1976 280Z Fuel Issues Troubleshooting

[Captain Obvious]

What he said. Hope you found the root problem!!

[Paulytunes]

So I was running fine through most of the summer, until mid-August when one of the connections to the water temperature sensors broke while I was on my way to support a Cub Scouts event and show the kids my 280Z. 

Since I was going to be sidelined for awhile waiting for the new switch to arrive from Z Car Depot, I decided now would be a good time to flush out the coolant, replace the thermostat, etc.  No good deed goes unpunished.  I found one of the thermostat lower housing bolt holes to be over-bored and filled with thread sealer:    

Of course I discovered this after I had reconnected everything, got my 280Z to start, and then when the T-stat opened, it showered the connections and proceeded to cause a short and burned up my fusible links.  

So, I ended up ordering a new fusible links, a lower housing, and other parts and again was waiting for them to arrive.  I got everything back together and it started but was really rough.  I thought maybe I had swapped the thermo-time switch and water temperature sensor connections, but after tracing the wires back using the FSM and 1976 wiring diagram, I verified all was connected as it should be.  When the engine is cold, it will start but idle really rough then eventually dies after a minute or two or applying throttle. 

I did the light test today from page EF-51 of the 1976 FSM, and I notice that there is no difference in brightness from the flashes of the light when cranking when the cold start valve is connected and removed.  This was witnessed on the No.1 and No.4 injector connections, as the FSM instructs.  The FSM states "if the lamp does not flash, or if the lamp does not become brighter when the cooling water temperature sensor harness connector is removed, it indicates that the control unit is faulty.  Replace the control unit, and carry out the inspection again as described above."

So my questions are:

1. Is there any other quick ways that I can determine that my ECU has failed.

2. Assuming I have a bad ECU, what is the reliability of used ECUs?  Are they similar to the Transistor Ignition Unit where a used one that I find (I assume there is no more NOS available from Nissan) will be living on borrowed time and I could expect to have the same sort of failure at any given time, whether it is days, months, or years down the road?

3.  If #2 is true and used ECUs will fail, has anyone tried the FAST EFI ($1,600) or other more reliable/modern fuel injection system that can chime in on their experience and whether this is a recommended option or not? 

Thanks in advance for any input you may have and thanks for reading.    

[Yarb]

There are folks here on the forum that have tested factory ECU’s and have them as spares. As far as the fast EFI system I’ve heard very little other than a friend on the forum tried it and it did not go well for him. I would reach out and see what you can find here on a tested ECU that someone has in their stash. Again the longevity of a replacement is hit and miss but I would definitely try that first IMHO.

[Zed Head]

4 hours ago, Paulytunes said:

The FSM states "if the lamp does not flash, or if the lamp does not become brighter when the cooling water temperature sensor harness connector is removed, it indicates that the control unit is faulty.  Replace the control unit, and carry out the inspection again as described above."

The FSM instruction comes after the test of resistance at Pin 13 at the ECU connector.  The assumption is that the temperature circuit is complete and working correctly all the way to the ECU.  You need to be sure that the ECU is getting the proper information.  Measure resistance at the pins and compare to the table of resistance versus temperature.

From the 1981 Guide -

 

[Paulytunes]

10 hours ago, Yarb said:

There are folks here on the forum that have tested factory ECU’s and have them as spares. As far as the fast EFI system I’ve heard very little other than a friend on the forum tried it and it did not go well for him. I would reach out and see what you can find here on a tested ECU that someone has in their stash. Again the longevity of a replacement is hit and miss but I would definitely try that first IMHO.

That's what I was afraid of - the Fast EFI almost looks too good to be true.  I also really don't want to stray too far away from stock if I can help it.   

[Paulytunes]

8 hours ago, Zed Head said:

The FSM instruction comes after the test of resistance at Pin 13 at the ECU connector.  The assumption is that the temperature circuit is complete and working correctly all the way to the ECU.  You need to be sure that the ECU is getting the proper information.  Measure resistance at the pins and compare to the table of resistance versus temperature.

From the 1981 Guide -

 

Thanks!  I will test the resistance at the ECU next.  I'll be looking for a higher resistance reading since it is starting to get cooler here and my garage is not insulated. 

[SteveJ]

7 hours ago, Paulytunes said:

That's what I was afraid of - the Fast EFI almost looks too good to be true.  I also really don't want to stray too far away from stock if I can help it.   

On the other hand, I have a friend who has been using the Fast EFI for years, and this is a 280Z that he drives to every ZCON and a few other events, such as Branson ZFest, every year. He puts more miles on his 280Z than I do in my daily and other cars combined.

Edited October 15 by SteveJ

[Paulytunes]

Update: so I tested the temperature transmitter. It has the appropriate resistance for the coolant temperature. 

However, when I test the connection pins at the wiring harness, I get zero continuity. This is for pins 6 and 8, 7 and 8, 8 and 9, and pin 13 and ground. This leads me to believe that maybe the wiring harness is possibly bad. Could I have ruined the whole harness when I unintentionally gave the lower thermostat housing wiring connections a coolant shower and blew out my fusible links?

If so, I feel like an idiot and that one's partially on me. Also partially on whichever previous owner decided to over bore the thermostat bolt, and Nissan for using non-waterproof electrical connections under a gasketed connections for coolant. 🤦‍♂️

[Zed Head]

1 hour ago, Paulytunes said:

This is for pins 6 and 8, 7 and 8, 8 and 9, and pin 13 and ground.

Not clear what you mean when you list those numbers.  The first three pairs are AFM pins.  Were you doing the AFM test procedure?  Not uncommon to have the plug fall off of the bottom of the AFM, since gravity is pulling on it and the clip sometimes doesn't get clipped in when you reinstall the AFM.

It might just be that the AFM plug fell off of the AFM and the bullet connector over the intake manifold for the coolant temperature sensor is unplugged.  One big plug and one small one.

[Paulytunes]

1 hour ago, Zed Head said:

Not clear what you mean when you list those numbers.  The first three pairs are AFM pins.  Were you doing the AFM test procedure?  Not uncommon to have the plug fall off of the bottom of the AFM, since gravity is pulling on it and the clip sometimes doesn't get clipped in when you reinstall the AFM.

It might just be that the AFM plug fell off of the AFM and the bullet connector over the intake manifold for the coolant temperature sensor is unplugged.  One big plug and one small one.

I decided to go back to the beginning of the 1976 FSM (Page EF-21) and attempted to diagnose why the engine cranks but won't start.  It listed the AFM test first, so I went ahead and did that.  I skipped over the fuel pump (since I recently replaced it), and then moved to the water temperature sensor test.  I checked the connections at the AFM and Water Temp Sensor, both were snug.  Bullet connections are snug too.  I'm at a loss as to why I am not getting any continuity unless I am either doing the test wrong or I managed to really fry the wiring after I accidently and inadvertently wet the connections and burned up the fusible links.    

Edited October 20 by Paulytunes

[Paulytunes]

So as I continue to troubleshoot, I pulled out the ecu to inspect it.  When I unscrewed it and examined it, I noticed a qr code. When I scanned it, I am sent to a website that no longer exists.  The website was Installapart.com. It appears that Installapart is no longer in business. Were they a rebuilder of ecus?  Why did they go out of business?  Has anyone here ever heard of Installapart or used their ecu services?  

[SteveJ]

You can see the site using the internet wayback machine: https://web.archive.org/web/20180307072216/http://www.installapart.com/