1976 280Z Fuel Issues Troubleshooting

[Paulytunes]

Update:  so after some late night reading of the FSM, I found on p.BE-95 that the yellow wire is indeed supposed to be connected to the BCDD.  The black wire is supposed to be connected to the ignition coil external resistor positive terminal.  I will connect these soon and report back.  I doubt this could be the root cause of my problem, but I do not think thses should be disconnected and hanging free and dangling in the engine compartment.

Edited July 21, 2023 by Paulytunes
corrections

[siteunseen]

That black ground looks like the one off the AFM mount. Looking, I found a thread that might be just what you mentioned. Good luck!

https://www.google.com/search?client=ms-android-americamovil-us-revc&q=280z+afm+ground+location+classiczcars.com&tbm=isch&sa=X&ved=2ahUKEwjw3-_G4KCAAxVWjIkEHXMCCvoQ0pQJegQIChAB&biw=320&bih=545&dpr=2.25

 

 

Edited July 21, 2023 by siteunseen

[Yarb]

If that’s the ground from the AFM iirc it’s a short double lugged wire going from the bottom of the AFM to the ground point on top where it attaches to the frame.

[Zed Head]

The key part of the "failing ignition module" statement is the "ing".  It's not failed, it's failing.  The heat generated from higher RPM must cause something to stop operating correctly, causing too many sparks.  At least, that's how mine seemed to be failing.  So, testing it cold won't show the problem.  It would be an intermittent problem.

Post a picture of the circuit board inside the module if you want to give it an ocular assessment.  Maybe somebody will see a burnt trace or leaking capacitor.  Any visible signs would be on the circuit board.

Edited July 22, 2023 by Zed Head
fat fingers

[Paulytunes]

20 hours ago, Zed Head said:

The key part of the "failing ignition module" statement is the "ing".  It's not failed, it's failing.  The heat generated from higher RPM must cause something to stop operating correctly, causing too many sparks.  At least, that's how mine seemed to be failing.  So, testing it cold won't show the problem.  It would be an intermittent problem.

Post a picture of the circuit board inside the module if you want to give it an ocular assessment.  Maybe somebody will see a burnt trace or leaking capacitor.  Any visible signs would be on the circuit board.

I did get a chance to do more today.  I reconnected the ground at the AFM.  The BCDD was connected to another wire which came out of a harness that included the connections for the water temperature sensor.  When I disconnected the BCDD plug and connected it to the yellow plug, the idle ramps up to 2000 RPM and stays there.  Maybe this was a connection meant for the A/T equipped cars?  I figure the BCDD was connected to where it is supposed to be so I just put it back where it was and idle speed returned to normal, around 800 RPM.  

I did also take the Transistor Ignition Module apart and visually inspected.  I wasn't able to see any bad resistors, but then again my eyes are 48 years old and getting worse with age, and I am a mechanical engineer that knows only enough electrical to be dangerous.  Here are a few photos.  The only thing that I did notice was that on the back side of the board where the soldering connections are, the one side of it seems to have a lot more blemishes or bubbles.  Not sure if that's a sign that the board is bad or if it is nothing.    

[Zed Head]

I didn't really think that you would find anything but it was worth a look.  It's not clear how the ignition modules fail, but they do at a pretty regular rate.

If it was mine I would take it for a drive and see if the problem repeats.  Take extra care to note what happens when it does.  You only have this one incident to guess about.  Stop immediately when it happens and let things cool down for a few seconds.  Restart and see what happens.  You need more data.

On 7/2/2023 at 7:04 PM, Paulytunes said:

On the drive home, about 20 miles in, or just as I was 3/4 of the way through the Harbor Tunnel, the engine started to misfire and sputter when I gave it gas and above 3000rpm.  I was able to get it to my exit by driving gently and keeping the engine speed below 2500rpm, until I reached about 30 miles in (or ~35-40 minutes of driving).  Then all Hell broke loose, the car stalled repeatedly and it was a challenge to make it the last few miles home.  I eventually did.  When I started it about two hours later, all was well and you never would have guessed there had been an issue.  I did notice the gas cap was extremely tight, enough that I had to tap it with a rubber mallet to loosen it.  One suggestion I received was to drill a small hole in the gas cap as it may be a venting issue.  I didn’t want to do that, especially after researching and finding that replacement caps for MY1976 are ~$200!

 

[Yarb]

From looking at the pic of the coil, An inexpensive solution would be to replace the coil. NGK offers one on Amazon that’s very reasonable.

