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  1. #1

    Default Mike at asc enthusiasts says run this past JACOOK

    The car is an 84 McLaren Capri style with the 302 cfi setup. 55.000 miles, not rolled over.

    If anyone can lend some advice about a power drop-off under certain conditions, that would be helpful.

    If tank is full, I have all the power I want.

    Below 3/4 tank, while on an incline, power seems to be intermittent, as the rpm climbs conditions worsen. improve a little on flat land and goes down hill a little better. We're talking highway speeds here. Hardly occurs at around town speeds.

    My first thought is the fuel pump. (not another one...), just did one on my 87 McLaren.

    Then I read that the CFI cars have a return pump also, and the mechanic at work is confusing me talking about vacuum lines and such.

    I can tell that this is something that I will have to educate myself about. I don't even know that I'm on the right track.

    Ignition problems enter into my mind as well.

    Anyone have any ideas or experience with these symptoms. I really want to analyze all the possibilities and perform whatever tests I can to determine the problem before I spend any money unnecessarily.

    I have been reading on the MAP sensor and related problems, but in my mind, an electrical component gone bad, does not explain why the problem goes away when I top off the petrol. I'm thinking secondary fuel pump, but I'm looking for a difinetive answer before I spend. And that's never how it happens unless your well informed technically.
    Last edited by Darkhorse40; 03-03-2011 at 04:52 PM.

  2. #2
    FEP Member 85.0's Avatar
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    Default

    early CFI cars had an in-tank low pressure pump and an external high pressure pump

  3. #3
    FEP Super Member 86fiveoh's Avatar
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    Default

    Baffle come loose in the tank? So when your on certain angles it isn't picking up fuel.

  4. #4

    Default

    Even with 3/4 of a tank?? We're not talking bottom of the cell.

  5. #5

    Default

    Really? Wow. And welcome to FEP!

    From what you're describing, I'm going to vote for the lift pump inside the tank. I agree, the
    fact that it's sensitive to fuel level in the tank does narrow things down a bit.

    The '84 CFI uses two fuel pumps. The one in the tank is a low-pressure lift pump, whose only
    job is to feed the external high-pressure one. The return side of the CFI fuel system is not much
    different than what's used on the later SEFI cars. If the lift pump fails, or the hose connecting
    the pump to the pump hanger shreds, you can get fuel starvation. When the tank is full, the
    external pump can still pull plenty of fuel, even without the lift pump, but it will often be noisy
    because it's cavitating. As the fuel level in the tank falls, the cavitation gets worse, and starts
    to affect fuel pressure. I've also seen the fuel pump hose inside the tank disintegrate, with similar
    symptoms.

    Disconnect the line from the inlet of the external pump, and extend the hose so it can pump into
    a gas can that's above the height of the gas tank. Then turn the key on, and see if you get any
    fuel flow out of your extension hose when the pumps go through the prime cycle. If the pump
    and internal hose are good, you should get about an ounce or two of fuel for each prime cycle.

    If you don't get any fuel, you'll need to drop the tank to see whether it's the pump, the connections,
    or the internal hose.

    Halfway through 1985, the CFI system was changed to the later style single high-pressure pump.
    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

  6. #6

    Default

    Thanks, Jeff...thats sounds like good info and reasoning. I'm a guy who always wants to know why something is...not just what...Thanks, again.

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