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stravi757

280z Intermittently Engine Wont start

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Hey. I have been struggling to trace down for some time an intermittent issue with my Z. The engine runs perfect besides this issue. Not a hiccup. It makes great smooth power, passes smog Extremely well, idles well, it basically runs exactly the same it has for the last three years except for this recent issue.

Its a stock 1978 280z which I DD . The only modification that comes to mind is I have safteyhub 150 I installed years ago.

Problem: The Engine will intermittently not start(it doesnt matter if its been cold and sitting or warm). It started happening months ago, It always starts back up, but the problem has progressively become  frequent, and it takes longer too start when it does happen as time goes on.

 

I have traced down the problem to this. The injectors are not clicking while the turning the starter-motor.(  I get spark, starter motor turns totally normal as well )

But heres something interesting. I can get the engine to run When the intermittent problem occurs by push starting the car. So its only while the starter-motor is turning that the engine wont start. I thought that was weird. I tried to think of why that would happen. The only idea I have had is, that the START signal from the ignition switch wasn't going  to the #4 ECU pin. I checked and It is getting 12v at the pin.  (NOTE: I have also tried things like changing out the ECU and various other sensors which I have replacements of. ) 

I did notice that when I turned the ignition switch the START position with the starter motor connected and cranking, my voltage reading at Pin #4 was 9volts. Is it possible that is too low and is preventing the ecu from firing the injectors? The Battery is fairly new and doesnt seems to have any struggle cranking even though the voltage number is kinda low.

 

Any help would be great. I have been thinking and checking things longer than I can make a list of for weeks now. Hopefully I have described the problem well enough for some insight. Also Its been a while since I have posted, If there is information you think I am missing to make this post more useful, let me know, thanks.

 

 

 

 

 

Edited by stravi757

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The fact that it starts easily by push starting kind of suggests weak spark.  Could be poor current flow through the coil and ignition module.  You need high current to generate a good spark when the module cuts it.  The low voltage during starting won't help.

There's a color wiring diagram in the Downloads area.  You could trace the path and check the likely spots for resistance/crud.  Clean up the path for power to the coil and on to the module where it's grounded.  78 has the plug-in module, maybe remove it and clean it with some contact cleaner like Deoxit.  Might also be that your coil and ignition module are just getting old.

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I had a similar problem.  It was due to the ignition switch in the steering column "carboning up".  When turning the key fully Clockwise (100%)  to Crank/Start, only the electrical contact in the switch for the starter would make, the EFI/ignition contact was kaput and would not give spark.  The mystery was that this was intermittent... but becoming worse.   I found that if I turned the key to crank only ~ 80% to 90% of the way (where the electrical contacts would all make, it would start fine. Changing out the switch cured the problem.

ignition switch.jpg

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Test the start switch for intermittent contact with a continuity test (tone) in the start position. That mechanical switch is old and seen a lot of use.

 

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Those last two are good ones.  I had a 78 parts car that would catch, then let loose (catch-grind-whiiiiirrrr), many times before starting.  The pin in the switch was loose.  Years later after the car was long gone but I still had the switch, I figured out what was happening and restaked the pin with a drift.  It had just loosened up over time.  

The pins that you see in the video that Dave WM supplied.  You could wiggle the loose one with your fingers.  You can just see the staked ends also in the first image, above.

Edited by Zed Head

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On 5/21/2019 at 8:41 PM, Zed Head said:

The fact that it starts easily by push starting kind of suggests weak spark.  Could be poor current flow through the coil and ignition module.  You need high current to generate a good spark when the module cuts it.  The low voltage during starting won't help.

There's a color wiring diagram in the Downloads area.  You could trace the path and check the likely spots for resistance/crud.  Clean up the path for power to the coil and on to the module where it's grounded.  78 has the plug-in module, maybe remove it and clean it with some contact cleaner like Deoxit.  Might also be that your coil and ignition module are just getting old.

I tried using a different coil and a spare ignition module with no luck. I will track down the positive coil wire though. My spark does seems a little weak(yellow, not blue with either coil). The ignition module contacts look very clean but it wont hurt to spray some cleaner on those too.

 

On 5/22/2019 at 4:32 AM, 240260280 said:

I had a similar problem.  It was due to the ignition switch in the steering column "carboning up".  When turning the key fully Clockwise (100%)  to Crank/Start, only the electrical contact in the switch for the starter would make, the EFI/ignition contact was kaput and would not give spark.  The mystery was that this was intermittent... but becoming worse.   I found that if I turned the key to crank only ~ 80% to 90% of the way (where the electrical contacts would all make, it would start fine. Changing out the switch cured the problem.

