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Thread: 76 Z starts but will not idle.

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    Default 76 Z starts but will not idle.

    Alright so I've searched around and still cannot nail down the problem I'm having.

    I bought a 1976 280Z a few months back, ran and drove fine except for an exhaust leak at the manifold. I swapped the manifold for a header and ever since then it refuses to idle. The car will crank up and start, and it will stay running if you hold the gas and keep it in the upper rpms. But as soon as you let off the gas or try to let it idle it starts to stumble then shuts off. It almost sounds like its not running on all cylinders.

    Any idea what could be causing this? I've checked all of the fuel lines, filters, etc. It's not a smog motor and the only major things done to it are an A/C delete and a 5 speed from a 77Z

    Here's some pictures of the engine if that helps
    http://i.imgur.com/bqR4i7q.jpg
    http://i.imgur.com/5SejnLO.jpg
    http://i.imgur.com/WYkjXYu.jpg

    Thanks in advance, this has been driving me crazy

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    Maybe your firing order is off. I can't tell from the picture, but it doesn't look right. 1-5-3-6-2-4, counterclockwise. The engine will start and run with the plug wires backward, clockwise. These engines will also run on three cylinders, maybe even two.

    OR, maybe you have a vacuum leak that is letting air past the AFM vane. There's a switch in the AFM that opens, cutting power to the fuel pump relay, if air flow drops too low.

    You might have left a fitting on the intake manifold open. All air must pass through the AFM, except for a very tiny amount for the AFM idle bypass, and the charcoal canister.
    1976 280Z, with some minor modifications

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    it looks like there's been some work in the hose dept... i'd check the FSM for proper vacuum routing. it looks a little off to me - for one thing, i see a vacuum line going to the top of the throttle linkage dashpot, pretty sure that's just supposed to be open to the air, and that leads me to believe the vacuum line should be routed elsewhere.

    after you've checked every hose against the diagrams in the FSM and also checked for leaks (don't overlook the PCV hose underneath the intake manifold - those burn up and cause huge leaks) get a vacuum gauge on it and see where you're at.

    vacuum advance is a biggie as well - if not working properly you'll get lousy idle, especially with a leak.

    my bet is on vacuum issues - during the manifold replacement it's a good chance you didn't hook things back up correctly. also, i'm not sure about the smog setup on the 76, but check to ensure any smog fittings from the oem manifold are suitably plugged if the header has no such provision.
    '78 280z - Daily driver/work in progress...

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    Well I checked the firing order, it's correct. I took a look at the vacuum hoses and everything seems to be hooked up. What do you mean by the vacuum line going to the throttle linkage dashpot?.

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    Quote Originally Posted by 280Vette View Post
    What do you mean by the vacuum line going to the throttle linkage dashpot?.
    I circled it for him. That little Sorry game piece shouldn't have a hose attached. The other end of that hose either needs vacuum or supplies it to somewhere.
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    1976 280Z, with some minor modifications

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    what he said - and don't feel bad, i only know about this because i did it too...
    did you check the pcv hose? it's underneath the intake manifold, right next to the exhaust manifold and more than likely burnt up.

    it really sounds like a vacuum issue.
    '78 280z - Daily driver/work in progress...

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    Will I unhooked that line. It's connected to a t-coupling. One hose goes to the alternater the other to the throttle body. There's no vacuum coming from it so I'm assuming the end that was hooked up to the "sorry piece" needs to be hooked up to a vacuum source. I cannot find where it would go though.

    As for the PCV hose it looks okay, no cracks or anything

    http://i.imgur.com/42jf9YC.jpg

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    The vacuum comes from the throttle body. It's called ported vacuum and only sees vacuum when the throttle is off-idle. Throttle closed, there's no vacuum.

    And there are no hoses connected to the alternator.

    Great that you're digging in to doing your own work, but you should take notes when you take things apart and/or use the diagrams in the FSM when you put them back together. Based on the hoses to the dashpot and the alternator. there may be other things connected not-quite-right. That could be part of your problem. Off the bat, I'd say that your vacuum advance hose to the distributor does not have a vacuum source. Just a guess. Every hose and wire has a specific purpose and needs to be properly attached.

    You said that you checked the firing order, but did you check the rotation direction?
    1976 280Z, with some minor modifications

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    Sorry, not alternator, one hose goes to the distributor.

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    Then the hose with no home probably goes to the charcoal canister. But if it's open the distributor advance won't get its vacuum and you'll have a vacuum leak at the throttle body while driving.

    Your 76 might also have the vacuum advance solenoid, which only allows vacuum advance in top gear. Complicating hose routing. That's why taking notes is good. If you're not familiar with how all the various devices work it's easy to misplace something or leave it disconnected.

    The diagrams and descriptions are in the Emissions, and Engine Electrical, chapters.
    1976 280Z, with some minor modifications

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    Well I took a look at all of the hose routing (had to wait for it to stop raining) and the only thing I found was a small crack on the hose between the air flow meter and the throttle chamber. I fixed that and while it doe's seem like it'll try and idle a little bit longer, It still dies.

    I also noticed that some of the vacuum hoses don't quite look the same as the diagrams. But I compared the engine pics now, to a picture I took when I first bought the car (and it was running) and everything is hooked up the same. All my previous project cars have been carb'd, kind of missing that right now ha

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    my car ran when i got it from the PO but there were a ton of things messed up and huge holes in the vacuum system. everything was compensating for everything else. when i started fixing things and putting them right, things got worse before they got better. it actually took quite a bit of fiddling to get everything back to spec, but it was worth it. before it "ran" but now it rocks.

    keep the faith and go back to the fsm vs. what you may have had before. you may have to check other adjustments that were set out of spec to compensate for mis-connected and/or damaged vacuum stuff.
    '78 280z - Daily driver/work in progress...

