280Z Starts, Runs One Minute and Dies

[Erins.ZCar]

I was almost ready to deliver a 1976 280Z Restomod to my daughter 6 months late after her 16th Birthday! We started the car up and went to pull it into the shop for final buffing/touchups and low behold the engine died and would not restart. Needless to say my daughter was heartbroken. The car would crank but not start. If the engine was cold, it would start, run one minute or less and then die and not restart for hours.

 

At first check my plugs were all soaked with fuel so we thought "flooded" clean the plugs, suck out the cylinders dry and and try again. No luck, no start. Pulled the plugs and checked again, dry as a bone no fuel in cylinders. Next, even though the fuel pressure measured correct before and after the fuel rail, we replaced the fuel pressure regulator just in case and still not the solution. Started intense troubleshooting with the EFI Bible and FSM. Replaced the MAS after cleaning the contacts and still nothing! Cranks just fine when cold and would start and run for a minute and then die and refuse to start until cold again. Checked the throttle position sensor, air temp sensor, water temp sensor, cold start valve, and thermotime, nothing! Still would start when cold most of the time but die after less than a minute. Double and triple checked the injectors listening to ensure the injectors continued to fire after the engine started and we weren't losing pulse, still no good. So what does the bible say after all these checks, replace the ECU!

 

Luckily, I thought I already have a spare ECU for my 1977 FI 280Z. Guess what, doesn't work, wrong part number. Here's where ECU's get tricky I found out. The 1975-76 Auto Trans FI models use ECU A11-600, the 1977-78 Auto Trans FI models use A11-601. My 1976 280Z 4-Speed Coupe uses the A11-601 ECU! So off to Ebay to find an ECU to match A11-600 in my daughters car. Two weeks later it arrives and we plug it in and walla, nothing... It starts and runs less than a minute and dies and won't restart! Totally frustrated and confused we start the troubleshooting process again re-checking every pin on the ECU harness and we suddenly notice that Pin 1 is giving us varying voltages of .3 to 12.7 volts. At 12.7 volts the engines starts, runs less than a minute and dies, when we re-check the Pin 1 voltage and try to restart the engine we get .3 - .7 volts. Bingo! Finally we have a negative reading we can start tracing!

 

So where does Pin 1 on the ECU connect to? The Ignition Input Circuit! We started tracing the wiring harness for the Ignition system around the engine compartment and back under the dashboard and find terminal corrosion on the connectors under the passenger side glove box. Cleaned the terminals and connectors and applied a generous dose a electolytic grease and instant start and run! Thank goodness for excellant mechanics and friends who spent 2 weeks with me crawling under the dashboard and hood testing and retesting component after component to find the issue and resolve it!

 

I hope this might help someone else in the future. If your Pin 1 on the ECU measures anything less than 12 volts, you have an electircal problem not mechanical! You must have 12 volts on this pin for the car to start and run, if the votage drops after it starts and dies check the ignition circuit connections under the glovebox. Clean and grease those terminals because the corrosion heats up after ignition and interrupts the connection of power to your injectors. Good luck!

[Pharaohabq]

Thanks for posting this.  It may be related, but you might wonder Why are those terminals corroding, aside from it being a 35 year old car?

 

This isn't for certain it's your car, but it is common for older Z's to leak from the cowel area down the inside of the firewall into the carpets after a rain. This is because the sealer they used inside the cowel at the base of your windshield gets old and can crack.  It's also good to clean out all the debris that can accumulate under that cowel and make sure the drain tubes are flowing.  You can re-seal that cowel area with any good sealer and it should be fine for years.  This is one of the reasons that floor pans rust out, the carpets get wet and the floor rusts beneath them, even if the surface feels dry, the matting may not be.

 

Again, this may not be the case in your car, it could just be the age and where the car lived, ambient humidity and all.  I am glad you got the car running well for your daughter. I'm sure she'll be the envy of all the kids at school.

[Erins.ZCar]

As usual you are 100% correct in the cause of the corrosion, Pharaoh! I felt I had rambled on long enough about the issues I had and forgot completely to describe my findings for the cause. During the paint job, we removed the cowl panel and found rust thru in several small areas. Repaired that rust but failed to inspect under the dash intensely enough.

 

She gets a kick out of all the "old men" as she says who give her the thumbs up as she is driving!   Her friends at school are definitely jealous!

[Professor Threadkiller]

So where does Pin 1 on the ECU connect to?

 

If your Pin 1 on the ECU measures anything less than 12 volts, you have an electircal problem not mechanical! You must have 12 volts on this pin for the car to start and run,

 

Pin 1 is the input trigger signal for the ECU to fire the injectors. No pulses on pin 1? No pulses from the injectors. That's why it was dry.

 

Note that you should only see 12 volts on that pin when the engine is NOT running. Once it's running, you should see pulses coming from the distributor. If all you have is a voltmeter, then you would probably see those pulses as a DC voltage something less than 12 volts.

 

 

Edited August 22, 2013 by Professor Threadkiller