1976 280z, stock system.

Had some bogging at around 3000 rpm, adjusted the TVS.  Checked plugs (which are new, only been run when test firing engine).

I assume the best option will be to "GET A NEW INJECTOR", but I'm trying to avoid that right now... (I know I might have to eventually....)

All the plugs looked the same except one, Cylinder #5 was brand new looking.  Could be no spark, no fuel, or possibly being "steam cleaned" from a water (head gasket) leak.

Checked spark, swapped plugs, wires, etc...  SPARK IS GOOD TO ALL CYLINDERS.  Tested in multiple ways.  

Did the screwdriver test.  Verified all the other injectors have good "tapping" noise, the "bad" one was muffled or no "tap"....

 

Pulled the fuel rail, disconnected coil, turned engine over with rail connected with longer hose and set to spray on cardboard.  Confirmed that #5 fuel injector not spraying.  The others were.

Took bad injector off, and used the 9v method to get it opening/spraying off the car with spare injector connector.  i did this to my "spare" used injectors too.  Off the car, they all clicked and were not clogged.  

Measured resistance on the "bad" injector and the known good ones, about 3 ohms for all.  I've read most injectors should be 10-14 ohms, but maybe these are low impedance ones?  Either way, the ones that were working and the "bad" ones had the same resistance values. 

Anyways, still no fuel from the bad injector.  Swapped injector connectors to make sure it wasn't them.  Same result.  So I know the connectors are good.  

I then swapped the #5 and #6 injector on the rail.  Same issue, the "bad" injector (now in cylinder 6 position) wasn't spraying, the others were.  So this pinpointed the problem to the injector itself (not the fuel rail, not the electrical connections) 

Manually pressed the "pintle" on the bad injector with a dentist-type tool.  Voila, a nicely patterned fuel spray came out!  

Cranked again, no spray from this injector, others are good.

So I know this "bad" injector is not clogged, had same resistance as the other injectors, can spray, and has good power supply/input.  (as verified by switching connectors and position).  (I also moved the clean spark plug to #6 so I can monitor it).  

The other "spare" injectors I have seem to do the same thing (I thought it was odd that not 1 of the 4 spares were good, but will spray manually???)

What voltage does the injector get from the ECU?  I know they always have 12v, but the "pulse" is less?   I can get them to operate fine off of the car with 9 volts.  Maybe less voltage isn't enough?  But then why the same resistance as the others?  (V=IR)

 

What am I missing?  Or is it possible this/these injectors are still dead, despite the successful tests?  

Thanks 

 

^ Yes, I do believe  he did check electrical connectors and #5 connector worked with a different injector swapped in.

Quote from Post #1:

Quote

Anyways, still no fuel from the bad injector.  Swapped injector connectors to make sure it wasn't them.  Same result.  So I know the connectors are good.  

 

 

 

The thing about electrical connectors is that we tend to assume that if the plastic fits, the metal parts are touching and electricity can flow.

All I'm saying is make sure that electricity can actually pass through the injector coil.  I have a bunch of alligator clips, and wire, and stripped solid core wire that I've crushed in to probes, so that I can be certain of things like this.  How many times have we wiggled the plastic on a connector and seen it affect the actual electrical contacts?

This is all just to know if the it's really bad.  If he has a pile of spare injectors and one works, he could just throw it in and run it.  I tend to take my broken stuff apart to know why it's broken.  When I'm done it's usually more broken.  Sometimes it ends up fixed though.

Good news, tried again and I got one of the spare injectors to spray on the car;

The initially bad one would only drip fuel, no spray. 

So I swapped it with one of the spares, and it sprayed, so I buttoned it all up and ran it, and the injector now passes the "screwdriver stethoscope" test, clicks just like the others.  

I think the cleaning probably helped, possibly applying 9v may have applied enough magnetic force to un-stick the spare injector.  (It was not working properly on the first try either).   

So I suppose, in summary, what I've learned is:

-9 v won't necessarily fry an injector (but it could).  I only touched the connection to make it pulse though, not a constant hook up.

-the screwdriver stethoscope is a great method to verify if the injector is or is not working

-both pins on the injector should have 12 volts (if good)

-the injector should have a resistance of about 3 ohms (if good)

-the ferrules on the injectors can be a pain to remove, to replace the hose

-if you can get the injector to spray/operate off the car, it should theoretically work on the car, given that other items are in proper working condition  (when I did the 9 volt, I wan't able to exert 36 psi of force, so I only got a stream out of the injectors.  But that is enough to verify no clogging.)  However, just because it operates off the car doesn't mean it will operate CORRECTLY on the car.  ie) fuel spray pattern, etc...

 

Also, my car seems to shake less through the chassis, so the bad cylinder may have  been contributing to this issue (maybe not engine mounts)

I will be monitoring this cylinder's plug, as well as checking the injector via the stethoscope test as I go, making sure it KEEPS working....

I do not seem to have the missing/surging issue at higher RPMs right now, likely due to getting this injector to fire as well as adjusting the TVS to only contact at idle and very close to WOT.  I may need to adjust again.  Both of the TVS that I have seem to initially touch the WOT contact way too early, and one had never been opened, which I found odd.    I do hear a change when I unplug the TVS at idle, so it is operating (enriching the idle mixture).

Thanks, hope this comes in handy for those facing similar issues.  

-

When I first bought my 280 my mechanic bent those arms on the tps trying to get the stumble out. He'd twist the throttle rod and look then bend it some. Turns out it was the coolant sensor. I put a potentiometer in line and it runs great now. Fwiw