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Thread: engine dies when i pull out dipstick

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    Texan saridout's Avatar
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    Default engine dies when i pull out dipstick

    is it normal for the engine to die when the oil dipstick is removed? cause that's the problem i'm having.
    1976 280z Automatic

    my 280z flickr set

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    Removing the dipstick allows air into the engine that isn't being "counted" by the AFM and that's why it's dieing.

    I'm almost positive that my 76 doesn't die when I remove the dipstick while the engine is running. The RPMs will drop a bit but it stays running. What does your car idle at? Does it stall then die or just die right when you remove it?
    HLS30299157 1976 280Z

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    240Z Elec. Upgrade guy Zs-ondabrain's Avatar
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    Better question, Why would you pull the dipstick WHILE the engine is runnig?? You can't get a proper measurement unless the engine has sat, not running, for at least 5 minutes.

    Or am I confused?
    Dave
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    Funny this is brought up. I just had lunch with an old datsun mechanic who was looking my Z over. He mentioned a couple of things to watch for when it runs rough. One is that the dipstick has to have a tight seal and the other is that the oil fill cap gasket can go bad and cause idle problems. He said the vacuum on these old cars was so sensitive that any loss would cause issues that seem nearly impossible to find.

    Just this weekend, I started my turbo motor in my 280Z and it wouldn't hardly run. I had taken the power steering pump bracket off, leaving the open fuel pump boss without a cover. Covered it up and it runs! Not particularly well just yet, but it runs.

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    I was hoping this thread was sick off color joke... Instead I found a legitimate technical discussion. Prurient dipstick references obviously does not belong on this thread. Go here instead...

    http://www.google.com/search?hl=en&s...=Google+Search
    Lee - 2/72 240Z

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    Texan saridout's Avatar
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    Quote Originally Posted by Z Tyler Z View Post
    What does your car idle at? Does it stall then die or just die right when you remove it?
    i idle at about 650, and it sputters and stalls about 10 seconds after i pull the dipstick. i've just rebuilt it, and it's been running a little rough ever since.

    Zs-ondabrain: i pulled it on a lark, and i hadn't even moved it an inch out of the block when it started sounding dramatically different. i pulled it out the rest of the way and it died seconds later. my dad had never seen this behavior before in a car, and he flipped out, so i flipped out, cause i've spent the last 6 months rebuilding it. and here i am.

    IdahoKidd: thanks, that's helpful. it seemed like someone had once told me to check the dipstick for vacuum leaks when trying to fix a rough idle, but i haven't been able to find anything on the forum that mentioned that.

    does anyone else's die under these conditions?
    1976 280z Automatic

    my 280z flickr set

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    Totaly normal. Both my 78 Z and `83 BMW 320i do it. Some newer cars it simply runs rough or struggles. All your doing is creating a disturbence in the engine vacum, simple as that.
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    Texan saridout's Avatar
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    Quote Originally Posted by WingZr0 View Post
    Totaly normal. Both my 78 Z and `83 BMW 320i do it. Some newer cars it simply runs rough or struggles. All your doing is creating a disturbence in the engine vacum, simple as that.
    ok thank you i think i'll stop having a heart attack now, then.

    also, does anyone know what kind of seal is on the dipstick, and if it's available anywhere?
    Last edited by saridout; 01-12-2010 at 10:57 PM.
    1976 280z Automatic

    my 280z flickr set

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    Registered User Bonzi Lon's Avatar
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    From all the Datsun dip sticks I have, they appear to be hot molded rubber, probably around barbs on the shaft to keep it in place. Never cut one open. There will be a certin distance between the end of the stick and the top seal of the dip stick plug. If the rubber plug is defective, either by air leakage or not firmly attached to the metal stick, I would replace.

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    well shoot, i can get a brand new dipstick for under 12 bucks. i'll just do that. thanks everybody, this was really helpful.
    1976 280z Automatic

    my 280z flickr set

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    Registered User conedodger's Avatar
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    I agree with the several who have called this normal. You create a big vacuum leak when you do that and it kills the motor.
    You mention that you rebuilt and that it is running rough. Did you stick an aftermarket cam in? The stock injection on the late '75 on with LJet does not respond well to loss of vacuum signal. Most of the aftermarket cams I have seen will give you very little vacuum.
    Rob
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    Texan saridout's Avatar
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    Quote Originally Posted by conedodger View Post
    Did you stick an aftermarket cam in?
    nope. aside from a 20 over rebore and a replacement identical head, i haven't changed anything. it ran much rougher before the rebuild, in a different way. now it kind of misses and lopes a little, but never dies like it did before. i keep finding vacuum leaks and fixing them, such as the injector seals, and it improves incrementally with every leak i find. this could be just another one.

    my dad has worked mostly on german cars in the past. is the engine dying when the dipstick removed something that doesn't occur in german cars?
    1976 280z Automatic

    my 280z flickr set

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    Not in old school American V8s and apparently not Korean cars. My teenage daughter, bless her non mechanically inclined heart, checked the oil in her Kia Sportage and then tossed the dipstick in the trash can at the gas station. Drove it for a month. I open the hood and there is oil residue everywhere. This car makes a tremendous amount of positive crank pressure. Still ran like it always did though. (aka, slow, no power, etc )

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    Registered User conedodger's Avatar
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    Quote Originally Posted by saridout View Post
    nope. aside from a 20 over rebore and a replacement identical head, i haven't changed anything. it ran much rougher before the rebuild, in a different way. now it kind of misses and lopes a little, but never dies like it did before. i keep finding vacuum leaks and fixing them, such as the injector seals, and it improves incrementally with every leak i find. this could be just another one.

    my dad has worked mostly on german cars in the past. is the engine dying when the dipstick removed something that doesn't occur in german cars?
    Each car is individual although you will find that many of the early efi systems were made by Bosch and you will find many of the same characteristic patterns in these cars that used LJet, DJet etc... As an example, when my 914 was DJet, if I pulled a vacuum line to create a vacuum leak the engine would surge to 3000 RPM. My 911 which is a much later derivative of LJet than your 280Z is completely unaffected by removing the oil cap. By the way, you should also find the car kills when you remove the oil cap.

    The idle you posted is not really indicative of a vacuum leak. There is a procedure for testing individual efi components. It can be found in the FSM. You might consider running these tests. I had a situation not unlike yours and I checked the CHT resistance and found it to be higher than spec. Replacing it cleaned up the way the car ran in more than one way. Hydrocarbons down, driveability up. Because of that higher resistance the efi brain has to assume that the CHT is high and to protect the engine it increases injector pulse time.

    Pop the caps on your TPS and AFM. Each has a set of copper strips which can get gunked up with corrosion after years of use. Use a very soft pencil eracer to gently clean this off then replace the cover. Most efi components in the LJet system send resistance signals to the brain which controls pulse time on the batch fired injectors. If things get gunked up resistance can increase, sometimes to infinity.
    Last edited by conedodger; 01-13-2010 at 11:32 AM.
    Rob
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    Registered User tlorber's Avatar
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    I don't think it is a great idea to pull the dipstick while the engine is running. I remember doing it once on a car (I think it was a 1200 in college). A lobe on the crankshaft launched the dipstick into the air and it landed in the dirt. Luckily those cars thrive on abuse.

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