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1976 280Z Fuel Issues Troubleshooting


Paulytunes

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So here's my story.  I bought this car back in late April, as a running car that needed some work, including a fuel sending unit.  According to the seller, the engine was rebuilt about 6,000 miles ago and was in good running condition prior to the sale.  The car sat at my mechanic's shop for about a month while the correct fuel sending unit was ordered and delivered.  I picked it up about a month ago when finally completed.  

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!

I researched and thought this could be a venting issue, so I carefully removed the rear trim and cleaned the vent lines, checked the vent/expansion tank, and all seemed to be in order.  The charcoal canister appears to be operating properly as well.  I also replaced the fuel filter in the engine bay, as well as the fuel oil supply hoses. 

The above did not solve my issue, which has been getting progressively worse.  On the next drive, the issue happened again between the 20 to 30 minute timeframe.  The next drive it seemed to happen more quickly, say around 20 minutes.  I took it for a short drive, ~10 minutes, 4 miles last Tuesday, parked it for about 20 minutes, and it would not start.  I had to have Hagerty tow me back home, and of course, it started when I tried it again at home to put it in the garage.   

I did some research here, online, and consulted my Factory Service Manual, as well as talking to a few engineering friends.  One is convinced that I have sediment in my fuel tank that is causing a blockage, which I made worse by performing a full throttle acceleration.  From online research and others who had a similar problem, as well as the FSM, I started troubleshooting the EFI computer pins and Air Flow Meter.  I pulled the AFM last night, and tested it, thinking a had a bad temperature sensor (pin 27).  I figured that was too easy and I shouldn’t trust my cheap Harbor Freight multimeter, which I suspected had some issues when I was fiddling with it last night.  Today, with a new and higher quality multimeter, I found I was correct and my HF merch is suspect, my AFM is not.  So, I put it all back together and tried to see what would happen if I let the car warm up and then applied throttle while the Z was parked and took video (see attached and link below (if attachment fails to load)):

https://youtu.be/vDj18VLJOvg

Anyone here have this same problem and know what this could be based on similar experience, my description, and as shown in the video and noises?  The squeal when applying full throttle isn’t normal, is it?  I also noticed that when I gently squeeze the fuel return the idling seems to smooth out. 

 I’ll keep troubleshooting in the meantime.  I guess what I find out it isn’t will be verified to be in working order.  

Thanks in advance for any help,

Paul 

Edited by Paulytunes
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Your front fuel filter could be clogged but most likely you have crud in the tank. Try squeezing the fuel line from the top of the filter to the fuel rail, it should be very hard to squeeze. The easiest way to tell what's inside the tank would be install a clear filter coming out of the tank but before the the fuel pump. Good write up about that here...

http://atlanticz.ca/zclub/techtips/fuel/g3filter/index.htm

This whole collection of 280 information got mine running. And keep it running too. :beer:

http://atlanticz.ca/zclub/techtips/

Thanks @240260280z

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1 hour ago, siteunseen said:

Your front fuel filter could be clogged but most likely you have crud in the tank. Try squeezing the fuel line from the top of the filter to the fuel rail, it should be very hard to squeeze. The easiest way to tell what's inside the tank would be install a clear filter coming out of the tank but before the the fuel pump. Good write up about that here...

http://atlanticz.ca/zclub/techtips/fuel/g3filter/index.htm

This whole collection of 280 information got mine running. And keep it running too. :beer:

http://atlanticz.ca/zclub/techtips/

Thanks @240260280z

Siteunseen,

Thanks!  the pre-filter seems like a great idea and cheap insurance to ensure the crap in the tank gets captured before it makes its merry way to the engine fuel filter, or worse, to the injectors.  I did try to squeeze the supply line while the engine is running, it is very difficult to squeeze.  My next step is going to be the Fram fuel filter at the tank. Hopefully that resolves my problem.  If not, I guess I will continue troubleshooting.  I'll update once that is completed.

Paul 

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Are you absolutely sure the problem is fuel delivery, and not ignition?

Using a fuel pressure gauge you should be able to confirm or eliminate fuel delivery as the culprit. 

Using a timing light, and a tach/dwell meter you should be able to confirm if the ignition system is performing as it should.

When the mechanic had the tank out to replace the fuel gauge sending unit, did he not clean the tank and asses its condition? Also, there should be a nylon sock on the fuel pickup in the tank, sometimes they get clogged with debris and rust.

Also, an observation.

Are the short rubber hose bits from the fuel rail to the injectors original to the car? If so, they should be replaced. Many fuel injected Z cars have caught fire when these fail and fuel is dumped onto a hot exhaust manifold.
 

 

 

Edited by Racer X
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14 hours ago, Paulytunes said:

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.

Edit - didn't see the title, it doesn't show when you read a post.  Putting the details of your car in your signature makes it easy and consistent from post to post.  Good luck.

Can't tell what you're working with, looks like a 280Z, by the picture of the engine.  Your problem description fits a failing ignition module pretty well.  Does the tachometer needle behave normally while the engine is acting up?  Or does it jump around and read higher than it seems the actual RPM are?

Edited by Zed Head
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2 hours ago, Racer X said:

Are you absolutely sure the problem is fuel delivery, and not ignition?

