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Thread: Are more 280 owners noticing difficult restart when engine is hot?

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    Registered User deadflo's Avatar
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    Default Are more 280 owners noticing difficult restart when engine is hot?

    I just started noticing this condition in my 79 ZX. It only happens when you try to start the car after is has already run and been sitting for about fifteen minutes or so. Sputtering, missing, backfiring. Seems like a "hot soak" issue. I found this link on Zcar.com. Note two other long time 280 Z owners have had the issue recently, for the first time. I just celebrated 20 years with this car, and it's never happened before. Wonder if it's related to ethanol in gas these days? There is a great discussion of it at this link:

    http://www.zcar.com/forums/883144/va...-wanna-call-it

    Note the discussion includes references to the check valve on the fuel pump, and fuel pressure issues, but I still wonder about the alcohol fuel, given that it seems to be cropping up more in cars that have never had problems. I'm not even sure where to get non alcohol gas, since all pumps in Washington state say the gas "may contain up to 10 percent ethanol".

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    Merchant of Cool Z train's Avatar
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    Sounds like leaking fuel.Obvious targets are the Cold start injector and the 6 main ones.Cap the CS injector and see if it happens.If it still does,after you've cranked it for a bit,pull the plugs and see if any are wet.
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    Registered User deadflo's Avatar
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    I've had my cold start valve disconnected for about eight years now...
    on the other hand, I havent checked to see if it is leaking.

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    I have a 280z, and have the same issue. Rough idle after the car is hot, and turned off for 15mins. But starts up in the cold perfect! lol
    1977 280z
    HLS30 384688

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    Registered User deadflo's Avatar
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    Did you check out that link? Seems like more folks are encountering this all of a sudden, on cars that have never done it since new. Could be that fuel pressure issue, but Im wondering if it's related to gas with ethanol??

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    Registered User deadflo's Avatar
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    Oh yeah, I will check leaking cold start injector, but it's only happening in that 20 minute window or so after it has run. I can get it to clear out after it runs bad for a few seconds,it does not RUN bad when hot, just RESTARTS rough.

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    Quote Originally Posted by deadflo View Post
    Oh yeah, I will check leaking cold start injector, but it's only happening in that 20 minute window or so after it has run. I can get it to clear out after it runs bad for a few seconds,it does not RUN bad when hot, just RESTARTS rough.
    And when you get it started,it runs but is shaking all over and after a minute or two it smooths out and all is normal-right?
    Faster than anyone in Oceanside

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    Quote Originally Posted by deadflo View Post
    Did you check out that link? Seems like more folks are encountering this all of a sudden, on cars that have never done it since new. Could be that fuel pressure issue, but Im wondering if it's related to gas with ethanol??
    Yea, I checked the link out, but no solution

    I don't think it's fuel pressure issue related. (if you're meaning that it loses pressure after sitting) Because then, it would also have hard cold startups. My 280z has perfect cold start ups. Hot start ups are fine too, but not when it has sat 15-20mins. But if it sat for an hour or longer, then it starts up fine.
    1977 280z
    HLS30 384688

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    Registered User deadflo's Avatar
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    Ztrain, yes, it dies but if I give it some gas as I crank, I can get it to "clear out" after about 20 seconds or so, then runs fine.
    I will look at rhe cold start injector first. The reason I disconnected it years ago, was, it was wet with gas on the TOP of the connector.So it was leaking to an extent then, but stopped when I disconnected the wire to the thermotime switch.

    I found that link real interesting . Tony's info was very good, but I want to see if any of WashingtonZmans ideas work. I'm driving home from work soon, I'm gonna leave the hood open after I shut her down, and then try to restart in about fifteen minutes. We'll see if that changes anything. It has done that stumbling the last two times Ive gotten home and tried to restart.
    It isnt really hot enough for the fuel line blower to come on, so i cant tell if that helps anything. it would nice to wire that upto a switch somehow..

