Hey guys,

       back again to solve another mystery on my 1977 280z California spec coupe. So in short my number 1 cylinder doesn't fire (I have no idea how long it has been like this). Or if it does it is extremely weak.  Anyways, the reason I know this is that when I pull the spark plug wire the engine idle does not change noticeably.  Also the idle is slightly rough and will surge if I have it anywhere lower than 1000rpm, as well as the car doesn't like full throttle under load. I have also disconnected the fuel injector and that made no change at idle. Disconnected any other cylinder causes the idle to drop very noticeably. 

So, here are the tests I have run thus far.

First I checked for spark in a number of ways. 

• I pulled the #1 plug and had it zap the valve cover by cranking the engine over. worked fine, spark looked strong.
• I swapped plug wires just for the heck of it between #1 and #2. No change. Dead cylinder did not follow the wire
• I swapped spark plugs from cylinder #1 to #2 and vice versa. The dead cylinder did not follow the plug. Always dead on cylinder #1.

Next checked compression

• Even between #1 and #2 at 150psi. Didn't bother with the rest.
• Pulled valve cover and turned over motor. Valves opening and closing as should. The wipe pattern on the rockers looked very good.

Next I went to the fuel injector. Which is where I get confused.

• I listened for injector noise with a screwdriver. I swear I heard a 'tick tick tick' like all the others. However, I still heard that noise when disconnected. Possibly the sound from another injector is carrying through the fuel rail.
• Tested injector for ohms. It passed matching all other injectors.
• Next I checked the connector. It was fudged up, but I would get 12v with ignition on. Measured with a multimeter with  1 pin in the injector connector and the other pin in the injector connector and going to a ground on the intake manifold. Thus is is getting current. 
  • Just to be safe I rewired a new connector on. Tested perfect.
• Removed #1 fuel injector 
  • Tested with 12v batt very briefly to see if the solenoid would actuate. It did.
  • it also was not clogged and would spray fuel.
• Checked fuel rail for fuel coming out of #1 injector rail port. Worked perfect with starter signal disconnected and fuel pump on. So no clogs there. Gas looked crystal clear.
• Replaced #1 fuel injector
  • At this point might as well try. It did not help.
• Disconnected both #1 and #2 injectors while car was running. RPM dropped
  • Swapped #2 injector plug to #1 injector. No change in rpm.
  • Swapped #1 injector plug to #2 injector. It improved rpm.
    • however I did this test many times, and sometimes the rpm would not climb. It is not consistant.

So, what the heck is going on here. Is it possible that the ECM is for whatever reason not alternating the ground for cylinder #1? Or is it possible that the #1 injector is firing but angled somehow and completely missing the spark plug. I would like to emphasize that during this process I would check plug #1 consistently and I never noticed it really appear wet. As well as it appearance never changed in general. All the other cylinders have more carbon on them as they are running a bit rich right now. 

Any suggestions are welcomed, thank you!

 

 

 

Edited April 1, 20222 yr by ckurtz2

I think if you've tried swapping injectors and leads from other cylinders onto #1 and it doesn't make a difference, then it must be something about the route into the cylinder - either the valves aren't opening properly or there's something in the way - gasket maybe? 

Could need a new distributor cap and rotor button?

Good luck.

Good thought there Cliff. Wouldn’t that be an easy fix after what @ckurtz2went through the diagnostics on this one. Inexpensive as well!!

Respectfully submitted... Distributor cap doesn't really make sense here. He said he's getting good spark at number one. I think it's got to be a fuel problem somehow.

Really sounds like an issue with the injector or connector. Puzzling there too though since the diagnostics have been pretty thorough.

ckurtz2, You said you replaced the #1 injector and connector. Was the replacement injector new or used? And when you said you replaced the connector, how did you do that? Snip the old one off and connect in one of the aftermarket replacements?

Was your spark plug wet? At least to know if the fuel is getting into the chamber.

29 minutes ago, Captain Obvious said:

Respectfully submitted... Distributor cap doesn't really make sense here. He said he's getting good spark at number one. I think it's got to be a fuel problem somehow.

Really sounds like an issue with the injector or connector. Puzzling there too though since the diagnostics have been pretty thorough.

ckurtz2, You said you replaced the #1 injector and connector. Was the replacement injector new or used? And when you said you replaced the connector, how did you do that? Snip the old one off and connect in one of the aftermarket replacements?

Man, I was praying it was the distributor cap or rotor yesterday when I did all the testing. However, I checked this by removing the spark plug wire from the distributor cap and hovering it right over the #1 terminal. I could see the spark arcing for each revolution of the rotor. So I think that, in addition to all the other tests, rules out the cap and rotor.

Yes, so I got a remanufactured unit from AUS injection down here in Tempe, AZ https://www.ausinjector.com/mp-21024/ . The connector was already new where I just assembled on a new connector earlier in the year. However, this time I snipped the wires a tad further down the harness and wired on a new connector that was preassembled with the wire leads coming out.. There is no way it is shorting out at just the connector... I think

I really am just so confused. Because the #1 injector connector works on the #2 injector half the time. Sometimes the test works, sometimes it doesn't. The new and old connector seemed to make no difference. Always did the same thing.

In addition the #2 injector connector never seems to work on the #1 injector. Affect idle that is. 

I can't tell if I have two problems, or one. 

7 minutes ago, Barefootdan said:

Was your spark plug wet? At least to know if the fuel is getting into the chamber.

No. It had like a small drip of some sort of fluid on it. However, sometimes it would come out completely dry. Here is a photo I took in the beginning of the process yesterday.

Based on that and:
Disconnected both #1 and #2 injectors while car was running. RPM dropped

• Swapped #2 injector plug to #1 injector. No change in rpm.

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 noticed on my engines that #1 seems to run lean, the plugs are always whiter than the others.  I think it has to do with air flow, #1 must get more air.  So if your system is tuned to the edge of lean, #1 might be too lean to fire at idle.  Just a guess.  You could adjust the idle air screw to richen things up.  Screwing it in will divert more air past the vane, adding fuel.  You could also pop the black cover and move the counterweight.

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.

This is where a "color tune" plug  would come in real handy, lets you see inside the combustion chamber while its running. If they were not so darn expensive I would have 6 and use them anytime I was diag a problem with fuel mix/spark.  With one you can observe the problem cylinder then compare to a know good cylinder. Two would be easier just look at them and compare. All 6 is overkill but would be cool just to see if how the mix is on all at the same time. 

Edited April 1, 20222 yr by Dave WM

In my mind the engine would not run very good with all 6 plugs being "color tune". Unless the heat range just happened to be the same as required,

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!