car diesels when i shut it off - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 9 (permalink) Old 07-27-2007, 06:30 PM Thread Starter
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car diesels when i shut it off

Guys,

the car diesels really bad when i shut it off after running it for a bit. The temp out today is in the high 90's. I have changed plugs, cap rotor and have had the carbs synced. I believe the timing is ok. Not 100% on the timing though. I have 5 marks on the pulley and i made sure that the timing was on the mark that the mechanic had it set at before. which was the very top one. It idles fine and runs fine but when i go to turn it off it keeps on running for a bit. what could it be?

Joshua
Pasco, Washington
1971 240z-Stock L24, 4 speed, Centerline 17's, Tokico Illuminas adjustable struts, Tokico springs, MSA front and rear swaybar, rear disc, ZX Electric Dizzy, MSD and ZX alternator upgrade
1982 280zx- Sittin at the parents in Ore
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post #2 of 9 (permalink) Old 07-27-2007, 06:51 PM
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Re: car diesels when i shut it off

Crap gas? What are you running in your tank?

Fred
Tampa, FL

'74 260Z 2+2 Auto, 102K. Daily Driver. Mods: SU RoundTops, MSA Type II Body Kit, Twice Pipes, ZX Dizzy, E12-80, with MSD Blaster II Coil & MSD Wires. Tokico HP struts & lowering springs.
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post #3 of 9 (permalink) Old 07-27-2007, 07:53 PM
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Re: car diesels when i shut it off

High temps, lean mixture, high idle and wrong timing for the gas used causes "run-on." They used to have many dealership internal bulletins about this in the 70's when emissions controls became manditory. Norm K

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 #4 of 9 (permalink) Old 07-27-2007, 08:51 PM Thread Starter
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Re: car diesels when i shut it off

I had a friend tell me the same thing norm. At first i put in Plus gas and then last fill up i went regular. Problems started after the gas change. Also i think my idle is set a bit high. I have been getting crappy gas milage since i did the timing. I am at 60 miles with almost a half a tank. Car runs fine and idles fine but milage seems a bit off. Will put some plus in next fill up. Right all i have done is put in some Seafoam at lunch will see if it helps. thanks guys.

Joshua
Pasco, Washington
1971 240z-Stock L24, 4 speed, Centerline 17's, Tokico Illuminas adjustable struts, Tokico springs, MSA front and rear swaybar, rear disc, ZX Electric Dizzy, MSD and ZX alternator upgrade
1982 280zx- Sittin at the parents in Ore
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post #5 of 9 (permalink) Old 07-27-2007, 11:43 PM
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Back to premium

I'm in Florida, and if I run regular gas I run-on too. If I read you right, the problem started after your gas change. Run that tank out and fill up with 93 octane, then report back!

Fred
Tampa, FL

'74 260Z 2+2 Auto, 102K. Daily Driver. Mods: SU RoundTops, MSA Type II Body Kit, Twice Pipes, ZX Dizzy, E12-80, with MSD Blaster II Coil & MSD Wires. Tokico HP struts & lowering springs.
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post #6 of 9 (permalink) Old 07-28-2007, 03:04 AM
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Re: car diesels when i shut it off

My 240z gets very mild run on occasional with 89. Granted though I am useing Webber carbs that are not properly jetted, and I am still learning about timing and what not. I used the good old (herm, the motor sounds better when I ajust this to this) tuning method. Deff do not run regular crap gas, as the run on is only around when I use something thats not BP or Shell

'73 240z 4sp Silver, almost 100% stock SOLD
'78 280z LT1 SOLD
'90 300zx 2+2 Na 5sp red, SOLD
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post #7 of 9 (permalink) Old 07-28-2007, 07:17 AM
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Re: car diesels when i shut it off

I recently drove an older 1970 that was stored for 22 years. The thermostat would slowly creep up. It would diesel when hot and shut off.

I had to flush the rad a few times to get the sediment out and I also gave it more fuel. This seemes to keep the temp down after a couple hundred miles
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post #8 of 9 (permalink) Old 07-29-2007, 04:44 PM
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Re: car diesels when i shut it off

Mine also does this very frequently sometimes for a good 20-25 seconds i backed the timing off a few degrees and it hasent done it since. but it only happens on the very hot days.

79 2+2 fresh L28, N42 head shaved and shimmed all new hardware with cast flat tops, Isky Cam, 5-speed, holley 450cfm 4barrell. Msa 621 header. 2.5"exhaust, waiting on a turbo and collecting EFI components, eibach springs and tokico's, suspension technique
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post #9 of 9 (permalink) Old 07-30-2007, 12:18 PM
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Re: car diesels when i shut it off

this is probably because you have a lot of carbon build up, which in turn causes your compression ratio to climb and leads to the car still firing after turning it off. changing the timing will work, but it's not a fix. first step is to try some "seafoam". which is cheap, and may be effective.

watch out for the smoke, though.
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