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    You might try raising the idle speed to keep it running, while you do more diagnostic work. The rusty screw next to the thing that had the wrong hose on it (Post #5) is the idle adjustment. Turn it out to let more air in and the idle speed will increase. Might be enough to let it idle. Then you can use the old trick of spraying carburetor cleaner (carbs!, yay) around the various spots where there could be a vacuum leak. Injector seals to the manifold, intake manifold/head interface, PCV hose, EGR fittings, etc. If idle speed changes while you spray the outside, that means there's a leak. Keep fixing them and things will get better.
    1976 280Z, with some minor modifications

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    Sounds like vacuum issues to me too. Of course when you did the headers, you had to at least unbolt (maybe not remove) the intake manifold. Did you re-gasket both? These engines are notorious for their rusty studs and leaks around the #6 and (to a lesser extent) #1 intake runners. In fact on my engine, my #6 exhaust was blowing right into the #6 intake -- sort of an enhanced local EGR thing going on.

    I'm guessing all your vacuum lines are a lot more raggedy than you think. It's a cheap and easy project to replace the whole, sorry mess with new lines. Go buy a bunch of hoses/tubing at your local auto parts store, and go to it! Follow the diagrams in the factory service manual (far, far, far better than Hayes or Chilton's), which you can download for free here:

    XenonS30

    You might also replace that cracked intake boot, which will cause you to run leaner if/when it leaks. I don't know how you fixed it, but I would think a durable fix would be unlikely. That part is still available, as far as I'm aware. Courtesy Nissan might have it. Also check ebay (caution if dealing with reddit -- more expensive, with steep shipping).
    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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    MSA also has that intake boot. I would be curious to see if it will idle if you do what ZedHead recommended. There's a few other things you can do while its running but you already have a lot of things thrown at you. No need to get more confused right now. See if you can get it idling and lets go from there. And then maybe post a video of it.

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    Default Having the same problem on keeping the idle with a Far 311 Race Cam

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    Im having a similar problem. My car has a Far 311 Race Cam which is dropping from 1,100 to 500 RPM whenever i get stuck on heavy traffic, stalls and then dies. I did indeed remove the EGR system as the Servo Diaphgram was damaged.

    According to one of the members this is what i really have in my car:

    "a L26 crank makes my motor 79 mm stroke instead of the stock 73.7 mm
    stock bore is 83 mm for the L24 and the L26 motors
    my block has been bored out 1 mm to compensate for wear
    that makes my motor a 2.627 liter motor
    your E88 head from 1972 will give you about 8.7 to 1 compression
    FAR performance went out of business in 2002 so I have no cam specs
    311 could be their advertised cam duration
    if it is the same as BRE 311-------

    BRE 240Z 311/C-1 cam: At 0.001" lift: In open 33 deg Bef TDC In close 66 deg Aft BDC Ex open 66 deg Bef BDC Ex close 33 deg Aft TDC IN Lift at TDC 0.108" Total Lift 0.463"

    At 0.050" lift: In open 14 deg Bef TDC In close 45 deg Aft BDC Ex open 45 deg Bef BDC Ex close 12 deg Aft TDC

    IN Lift at TDC 0.108" IN Lift Total 0.463"

    EX Lift at TDC 0.097" EX Lift Total 0.469"

    HOW DO I SOLVE THIS IDLE PROBLEM? ANYONE?

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    I did change the idle screw and now it'll run for about 30 seconds, and a lot healthier, so it is getting better. I can hear what sounds like a vacuum hiss when the engine is running so now I guess I just need to track the hiss down. Sounds like it's coming somewhere over the #1 and #2 injectors

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    I put my valve cover gasket on upside down once and had a hiss around those injectors, vacuum leak. The flatter side up front on the gasket goes on the thermostat side.
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

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    It does idle now for the most part. Still sounds rough and stumbles and stutters and dies sometimes when I give it gas. I used a new intake/exhaust manifold gasket for the install. I also just noticed I do not have any clutch pressure. I don't know if it's related but the clutch was working fine before this all happened.

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    More clues. The Z.S.I unit will get you figured out!
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

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    Quote Originally Posted by 280Vette View Post
    . I can hear what sounds like a vacuum hiss when the engine is running so now I guess I just need to track the hiss down. Sounds like it's coming somewhere over the #1 and #2 injectors
    Carb cleaner does work if there's a leak. Idle speed will change when you spray it on the leak.
    1976 280Z, with some minor modifications

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    I sprayed carb cleaner on each of the hoses and did not noticed any change on the idle speed. Can you address exactly where shall i spray directly the carb cleaner?

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    The spraying of the carb cleaner is most effective on EFI systems. With carbs, you would spray at any connection points between the carbs and the head. The gasket surfaces and any vacuum hoses, like the big one for the brake booster.
    1976 280Z, with some minor modifications

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    Seems like the #1 and #2 manifold bolt wasn't tightened down enough. Tightened it up even more, played with the idle screw and timing a bit and now it runs. Ran for 10 minutes straight with no issues. I have some fine tuning to do, but for now I'm just glad it runs. Now I think I have to replace the clutch slave and lines, I think they deteriorated from not being used, but that should be pretty quick and easy.

    Thank you guys so much for the help

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    Have you cleaned your grounds yet? It really helps!

    http://atlanticz.ca/zclub/techtips/e...ons/index.html
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

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