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Discussion Starter #1 (Edited)
hello, I have a '83 280zx turbo. Me and my mechanic cannot find the cause of my Z to not start after running it. He said I'm losing the negative pulse from the injectors to the ecu but he cannot pin point it. The car wont start after you turn off the engine. It will only start after the engine has cool down for several hours. We already replaced the AFM, new distributor, new ngk wires, new fuel filter. We already checked the ECU and its working fine. Checked all the wirings, fuses, and relays, coolant temperature sensor, and still have the same problem of not starting after a good run when you turn off the engine. Need all your HELP please !!! Thank you.
 

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Well, obviously, #1 suggestion is: "don't park too far from home."

When you say "won't start," does that mean when you turn the key you get nothing? Not even fuel pump noise? Or does it mean the engine will turn over but not catch?

If the latter, does your auxiliary fan come on after you shut it off? This would be the plastic thingie that wraps over the valve cover. It should turn on upon hot shutdown - which is pretty much every time in Vegas - to cool the fuel rail so you don't get what used to be called vapor lock on carbureted cars. I think on fuelie cars it's called fuel boil, because the fuel gets so hot it boils and bubbles.

If the aux fan doesn't come on, try this: warm the car in your driveway until the point where it usually won't restart. Then shut off the engine and open the hood - all the way. Wait 15 mins. Try restarting. If it starts, it will be because the open hood allows the heat to dissipate more quickly. Usually with fuel boil the engine will start, but run crappy for 3-4 mins. Fuel boil happens due to the design of L-series FI engines - latent heat off the cooling engine 'boils' the fuel in the fuel rail.

I would also suggest that you check the vacuum system for tightness and clean/refresh all electrical contacts under the hood. Here's a good tutorial on it: http://atlanticz.ca/zclub/techtips/electricalconnections/index.html
 

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Discussion Starter #4
@6shutr, thank you for your opinion. I brought my Z to the office 8am. I went to lunch at 12 and the car started fine. After 30 mins in the restaurant, when I started the engine, it would turn over but won't catch. I popped the hood for 30 mins and still won't start until it won't crank anymore. We tried jump starting it and still no luck. I waited 2 hours until I gave up and called the towing company and had it towed to my mechanic's shop. The following day it started fine like nothing happened till my mechanic test drove it and turned off the engine and same problem happened to him and got the car towed again. We checked everything from the fuel pressure and followed all the steps in the FSM bible still losing negative pulses from the injectors going to ecu. I don't hear the cooling fans turning on when I shut off the engine. We checked all the electrical connections from the distributor and everything but still same problem everyday. It is a rare problem especially when there is no tech support available.
 

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Discussion Starter #5
Check your Ignitor(right next to your coil) and also check your CHTS.
Test Fuel pressur.....
Good luck
@borini63, we checked the igniter already and replaced it with a new one even if it's working fine. We replaced also the chts just to check if it's the problem but chts is also fine. Fuel pressure also checked all working fine. My mechanic said I'm losing the negative pulse from the injectors going back to ecu which he cannot pin point.
 

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@borini63, we checked the igniter already and replaced it with a new one even if it's working fine. We replaced also the chts just to check if it's the problem but chts is also fine. Fuel pressure also checked all working fine. My mechanic said I'm losing the negative pulse from the injectors going back to ecu which he cannot pin point.
Ok...did you check your Injectors relay,also is all your negative wires are grounded good?Also did you troubleshoot your ECU!?Soryy I am not trying to play the guess game!
 

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"We checked everything from the fuel pressure and followed all the steps in the FSM bible still losing negative pulses from the injectors going to ecu."

Your mechanic is....uh....
I'll be charitable here and say you should find another one as he's feeding you a line of BS and does NOT know how the system works.

Do this:
1) Buy a NOID light.
2) Go to Radio Shack and buy a can of Freez-It
3) The very next time it dies, pull the coil wire out of the center terminal of the distributor. Crank the engine. You will either have spark, or not.

If you do NOT have spark, you WILL NOT get fuel (ECU triggers firing of injectors every third pulse of the coil) Take the the can of Freez-it and blast your igniter. It should then have spark. If not, then the reluctor in your distributor is bad, or the connections between it or the igniter are bad.

Secondary test at this point, plug in your NOID Light and ground the negative terminal of the coil with a short wire jumper against a bare metal ground with the ignition on...the NOID Light should light every third tap. If it does not, see below.

If you DO have spark, plug in your NOID Light and see as you crank it, or as you do the above test that the NOID Light flashes every third spark.

If it does, the injectors may be bad, there may be a fuel issue, but the functionality of the circuit is intact.

If it does NOT flash every third spark produced, check the connection on the blue wire in the left kick panel that pigtails out of the main harness and goes into the ECU Harness. It's this wire that takes the gating signal from the coil to the ECU so it can count "1-2-3-PULSE-1-2-3-PULSE"

If the signal is there, then your ECU is overheating and needs replacement. Check your battery voltage, if you are chronically discharging your car through high electrical draws, the voltage can drop and roast the ECU, it's ground needs to be good or you roast the ECU, if the diode pack in your Alternator is going out and you see faint flickering of your lights, that car roast your ECU.


In short, injector pulses depend on spark pulses. If there is no spark pulse (no spark) there will be no fuel. The most common thing that causes this is an igniter or reluctor going bad. I don't care if you replaced them, it appears you have skipped VERIFYING they work when the problem is present.

This is a very basic system, there is no "negative pulse from the injectors to the ECU"

There is a gating pulse from the COIL to the ECU, and on every third one of those, the injectors get a ground and fire.

I make the ASSUMPTION you have verified your EFI Fusible Link for power to the injectors, as if it overheats and gets resistance, the injectors will not have the power necessary to pull in the solenoid and fire.

Verify what you THINK is "good" before skipping onwards in a rabbit hole wild goose chase searching for a "negative pulse from the injectors to the ECU" which does not, never has, nor ever WILL exist.

All signals originate on the distributor, coil, and ECU. The injectors are stupid solenoids that open when supplied with power from the fusible link, and which ground through the ECU.

If the ECU is not grounding, it's either bad, or it's not getting the imp put from the coil.

Period.
 

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Awwww crap... It was a turbo...

What you got above was NA troubleshooting.

The Freez-It still applies to the spark check and your Ignitor, just a few more front-end checks to do as the ECU interposed between the CAS and Ignitor unlike in the NA. And you have to make sure the Ignitor is properly, solidly grounded or "POOF!"

Check the signal from the CAS to the ECU on the wire...use 1-5V scale. THAT tells the ECU what is going on.

Still check if you have spark (that signal comes out of the ECU on the yellow wire.

If you got CAS Pulse, and no Yellow Wire Pulse while cranking, the ECU is Bad.

If you can short the coil as I stated above and get a NOID Light flash, then the ECUs park sensing circuit is good, and it's in your CAS, or the ECU Drivers for the Injectors.

Same basic dynamics at work: the CAS gives pulses to the ECU to tell the Ignitor to pulse the coil.
The ECU reads the pulses of the coil and fires the injectors. No spark, no gas.

Basically if you get CAS pulsing, and yellow wire pulsing, and no spark / no fuel, it's your Ignitor.

Turbo ECUs like to fry from diodes in the alternator. It's common they lose trigger to the yellow wire.
 
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