25 minutes ago, Paulytunes said:

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.

I found your Ford doppelganger from 2021.

https://www.ford-trucks.com/forums/1656335-91-f150-losing-spark-intermittently.html

"There is nothing I could find on the Computer that indicated where it came from or what calibration it is for. The only thing it had was a QR code that directed me to a site called "installapart" but the site itself looked closed."

10 hours ago, SteveJ said:

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

Thanks!  This was certainly an unexpected and unfortunate discovery.  I wasn't able to track down how to troubleshoot the ECU - those pages are probably long gone or that institutional knowledge died when the company went 6 feet under.  I have had nothing but trouble with aftermarket parts that one of the PO's installed - first the fuel pump now this.  I guess I am at a crossroads - Do I try to source a working 1976 Datsun 280Z ECU, go down the Resto mod path of installing a FAST ECU or other replacement system, or continue to struggle and troubleshoot with what I have (even though it may be an exercise in futility)?    

10 hours ago, Zed Head said:

I found your Ford doppelganger from 2021.

https://www.ford-trucks.com/forums/1656335-91-f150-losing-spark-intermittently.html

"There is nothing I could find on the Computer that indicated where it came from or what calibration it is for. The only thing it had was a QR code that directed me to a site called "installapart" but the site itself looked closed."

Zed Head - that is Interesting, thanks for finding that site.  The OP never does say what he did with the ECU.  

My 2 cents (45 cents)

If I owned a 280z, when I started having problems with the factory EFI system, I would ditch it and go to a more modern more easily tuned system

2 hours ago, Patcon said:

My 2 cents (45 cents)

If I owned a 280z, when I started having problems with the factory EFI system, I would ditch it and go to a more modern more easily tuned system

Don't let your wife read that!  

https://atlanticz.ca/zclub/techtips/  aka "Blue's Tech Tips" and this forum is all I needed and I don't have any cents.

 

 

 

So after much trial, error, troubleshooting, and going through the Fuel Injection Bible and FSM, I was able to get my 280Z running again.  The issues I have now:

1. I stupidly broke the plastic nipple on the stall dashpot while connecting the thermostat sensors and wiring:
2.  Idling is pretty high, around 2000rpm at cold start.  Occasionally, it will adjust down to 700 to 800 rpm and will sometimes stall.  Other times it will stay at 2000 rpm, unless I drive it and can force the RPMs lower with the gearing.  When I take it out of gear, it shoots right back up to 2000 rpm.  May be due to the temps here, which were between 55 and 60 degrees F today.  

I was able to temporarily fix the dashpot and reconnect the vacuum hose to it using a smaller diameter tube to insert into the part of the intact plastic and the vacuum hose until I can source a new dashpot assembly.  I'll continue to diagnose the high idling and see if this is due to something I am overlooking or a symptom of my rebuilt ECU not performing up to OEM standards.    

That nipple shouldn't have a vacuum source connected to it, it should be open to the air.  It's a common mistake.  Don't know why Nissan designed it that way.

A common problem with the pre-77 throttle bodies is that the blade gets gummed up and sticks open.  You might check that.  Next time it hangs at 2000 pull up on the throttle pedal with your toe or open the hood and press the linkage closed.

Another possibility is that the return spring rusted and broke.  It's hidden away, low and behind the TB.  Can't remember if you already addressed that possibility.

Finally, the other "hanging high" problem is caused by the BCDD.

 

Here's a drawing of the dashpot with no hose connected.

15 minutes ago, Zed Head said:

That nipple shouldn't have a vacuum source connected to it, it should be open to the air.  It's a common mistake.  Don't know why Nissan designed it that way.

A common problem with the pre-77 throttle bodies is that the blade gets gummed up and sticks open.  You might check that.  Next time it hangs at 2000 pull up on the throttle pedal with your toe or open the hood and press the linkage closed.