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    My 810 does the same thing.I've been toying with the idea of getting the injectors cleaned but hav not gotten off my ass to so it.
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    It's the alcohol in the fuel. It may also be a loss of residual fuel pressure. But that usually makes itself apparent by a hard start/extended crank/die out first thing in the morning. You might alleviate the problem somewhat by using gas with less alcohol. Install a second check valve between the fuel filter and the fuel rail. Sometimes a piece of crud from the tank will cause the check valve on the pump to hang open a bit and cause a loss in residual fuel pressure. But again---this usually will not cause a HOT restart problem---only cold start, first thing in the am. Short of removing the check valve on the pump to clean it---you might try tapping on it with the car running to dislodge any crud that might be present between the check ball and the seat. Your injectors may also be leaking a little causing a RICH hot-restart condition. The car will stumble till it clears the excess fuel. But that shouldn't last more than 15 or 20 seconds. I wouldn't worry about it. An EFI Z is NOT a perfect system. Relaible by 1970s standards and FAR superior to poor running, carburated domestic junk of that era. Believe me. I lived it.

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    I'm thinking alcohol too, Powerglide. Results of my non scientific test of: run car hard, park in sun with hood closed. Try to restart 15 minutes later.Stumbled and ran crappy both times I tried that.
    Then run hard, park in the shade with hood open. Try restart 15 minutes later. Ran fine both times!
    I'd like to hook up my auxillary cooling fan(that the ZX's have on the fuel rail) to run every time I shut her off. I need to figure out how...

    OH and again, this car has never had this issue in 20 years. And it now appears alcohol is in all the gas in Washington state, that I can figure out..
    Last edited by deadflo; 06-03-2010 at 02:17 PM.

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    Hot wire from the battery through a thermostatic switch......
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    No hard starting for me. My 280z has triiple webbers
    HLS30-217804 6/75 "The Unnatural One"

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    Hey Bill, try starting the triples when it's below Zero out...

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    We've had state mandated E10 (10% ethanol/alcohol) in our gasoline in Minnesota for years ... and my Z has never given me the issue you describe.

    Have you tried other gas stations? Some places have a proprietary E35 mix too.

    Sometimes when it's hot my car will take an extra half second of cranking (presumably due to a leaner fuel mixture), but otherwise no issue.

    10% mixtures of Ethanol were being used in places worldwide in the 1970's ... I have a hard time believing that all of a sudden introduction of a bit of ethanol into the gas would cause such severe problems. (If that's even what's going on)

    ... you'll also notice how these guys (on the original, linked thread) are talking about how running on 'summer gas' (i.e. less oxdized) gives them no issue.

    All things considered the fuel injection systems on our cars aren't all that complex, and Ethanol (in its purest form) is much cleaner and acidic than gasoline, and in many ways can act as a good decarbonizer.

    I've been tempted a few times to run E85 in my Z, without modification, just to see what happens... (Don't forget that E85 has an octane rating around 105 ... cheap racing fuel for those of you running high compression).
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    my 78 z has also picked up this habit of starting rough after sitting for 15-20 minutes...i can fast idle for a minute or so and it goes away, but if not it's pretty rough...
    the cold start injector and the thermotine switch are the only FI components i'v never changed, I've been tempted to swap them out to see if it goes away...(they test ok according to the FSM.) everything else is new under the hood...why stop now...
    ."There are two types of car enthusiasts:
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    I, of course, am in the second group."

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    Quote Originally Posted by deadflo View Post
    Hey Bill, try starting the triples when it's below Zero out...
    Move to Arkansas and you won't have that problem
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    Open your hood right after you shut it off. Try to start in 15 Put you hand on the fuel rail after the car is off....hot as sin.....btu rating goes way down on hot fuel.....This happens every time i shut my MS powered efi off. Its hot under there. It is indeed a Heat Soak like issue. Nissan took notice put a fan in there. Took notice again on the z31 and put in a fuel temp sensor and fuel temp map.
    Last edited by yetterben; 06-03-2010 at 09:23 PM.

