With#4 plug out, I fired the engine

[Chris Lovell]

My #4 cylinder is dead. I am getting great spark with a clean plug. But when i pull the ignition wire from distributor or plug with the engine running, there is no difference at all in engine sound or idle. So, I left the plug out (plug hole leaving direct external access to the #4 chamber) and fired the engine again. The engine labored to life and the noise, loud like straight pipe blasts, came from the engine. Do you think the exhaust valve is stuck open? Does this happen? Obviously I can pull the valve covers and have a look but am seeking some experience in advance.
Thanks,
CL

Current stats:
'88 Cab 3.2
Not driven for 2 months
Mouse nest in trunk beside brake booster now removed. Little sh*$ts ate through two wires and stripped two other. All repaired.
Cold air today 32 deg. Problem still there when engine came up to temp.

[DanielDudley]

Your fuel injector is most likely the cause of this.

[Hugh R]

Why don't you put a compression gauge on the #4 plug hole and rotate the engine by hand and see what happens.

[Joe Bob]

If the hole has compression, it's the injector.

[rattlsnak]

Actually it would be better to jump the starter and then take a compression reading, but the loud exhaust type noise is normal with the plug out.

[911pcars]

Easy stuff first. Got spark at number 4 cylinder?

If so, next, take a compression test of all cylinders, then compare results before venturing further/buying anything. Must have a threshold amount of compression to produce power. If compression pressure is within specs, the rings and valves are probably working okay.

Sherwood

[Chris Lovell]

Perfect. Simple compression test first. Injector second. Yes, good spark. (don't ask how I know) Thanks all.
And, it donned on me the loud exhaust sound is normal. Duh ...

[Mitch Leland]

Like Daniel said if you have compression it's probably your injector. Sometimes you can just tap on the injector and it will kick off...

[efhughes3]

It is common for injectors to stick when a motor sits a while.

[911pcars]

If you can, swap injectors, then retest to isolate and confirm.

Sherwood

[tseybold]

This is too much I have been trouble shooting my 80SC for the last week . Installed new plugs, new rotor,cap, ran through fuel pressure tests and then decided to pull the new plugs to see how they look after a week of trouble shooting engine time only. Well I pulled all plugs and they appear to normal except no 5 looks like it's still brad new , never installed???
The car has been running crappy, like it has a head clap or something.
I checked spark all good , pulled the fuel injector this evening , getting a nice fine mist. Went on to pull some compression test, I got 120 out of no 5 and 6 etc. The lowest Igot was 110 out of no .1??
I guess next is to pull valve covers and check for problem(s) there.
If the intake valve, or spring etc was damaged would the spark plug not fire??
I like you can pull the plug wire off and no difference in running condition. The car has all the upgrades, pop off, chain tensioner, and only has around 90,000 original miles. Heres a photo of the spark plugs
Any input, Tony???

[DanielDudley]

You must have fuel and spark and air. It gets squished in the cylinder and then fires.

A clogged injector will give you no fuel, so the spark won't ignite anything, and the plug would look like it never saw combustion, because it never did.

A compression test is putting a compression testing gauge on the spark plug hole and seeing if the rings or valves are tight enough to squish the air and fuel. It will tell you if you need to take the valve covers off, which you probably don't, because your plug is so clean you are almost certainly getting no fuel hence the clogged injector diagnosis.

A compression tester is about 19 bucks at a Pep Boys type Autozone establishment. You screw it to the spark plug hole, and turn the engine over with the spark disabled. This is commonly done by unplugging the coil wire fron the dizzy, and possibly grounding it.

However... Consider that a fuel injector has a tiny little nozzle to inject a fine spray of fuel. Really tiny, for a fine mist. They clog or get stuck fairly easily, and then all the compression and spark in the world will not make a fire in a cylinder with no fuel. You can flick a Bic all day, but if you don't push down the button that releases butane, the lighter won't light.


Your lighter isn't lighting, but you have spark. You can check for fuel, or you can check for compression. My money is on the injector.