[Yarb]

When I said solution I mean it’s a variable that could be causing an issue. Either way coil’s don’t last forever.

[Paulytunes]

9 hours ago, Zed Head said:

I didn't really think that you would find anything but it was worth a look.  It's not clear how the ignition modules fail, but they do at a pretty regular rate.

If it was mine I would take it for a drive and see if the problem repeats.  Take extra care to note what happens when it does.  You only have this one incident to guess about.  Stop immediately when it happens and let things cool down for a few seconds.  Restart and see what happens.  You need more data.

 

Out of the times I have driven it, the only time that I did not have the car start to stutter was a trip under 10 minutes in total duration.  The issue is recurring almost every time I drive it and until I get this resolved, I am gun shy of driving the Z anywhere more than a few miles from home.  

Trip 1 was driving it home from the mechanic where I first noticed the issue.  Detailed in my first post above.

Trip 2 - this was after I had replaced the fuel filter, and thought maybe that was the issue.  The problem occurred around twenty minutes after driving, shortly after a full throttle acceleration from a rolling start to about ~50mph.  I was able to limp home and kept the rpms under 3000.

Trip 3 - I took my Dad for a ride to Lowes after going through all the fuel vents, about 6 miles roundtrip.  Stuttered on the way home, probably at around the last mile of the trip.  Limped home again.  When I tried to start it immediately afterwards, noticed idle was rough and it wanted to stall, but would restart.

Trip 4 - Took a friend on a drive to Costco (5 miles), no issues on the way there.  Did one full throttle pull, similar to trip 2.  When we were going to come home (after about 20 minutes stopped), the Z would not start after multiple attempts.  This is what made me think it had to be a fuel issue.  I had to get a tow home b/c I didn't think to just let the car sit for about an hour and all would likely well again.  Of course, once home and the tow driver had left, the Z started immediately and I got it back into my garage.  

Since the tow, I really have not driven it (due to my paranoia that I am going to get stranded again and also due to the fact that we went on vacation).  I've done some troubleshooting in the garage and driven around the neighborhood. 

[Paulytunes]

1 hour ago, Yarb said:

When I said solution I mean it’s a variable that could be causing an issue. Either way coil’s don’t last forever.

So far I have not found the smoking gun, but I am really toying with replacing the coil and doing the GM HEI mod to bypass the TIU.  However, I am a little hesitant to try to wire it up, as it seems the 1976 TIU is different than the one in EuroDat's excellent instructions, which is based on a 1977 model.  I guess back in the 1970's and 1980's the changes from MY to MY were substantial instead of minor and cosmetic like they are today.  

As you noticed, the coil looks pretty well aged.  I'm not sure if it is the original coil, but maybe it is a contributing factor.  I think one of my next steps will be to test the coil according to the FSM.  It is not hot to the touch after driving.

[Zed Head]

Actually you have the simplest version of the ignition modules, with just one coil control circuit.  You can try the swap in the engine bay, next to the coil, without doing anything to the factory module except unplugging it. Edit - actually disconnecting since you don't have a plug.  EuroDat's mod is the slick, looks factory, swap method.

But there are clues that you haven't mentioned.  You've talked about RPM and the lazy tach needle the next day but haven't described what the needle is doing while it's running poorly.  That's a good clue.  If the needle is not steady and following engine speed correctly then that's a sign of spark problems.  

The other common electronics problem is the ECU solder joints.  The test for that is to bang on the side of the ECU when things are acting up and see if there's a change.

Edited July 24, 2023 by Zed Head

[Paulytunes]

Update:  So I went ahead and replaced the coil and swapped out the TIU with an HEI Coil.  I followed EuroDat's instructions but modified it (see the photo of schematic wiring diagram).  The HEI is a Petronix D2000 and the coil is a Petronix Flamethrower 0.3 ohm.  I was very reluctant to cut the wires on the TIU, so I also bought a terminal block from Lowes and mounted it to the TIU box.  I finished wiring it up today, reconnected the battery, said a little prayer and started the Z up.  I let the engine warm up and idle seemed to smooth out around 800rpm.

The issue that I am having now is that when I apply throttle, and anytime I exceed 2000rpm, the engine immediately stalls.  It starts right back up again, but the problem repeats.  I tried swapping out the red and brown wires to see if that would make a difference.  The problem is the same.  Could I have messed up the green and red wires?  Or should I have bypassed the resistor and wired straight to the coil?  I am also toying with putting the old coil back in to see if there is any difference.  I took off the distributor cap, but I did not see anything odd.  Any advice or tips?  Thanks in advance for any help.