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Thread: CFI

  1. #1

    Default CFI

    Did a leak down test on the CFI unit. It doesn't hold at all. Less than a minute the PSI drops.

    Injector spray is ok. Nothing bad.

    But, I'm thinking the CFI unit needs a rebuild. New injector o-rings and all.

    Link

    This is for the 85 LTD LX
    1985 Mustang GT Mild 331 4bbl 5 spd, 1985 SEFI LTD LX AOD.
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  2. #2
    FEP Member slpr50ltd's Avatar
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    Will be interested to see if that resolves your issue! Good luck!!
    Last edited by slpr50ltd; 04-24-2012 at 05:01 PM.
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  3. #3
    FEP Senior Member 4EYED85's Avatar
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    What kind of issue are we trying to solve?

  4. #4

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    Well, the fact that the System doesn't hold pressure for even a minute when the car is off is one issue.

    Still has an off idle hesitation. Not been able to get rid of that no matter what.

    Constant Code 41R in KOER. New O2.
    1985 Mustang GT Mild 331 4bbl 5 spd, 1985 SEFI LTD LX AOD.
    Cardomain: http://www.cardomain.com/ride/565542
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  5. #5

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    Unless the fuel is actually leaking down the throttle body, you're describing a symptom
    of a failing fuel pressure regulator.

    KOER 41 on CFI is a lean condition.
    Last edited by JACook; 04-24-2012 at 06:01 PM.
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    Jeff Cook

    '79 Mont StaWag, 5.0, 58K original miles ... '81 Futura Coupe, 3.3, 62K original miles ...
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    '65 notch, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ... '68 Vert 307 4-speed...
    (And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune)

  6. #6

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    Quote Originally Posted by JACook View Post
    Unless the fuel is actually leaking down the throttle body, you're describing a symptom
    of a failing fuel pressure regulator.

    KOER 41 on CFI is a lean condition.
    Thanks Jeff. I'll swap out the FPR!
    1985 Mustang GT Mild 331 4bbl 5 spd, 1985 SEFI LTD LX AOD.
    Cardomain: http://www.cardomain.com/ride/565542
    Mid Size LTD LX Facebook page! http://www.facebook.com/groups/233213650060739/

  7. #7

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    Btw: could the fuel pressure regulator not holding pressure when the motor isnt running cause the lean issue when running? The psi when running is 39psi.
    1985 Mustang GT Mild 331 4bbl 5 spd, 1985 SEFI LTD LX AOD.
    Cardomain: http://www.cardomain.com/ride/565542
    Mid Size LTD LX Facebook page! http://www.facebook.com/groups/233213650060739/

  8. #8
    FEP Power Member MAD MIKE's Avatar
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    Quote Originally Posted by Marz View Post
    Btw: could the fuel pressure regulator not holding pressure when the motor isnt running cause the lean issue when running? The psi when running is 39psi.
    The regulator does not open until a set pressure via the spring on the diaphragm. The amount of vacuum applied to the diaphragm will vary the amount of pressure created in the system.

    You can check to see if the regulator is working by attaching a vacuum pump to the port on the diaphragm and a fuel pressure gauge on the fuel line. With the car ON you should be able to change the fuel pressure by applying more or less pressure. If this does not change the fuel pressure the regulator is most likely fubar.

    Also check for fuel leaks and verify that none of your fuel lines are old and cracked.

    If the FPR checks out, dead head the fuel line from the fuel tank/pump and install a fuel pressure gauge. Turn the car to ON and the pressure should build. Then turn the car to off. If the pressure drops off then the check valve inside the pump may be faulty. This is usually internal to the pump itself and cannot be repaired. Requiring pump replacement. There may also be a pressure valve of sorts in the pump to prevent over pressure in the system. If this has failed it may also prevent pressure build up or retention in the system.
    -Michael
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  9. #9

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    Quote Originally Posted by MAD MIKE View Post
    The regulator does not open until a set pressure via the spring on the diaphragm. The amount of vacuum applied to the diaphragm will vary the amount of pressure created in the system.

    You can check to see if the regulator is working by attaching a vacuum pump to the port on the diaphragm and a fuel pressure gauge on the fuel line. With the car ON you should be able to change the fuel pressure by applying more or less pressure. If this does not change the fuel pressure the regulator is most likely fubar.

    Also check for fuel leaks and verify that none of your fuel lines are old and cracked.

    If the FPR checks out, dead head the fuel line from the fuel tank/pump and install a fuel pressure gauge. Turn the car to ON and the pressure should build. Then turn the car to off. If the pressure drops off then the check valve inside the pump may be faulty. This is usually internal to the pump itself and cannot be repaired. Requiring pump replacement. There may also be a pressure valve of sorts in the pump to prevent over pressure in the system. If this has failed it may also prevent pressure build up or retention in the system.
    Um. The CFI Fuel pressure regulators did not have a vacuum port like the SEFI cars.
    1985 Mustang GT Mild 331 4bbl 5 spd, 1985 SEFI LTD LX AOD.
    Cardomain: http://www.cardomain.com/ride/565542
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  10. #10
    FEP Member LSCR351's Avatar
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    I would bet on it NOT being the FPR, but a leak in a line or fitting. How about the little rubber hose in the tank, number one failure.
    69 Mustang Fastback= EXPENSIVE
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  11. #11

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    Quote Originally Posted by Marz View Post
    Btw: could the fuel pressure regulator not holding pressure when the motor isnt running cause the lean issue when running? The psi when running is 39psi.
    Not as such, but if a regulator is misbehaving one way, it may be misbehaving another.
    It's one thing to have correct fuel pressure at idle, but that doesn't necessarily mean it's
    staying at 39PSI when you're moving.

