1977 Cylinder #1 Mystery

[Captain Obvious]

Good point guys. Just because it shows "continuity" doesn't mean it's a good hard low Ohmic connection.

[ckurtz2]

Wow, thank you everyone for the replies! All this information is great. 

       I did not disconnect the other injectors when doing the voltage test, so I will make sure to correct that mistake, super helpful.

       I also am beginning to think there is some sort of intermittent break in the harness like CO and everyone else mentioned. Here is why. The connection at the dropping resistors seemed kind of loose. Such that it wasn't pushed in all the way (was at a slight angle), however, when I tried to push it in all the way it looked like it physically couldn't reach, seemed like too much tension was being put on the wires. I kinda just pushed it in further, but now it seems really hard to take out. Anyways, at the time I didn't think too much of it.

    One of my friends was over and had never seen the car start, so I said why not I'll start it and see if for whatever reason #1 noid light starts working again. And so I did this and waboom it was working. I connected it back to the car and boom idle change. I was astonished, to be honest, and now #1 works. So I checked for voltage down at the ECM again and there it was, #1 was reading voltage on pin 15. I would also like to mention I test drove the car immediately after #1 was firing again, and it was bucking much more than before. 

    Noticing the motor seemed like it was running just as rough as before if not rougher, I pulled plug wires and now it looks like #5 isn't firing properly. I notice an ever so slight rpm change (before it was a lot more apparent). Ok, weird. I checked voltage back at the ECM for #5 and it was reading fine. I then checked with a noid light on #5 and it seemed to be flashing ok.

     If the only thing I touched was the dropping resistor connector, I would think that the two issues are related. However both connector ends seem fine, it is just hard to get the two to mate. 

     The leads on my multimeter are too small to reach places, so I need to get longer ones before I am able to properly go through the harness:(

    Not really sure what any of this means yet, as even though the dropping resistor connector isn't pushed in all the way, it is 100% making contact with the male and female inputs. Does anyone have a photo of the connection of the two? I can't tell if mine should go further together or not.

[Yarb]

If you haven’t already, Disconnect the dropping resistor component from the mount. Fully inspect the connections and contacts. It’s in a tight spot. Sounds like some of your issues reside there. 

[Zed Head]

4 hours ago, ckurtz2 said:

I would also like to mention I test drove the car immediately after #1 was firing again, and it was bucking much more than before. 

The bucking sounds like the typical lean mixture problem.  Solved with the potentiometer in the coolant temperature circuit to richen things up.

[siteunseen]

I agree! That's the exact word I used in 2011. It would buck like hell up to 2,500RPM then pull good.

[Zed Head]

From up north -

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

[ckurtz2]

So, I agree with you both that I think the mixture is off at certain RPMs, especially high RPM. However, the bucking at idle is completely new.

                  I want to mention that my Z has the 260s cam, and I knew it was going to need a lot of tuning to get the original EFI to work right (adjusting the AFM flapper, timing, etc etc). Many people advised against it, but I believe with such a small cam most of it can be tuned out. However, I still think that something electrically or mechanically is amiss in my car, because cylinder number 5 now seems to have almost no change to idle or engine when at a little higher rpm. In addition, it is just running in general a lot worse than it used to before I started having these weird problems. 

Here is a what gave me faith with the stock EFI and the 260s cam. https://www.zcar.com/threads/biggest-cam-for-stock-efi.292280/

"I ran the Deltacams 260 cam with stock efi and it ran great. I ran the cam for a few years then sold the car since I had to many z's. Yes, 110.00 plus shipping. Don't forget the thicker lashpads to make up for the regrind. 0.160" thickness from courtesy nissan for another 36.00.
this cam does require some tuning to the stock efi. Run more ignition timing, loosen up the afm flapper a few teeth, adjust the tps to the off idle position.
You can run stock ignition timing if you move the vacuum advance to a manifold vacuum source. This will add vacuum advance at idle, so it will make the engine idle with 30 degrees of timing (10 initial + 20 vacuum advance).
the cam has a very slight lope at idle. pulls hard to 6000 rpm. a nice improvement in my car.
A 260 cam should idle in the 16 to 17inhg range. Lower than expected vacuum is a sign of low ignition timing and improper air/fuel ratio. A Z efi computer doesn't measure vacuum like a modern efi system, The only thing in a Z efi system that measures vacuum is the fuel pressure regulator"

     That being said, my vacuum is currently at around 15hg at 950rpm. So I either have a really bad AFR, vacuum leak, weird electrical issue, or it's that semi dead cylinder, or likely all of the above causing bad AFR. Thanks for mentioning the water temp sensor tweak, it is a great gadget. I made one many moons ago, and tried it to see if it would fix anything at high or low rpm following that comment. Didn't do much except bog the motor down with fuel, so I don't think the problem lies there. 

     I am going to be taking it to a shop this weekend where they can actually measure my AFR, smoke test it, do real electrical work etc using all the big boy tools I don't have. As well as tune the EFI for the cam. I will update this forum once they find the issue(s), so to keep everyone informed.