Using a fuel presser gauge you should be able to confirm or eliminate fuel delivery as the culprit. 

Using a timing light, and a tach/dwell meter you should be able to confirm if the ignition system is performing as it should.

When the mechanic had the tank out to replace the fuel gauge sending unit, did he not clean the tank and asses its condition? Also, there should be a nylon sock on the fuel pickup in the tank, sometimes they get clogged with debris and rust.

Also, an observation.

Are the short rubber hose bits from the fuel rail to the injectors original to the car? If so, they should be replaced. Many fuel injected Z cars have caught fire when these fail and fuel is dumped onto a hot exhaust manifold.

No, not absolutely sure, I figured fuel delivery was the first place to start.  I'll look into the ignition next.  

He did not mention that there were any issues with the fuel tank, but I will need to confirm.  He did ask me to check the ignition coil to see if it was hot to the touch after driving it.  As far as I could tell, it was close to ambient temp.  I cannot very easily take it back to him to evaluate since he's over 30 miles away and I certainly do not think it would be safe or feasible to drive it there.

As far as the rubber hoses, they do not look very new.  I would have thought the P.O. would have replaced them when the engine was out of the car and under his restoration performed but maybe not.  I will replace them so that I am sure of when they were new and eliminate the potential worry.

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1 hour ago, Zed Head said:

Edit - didn't see the title, it doesn't show when you read a post.  Putting the details of your car in your signature makes it easy and consistent from post to post.  Good luck.

Can't tell what you're working with, looks like a 280Z, by the picture of the engine.  Your problem description fits a failing ignition module pretty well.  Does the tachometer needle behave normally while the engine is acting up?  Or does it jump around and read higher than it seems the actual RPM are?

Zed Head - good idea, I will update my signature.

It's a 1976 280Z 2+2.  Tachometer operation seems normal.  The car is still relatively new to me, so I don't perceive that it is reading incorrectly.  I did notice that it bounces around after it tries to return to idle once I apply full throttle and it starts to have the misfires.  I may go and try to test and watch the tach to make sure there's no crazy needle operation.

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It will only happen when the problem is happening.  The module gets hot and starts firing the coil at a higher rate than designed.  Extra sparks out of time, and extra fuel because the EFI is controlled by spark.  Let the module cool down and it works properly.

Mine would do it whenever I got above 3000 RPM.  I could cruise around at low RPM, get on it, and end up having to pull over and restart.  The tach would show 4000 or so when I knew it was only about 2500, plus it was quivering and jumping around.
 

Just clues to look for.  

Edited by Zed Head
then > than
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2 hours ago, Paulytunes said:

Zed Head - good idea, I will update my signature.

It's a 1976 280Z 2+2.  Tachometer operation seems normal.  The car is still relatively new to me, so I don't perceive that it is reading incorrectly.  I did notice that it bounces around after it tries to return to idle once I apply full throttle and it starts to have the misfires.  I may go and try to test and watch the tach to make sure there's no crazy needle operation.

When I posted the post above I had only read the last short post of yours.  What you wrote here is a very good description of a failing ignition module.  It's how mine acted as it was crapping out.

Search "HEI ignition module" on the site for a cheap and pretty easy swap to a more modern, by just a little, cheap ignition module.  You can also find them around the internet, but a used one is going to be on its way to failure also.

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On 7/3/2023 at 1:15 PM, Paulytunes said:

One thing I did just notice, is that it seems to take a long time to get back to idle once revved up beyond 3000rpm.  Other than that, no odd tachometer operation.

That could be the BCDD out of adjustment. When that gets out of whack the idle stays higher longer than normal. 

https://www.google.com/search?q=bcdd+adjustment+classiczcars.com+site:www.classiczcars.com&client=ms-android-americamovil-us-revc&prmd=visn&sa=X&ved=2ahUKEwjS1bCp1vX_AhVyj4kEHSgQB-wQrQIoBHoECA4QBQ&biw=320&bih=545&dpr=2.25

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  • 3 weeks later...

So I finally had a chance to do some troubleshooting today after coming back from a family vacation.  I didn't find anything odd with the transistor ignition unit, looks to be in good shape and younger than 47 years.  Getting ready to test it, but do I need to fully disconnect it to test resistance?  The FSM says in the first paragraph to disconnect the battery and remove it to test, but then says to turn the ignition on (assuming with it removed or not connected and check using the multimeter).  Sorry for the likely stupid question, just not following exactly how I should go about testing it.  I don't have an oscilloscope, so I would only be checking voltage, resistance, and continuity with my multimeter.  

 

I did find two disconnected wires in the engine compartment, near the ignition coil.  The first is a yellow wire originating from Engine Wiring Harness #2 with a bullet end connection.  I'm not sure why the P.O. would have left this disconnected?  It is shown on the second photo, near my index finger.  My best guess is that this is supposed to go to the BCCD or the water temperature sensor if I am reading the 1976 wiring diagram correctly.  I think it is the former and not the latter based on the length of the wire.  

The second disconnected wire appears to be a ground connection for the small device attached to the ignition coil mounting bracket in the third photo.  Can anyone tell me what this device does?  Is this stock or aftermarket?  I don't see anything in the FSM showing this device, but I might not be looking in the right section.  

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