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  1. #1
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    Default CFI 5.0 running lean

    I have an 84 5.0 that seems to be running a little lean. I changed the plugs yesterday and there all white. The car is all stock except a single 2.5 in exhaust into a turbo muffler. The EGR has been unplugged and hose plugged. It also has a problem with running at high idle speeds when you come to a stop which eventually idles down. Then the other night I took it to a speed of about 80 and when I backed off it backfired and blew the muffler. I'm not sure if this is all connected there seems to be a few problems I'm facing...thanks

  2. #2

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    Start checking for vacuum leaks around the throttle body and intake.
    Jim DeAngelis
    Cornucopia of Useless Knowledge
    Connoisseur of Dearborn Ferrous Oxide
    '83 GT hatch, currently under the knife
    '79 Capri 2.3L n/a, Medium Copper metallic, survivor
    (bought from MRausch82)

  3. #3
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    Default

    I couldn't find any vacuum leaks. Is there any truth in a possible water temp sensor. I was told this and when I'm running the heater blows very hot but the temp guage hardly moves.

  4. #4

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    gauge sending unit and ECT (Engine Coolant Temp sensor) are two different parts, not connected. And if the ECT were reading cold, it would run rich, not lean.
    Jim DeAngelis
    Cornucopia of Useless Knowledge
    Connoisseur of Dearborn Ferrous Oxide
    '83 GT hatch, currently under the knife
    '79 Capri 2.3L n/a, Medium Copper metallic, survivor
    (bought from MRausch82)

  5. #5

    Default

    check fuel pressure AND flow. I still think you need to check for vacuum leaks again. Did you disconnect and block the line to the brake booster? The booster can leak and cause this issue. Be sure your PCV system is working correctly, too. Make sure the valve is correct and not a cheap quality unit.
    Jim DeAngelis
    Cornucopia of Useless Knowledge
    Connoisseur of Dearborn Ferrous Oxide
    '83 GT hatch, currently under the knife
    '79 Capri 2.3L n/a, Medium Copper metallic, survivor
    (bought from MRausch82)

  6. #6

    Default

    Definitely replace the PCV while you are poking around, I found my vacuum hose was stiff and leaking on mine. The fixed all kinds of idle and lean issues. Have you sprayed cleaner around the cfi base and other important 'vacuum' areas?

    Throwing codes?

  7. #7

    Default

    If there was enough fuel in the exhaust to be able to backfire and blow out the muffler, I have to question your
    diagnosis that it's running lean. Reading plugs in engines with EFI, and with unleaded fuel, is not nearly as easy
    as what you see in those old plug reading charts.

    First thing you should do is pull codes. No, actually, the first thing you should do is reconnect the EGR, because
    with it disconnected, the CFI system is probably not running closed-loop. The 5.0 CFI system uses EGR for more
    than just NOx reduction. For example, EGR is actually part of the idle speed control strategy. I suspect your high
    idle speed is because the VOTM (throttle kicker) is active, which is also a pretty good sign of open loop operation
    (or the ECU thinks the A/C is on).

    With the EGR reconnected, the KOEO/KOER tests should be run to verify the basics, and check the fuel pressure.
    Two things CFI is really picky about are fuel pressure, and a clean MAP sensor signal. Verify that the MAP sensor
    hose has no cracks, and is a straight run from the intake manifold to the sensor, with nothing else tee'd in. The
    fuel pressure spec is 39 ± 2. Mine likes to be closer to 41, especially while it's in open loop warming up.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  8. #8
    FEP Senior Member Matt J's Avatar
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    Default

    Listen to that Mr. Cook, he's the smartest man in the world when it comes to your CFI system.

    If you're planning on keeping it stock then I recommend buying a test unit that you can plug right into your onboard computer. I got one on Amazon for about thirty bucks, it's easier than using a test light, stores your codes and if you like can help you clear the old codes from the car's computer when you need to do that. That computer is super helpful for diagnosing your problems and keeping things running right. The computer is 80's tech, but it works well. Keep in mind, though, that EVERYTHING is run by vacuum, so a tiny leak on any of those 30 year old hoses can mess with a sensor or something else. Definitely plug everything back in, and start working the problems one at at time. It takes a while to unwind 30 years of shadetree mechanic work, remembering that back in the 80s most car guys had no need of vacuum hoses or computer controls so they'd think nothing of unplugging something. Trust me, when you get it right it's absolutely foolproof and is great for cruising.

  9. #9

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    I will add a second to all of that. Although I have been pushing the cfi limits (soon to push it even further), I have normally gotten it running perfectly within only a few days using the excellent suggestions from these guys. I got my computer from the local aotuzone for 30 too, so it can be an impulse buy and very much worth it.

  10. #10
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    I very much appreciate your help. I will do some more on it in the next few days. Tomorrow I have to repair my wifes pontiac. It's the only day the wheels aren't turning if you know what I mean. I will check out a new EGR valve while I'm at it. Thanks guys

  11. #11

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    You can just clean up yours. Check to make sure the vacuum actuator is functioning but everything else in the actual egr is unbreakable and easily cleaned. Mine was disconnected when I bought the car and simply reconnecting the vacuum fixed almost all of the issues it was having.

  12. #12

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    I'd definitely plug that EGR back in. I accidentally left the electrical connector unplugged on my 85 LTD LX with CFI, it ran just like you are describing.

    Mike

  13. #13
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    Well I finally got enough time to work on my car instead of mamas car. I plugged the EGR back into vacuum and drove it for a couple of days and it ran horribly. I used some brake clean and cleaned it out a bit. I ran it for a week and it seemed to run very well until today. It started running very rough and the throttle response was bad also. I cleaned it one more time so we'll wait and see.

  14. #14

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    I may be magical thinking but I would reset the computer too (disconnect the battery for a little while). Did you grab a code reader? You may want to check your TPS while you are at it. Again a super easy replacement part if you have the CFI off for EGR work anyway.

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