Another possibility is that the return spring rusted and broke.  It's hidden away, low and behind the TB.  Can't remember if you already addressed that possibility.

Finally, the other "hanging high" problem is caused by the BCDD.

 

Here's a drawing of the dashpot with no hose connected.

Thanks, I'll look into that.  So should that vacuum house then be open to the air or connect to something else that I am not seeing?  There's a three way tee, which was always connected to the dashpot nipple, a vacuum port on the bottom of the AFM, and also to the charcoal canister vent on the other side of the engine bay. 

The dashpot connection does indeed seem to be common, many other L28 engine photos online show it connected.  

The three way T should go to the ported vacuum on the TB, the charcoal canister, and the distributor vacuum advance mechanism.

Here's a good place to browse pictures.

https://bringatrailer.com/search/?s=1976+280z

https://bringatrailer.com/listing/1976-datsun-280z-88/

Over the past few months, I have been trying to continue to troubleshoot my high idle issues. I had it parked and applied throttle. It was stuttering and backfiring at high rpms, and then I noticed a hissing sound coming from the rear. I looked below, saw a puddle of gasoline on the garage floor, and found that my fuel damper had sprung a leak. This is the second one to fail since I replaced the aftermarket fuel pump with a slightly used OEM fuel pump.

I came to find that the fuel dampers are incredibly hard (if not impossible) to find. It looks like the damper is no longer manufactured. An internet search revealed that these were also used on BMWs. But any mention of these 3 letters in the part search seems to add a 3x multiplier to the cost and it is also not available after hours of scouring the internet. So I ended up buying an aftermarket damper from Z Car Depot and made by Radium Engineering. Once I had the aftermarket damper in hand, I plumbed everything up and resumed troubleshooting.

The new damper fixed the high idling problem, as it only idles high when cold, but then eventually settles down to ~800rpm when warmed up. It has a hard time keeping from stalling once the idle drops, and this is regardless of what adjustments I make to the idle speed screw. Applying throttle leads to backfiring and stuttering around 3000rpm, usually followed by a stall. This was the status yesterday.

I troubleshooted more today and noticed that I somehow was missing the Air Flow Meter ground wire connection, so I fixed that. Now when I try to start it, I can get it to start, but stalling is almost immediate. Also, applying throttle has no effect, other than forcing a stall. I also noticed the pressure gauge I installed between the fuel filter and engine fuel supply tubing is now frozen at 10 psig. I also read through the "Purs like a kitten thread" (sic) and other threads found by searching, tried much of the troubleshooting in the FSM and Fuel Injection Bible, and other service manuals, but I have not been able to find a smoking gun or root cause of my issue. I can certainly relate to all those "that have been to hell and back with the factory EFI system," as someone said in one of the numerous posts I read. I am also beginning to think either my 280Z or I am cursed. Anyone know of a good Datsun mechanic in the Baltimore, MD area? I don't want to give up, but I am starting to lose hope.

Edited Sunday at 03:39 AM2 days by Paulytunes

I should also mention that my 280Z does not have the vacuum switching valve shown in most of the diagrams and photos I have seen in the FSM, other manuals, photos, etc. It seems one of the previous owners removed it. Is there a vacuum line that should be connected to it, and if so, should I plug that if the vacuum switching valve isn't there? I wouldn't think that this would cause my current issues.

But it does appear that this was the vacuum line that the previous owner placed on to the dashpot nipple.

Edited Sunday at 03:49 AM2 days by Paulytunes
additional info

I would make sure that you have ~ 36 psi of fuel pressure. The whole system is designed around that number.

The vacuum switch is probably for the vacuum advance hose to the distributor. Vacuum advance is turned off on the manual transmission cars in gear 1 - 3, I assume for emissions. I would just bypass the switch and run full time vacuum advance.

The stalling might be because the plug has fallen out of the bottom of the AFM. That happened to me once. Those funky wire clips on the plug are hard to get fully seated and they didn't leave much slack in the harness under there.