#5 cylinder not firing - what are my options? [Archive] - Chevelle Tech

: #5 cylinder not firing - what are my options?

Sep 29th, 09, 3:42 PM
I took my car in to get a second opinion on a compression test and got some very bad news. my compression ended up being much higher than I was originally told (good news), but my #5 cylinder is not firing (not so good news).

the mechanic showed me by pulling the #4 wire off the distro cap and hearing the difference when it was connected vs unconnected. then he showed me #5, which had no difference either way.

it probably looks like I need an engine rebuild or a new engine (it's a toss up right now), but don't have the funds yet.

What are my options right now? I just want to cruise until I can afford a rebuild/new engine. What harm will be caused with a cylinder not firing? How often should i change my oil, now that fuel is probably leaking into my oil pan?

Let me know what ya'll think.

Sep 29th, 09, 4:17 PM
Swap a plug wire from one that's firing and see if the 'not firing' follows the wire.
If it does ,get new wires.
Pull the plug on #5 and have a look see.
Might swap plug same as wire to see if that moves the problem.
If it does get new plugs.
If those don't work ,pull the valve cover and see if the rockers on #5 are moving the same rate as the others.

Sep 29th, 09, 4:20 PM
What was the compression in the cylinder not firing?

Sep 29th, 09, 4:47 PM
Didn't the mechanic you were talking to give you some idea of why that cylinder wasn't firing? Did he perhaps suggest what to do to fix it?

Probably in the plugs, wires or distributor cap. You could probably replace them all for less than $100. If the cylinder has compression it's not a bad valve or bad rings so that's a good thing. One misfiring cylinder doesn't necessarily mean you need a rebuild.....

Sep 29th, 09, 5:04 PM
Many things can cause a cylinder to not fire, especially at idle. As stated above, pull the plug on #5 and see what you got. If it is oil-free, it should not take much to get it going again. Check for vacuum leaks , such as a bad gasket or maybe a vacuum hose on the #5 runner that is leaking. Swapping the plug and wires is certainly a cheap and effective way to start.

Sep 29th, 09, 5:23 PM
Thanks for the suggestions.

within the last 200 miles i've replaced the
- distro cap and rotor
- upgraded wires to 8.5

I believe the test yielded zero compression, but I'll call to make sure. the shop suggested it might be a warn camshaft lobe. i'll swap plugs, and see how that goes.

Sep 29th, 09, 5:45 PM
You might have mentioned that you had 0 compression in your 1st post.
All you said was
my compression ended up being much higher than I was originally told
but no other info.

Sep 29th, 09, 5:46 PM
Well, that's a whole different ball game. If cylinder #5 has no compression, no amount of ignition parts will fix that problem. First you stated it had compression now you say it does not. Which is it? The route to fixing things is a WHOLE lot different depending on whether that cylinder has good compression or not.

Sep 29th, 09, 6:04 PM
OK ,back to what I said earlier
pull the valve cover and see if the rockers on #5 are moving the same rate as the others.
It'll make a difference if it's the intake or the exhaust as to any further damage.
If the intake isn't working ,they'll be less flow of air/fuel into the cylinder so less cylinder washdown.
If it's the exhaust, the engine will be fighting the compressed air/fuel as it's got nowhere to escape.
Also keep in mind that if you've wiped a cam lobe or 2 ,that you now have metallic debris floating around the inside of the engine - not good.
Keep us posted.

Sep 29th, 09, 6:53 PM
sorry for the confusion, the first shop that ran the compression test told me it was 75-80 psi, on all cylinders. i thought that was pretty low so i brought it to another shop and said my compression is 120 psi for most of them...one was 110, and Johnny #5 was not not alive.
**just called the shop and they said #5 still had compression at 120psi and it did indeed have spark**..so i guess i won't be swapping plugs.

if it's the camshaft lobe...that's bad. I'll have to pull the valve covers to check.

thanks for all the suggestions so far....any other suggestions?

Sep 29th, 09, 7:33 PM
**just called the shop and they said #5 still had compression at 120psi
MORE than enough to make the cylinder run; although not as much as you might want it to have. I like ~150 as a minimum.
and it did indeed have spark**
WHERE did it have spark? At the plug end of the wire?

..so i guess i won't be swapping plugs.
A fouled plug, or one with a damaged porcelain (cracked, for instance) will still cause a dead cylinder even if the wire leading to it has spark.

You have compression, you (probably) have spark. After verifying the condition of the plug, you'll be looking for the vacuum leaks as previously suggested.

Although the camshaft/rockers may be going bad--if you have compression the cylinder should run. Valvetrain is not the first thing I'd be checking, here.

Sep 29th, 09, 8:21 PM
i'm checking my notes from my first shop and they said
nox system unit removed and vacuum hoses need to be hooked up correctly

also mentioned in my notes are
the PC system needs the right pcv valve and hose
i have no idea what this does.

oh look at this...found at the very end of my notes
needs to repair vaccum leaks

interesting. I'm going to have to take a look at this. fingers are crossed, I hope the vacuum leak is the problem.

thanks everyone.

Sep 29th, 09, 8:30 PM
I think you should of bought a compression gauge for $30 bucks and saved yourself some time and money. If you don't know how to check your compression then, that's when this site comes in handy and we/somebody will walk you through it. Just a thought. But if you have 120psi, thatís more than enough pressure to fire that johnny boy unless you wiped the cam. Yup time to pull the Valve cover.