fuel pressure spec

Topic: fuel pressure spec (Read 6133 times) previous topic - next topic

fuel pressure spec

January 24, 2009, 07:57:51 AM

what is the fuel pressure spec for a 84 bird 2bbl fi
at idle i have about 42lbs but it doesnt change when i open the throttle
mike

fuel pressure spec

Reply #1 – January 24, 2009, 10:32:23 AM

I think I remember that's a good reading for a CFI 5.0L and there is no pressure change on rev up with a CFI system.

fuel pressure spec

Reply #2 – January 24, 2009, 11:33:46 AM

stock idle is 40lbs

as throttle is applied, the fp will decrease under load (ie-transmission is topping out between gears)

check out my diy link below with pretty much everything ive said below to include links to topics here about various things.

To test the fp correctly so you can simulate problems, connect fp tester then duct tape the guage to your windshield. Drive your car and watch your guage. If the presure drops below 25psi between transmissin gear shifts, I would be looking at a replacement.

A good replacement is the 1990 supercharge 3.8L fuel pump you can purchase at your parts store. It is just the pump only and you reuse your housing and rubber boot assembly.

typically people find the 2'' long 90deg bent rubber hose in the fuel pump assembly has a crack in it. This causes the pump to dump fuel back into the tank and some up to the engine.

The CFI has a stock adjustable fuel presure regulator also. the small freeze plut atop of the FPR which is mounted on the top of the cfi can be drilled out to reveal an allan screw adjustment. 1 turn equals about ~@ 2psi.

If your wanting to wake up the air flow ,, remove CFI and take it apart so that you can hone out the upper half just below the butterflies. The 3.8CFI has a huge air restricton where as the 5.0 is not so bad but still has some form of hour glass bottle neck.

In addition, there is a tiny tear drop filter screen at the top of each injector which can be removed with no ill effects that i saw. You have the option to change your main fuel filter out more often to compensate for this or install a secondary filter up on the line that feeds the pass side fuel feed line. If you want to cure that age old "hesitation" issue when you stop the gas but there is a huge delay in response,,then pull the injector screens.

In a way, CFI guys are lucky when you need a random amount of gas for yard work. You simply disconnect the pass fuel feed , stick that end into your gas can, jumper the tan/light green wire at the eec test connector to ground, turn on the key, the fuel pump will run full time. when the can gets full, turn key off, fuel pump will take longer than usual to shut off like 5 sec then it will cut out.

scott

fuel pressure spec

Reply #3 – January 24, 2009, 11:36:12 AM

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fuel pressure spec

Reply #4 – January 24, 2009, 12:38:26 PM

with a low pressure pump in tank,a high pressure outside how wud i do the supercoupe pump mod?
the problem i am having is the engine will not start on its own,i have to push pedal to floor while cranking it over
mike

fuel pressure spec

Reply #5 – January 24, 2009, 01:07:19 PM

my fuel pressure wont move,engine running,in gear brake applied gas pedAL to floor trying to get a tire to spin and the pressure remains steady at 42 lbs butt it wont break loose and spin.it acts as if the exhaust is clogged butt i know its not,no ler or tailpipe yet

fuel pressure spec

Reply #6 – January 24, 2009, 03:21:27 PM

Quote from: joker77_2005;253347

the problem i am having is the engine will not start on its own,i have to push pedal to floor while cranking it over
mike

Have you checked codes(I'm guessing no)??? You most certainly have a issue other than fuel pressure...

fuel pressure spec

Reply #7 – January 24, 2009, 03:22:30 PM

Quote from: joker77_2005;253347

the problem i am having is the engine will not start on its own,i have to push pedal to floor while cranking it over
mike

Have you checked codes(I'm guessing no)??? You most certainly have a issue other than fuel pressure...

May very well have a TPS or Idle speed motor problem...

fuel pressure spec

Reply #8 – January 24, 2009, 03:29:50 PM

nocodes what so ever,at idle tps shows 1.003 volts with a smooth transition to wot 4.57 volts
the idle speed selonoid is good,will hold idle fine,also jacks the idle up when i turn the a/c on
whats is the vacum spec that these engines should pull at idle?
mike

fuel pressure spec

Reply #9 – January 24, 2009, 04:42:11 PM

Quote

my fuel pressure wont move

Quote

whats is the vacum spec that these engines should pull at idle?

Here's an interesting animation for vacuum diagnostics:
http://sbftech.com/index.php/topic,3020.0.html
Click on each scenario. It's a very nice tutorial.

For the exact values, I'm not sure, but I BELIEVE it's gonna be around 20" Hg @ idle...

fuel pressure spec

Reply #10 – January 24, 2009, 04:57:29 PM

you guys are pretty nice,most other forums i go on i get buttholes telling me to use the search,or figure it out on my own
anyway at idle i have about 15in of vacum,i am thinking the egr valve is not closing fully,i tried cleaning the carbon off butt still have the prob and the egrp sensor is showing 1.30-1.40 volts at idle,and i belive it should be closer to 1.0 volts.with that leak at the egr valve the fuel pressure reg is probly not getting enough vacum to regulate the pressure down any
does that sound right?
mike
mike

fuel pressure spec

Reply #11 – January 24, 2009, 07:37:55 PM

Quote from: joker77_2005;253391

y.with that leak at the egr valve the fuel pressure reg is probly not getting enough vacum to regulate the pressure down any
does that sound right?
mike
mike

That's a possibility, but remember this... Vacuum plays no part at cranking speeds, whatever you starting problem is, it isn't vac or fuel pressure related...

Going to full throttle puts the EEC system in dechoke mode which shuts off the injectors(to clear a flooded engine)... Only thing is I'm not sure a '84 CFI has this function, I know it's on all SEFI EEC systems... Unfortunately I don't have any info older than '86...

fuel pressure spec

Reply #12 – January 25, 2009, 03:00:33 AM

Im not really clear on what your problem is. You hinted at it on your previous post saying it "acts clogged". Initially I didnt think you had a problem at all, but a question.

What specifically is the car doing wrong?

You said no codes at all,, with that being the case you would have one code only so what was it? You should have gotten code 11. You cant avoid getting atleast one code if it's done right.

With no codes,, your running in open loop.

fuel pressure spec

Reply #13 – January 25, 2009, 04:54:23 AM

yea the code 11 i ignore on koer, only code.
on koeo i get 11 ,and 34 egrp out of spec,which led me to check voltage on the egrp which was 1.35 ish volts.no cel while it is running
when i start it i cold i tap the gas to set the choke and it fires right up.
after it is warm i have to all but wot to get it to start
driving down the road moderate throttle is runs ok,kinda lacks power.
on wot it acts sluggish with no power,like the exhaust is clogged.
if i let off of wot just a little then it gains a little power but still acts slggishs
all filters,plugs wires,cap,rotor,pcv are new
mike

fuel pressure spec

Reply #14 – January 25, 2009, 09:34:08 AM

Ummm(looking at ceiling) Assuming the iginition system is Ok, WOT throttle problems are commonly caused by a weak fuel pump that cannot keep up with demand... Have you checked F/P while driving the car???