# '85 300zxt that shuts down - need help



## 300jet (Mar 31, 2004)

just got my australian turbo z auto on the road and it has a real problem.

runs good, idles fine, is timed correctly and seems fine. 15degrees btdc- the sticker under the bonnet said so.(or hood for you americans)

when taking off, whether it's flat chat or just gentle it will accelerate until the turbo starts to take over and then all of a sudden it will shut off the power completely. If you keep your foot halfway down it will then start power and lose power at equal intervals, giving the stop start sensation.

i can hear pinging from the motor before it shuts off. So could it be the knock sensor making the ecu crack the shits? what does happen when a knock is sensed by the ecu? i know it retards, but how far?

or could it be my speed sensor?

or any other ideas? i'm about to do a ecu diag tomorrow though.


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## Zen31ZR (Mar 24, 2004)

I'd say it's likely you have an intake leak. Either after the MAF or after the turbo itself. One will make you run way rich (after turbo) , the other will make you run way lean (after MAF , pre-turbo). Since you are hearing serious knock before the engine shuts down , I'm going to assume its probably a big after-MAF leak. Check the piping between the MAF and the turbo itself , all .65 meters of it. The inlet to the turbo itself may also be loose , you'll likely have to crawl under the car to check that.


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## Zcrazy (May 26, 2004)

*Check your TBS*

Check your throttle position sensor.
That is my 2 cents.


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## 300jet (Mar 31, 2004)

did diagnostic,

gave me the throttle position sensor, which i fixed the harness and can't figure out the order of the wires.

also gave me code 41, which is not in my manual, does anyone know what this is?

drove it again for more hints and came up with this.

park on top of a hill, put auto in n, engine revs as hard as you want, take handbrake off and roll down hill reving a constant 3000rpm. all fine, untill 35km/h, then engine goes idle for about 1sec, then revs for 1sec, and so on. but i am rolling and there is no load on engine.

in other words as soon as the car is rolling more than 35km/h the engine kills itself every 2 seconds or so for about 1 second. And the ecu did not pick an error with the vehicle speed sensor.

any ideas? i'm going to unplug the speedo cable out of the auto and see what happens.


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## Zen31ZR (Mar 24, 2004)

300jet said:


> did diagnostic,
> 
> gave me the throttle position sensor, which i fixed the harness and can't figure out the order of the wires.
> 
> ...


Look in the thread below you for fault codes , though I really don't know how much different the AU spec Zs are , the codes listed are for the American cars. As far as the hunting idle is concerned , try bumping or slowing the idle by a couple hundred rpm , should be a screw up by the throttle body. On some cars this means there is a problem with the idle air control unit , changing the rpm setting can make the problem go away. And no your speed sensor would not be the problem in this case , the hunting idle indicates the speed sensor is in fact working , the ECU is definitely reacting to it. The ECU is sending inputs to the IAC unit regarding vehicle speed versus engine speed , and the IAC is just reacting incorrectly. Adjusting the IAC back into its normal range may work. Your idle should be stable at slightly above normal idle when rolling in neutral. Most 5-spd Zs idle at 600 rpm (mine does) , I think the autos might idle a couple hundred rpm higher when in neutral and stopped.


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