[DanielDudley]

Sorry. Read, but no comprehension. Spark plugs do occasionally come from the factory as bad units, but a cracked or worn distributor cap can ground out the spark to the plug, as can a bad plug wire.

You have exceeded the limits of my ability here. Many people have mixture or warm up regulator issues when the weather gets colder. I suppose you would want to check your head studs if you are getting a funny sound, just to eliminate them as a factor, but I will leave you to the more experienced on this.

Personally, I would throw in some Techron, on the off chance that the injector is partially clogged. It has cleaned up many minor running issues for me over the years

[ossiblue]

Originally Posted by tseybold

This is too much I have been trouble shooting my 80SC for the last week . Installed new plugs, new rotor,cap, ran through fuel pressure tests and then decided to pull the new plugs to see how they look after a week of trouble shooting engine time only. Well I pulled all plugs and they appear to normal except no 5 looks like it's still brad new , never installed???
The car has been running crappy, like it has a head clap or something.
I checked spark all good , pulled the fuel injector this evening , getting a nice fine mist. Went on to pull some compression test, I got 120 out of no 5 and 6 etc. The lowest Igot was 110 out of no .1??
I guess next is to pull valve covers and check for problem(s) there.
If the intake valve, or spring etc was damaged would the spark plug not fire??
I like you can pull the plug wire off and no difference in running condition. The car has all the upgrades, pop off, chain tensioner, and only has around 90,000 original miles. Heres a photo of the spark plugs
Any input, Tony???

If the intake valve was damaged and not opening, I'm certain you'd hear it in the valve train as the rocker arm would be banging away on a fixed object--the valve stem. If the valve was bent, it would likely be stuck open (pushed down by the rocker) and would show up as low compression. Ditto, a broken spring. It doesn't seem you have either of these situations.

Have you checked the resistance of your plug wires and connectors? If you have Beru connectors, sometimes the internal resistors break down and you will lose continuity in the plug connector under running conditions or if you test them and tap the connector at the same time. Try swapping just the connector from a good cylinder to #5 and see if the problem follows the connector.

Other than the above, I'm stumped as to what may be going on as things seem to be checking out correctly. Let us know anything you discover.

BTW, you should probably start a new thread as Chris (the original poster) still does not have a solution to his problem and responses to two different posters causes confusion.

[Flat Six]

Originally Posted by Chris Lovell

My #4 cylinder is dead. I am getting great spark with a clean plug. But when i pull the ignition wire from distributor or plug with the engine running, there is no difference at all in engine sound or idle. So, I left the plug out (plug hole leaving direct external access to the #4 chamber) and fired the engine again. The engine labored to life and the noise, loud like straight pipe blasts, came from the engine. Do you think the exhaust valve is stuck open? Does this happen? Obviously I can pull the valve covers and have a look but am seeking some experience in advance.

+1 on compression test; if good then no real issue w/rings and/or valve sealing. Should then look elsewhere.

Not trying to be a smarta$$, but did you double-check the spark plug gap and plug wire resistance? In free air (e.g., plug held against engine ground) you can get spark across a really wide gap, but not fire in combustion chamber conditions. Not likely, but worth a quick double-check.

Also +1 on injector. After turning engine off, tiny drop of fuel on injector tip evaporates/carbonizes. The more this happens, the more carbon builds up on the injector, creating flow & pattern issues (affects atomization). Add couple of months of non-op and the deposits harden more. Injector cleaner for sure (Techron's really good, and I also like Red Line SL-1 and Ventil Sauber. Remember to change oil after running through a tank, though). If injector cleaner doesn't work, I'd pull the injectors and manually clean w/spray fuel injection cleaner and a soft bristle brush. Remember to re-install w/new seals/o-rings.

Good luck, and hope this helps. Post an update when you can?

Dale

[Joe Bob]

Have you tried swapping injectors with another hole and/or measured the output per the specifications?

[zippy_gg]

It probably wouldn't hurt to send your injectors to be professionaly cleaned and tested. They will come back with new seals and a test result showing before and after. I used Witch Hunter Performance in the past and they did a great job.
Let's face it, your injectors are 20 + years old...