Does this sound like a burnt valve?

Jazzer · Post by **Jazzer** » 23 Sep 2016, 08:04

Thanks for all the help and advice, folks. I put new plugs in this morning but I still have the same problem: misfire on cylinder 4 at idle only, runs beautifully smooth above 1000 rpm's. Even though the injector sounded normal, I have a hunch it might be the culprit. I'm heading to harbor freight now to pick up a cheap compression tester so I can check that as well. Here's a pic of what 16 year old plugs look like, by the way...

: 16 year old plugs

Post by **erikv11** » 23 Sep 2016, 08:44

You can swap injectors around too, that's what I'd do after the compression test. Be careful with the rubber seals so they don't tear, they are also 20 years old.

Plug #4 isn't wet with gas or washed clean from lack of firing, or washed clean from a coolant leak, still at this point you gotta just hope compression is OK.

Jazzer · Post by **Jazzer** » 23 Sep 2016, 09:53

Well folks, cue the sad music: a dry compression test has shown no compression in cylinder 4. Here are the numbers:
1: 170
2: 170
3: 165
4: 0
5: 150
At this point can I assume it's a valve problem then? Obviously I'm bummed, but at least I can start planning for a rebuild. Robert has some great videos that should help me jump in the deep end, so to speak. I should also unplug the injector, I'm assuming, since it's still my daily driver.

Post by **kcodyjr** » 23 Sep 2016, 10:22

No, you can't assume it's valves; it could also be head gasket, rings, cracked block or head, or damaged piston.

But yes, you could have a valve that looks like the half-eaten donut the cop just dropped on the ground.

There's no other way: you've got to pull the head and take a look.

Post by **kcodyjr** » 23 Sep 2016, 10:23

... and in any of those cases, how the blazes is it smoothing out at higher RPM?

Could it still be misfiring but just not skipping and farting because of the extra energy in the flywheel?

Post by **erikv11** » 23 Sep 2016, 10:46

There's no way to know without looking, but I would say 99.9% chance it has a burned exhaust valve. Good call in your opening post, had me fooled.

They do run smoothly on 4 cylinders, but not usually like butter. If you just unplug the #4 injector you can run it a pretty long time, as long as you can put up with the CEL.

Jazzer · Post by **Jazzer** » 23 Sep 2016, 11:01

Ok, I'll be blocking out some time in early October to dive in. In the meantime I'll be reading up and checking out some tutorials, so feel free to add any suggestions. I'll be sure to give some updates.

Jazzer · Post by **Jazzer** » 23 Sep 2016, 21:32

Back so soon...
So I disconnected the #4 fuel injector...drove about a mile and stopped and plugged it back in. It was WAY too erratic compared to what I was experiencing with just the idle misfire. The part that has me confused is that the misfire disappears at highway speeds; I cleared the code while driving and the cel didn't come back on until I slowed back down to an idle. Wouldn't that mean that (at highway speed, at least) the cylinder was getting compression, that the plug was sparking, that fuel was ignited? My mpg is no different than before. I just don't know enough about internal combustion, which is why I listen to you fine folks. Perhaps it's a piston/ring problem? Would it need to be overheating to be a head gasket problem? Just throwing out ideas...

Post by **abscate** » 24 Sep 2016, 01:07

It could be a sticking valve which is only occurring at idle. I agree that it sounds like things are ok at speed.

Short of pulling off the hood and doing a compression check on the road...this must be you tubed.......tough to nail down.

Maybe someone could recommend a sticking valve treatment like Bardahl or something?

Post by **Clemens** » 24 Sep 2016, 13:39

Stull hard to believe that nailing a car to merge into traffic burns a valve. If that did it it would have died soon anyhow.