    Have you checked with a timing light that the spark advances when you crack the throttle?

    Quote Originally Posted by LSCR351 View Post
    I would bet on it NOT being the FPR, but a leak in a line or fitting. How about the little rubber hose in the tank, number one failure.
    The CFI fuel pressure regulator is supposed to maintain pressure at the throttle body even
    if there's no pressure in the supply line.
    Last edited by JACook; 04-25-2012 at 01:03 AM.
    Cheers,
    Jeff Cook

    '79 Mont StaWag, 5.0, 58K original miles ... '81 Futura Coupe, 3.3, 62K original miles ...
    '85 GT 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT CFI/AOD Vert ...
    '65 notch, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ... '68 Vert 307 4-speed...
    (And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune)

  12. #12

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    Quote Originally Posted by JACook View Post
    Not as such, but if a regulator is misbehaving one way, it may be misbehaving another.
    It's one thing to have correct fuel pressure at idle, but that doesn't necessarily mean it's
    staying at 39PSI when you're moving.

    Have you checked with a timing light that the spark advances when you crack the throttle?
    Hmm. I've not done that. I'll do that and post right back.

    Edit: Just checked... The spark advances when the throttle is cracked.
    Last edited by Marz; 04-25-2012 at 01:32 AM.
    1985 Mustang GT Mild 331 4bbl 5 spd, 1985 SEFI LTD LX AOD.
    Cardomain: http://www.cardomain.com/ride/565542
    Mid Size LTD LX Facebook page! http://www.facebook.com/groups/233213650060739/

  13. #13
    FEP Power Member MAD MIKE's Avatar
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    Quote Originally Posted by Marz View Post
    Um. The CFI Fuel pressure regulators did not have a vacuum port like the SEFI cars.
    I was sure there was a test port on the CFI unit for testing the FPR. That would be an oversight by Ford if there was no way to test the FPR in situ.
    -Michael
    '79 Fairmont 5dr 'car guy safe' MM Tech Tips StopTech Brake Bias StopTech White Papers

  14. #14

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    Quote Originally Posted by MAD MIKE View Post
    I was sure there was a test port on the CFI unit for testing the FPR. That would be an oversight by Ford if there was no way to test the FPR in situ.
    There is a fuel pressure test port. But it's on top of the TB.
    1985 Mustang GT Mild 331 4bbl 5 spd, 1985 SEFI LTD LX AOD.
    Cardomain: http://www.cardomain.com/ride/565542
    Mid Size LTD LX Facebook page! http://www.facebook.com/groups/233213650060739/

  15. #15

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    I had a similar issue with mine a while back, I took off the hood and proped the pressure gauge where I could see it while driving to see if I was getting good pressure under load. It wasnt, but I was at 38 psi. I think these things want 40-42 to run well. I put a socket over the fpr and gave it a few light taps to literally push it in, effectively lowering the diaphram and upping the pressure. I did it with the car running as to not go to far. a few light taps bumped it up to 40. Took it for a drive and it ran great with absolutely no hesitation. it doesnt seem to be running rich, and isnt throwing a rich o2 code. I believe I was getting a lean code prior. I have put a few thousand miles on it since and it is still running great. I have a hunch the stock FPR is set to be JUST good enough to run it, but run it pretty lean, as to get better mileage.

    ford didnt like to feed these cfi cars much fuel for some reason. In my old 85 tempo with cfi ANY mod would max the fuel system. Just a custom made long tube header, cat delete, a high flow muffler and a custom made cold air system was enough to make it run lean enough to get some hesitation. The injector was maxed out on that car. I upped the pressure (that car had an adjusting screw) and it did nothing. I ended up having to swap in a higher flow injector along with tweaking pressure. Never had an issue after. I also tried a cfi TB rebuild kit on said car and that did no good either.
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  16. #16
    FEP Member LSCR351's Avatar
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    Quote Originally Posted by JACook View Post



    The CFI fuel pressure regulator is supposed to maintain pressure at the throttle body even
    if there's no pressure in the supply line.
    So you are saying if you attach a fuel pressure gauge to the test port on top of the throttle-body and it is reading pressure, that you can unhook the 2 lines on the back and it will STILL hold pressure?
    I think not. You can take the return line off and keep pressure, but as soon as you crack that main line fitting loose, POOF, there went the pressure. If you don't beleive me, try it for yourself.
    69 Mustang Fastback= EXPENSIVE
    84 SVO= project pick up the front wheels
    86 Coupe= project show car
    87 Mark-VII Vortech'd351/T56= TROUBLE
    93 Town&Country= DD/work van
    96 F150 Lightning FlareSide= boat hauler
    99 P71 "The PO-RAUDER"= weekend ride
    00 Excursion 7.3PSD= everything hauler
    97 Exploraineer Sport V8= wife's DD
    93 GT 2.3t/T5= wife's backup ride
    05 F250 V10 SCSB= wife's toy

  17. #17

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    Screw this. I asked MoeIII if he'll convert my LTD LX to a stock SEFI system. He did a great job on his LTD LX with the GT40 swap. And I don't care about mucho HP, I just want a reliable driver. I'll be dropping the car off at his place with all the parts soon. I'm tired of constantly having issues with CFI. I want something as reliable as my mothers 89 GT. Two years and she's never had an issue. Where this CFI has always had issues.
    1985 Mustang GT Mild 331 4bbl 5 spd, 1985 SEFI LTD LX AOD.
    Cardomain: http://www.cardomain.com/ride/565542
    Mid Size LTD LX Facebook page! http://www.facebook.com/groups/233213650060739/

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