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Thread: 77 280z running like poop

  1. #1
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    Default 77 280z running like poop

    I have a 1977 280z with running issues. What's wrong is that when I start the car, it cranks over fine and will start fine but after the initial start it will immediately bog down and either die or run on like 3-4 cylinders It helps tons when I push the AFM in about 25% of the way, but If I let it go on its own the car sputters and bogs down again or dies. With the AFM pushed on full (the top cover is off) I can slowly push the car up to a fairly high rpm, 5000 or so, but I can't seem to do quick revs or the car will backfire even with it in all the way.
    Here are some of the things I've replaced:
    -New cap and plug wires (with relatively new plugs; they're NGK, don't worry)
    -New fuel filter
    -New seals for the fuel injectors
    -New fuel regulator
    -New coil
    Here are some things I've done:
    -Cleaned the fuel lines
    -Set the timing
    -Tested the fuel pump (It works and puts out about 36 pounds of pressure between the new filter and the rail)
    -Tried a different ECU and a different AFM (Both came with the car and both give the same results)
    -I did do a compression test awhile ago and everything was fine, and I should be able to do another compression test tomorrow afternoon
    -I checked to see if the injectors work by taking them fully out of the car starting it and see them all work correctly
    -I did check the voltage of the clips going to each of the fuel injectors and those all work fine
    -I checked the points in the ECU that go to both the AFM and the fuel injectors both also came out fine
    -I checked the electrics in the AFM itself and everything seems fine (it's also possible to hear the fuel pump working when the AFM is puched in slightly)
    If anyone has an idea of what might be going on please reply, I feel like by now everything should be working at least sort of correctly. I'm at the point where digging into my pocket and sending it to a mechanics shop or buying a Megasquirt system would be better than wasting anymore time on it. Would maybe replacing the whole AFM do me any good? Could it be a bad sensor sending a bad signal to the ECU? I appreciate anyone's input!

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  2. #2
    Registered User EuroDat's Avatar
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    When you say you checked, do you mean checked by following the FSM of FI Bible? The so called bible has a great diagnostic section you can go through with the FSM. Just need a multimeter and some cable to do voltage tests. Only needs a bad connection to mix up the ECU.

    Here is a link to the FSM and the "FI Electronic fule injection guide" is in the Others section further down the page.
    XenonS30

    Chas
    Chas
    5/77 280Z HLS30 403100 with some modifications
    Original colour: 305 Light Blue. The PO changed it to Red

  3. #3
    Registered User siteunseen's Avatar
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    Backfiring out the tail pipe and sooty = RICH, not enough air. make sure the air filter and piping are clear and clean all your electrical grounds, http://atlanticz.ca/zclub/techtips/e...ons/index.html
    Backfiring out the Throttle Body = LEAN, too much air. Vacuum leak can be found by using the "yogurt cup test", put that in search box up top.
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

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    When you push the AFM open, what you're doing is delivering more fuel (and the same amount of air). In other words, you're richening the mixture by pushing the AFM flap open.

    Considering you've already replaced or tried swapping everything, I think you probably have some vacuum leak issues (probably big ones). You should start by replacing every inch of vacuum line. Then check for vacuum leaks with the "yogurt cup test." After you've eliminated rotten tubing, the following common leak sources are left:

    -- Intake manifold - to -head junction, especially around #1 and #6
    -- Bad power brake booster
    -- Ripped/cracked "accordion" boot between AFM and throttle, resulting in unmetered air
    -- Disconnected or improperly connected vacuum lines
    -- Leaking items connected to vacuum lines, e.g. mode selector switch for heat/AC system (which can be re-furbed very easily)

    Have you checked your throttle position sensor? It's the little square, black switch assembly on the side of your throttle. It should be adjusted per the FSM.

    You might also have an ECU drift issue. The Hitachi ECUs ('78 and I believe also '77) tend to drift leaner and leaner with age. This can be corrected by adding the right resistance to the coolant temp sensor circuit. If you do want or need a new ECU, Superlen has been working on one specific to the Z and will be releasing it pretty soon. The intent is that it will be plug-and-play, or as close to P&P as is feasible with these old cars. It's called "Hellfire," and there are a couple of current threads about it.
    siteunseen likes this.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    Registered User ZCurves's Avatar
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    Looking for a similar problem myself... I did the old 'Screwdriver To The Ear Test' on each injector. Discovered my number one injector had failed. I also created a test lamp and confirmed that there was a pulse being sent to the injector - just that the injector had seized. Now I am replacing that injector and resealing the rest....
    Andrew (ZCurves)
    1978 Coupe - HLS30-440105
    Spring, Texas USA

    pro deo et patria
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    Z geek at large FastWoman's Avatar
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    Andrew, it's perhaps an occupational hazard (former neurobiologist), but I can't think of the "screwdriver to the ear test" without thinking of Phineas Gage:

    Phineas Gage - Wikipedia, the free encyclopedia

    My son told me over the phone about the old screwdriver trick, and I immediately ordered him a mechanic's stethoscope, which works a TON better than a screwdriver and is also safer -- and probably even cheaper. Harbor Freight -- best few dollars you'll ever spend on a tool!
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

  7. #7
    Registered User EuroDat's Avatar
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    That screwdriver trick is often mentioned in older factory service manuals. Its even shown in our FI Bible on page 36
    Ive used it at work on a homogenizer we use for cell breaking. The young guys thought I was crazy, but I found number 4 vavle had something in it and it did, an o-ring. That shut them up

    You are right Sarah, The mechanics stethoscope is 10 times better, but if you don't have anything else a screwdriver will do.
    Last edited by EuroDat; 04-07-2014 at 10:12 PM.
    Chas
    5/77 280Z HLS30 403100 with some modifications
    Original colour: 305 Light Blue. The PO changed it to Red

  8. #8
    Registered User ZCurves's Avatar
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    Yes, I have the stethoscope but I was too lazy to walk into the garage. Besides I enjoy getting grease in my ear from the screwdriver handle!
    Andrew (ZCurves)
    1978 Coupe - HLS30-440105
    Spring, Texas USA

    pro deo et patria
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    Have you cleaned the throttle body since you have had the car ? does the IAC help at all ?

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