1977 280Z Runs Rough and No Tach

[Datsun7]

New to the forum so please go easy on me! LOL! I have a 1977 280z. It was running fine and then died while idling in the driveway. I restarted and it is idling a bit rough.... when you give it gas it breaks up at certain RPMs. Really rough run up and not drivable but will maintain a rough idle.... At the same time this happened the tach stopped working. I have to assume the rough running and tach are related? I changed the ignition coil and cleaned up the terminal block connections that connect to the coil. Would appreciate any feedback and or suggestions.

[Av8ferg]

Welcome to the forum. The folks on here love to help Z owners with problems, so you’ve come to the right place for quality advice.
So, I going to ask the questions most would ask before we get the ball rolling.
1. What is the recent history of this car. Did you just buy it? Has it been sitting, was it a weekend driver etc.
2. What recent work has been done on the car?
3. Is your car stock for the most part or modified.

So fill in some more details so we can start to narrow down the problem.


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[Datsun7]

Thanks! Appreciate you responding.... and great questions.  See below:

 

#1 I purchased the car about 2 months ago. It had been running fine in the short time I have owned it...... It did sit in a garage and according to the last owner he drove it a couple times a month but short local trips over the last 20 years. So hard to tell for sure how often it was driven....

#2 According to the last owner and the paperwork in the glove box. The injectors where cleaned about 2 years ago and it looks like the fuel lines under the hood have been changed. I did replace the fuel filter, and the one I removed had some sediment come out of it. After running it with the new fuel filter a few times the fuel appears clean as I removed the new filter and drained it to see what "gunk" may have come out. Looked clean.

#3 The car is completely stock under the hood..... Still has the original engine with 92K miles.

 

Thanks again for you thoughts.

 

[Zed Head]

1 hour ago, Datsun7 said:

Really rough run up and not drivable but will maintain a rough idle.... At the same time this happened the tach stopped working. 

If stopped working means it just quivers and jumps or it doesn't read right, that sounds like the ignition module.  They go bad often these days after 40+ years.

[Datsun7]

Thanks for the response. The stack does not move at all. No jumps or quivers that I see. Is the ignition control module next to the fuse box on the passenger side of the lower foot well?

[Zed Head]

A dead tach could be a problem also.  If it is shorted out it might be hindering the "break" part of the make-it-break-it spark generation cycle, since it's connected to the coil negative terminal.   Has it always been that way?

Yes, the module is up in front of the fuse panel.  

The parts on the 280Z EFI cars are interconnected.  Problems with one system can cause problems with another.  You might have some troubleshooting ahead of you.

[Datsun7]

Just a follow up...and thanks to all who responded!!! Tach still not working but rough idle and rough running problem was the ground at the distributor. Still working on the tach issue... UGH!!!

[SteveJ]

Make sure the resistor is connected between the ignition and the tachometer.

[Datsun7]

Thanks.... I will check it....Is that located under the dash?

[Dave WM]

passenger side

[Zed Head]

It looks like this, below, but if it's intact it will just be a squarish lump in the wiring harness.  If the harness is broken open and you only see the wired piece, with the bullet connector bare, you'll know.

[Datsun7]

So the resistor location is under the passenger side dash? or located near the keyed ignition when you remove the cover?

 

Also....What does the resistor due above the ignition coil under the hood?  

 

Sure appreciate everyone's input!!!