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1975 Nissan 280Z After warming up, the car tends to stall/d

Tiny
REVOLUTION0
  • MEMBER
  • 1975 NISSAN 280Z
  • 6 CYL
  • 2WD
  • MANUAL
  • 120,000 MILES
Once the vehicle reaches normal operating temperature the car becomes prone to dying. It will instantly restart, but will die as soon as it is started. If I slightly press on the gas while starting the car will start and stay started at about 2,000 RPM. What seems to trigger the dying is a combination of accessory usage and low RPM. For example, if at idle RPM and I begin to turn on the headlights, rear defogger and heater, the car will most likely die if it is warm. I noticed the amp meter goes from -60a to +60a and when first started, it sits at 20-30a, but after warming up it will be at about 3-6a. If an accessory such as a headlight is turned on, it jerks into negative amperage but quickly returns to positive amperage. If I continue turning the lights on and off the car will die assuming it is warm. I believe the problem is the alternator/voltage regulator but would like a second opinion as I've heard EGR, MAF and IAC could cause this problem too.
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Sunday, January 24th, 2010 AT 7:29 PM

12 Replies

Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Hi
Yes a test of charging system to eliminate that as a cause. Are you running stock Hitachi SU carbs?
Let me know
Thanks for donate
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Monday, January 25th, 2010 AT 9:11 AM
Tiny
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It's actually using direct port fuel injection. I took some pictures and video today but was not able to upload them. I have replaced the alternator and ordered a voltage regulator that should be in tomorrow. I took the old voltage regulator off and inspected and found a very small amount of green corrosion with signs that there have been liquid damage (warped gasket seal inside the regulator). After replacing the alternator it still dies once warm and seems like it's trying to charge better but after warming up the amperage meter shows it going down again to about 2 amps to 6 amps. Also a new symptom showed up- instead of having accessories running to stall, it will stall if the engine is warmed up and I rev the engine and quickly release my foot foot from the gas pedal. I'll install the regulator tomorrow, take pictures and video and post them asap. Any advice until then would be greatly appreciated- thank you
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Tuesday, January 26th, 2010 AT 1:40 AM
Tiny
DOCFIXIT
  • MECHANIC
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Would you post the engine type/number should be on a plate on bulkhead. Yes pics would be great
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Wednesday, January 27th, 2010 AT 9:06 AM
Tiny
REVOLUTION0
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Voltage regulator was delayed until today- I picked it up from the parts store and installed it. Retried running it and same results: works fine in the cold but once warm it dies at idle when using accessories (headlights and heater). I also ended up replacing the ignition coil thinking that might help but same results. I also checked vacuum lines and found a loose line coming from the vacuum advance to the intake manifold which I tightened using a small clamp. Checked the distributor rotor and cap but they looked nearly new. Tested the car again and the exact same problem occurred- dies when warm using accessories during idle.
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Wednesday, January 27th, 2010 AT 8:06 PM
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Need to do some basic tests put volt meter on battery what is voltage reading? Start engine what is voltage? Need to check fuel pressure @35 psi. If good find fuel pressure regulator small can thing with vacuum hose attached remove hose fuel pressure should increase. Also attach vacuum gague to intake what is reading at idle? Is car new to you? Do you have a repair manual?
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Thursday, January 28th, 2010 AT 8:42 AM
Tiny
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The battery is also brand new and high performance (more cold cranking amp output than oem). Volt meter shows very little fluctuation while on (between 13.8 Volts and 14 volts) at cold and warm idle. I was unable to find a parts store that had a fuel pressure tester available but was able to obtain a vacuum tester. I used the main vacuum line that leads to the vacuum advance on the distributor using a "T" connector. During idle (cold and warm) it registered at about 18-19 inches of mercury. When I pressed on the gas though, it dropped nearly instantly to 5-10 inches of mercury. If I sustain 2000 RPM it will initially drop to 5-10 inches mercury but slowly recover to about 15 inches mercury. From what my test kit says this would indicate faulty catalytic converter but I removed the catalytic converter to test this and the problem still exists
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Saturday, January 30th, 2010 AT 11:55 PM
Tiny
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I figured I would post back my success for anyone else who has had similar issues as mine. After disassembling the cover to the MAF sensor and watching it's operation I learned that a solenoid arm was being actuated that appears to essentially short the circuit so it appeared the MAF would no longer send information during that short which caused the computer to not understand the proper air mixture- killing the car. After adjusting this arm so it would no longer be actuated during operation of the vehicle it no longer dies. :)
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Saturday, March 27th, 2010 AT 2:56 PM
Tiny
DOCFIXIT
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You mean the air flow meter in air intake?
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Tuesday, March 30th, 2010 AT 2:51 PM
Tiny
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Yes. And I mistakenly posted that wrong- the meter itself is actually an "open" circuit while the car is not running and is "completed" when the meter moves as a result of airflow. During normal operation the circuit should remain "completed" so long as the car is running. But instead what it would do is drop back so far (as if it lost airflow) and open the circuit again and I'd imagine that open circuit means the computer was no longer receiving a signal. So we actually adjusted it so the circuit always is completed. The car is still running magnificant. I'm no mechanic, but a running car is a running car so I'm happy!
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Thursday, April 1st, 2010 AT 12:18 AM
Tiny
CAP51
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HI JUST FOUND YOUR POST RE: THE ADJUSTMENT U MADE ON THE MAF TO KEEP THE SYSTEM "CONNECTED" I THINK I HAVE THE SAME PROBLEM WITH MY 75 280Z COULD U PLS TELL ME IN MORE DETAIL WHAT YOU DID WITH THE NEEDLE/ARM TO KEEP THE CONNECTION
THANKS MUCH