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    KD Matt,
    Here in the Spokane area we did have mandated 10 percent ethanol for many years in the winter months, but I never drove this Z in the winter.
    You may recall Congress passing the ethanol bill about two years that mandated increasing the use of ethanol in gas sold in the US.In the last year, the gas pumps in Washington have read "this gas MAY contain a blend of up to ten percent ethanol."
    Apparently my car is now reacting to it. It could be something else, but I'm basing this in part on reports that other FI owners are having similar issues. I know it's definitely a heat related issue, given the little experiment I did yesterday starting the car with hood open and closed. I do plan to buy gas at some different places to see what happens. I also have the option of going over to Idaho to fill up, to see if it's any different.

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    A new thread here regarding another report of vapor lock:
    http://www.classiczcars.com/forums/s...threadid=38754

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    and the new Oxygenated fuels break loose particles and such like water does. Fuel slows rust by not allowing oxygen to reach the bare metal but Oxygenated fuel gives the rust air to help it rust. Kind of a catch 22, better oxygen in the fuel but it can loosen deposits and clog the filter and such.

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    Registered User Walter Moore's Avatar
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    Quote Originally Posted by deadflo View Post
    Hey Bill, try starting the triples when it's below Zero out...
    You actually drive your Z when it is below zero?
    '71 240Z, Because any fool can drive fast in a straight line.

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    Quote Originally Posted by Walter Moore View Post
    You actually drive your Z when it is below zero?
    I do. But we don't salt the roads here...
    Arne - Former owner, HLS30-37705, 7/71, 905 Red
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    I'll try and find the thread on NWN, but this same topic came up. One member posted a link to a site that had a decent list of gas stations that don't use any ethanol.

    I'll edit this post once I find it.
    HLS30299157 1976 280Z

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    I've had to a couple of times long ago. The FI systems are sure alot more reliable in cold start than carbs. Especially non enriched triple webers.

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    Quote Originally Posted by Z Tyler Z View Post
    I'll try and find the thread on NWN, but this same topic came up. One member posted a link to a site that had a decent list of gas stations that don't use any ethanol.

    I'll edit this post once I find it.
    Cool to know Z Tyler!
    NWN=Northwest News Network??

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    Quote Originally Posted by deadflo View Post
    Cool to know Z Tyler!
    NWN=Northwest News Network??
    Finally found the link, sadly none in Everett or Spokane.

    http://pure-gas.org/index.jsp?stateprov=WA

    The site also has many other states listed for those that are interested. Also NWN = Northwest Nissans. More of a 240sx forum but they generally host good meets.
    HLS30299157 1976 280Z

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    Thanks, Tyler! Only Colville near me over here, but still 60 miles away! Maybe I'll try Idaho..

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    FWIW-we don't have ethanol in our gas here and i'm havingf the same issue.
    Faster than anyone in Oceanside

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    Quote Originally Posted by Z train View Post
    FWIW-we don't have ethanol in our gas here and i'm havingf the same issue.
    Are you sure, Z train? I know the federal mandate to use 10 percent ethanol is making it's way into most states. Have you looked at the gas pumps where you are and read the "fine print" lately?

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    Anywhere in town I've bought gas in the last 2-3 years has been 10% ethanol, with 85% ethanol popping up here and there.

    The only places that have straight gasoline anymore are way out in the country around these parts.
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    Default 280zx manifold cooling fan?

    I'll try the hood pop trick, and see if that improves things. Pretty lame that those ugly louvers datsun cut into the 280's hoods aren't doing their job...has anyone dabbled with installing a 280zx manifold cooling fan on their 77-78 z's? My valve cover and block both have extra bosses and tapped holes, which might work for installing the fan and duct, with a little modification...I'm thinking of using a thermostat switch, so it will run for a little while after the engine is shut down...any thoughts on this?
    ."There are two types of car enthusiasts:
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