Engine that Diesels after shut off - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 13 (permalink) Old 01-02-2010, 01:47 AM Thread Starter
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Engine that Diesels after shut off

Hi all,

I am a new proud owner of a beautiful 1970 240z and I have noticed a couple things about the car that seem like easy fixes, but I would like to hear a little from the you all.

First thing that really stands out is when I shut off my car, the engine continues to try to run. Do these cars have an electronic shut off valve in the carb to prevent this from happening. I think the problem will be remedied a bit after I do a fuel treatment along with a nice fresh tank of gas. What Octane do you guys suggest for the original Inline 6. I haven't noticed any engine ping under acceleration.

Second, the car seems to run a little hot, though I am not really sure if i trust the temp guage yet. When I am in stop and go, the temp goes just passed 3/4 on the guage. It seems to do it pretty quickly like maybe 5 minutes of slow driving. It immediately goes back to half way once I am under way for more than 30 seconds. Probably will get its oil changed soon, any suggestions for weight and brand.

Lastly, The **** hood latch keeps popping up. Know of any sources to obtain a new mechanism.

Once I can get my hands on a camera I will surely post some pics of the car

Cheers

SPD

1970 240z with original 2.4L and a 5 speed Transmission
Lowered, Stiff Springs, Custom Wheels and Paint.
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post #2 of 13 (permalink) Old 01-02-2010, 02:47 AM
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Re: Engine that Diesels after shut off

Maybe you should get a fan clutch before you burn it up. NK

I once worked at a real Datsun dealer. Training at Nissan Gardena was the best any car dealer had, in my opinion. Norm K.
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post #3 of 13 (permalink) Old 01-02-2010, 03:11 AM
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Re: Engine that Diesels after shut off

Dieseling is usually caused by a hot motor + low octane fuel and or idle setting too high. Drag the clutch on shutoff till you figure it out to prevent reverse rotation which can be very bad! Where do you live? Regardless, I recommend Castrol 15W/40 Diesel oil as it retains the the good lube additives that favor long cam life (but O2 sensors and cats don't like them). I always run the 93 octane if for nothing else than for the detergents that only high octane contains. (notable exception is Chevron fuel which contains Techron in ALL grades and Techron is definitely the detergent of choice!). This alone might cure the run-on condition. As for the temp issue, you might have a faulty fan clutch or you live in a hot area and the two row core OE radiator is marginal. I recommend a 195 deg. tstat for optimum cooling efficiency. If the clutch is good and cooling adequate (which I doubt it is) and run-on still occurred, you could drop to a 185 deg t'stat. I personally run an electric fan which helps in stop and go and takes a load off the water pump. I also use a three row core 280 rad which fits if you trim the lower mounting flanges.
The post on the hood has a locknut which you can loosen and adjust the post longer to ensure full engagement into the latch. Good Luck!
Nick

Syracuse, NY 1.)Horner's five thumb postulate..."Experience varies in proportion to amount of equipment ruined" 2.) "Everything takes longer than it does" 3.)"Electronics run on smoke...just don't let the smoke out!" (A.A.S.E.E.T.) 4.) I "FIXED" it, and now it doesn't work"
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post #4 of 13 (permalink) Old 01-02-2010, 09:02 AM
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Re: Engine that Diesels after shut off

My dads 71 Caddy Hearse would diesel after a long hot day of driving. It turned out that it was timing being way off. He had a "trust worthy" friend look at the timing and said it was ok... but when we looked at it it was way off and I am surprised the thing ran. After we adjusted it back to where it should be it hasn't dieseled since.

Good Luck!

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2017 Ford Edge 2.0T
1980 280zx with 82 Turbo motor and MS2, E85, LS2 COP, and TO4e.
Rochester, New York

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post #5 of 13 (permalink) Old 01-02-2010, 10:13 AM
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Re: Engine that Diesels after shut off

I fail to see how timing would be an issue on overrun as with the ignition OFF, there is no timing!
Nick

Syracuse, NY 1.)Horner's five thumb postulate..."Experience varies in proportion to amount of equipment ruined" 2.) "Everything takes longer than it does" 3.)"Electronics run on smoke...just don't let the smoke out!" (A.A.S.E.E.T.) 4.) I "FIXED" it, and now it doesn't work"
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post #6 of 13 (permalink) Old 01-02-2010, 10:42 AM
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Re: Engine that Diesels after shut off

Sorry Speed but timing being off can cause the engine to run very hot which ignites the residual fuel in the combustion chamber. Every time it fires it pulls in a little bit of fuel and will continue to ignite it until things cool down. The key does not need to be on, all you need is fuel, air and a source of spark (heat) for combustion.
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post #7 of 13 (permalink) Old 01-02-2010, 06:43 PM Thread Starter
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Re: Engine that Diesels after shut off

I live in Los Angeles so it is actually quite warm right now.

Where should the idle be at. right now it is around 1100 RPM.

I am really unsure that the car is really getting hot, since about half the guages in the car don't work properly. Found out the hard way that the gas guage doesn't work this afternoon. It doesn't really feel like it is that hot right after I shut it off. Don't have a timing light at my disposal so i guess i will have to wait to take it to the mechanic next week.

Thanks Everynone

1970 240z with original 2.4L and a 5 speed Transmission
Lowered, Stiff Springs, Custom Wheels and Paint.
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post #8 of 13 (permalink) Old 01-02-2010, 07:20 PM
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Re: Engine that Diesels after shut off

You know you can buy a timing light and do it yourself! much cheaper to take your car to a shop...

One on ebay going to end in 12 mins for only 7.25 right now...

http://shop.ebay.com/items/timing%20..._dmd=1&_sop=12

77 280Z with SBC, 700R4, Vette C4 IRS W/11.5 rear disk, Centerlines 16x9.5 W/BF G 245x45ZR Comp T/A Rear and 15x7 Ft W/BF Goodrich Euro 225x15 on ft. Soon to have Coleman 12.2x1.25, x-drilled, zinc plated, Rotors W/Billet Outlaw 4000. Z U V8ter
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post #9 of 13 (permalink) Old 01-02-2010, 07:38 PM
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Re: Engine that Diesels after shut off

You could back the idle to 900 rpm, but I suspect a mechanic is in your future....
Nick

Syracuse, NY 1.)Horner's five thumb postulate..."Experience varies in proportion to amount of equipment ruined" 2.) "Everything takes longer than it does" 3.)"Electronics run on smoke...just don't let the smoke out!" (A.A.S.E.E.T.) 4.) I "FIXED" it, and now it doesn't work"
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post #10 of 13 (permalink) Old 01-03-2010, 06:16 PM Thread Starter
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Re: Engine that Diesels after shut off

Spent all day wrenching on my Z. Checked the Ignition timing and the vacuum advance. While it was cold I checked the fan speed and then drove it to get warm and checked to see if the fan sped up. It did. Then it occured to me that, maybe the previous owner didn't do the basics. So I checked the coolent level and what do you know, it was nearly empty. Filled it up and drove the car and now when it is warm it hangs out just below the middle line. I guess I should have checked that first. But I at least got to learn a few things about the car. Like it having electronic ignition. Also it doesn't diesel anymore.

Thanks for the help

SPD

1970 240z with original 2.4L and a 5 speed Transmission
Lowered, Stiff Springs, Custom Wheels and Paint.
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