 

Interesting problem. I had my stock switch begin to go out a couple years ago. which I have replaced and it would not make contact with the start signal vs. losing contact with the "ON". I dont think this is my problem though because my coil is making spark still. I tried using a spare ignition switch anyway too with no luck.

On 5/22/2019 at 5:35 AM, Dave WM said:

Test the start switch for intermittent contact with a continuity test (tone) in the start position. That mechanical switch is old and seen a lot of use.

 

thanks for sharing the video. I learned something new!

 

I tried putting electrical tape over ecu pin #4 to try and "replicate" a push start scenario today and it didnt work. just an experiment I thought was worth seeing out when I got home from work.

Edited by stravi757

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On 5/21/2019 at 8:10 PM, stravi757 said:

I did notice that when I turned the ignition switch the START position with the starter motor connected and cranking, my voltage reading at Pin #4 was 9volts. Is it possible that is too low and is preventing the ecu from firing the injectors? The Battery is fairly new and doesnt seems to have any struggle cranking even though the voltage number is kinda low.

Maybe your CSV and/or thermotime switch is drawing too much current.  It's on a parallel circuit with Pin 4.  Instead of covering Pin 4, maybe disconnect the CSV and thermotime switch.  It might delay starting but it should start if that's the problem.  I don't have a CSV anymore and my car starts.  I usally give it about 5 crank/spins, wait about 30 seconds for fuel to vaporize then start it up.

You might also try starting fluid just to see if you have a no-spark or a weak spark or an injection problem.

Finally, I just remembered that I had a starting problem once, but it was when things were hot.  My EFI relay was fried and opened up when it got hot.  So, the EFI and fuel pump relay's are a possibility too.

image.png

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I found the problem. Zed Head sent me in the right direction when he recommended looking at the coil wiring. Years ago I cut signal wires to the distributor on the main harness. I crimped them back together but not very well. the wires were able to pull out of the crimp by hand. I put the wires back together again and the problem has gone away. 

lesson: young self did things inadequately, those problem will haunt you years later.

 

Thanks for all the help  everyone.

Edited by stravi757
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So It turns out the problem was not solved. It has come back. I am still struggling to figure out whats the problem.

The problem continues to persist the same way. The injectors intermittently wont open open while cranking(tested with noid light), once the engine is running it stays running. It will start right away If you push start the car.

I have tested the ecu pins and they all check out fine

12v at pin #1(negative coil) I immediately check this wire for power when the engine decides to not start

12v at pin #10(ecu B+)

12v at all injector pins

12v at pin #4 - When IGNITION is in the "start" position (start switch enrichment signal)

harness ground wires all have continuity

 

I have tested with a couple different ecus, no difference.

 

Edited by stravi757

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On 5/24/2019 at 8:54 AM, Zed Head said:

Maybe your CSV and/or thermotime switch is drawing too much current.  It's on a parallel circuit with Pin 4.  Instead of covering Pin 4, maybe disconnect the CSV and thermotime switch.  It might delay starting but it should start if that's the problem.  I don't have a CSV anymore and my car starts.  I usally give it about 5 crank/spins, wait about 30 seconds for fuel to vaporize then start it up.

You might also try starting fluid just to see if you have a no-spark or a weak spark or an injection problem.

Finally, I just remembered that I had a starting problem once, but it was when things were hot.  My EFI relay was fried and opened up when it got hot.  So, the EFI and fuel pump relay's are a possibility too.

 

I do not have the cold start valve or thermo time switch hooked up.

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did you ever test the ign switch as mentioned before, I mean out of the car with a multimeter on tone?

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21 hours ago, Dave WM said:

did you ever test the ign switch as mentioned before, I mean out of the car with a multimeter on tone?

yes, and also swapped it out with a know working spare

I grounded the negative coil wire with the ignition turned on, and the injector will open(confirmed) every third tap. I tried this when the car was not starting by cranking.(edit, fluke test due to intermittence)

EDIT. I tried grounding the negative coil wire again when the problem occurred, and the injectors were not opening every third tap ( this is the difficulty with intermittency) 

 

I tested the negative coil wire(disconnected from the coil post) for continuity to ECU Pin #1, and it read zero resistance. It was reading correct voltage to pin #1 when given power as well. Im confident the signal to pin #1 is fine. My next step is to try and ground the injectors from the ECU connection manually to see if that will fire the injectors. Im waiting for the problem to come back to test that...

Edited by stravi757

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I still havent found anything conclusive. I did remove/pull the pins from the connectors of the EFI Main Relay and the fusible links. They were a little corroded but not badly. They all tested fine prior. Since I cleaned them the car has started without issue. I will find out through time if it corrected the problem.

Edited by stravi757
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