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THE BACKGROUND INFO:

Rat box 87 300zx auto (new paint and interior now so at least it looks nice)
Ever since I got this car it's had a few different things wrong with it, in order for it to idle properly one of the stupid previous owners had it idling with the thottle cable adjustment. Probably the same idiot who put in the non turbo, ecu which was also for the wrong year and transmission, yeah that was a tough problem to find!! I also found a few other misc. parts from non-turbo. It has also always had the ever to common sputtering and rough running until you get down the street, I replaced the chts and ensured no problems with the wiring, it didn't help. Well lately after it sat for a little while, it seemed to have gotten worse, it would now start up and idle fine for about 30 seconds than it would make an odd clunk sound and then stall out. Suspected fpr so I ran some tests, no problems, racked my brain, quadruple checked for vacuum/intake leaks, ran some more tests, eventually figured out that the big selenoid on the AAC was what was making the clunk and then killing the engine, I was able to duplicate it every time I disconnected the connector to the selenoid while the car was idling. I took my multi meter, and upon starting the car with it connected I backprobed it and it read 12v, after a minute it would soon 'clunk' (de-energize) I couldn't tell if the voltage was droping as the engine would quickly die (this part doesn't receive key-on or key-run power. So my next step, since I now knew it requires a full twelve volts was to unplug the connector and run a power and ground wire right from the battery to the AAC selenoid, this made it idle flawless,no more stalling and then starting right back up, well not flawless, it was fairly high, Upon setting the throttle cable freeplay back to normal the Z idled right were it should! I also checked the voltage at the disconnected connector while it had been running for a minute or two and it read about 9.5 volts?? I then set my ignition timing and was a happy man....but

THE QUESTION:
It's now idling and revving perfect cold or hot with the temporary jumper wire energizing the AAC selenoid, (if I disconnect it it will clunk and die though) I need more information about how the AAC selonoid circuit functions, I'm geussing it is controlled by the eccs? Does it apply power or switch off the ground or what? Any sensors involved with this? Basically I'm looking to find out any and as much info about the AAC and/or it's control circuit as I can. I need to know what my next step should be in diagnosing this. Thank you very much guys.

Sincerely,
Kevgoods
 

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It would die if there is no signal, The signal does come from the ecu. If it runs fine with a different 12v wire then the signal must be broken or grounding out some where. Trace the wires to the ecu and test the wire at the ecu and then test the voltage at the connetor agian and see if there is any difference in your voltage. If you cant figure it out run a wire from your ignition switch to the to the ACC and it should be fine. Just dont leave it on the battery it will drain your battery over time. good luck



Post Edited (Apr 17, 5:38pm)
 

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Your next step would be acquire the factory shop manual. Almost everything you need is in there. The previous owner botched things because he/she/it didn't use the FSM.

The AAC gets a 160Hz signal from the ECU, using pulse width modulation to control opening duration and hence air quantity through the AAC (a bit like a fuel injector).
It is unlikely you would measure 12V between the contacts of the connected and running AAC, more like 6-8V if everything is normal.

The AAC is used by the ECU to "fine tune" the idle. The engine should idle without the AAC connected, but at a lower rpm than spec.



Post Edited (Apr 17, 11:34pm)
 

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It will not idle without the ACC. Its either on or its off. I checked my car and it is getting 11.90 volts when revving the engine the signal did not change with engine speed.
 
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