1977 Cylinder #1 Mystery

[ckurtz2]

7 hours ago, Barefootdan said:

 

It seems like a fuel issue first. I know its a pain, but maybe swap injector #2 with #1 to see if the issue follows? This can rule out the injector itself. Also, check continuity between injector #1 and your ECM, Pin 15. See Pg. 64:
https://www.atlanticz.ca/zclub/techtips/efisystem/280zfuelinjectionbook.pdf

I will make sure to do this and will update you this Sunday when I am able to work on the car again. Thanks!

[ckurtz2]

7 hours ago, Zed Head said:

The dead cylinder might be only happening at idle.  That might explain why the plug porcelain is dark, indicating combustion at some time.  A dead cylinder with a new plug should be "like-new" white.

Now, I was super intrigued by your post as it would make sense. However, I remember playing with the idle enrichment screw on the AFM to see what was happening if the motor was lean or not. Lets just say I fouled some plugs whoops. But here was cylinder 1 compared to #2, Which I think pretty accurately confirms no boom🔥 is happening in #1:(

[Zed Head]

It does look more like injector alone.

You can do a lot before swapping injectors.  You can measure resistance across the pins.  Should be about 2.5 ohms.  You can connect a 9 volt battery across the terminals, with a fuel pressure gauge connected.  You should hear it click and see pressure drop as the fuel is squirted in to the cylinder.  You can put a noid light in the injector plug and see if it flashes while the engine is running.

If you had a bad vacuum leak at the injector you might also get a lean misfire.  You could check that by squirting starting fluid or carb cleaner at the injector gasket while the engine is running.  Should get some fire then if there's a leak.  That might explain why you're hearing the right noises and seeing sparks but not getting fire.

 

[Captain Obvious]

Well if you're having the same behavior with a new replacement injector, I don't think it's the injector (directly). And if you've replaced the connector and can swap them around like that and not ever get an RPM drop when you disconnect #1, then I'm running out of ideas.

I like ZH's thoughts about a vacuum leak at that cylinder. Maybe right at the injector seal. Although I find it hard to believe the leak would be so bad it would prevent the cylinder from firing. Worth looking into though.

Agreed that this is an application where a couple color tunes would really come in handy.

[ckurtz2]

Ok thanks guys! 

I think after reading these recommendations I will do as follows: Test with a circuit tester to see if the light flashes at #1 connector. Check the proper pins on the ECM. Then check for vacuum leak. Then swap #1 and #2 injectors to see if the problem follows the injector.

Yes, I sure wish I had some color tunes.

After that I think I'm out of ideas and tools:(

@Zed Head the resistance at the injector is good at 2.7ohm if I remember correct. Matched the others. In addition the solenoid fires. Tested with a 9v batt. I don't have a fuel pressure gauge unfortunately.

Thank you everyone for the help!

 

[Reptoid Overlords]

Something about that #2 plug looks like it's getting a rich mixture.  Not sure if it's a clue or not but it sure looks too rich to me.  I'm wondering if all of the plugs removed would reveal wildly uneven mixtures throughout all  6 cylinders.  Perhaps that would tell us something?  I haven't quite worked out what all that would mean if anything at all.

Edited April 2, 2022 by Reptoid Overlords

[ckurtz2]

@Reptoid Overlords

You are 100% correct that the plug was carbon fouled to a rich mixture. When I originally noticed the motor was running rough, it was behaving exactly like the motor did when it was running super lean across all cylinders.

So I probably did exactly what you shouldn't do, but I richened the idle mixture screw on the AFM to see if it made a positive difference. It didn't, just choked out the motor. I since corrected the AFM back to normal and the plugs all look good again besides #1.

However, right after running the motor super rich is where I decided to get smart and see if every cylinder was firing. That was when I made the discovery that #1 wasn't. Super easy to tell with the carbon fouled plug, and then other from #1.

[Dave WM]

I too agree with ZH and an air leak at an injector o ring. I suggest you seal up the intake at the entrance to the AFM and smoke it out using the brake vacuum port. You dont even need an expensive smoke machine, just a cheap cigar and puff the smoke in. Look for the smoke. I found I had missed an o ring this way. I can not recall the problems I was having with the car at the time, or if they were the same as you are currently having. But it was def a running issue.

[ckurtz2]

Ok guys, time to get some electrical wizards on this thread.

                 So, I started out by renting some noid lights from O'reilly. Here is what I discovered. When the engine was cranking over I saw the noid light on #1 flash a few times then quit once the engine started (cold start). So, I disconnected and reconnected it a few times and it wouldn't light up. I did this a few times and once the motor heated up a little then it started working (flashing). Ok interesting... I put the connector back on #1 and noticed seemingly no idle change. Put noid light on #2 and it worked (flashed) fine, trying this on every cylinder up to #6 (My poor motor lol, did this while the engine was running).  So I turned off the car reconnected the noid light to #1 and started the car. Once again no noid light flashes. Put it on #2 and started flashing normally. 

I also observed that the noid light would get brighter at higher rpm on other cylinders if that means anything ( I am assuming the light just appears brighter because it is flashing more consistently). 

So here are my points of confusion. First, why would it seem that the injector connector works only part of the time? In addition, once it was working wouldn't that make the #1 cylinder come back to life once I connected it. Something very odd is definitely happening here... 

I DID THIS AFTER WRITING THE ABOVE^^

Ok so next I went to the wiring harness check recommended by @Barefootdan.

         Testing each pin for the injectors at the ECM with the ignition on for proper voltage. Every pin tested perfect except #15 which is injector #1. To be honest I am lost inside the FSM on what to check next. Any help would be appreciated!

[Zed Head]

You're making good progress.  You probably have a bad connection somewhere in the wiring harness.  The most likely spot is at the dropping resistors, which are underneath and behind the washer fluid jug.  Some screws hold them in.  I would go there and take a look.  That's where the power passes.  You can check voltage in to the resistors at the plug too.  Several injectors are fed through each resistor, so check each wire carefully.

Edit, actually voltage in to the resistor would affect several injectors.  Focus on voltage out.

 

Edited April 3, 2022 by Zed Head

[Barefootdan]

Making progress! So we know at least there is an issue electrically. 
 

On the page 64 of the EFI bible, you can see that if the test failed, which it did, that you can do a few tests next using the FSM. 
http://www.xenonzcar.com/s30/fsm.html

 

here’s a list of all the years and their FSM, start from the first recommendation on EF-42 then go down the list. Possible your dropping resistor or relay is bad  

Edit: @Zed Headbeat me to it! 😂

Edited April 3, 2022 by Barefootdan

[ckurtz2]

Thanks guys. Time to start poking and probing.

        Is it me or does all the recommendations like EF-42 seem like it is for the wrong cylinder according to the FSM. It looks like EF-52 is the one I should start following?

       Also I am admittingly a 100% noob at reading electrical diagrams and wiring. Do I just check for continuity between each section of the harness as per the diagram on the positive side. And then the negative side. And if those check out then do I start testing relays and resistors to see if those units themselves failed?