CARL
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Wednesday, October 28th, 2015 AT 10:23 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
FEATURES IN Picture 1: you will have to fool around to get this right. Not much info is given on this. See pic
The big grey chuck of metal is a counterweight. It is used to offset the weight of the wind vane "flap" in the air path.

The "Return to Zero Shock Absorber" is simply spring metal that absorbs the shock of the rotating Counterweight and Flap when the air flow stops. It prevents the AFM from beating itself to death every time the engine is stopped.

The Black Wheel and Coil Spring is the mechanism that controls how far the flap opens when air flows through the throttle body. This is the heart of the AFM and if the spring is set incorrectly, the related voltage to the ECU will be wrong and it will send too much or too little fuel. If the spring is wound too tight, the AFM's flap will not move enough and the ECU will not send enough fuel thus a lean mixture will occur. If the spring is wound too loose, the AFM's flap will move too much and the ECU will send too much fuel thus a rich mixture will occur.

IT IS IMPORTANT TO POINT OUT THAT THE BLACK WHEEL IS UNDER TENSION AND THAT REMOVING THE LOCKING SCREW WILL RESULT IN IT GOING "SPRONG" and RECOILING.

BE SURE TO MARK A TOOTH PRIOR TO TOUCHING THE LOCKING SCREW! Besides I have not got to that step yet so hands off! :)

You will also notice a blob of silicone or glue. If this is broken, you can immediately determine that the AFM was "messed with". Upon inspection of my 77z, the previous owner had obviously turned the black wheel about 10 tooth-steps to the lean side as a smaller part of the blob had been separated and was 10 teeth to the right.

Please note the reference mark that I scribed into the black wheel. It is impossible to see but there is a corresponding scribe mark in the cast metal body as well. (It is good to have both wheel and body scribed in the same location. Preferably at the centre of a tooth.

Idle Flow Adjust
This allows you to tweak the position of the AFM flap at idle thus you can control the rich/lean mixture. This adjustment controls the air flowing around the flap in a "bypass" passage under the AFM's main passage. It works in a similar fashion to the idle set screw in the throttle body.
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Thursday, November 5th, 2015 AT 12:53 PM
Tiny
HMAC300
  • MECHANIC
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Here is another pic showing which way to move it for more or less fuel...... also you might check this link out. http://www.atlanticz.ca/zclub/techtips/afm/
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Thursday, November 5th, 2015 AT 12:57 PM

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