1977 280z Ignition Woes

[ckurtz2]

Hey Guys,

I battled a number fuel injection issues in a previous forum.

 With that system running right, I now have narrowed down the stumbling idle to something ignition related. The car takes a few seconds to start up, but when it roars to life it holds an idle. However, you can hear a clear miss, and the motor will buck around. I also want to note that I can free rev the car and it seems to smooth out at higher RPM. 

My first question is about the spark plug wires that I came across. These are/were brand new NGK wires from Zcardepot I installed last winter. The car has probably seen about 30 minutes of idling/revving in a garage since then, while battling injection issues. It seems as if the sealer around the wires has overheated and separated at the boot. What could this be caused by and why? Would this cause arcing around the engine?

spark plugs don't look fouled. NGK-BPR5EGP

I attached photos of 3 wires that seemed to have gone bad, and 1 photo of a wire that still seems to be in good shape. 

[Zed Head]

That would not cause a miss, I think.  Does anything change if you move the wires around while the engine is idling?

Too many pages in your other thread and can't remember what you're using for ignition.  All kinds of odd things are possible.  You can even put the wires on in reverse rotation and the engine will start and run.  I did it once, by accident.  Got #1 right but the others were all backward.  It ran like crap.

[siteunseen]

Have you cleaned the cold temp sensor in the thermostat housing then the bullet connections about a foot back in the wiring? Your choice of the word "bucking" got my attention as that the exact way I described my '77s rough running up to 2,500 rpm then it ran good with good pull.

Here's the "fix" but look through and you'll see the bullet connections, make sure they're clean and tight. The plastic connector to the thermo housing should be clean and tight. Last but not least take the brass sensor out and shine it up with some sandpaper or steel wool.

https://www.atlanticz.ca/zclub/techtips/tempsensorpot/index.html

[ckurtz2]

1 hour ago, Zed Head said:

That would not cause a miss, I think.  Does anything change if you move the wires around while the engine is idling?

Too many pages in your other thread and can't remember what you're using for ignition.  All kinds of odd things are possible.  You can even put the wires on in reverse rotation and the engine will start and run.  I did it once, by accident.  Got #1 right but the others were all backward.  It ran like crap.

Haha, me two. First time I started it, I mixed it up and it wouldn't start. Went for the starting fluid😞 Sounded like a 12 gauge it backfired so bad🙂 Kinda cool, kinda terrifying. Equally stupid

Anyways. For ignition I am running a Petronix Flamethrower 2  0.6ohm coil. I am running a stock distributor, but I just had it sent off to Advanced Distributors in Minnesota to be rebuilt and recurved. It looked pretty crummy inside, and I don't trust remanned units due to reports of inconsistencies. I am still using the factory ICM, ballast resistor, etc. 

I did clean the thermo sensor before I put the motor together. However, the engine doesn't seem to be affected with it connected or not, so I just leave it unconnected living in Arizona. All the bullet connectors are solid. I wired in the resistor for the WTS so I can adjust how rich the motor runs. No matter how rich she still likes to buck. All makes me think it is ignition.

I also pulled apart the Ignition Control Module. It had oxidation and rust spots on the outside. The circuit board looks brand new inside, so I just let that be.

Wish I could run it and see if moving the wires caused problems, or if it arced in the dark. Running out of things to look at, but those new wires going bad must mean something.

 

 

 

[AK260]

From the photos I wouldn’t say your wires have “gone bad” as such - it looks like they have put some kind of sealant between the boot and the cable to prevent moisture ingress. The sealant coming off should not cause a misfire.

The way to tell if your leads are bad is to get a multi-meter set on resistance test. Then connect both ends of the leads onto the probes and hold them securely in place with your fingers. First measure the resistance which should be in the order of kilo ohms 10k-20k ohms per metre if they are carbon wires - it will be a different reading for each lead as the resistivity is related to the length of the lead and each one is a different length.

Then when you are satisfied that you don’t have a lead with a total break in it, while holding the probes onto each end, “wiggle” each lead and see if the resistance changes dramatically.

I had some Magnecore KV85 cables that went bad and two of them would go to mega ohms as I wiggled them. I also had symptoms like bucking and backfiring / popping when I went onto the accelerator pedal, as there was unburnt fuel hitting the end of the tail pipe.

Is your “missing” random or rhythmical? Now to throw a spanner in the works, often time a vacuum leak can manifest symptoms that seem like an electrical issue and cause random missing. This only manifests itself at idle : part throttle conditions when manifold vacuum is high but the car runs like a dream at WOT!

Once you have exhausted possibilities of electrics (or even during your troubleshooting), check your intake for any leaks (gaskets, bad hoses, etc).

[dutchzcarguy]

12 hours ago, ckurtz2 said:

spark plugs don't look fouled. NGK-BPR5EGP

Should they not be BPR6ES plugs?   so not 5 but 6  (Has to do with hotter/colder..) 

[siteunseen]

I run BP6ES in both my Zs with wider gap for the ZX dizzy in the 240. I did a lot of reading way back when and the general consensous from the other members were the 5s weren't much different with the newer gas we have now. I think the plugs he has are available in-store but the BP6ES is an overnight thing around here anyway. 

[ckurtz2]

5 hours ago, siteunseen said:

I run BP6ES in both my Zs with wider gap for the ZX dizzy in the 240. I did a lot of reading way back when and the general consensous from the other members were the 5s weren't much different with the newer gas we have now. I think the plugs he has are available in-store but the BP6ES is an overnight thing around here anyway. 

This intrigued me, as an issue I wasn't aware of, so I did some digging and came across this link. https://www.atlanticz.ca/zclub/techtips/plugs/index.html

Inside the ink I found this:

Historical Z Plugs

-1970-1974 240 and 260Z's came with BP6ES
-1975-76 280Z's came with B6ES
-1977-'79 280Z and 280ZX's came with B6ES-11
-1980 280ZX's came with BP6ES-11
-1981-82 280ZX's came with BPR6ES-11

so, I believe I am running the wrong plugs. Which is weird, because AutoZone recommended the NGK-BPR5EGP which is a hotter plug. Do you think it would be worth it to switch to the B6ES-11? I wonder if for some odd reason these plugs make the car unhappy. @dutchzcarguy thank you for the great catch.

 

@AK260 Interesting, I will take  a look at those resistance tests when I get home. The miss Is rhythmical at times in the sense that I can watch the RPM gauge bounce. However, when the gauge isn't bouncing and the engine is still missing, it seems random, as there are just distinct muffled gurgles out the exhaust with constant engine bucking. 

Regarding vacuum, it reads perfect, as I did all the tests and corrected issues in a previous forum post. Lots of new rubber everywhere. 

 

 

 

 

Edited September 3, 2021 by ckurtz2

[Zed Head]

21 hours ago, ckurtz2 said:

Would this cause arcing around the engine?

Darkness can help diagnose spark loss problems.

 

[Mark Maras]

@jalexquijano take a look at the video above.

[AK260]

Darkness can help diagnose spark loss problems.
 

Absolutely love this!! I did a similar thing with mine and also used a water mist spray. I did get some very odd looks standing on the side of a dark road spraying my engine with a plant mist spray! :p


But I did discover my coil arcing onto itself!! It did it rarely and randomly without encouragement and very clear /regularly with the mist spray.

This is a great test to do - why didn’t I think of recommending it! Way to go Zed Head!

[Zed Head]

Google read my mind and placed the video in front of me.  I  added the effort of clicking and wrote some words.

Anyone who tries this must make a video and post it.