pressure, Cam/Ignition Timing, Injector Flow, Ignition System Efficiency, Engine Mechanical etc.) the controller assumes they are all correct when it makes fuel/spark advance corrections.
Verify your basics are correct and then verify MAP Sensor calibration is correct.
 
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