Cylinder 5 is dead

[TURBO2]

I have a 1986 GN and yesterday it started to run with a heavy miss. I went back home to check it out and I found that cylinder 5 is dead. I changed out the coil, spark plug, and plug wire and it was still dead. I checked the #5 injector wire and the noid light was blinking, so that should point to a dead injector. I have never seen an injector just completely up and die, is this common, or am I missing something?

 

[CS99]

Pull valve cover. Rocker rail may be broke.

 

[TURBO2]

Pull valve cover. Rocker rail may be broke.

Wouldn't that cause a lot of ticking and clatter?

 

[CS99]

Maybe, maybe not. I would check that first before you pull the motor.

 

[CS99]

Do a compression test on that cylinder, if you don't wanna pull valve cover.

 

[Anthony P]

I have a 1986 GN and yesterday it started to run with a heavy miss. ... I checked the #5 injector wire and the noid light was blinking, so that should point to a dead injector. I have never seen an injector just completely up and die, is this common, or am I missing something?

I have seen the factory Bosch pintle-style injector fail to operate. Only a handful over a few decades, but it happens. For the problematic injectors, the coil was not shorted but the injector just would not pulse.

Sometimes, a stuck injector will begin operating again if you tap on the body a few times. This is easier to see when the injector is installed in a flow bench for testing/analysis. If an injector seems stuck and begins reacting to the electrical pulse signals again, that injector should still be replaced. Just because it is now working does not dismiss the possibility / probability that it will stop working again.

Below is a pic of set of stock injectors on the flow bench at RCG back in 2019. I camped out at the flow bench to flow / clean anyone's injectors that showed up that week.

In the pic below, cylinder position 2 is the stock Bosch calibration injector while cylinders 3 - 8 are the six OE injectors with 70K miles. The #3 injector of this set of six failed to react to the pulse signals.


Setting up the injectors to pulse while in the ultrasonic cleaner did not result in getting this injector working. John Spina noticed me stop, stare and scratch my head trying to figure out this injector problem while playing around with a multimeter. He was the one to suggest tapping on it while pulsing in the ultrasonic cleaner. That worked as the injector began working again. as you can see, post cleaning and flowing all injectors are working well.


I installed this set of injectors on my flow bench once I got home and randomly performed testing over the next year or so. There were times that this problematic injector would not respond to impulse signals. However, tapping on it again with a screwdriver would get it pulsing again.

So, yes, an injector can stop working even though there is no physical damage and the injector's coil is not shorted. And even though tapping on a stuck injector can revive it, that injector and perhaps the whole set should be replaced, depending on age, format, and function.

 

[BEATAV8]

Compression test.
Even before that you can remove the oil fill cap and see if the engine is huffing compression out through the crankcase. It'd be obvious. puff puff puff

 

[TURBO2]

Thanks for all of the replies.

 

[Reggie West]

Compression tester is $30 on Amazon.

 

[TURBO2]

I finally got the time to check it out. #5 cylinder has 136psi for compression. I double checked and it does have spark on that cylinder, and the fuel injector does click when I put power to it.

 

[SCOOBY DOO]

Check for a cracked rocker. Had this happen a couple of times. No noise...just lost a couple of cylinders going through the traps.

 

[TURBO2]

Check for a cracked rocker. Had this happen a couple of times. No noise...just lost a couple of cylinders going through the traps.

I pulled the valve cover today and everything is mint. Valves, springs, rockers, and pushrods all look like new.