How to diagnose dead cylinder?

[AusHou]

So 5 cylinders may be cool on a Volvo, but not here.

I'd been getting lousy gas milage, "LH HEGO lean", and "LH adaptive rich fuel limit reached", so I thought, gee, I'll replace the HEGOs. $85, done.
Still getting "LH HEGO lean", and engine feels a bit rough, so run the full cylinder balance test: #5 fails all 3 passes (==> considered dead).

Oh, great. Oh, ****!

So how do I diagnose a dead cylinder? How can I tell if it's fuel, or spark, or something much worse?

'95 MTX, 72k, plugs not original but unknown how old.

Thanks!

 

[RStalveyARFF]

you can run the cylinder balance test, which you'd activate after the finish of the KEOR. You'd blip the throttle after all the codes are displayed, and it will cut the fuel on each of the cylinders, and look for a drop in RPM. If the RPM's do not drop when it has cut fuel to a cylinder, then that cylinder is obviously dead, and will display so. Check shotimes, under the KOER test, and it'll explain it to more detail.

 

[AusHou]

Yes, that's why I ran the full test, all three passes, and the #5 failed all there. See my message above.

The question is, What Do I Do Now?

 

[Diameg]

Check the plug wire for that (and all) cylinders.

You may very well have oil in the plug well, and the plug/wire or both may be damaged.
I had that happen and replaced my plugs and wires, plus plug well gaskets, and it ran as good as new.

 

[clintonk]

This sounds exactly like what happened on my '90 last year. It was down on power and running rough, and the cylinder balance test showed one completely dead cylinder. I replaced plugs and wires to no avail. It turned out to be a bad fuel injector. I proved this by labeling the injectors and swapping them to different positions. When the dead cylinder followed the suspect injector, I ordered a used set from a list member. No problems since.

Clinton Knight
'90 White 182K
'95 Green 50K

 

[AusHou]

Well, just running on theory and guesses (no experience whatsoever), I learned to test and change plugs, replaced the #5, and showed that it is sparking just fine.

Cylinder balance test still reports #5 completely dead. So, if it's not spark, unless it's a cylinder catastrophe, it's probably fuel.

Is there any way to tell if an injector is working? The #5 is the centre-LH cylinder, so it's the easiest to get to, but I can't even reach
it with a finger because of the intake.

Is the next step to pull the intake and replace the injector, and if so how hard is that? If the intake has never been pulled in 70k miles,
are the gaskets still reusable? Heck, where do you even get a replacement injector?

 

[olympic]

SHOshop sells a set of cleaned and balanced injecters for like $160(less than the price of 1 new one!) You have to send them you old ones as a core though. Before doing that, do a compression test on that cylinder to see if it's not a burnt valve or rings. No use spending money on injecters if the cylinder has no compression.

 

[clintonk]

olympic is right, do a compression test before spending more money. Also, try sniffing the exhaust from a cold engine; if it's a spark problem, you'll smell the unburned fuel.

It's possible to run the motor without the intake, you just have to reconnect the ignition module and ground the crossover tube. I did this so I could watch fuel being squirted into the heads. Nearly singed my eyebrows, though, so be careful. But my bad injector was intermittent, so this check and even a bench test/cleaning didn't detect the problem.

If money is no issue, just get the replacement injectors from SHOShop or SPMotorsports. If it is, move the injectors around and rerun the cylinder balance test.

Clinton Knight
'90 White 182K
'95 Green 50K