    I would also like to mention if I get it running right with the 260s cam I will make a separate thread as a guide on how to tune the EFI for it, so members can use it as info in the future, knowing that putting a cam in the stock EFI is a highly debated topic. Thank you everyone for the help thus far! I genuinely would have zero headway when working on the Z without help from this forum:)

    

       

 

               

                 

[Captain Obvious]

So it really sounds like you've got weak / dirty connections in the EFI system, and that's not unusual at all. Very common situation for these cars.

If you're going to take your car in for some tuning work, you need to be absolutely double dog sure that all your EFI connections are clean, solid, and reliable.

Top priorities for me? If all of your connectors are still original (except for injector #1 which you have already replaced), I would go ahead and replace the other five injector connectors and polish up the pins on the injectors. I would also replace the temperature sensor connector with new, and polish the temp sensor pins. I would pull and polish up the dropping resistor connections. Lastly, I would inspect the AFM connector and polish up everything there too.

Hope it's that simple!

[Zed Head]

Didn't know you were running a lumpy cam.

That thread from zcar.com is interesting.  A lot of what would be considered bad advice on how to get the 260 cam to run "right".  Fiddle with the AFM, run direct vacuum advance, adjust the TVS so it's off-idle.  wangsman's version of "runs great" seems to be pulling hard to 6000 RPM.  Your issue is at idle.  You can tell from the comments that some of the opinion might be more of an "I made it work" view.  I'll bet their cars smelled like raw gas at idle.  No offense to the two guys that said it can run just fine with the lumpy cam, but that's how the brain works.  We probably all have memories of the guy in high school that thought his car was fantastic but nobody wanted to ride with him.

@Jeff G 78 is one of the guys in the thread.  He knows a bit about how to get these engines to "run right".

It will be entertaining to see where you end up.  How are you going to write a guide if you take it to a tuning shop?  What goals will you set for the tuners?  Today's tuners only know how to use computers to tune automotive computers (I just saw one of those car repair videos that the guy titled "millenial vs. carburetor" or something like that) .  Take special note of the looks on their faces when they see what you're working with.  Should be fun.

[ckurtz2]

@Captain Obvious Just got some new bullet connectors, some DeoxIT, and other stuff to redo the bullet connectors around the engine bay. All of them look pretty bad:( All the injector connectors are new, tps, water temp sensor to thermostat housing connector, alternator connections, battery wires, etc. The water temp sensor bullet connectors, however look pretty bad. The AFM is a rebuilt unit so the connections are solid, however, I think I will clean up the connector from the harness side. Same with cleaning the dropping resistors. Thanks for the recommendation!

@Zed Head Yep the cam was an important part I didn't mention. I figured I'd leave it out though until the end, because I know my current problem is not related to it. Thanks for the contact! I agree that the modifications seemed a little odd, but they all made sense to me except removing the dizzy advance. I agree, I don't want to band aid solution the car. However, if it still has trouble on the top end running lean due to the extra air coming in, then loosening the AFM just a little doesn't seem like a terrible idea to me. By guide, I mean that I am going to essentially play with the EFI until I get it right to the best of my ability and share with the community what was done, if anything.  In addition, just an overall review on how good or terrible it runs on stock EFI. 

     HAH!, my tuning shop is Chuck from Sakura in AZ. I don't think any fancy computers or anything will be used, just the ole noggin. This is my first Z that has never quite run right, and they know a lot more about how Zs are supposed to look/run etc, and have a lot more experience in troubleshooting than I do. If I never get it quite perfect, so be it, but I want to get as close as possible. As long as it doesn't hurt the engine and is daily driveable, I can always swap to a different EMS later (with my track record with the EFI system on this car so far, it is seeming O so likely. I don't want to throw in the bag yet though).

    Man I would love to bring it into a standard "tuning" or automotive shop for work just to see them struggle. However, having worked at crap shop  in high-school myself, full of dishonest and terrible techs, I will never let someone I don't trust ever touch the car with a tool. 

 

 

[Captain Obvious]

Good luck with the remainder of the connector cleanup. Note that issues with the coolant temp sensor would affect all cylinders, not just one (so that's not what was causing your misfire on #1 only). But in any event, it's a very important input to the EFI system and it must be clean and reliable.

And don't forget to clean up the other sides of all those new connectors you've already installed. The male "outie" pins on the fuel injectors, for example.

Some people in the past have had issues at the large connector right at the ECU, but I've never seen an issue there. In my experience, that connection point is clean and shiny because it's lived its life inside the interior of the car instead of out in the engine compartment. Worth a peek though, just in case your car sat for a long time in a high humidity area, or had a water leak from a window or cowl drain or something.

[Jeff G 78]

10 hours ago, Zed Head said:

 

@Jeff G 78 is one of the guys in the thread.  He knows a bit about how to get these engines to "run right".

 

Let me read through the thread and see if I can offer anything.