I just installed a new set of summit shorti headers on my 84 Z28. The headers are painted black so the paint is disenigrating away to powder on all of the primary tubes except the primary tube on the number seven cylinder. That tube still looks as if its brand new. Could this be from a non firing cylinder? The engine is a rebuilt carburated 350 with nothing real special done to it besides an edlebrock intake and edlebrock carb. Thanks in advance.

 

Running on 7 cilinders will cause heavy vibrations,slow acceleration,bad idling and strange exhaust noises!

 

<Running on 7 cilinders will cause heavy vibrations,slow <acceleration,bad idling and strange exhaust noises!

These things are not happening , but what is the explanation for the header tube not getting hot?

 

When you first start the motor and its cold,(So you don't burn yourself) pull the spark plug on that cylinder and see what happens.

Also check to see if fuel sprays out of the spark plug hole to see if the fuel injector is working.

 

i dont think i like that idea. Dont think pulling the spark plug while the car is running is a good idea. Not sure what kind of damage it could do but its probably one of the worst noises youll ever hear.

 

i highly doubt it would do any harm unless you run on 7 for an extended period of time

 

id agree about the harm thing but when you pull the plug with the car running (dont ask how i know) that cylinder loses compression out of the hole and it makes this massive popping noise that you really really dont want to hear. My sugestion while its not the cheapest is take it to a mechanic/gm dealership that has a scope and it can tell you if a cylinder isnt pulling its weight.

 

You could always let the engine run for a few min then mist some water on the headers... If the water stays then you've got a dead hole, should sizzle right off.

 

Better yet, hook your timing light to the #7 plug wire and see if it is firing, if it is a carbed engine then it has to be getting gas if all the others are (unless there is a huge blockage in the manifold) So the only other thing missing is spark. Also, if the light fires then check the plug itself, it may be defective.

 

I think he meant to pull off the plug WIRE on that cylinder while it's idling. Use a pair of insulated pliers when you pull the wire off the plug...or you may get zapped!

If your idle drops around 200 RPM's, that cylinder was firing and maybe the paint just adhered better on that tube as compared to the others...

 

Well, I'll add more things to make it clear.

To check if fuel getting into the combustion chamber, remove all of the plug wires while motor is off, and take that spark plug out. Crank the motor over, and if fuel sprays out, you know you have fuel.

If you do not feel comfortable pulling the plug while the motor is running, remove all the spark plug wires, and take the one spark plug out. Hook it up to the proper spark plug wire, making sure it is away from anything that can catch on fire. Start the motor and see what happens.

 

Try this. Its the easiest so far and shouldn't make any awkward noises.

You have a tach, right? If yes, then while it is idleing, unplug the #7 spark plug wire from the plug and check the tach to see if the revs drop. If they drop, #7 is working. If they dont move at all, then #7 isn't working.

 

how did the plug itself for that cyl. look? Was it clean/sooted up/soaked with gas? If you want to check to see if its firing, jsut unplug it (the wire) and see of the egnine runs differently. Also check the distributer cap for carbon tracking/excessive wear, spark plug gap (proper gap listed on the label on the underside of the hood), and check the resistance of the spark plug wire itself. I dont remember what it should be for the stock ones, though but something like 5k ohms per foot sticks in my head. If the wire has real high resistance or the rotor has been carbon tracked youll need to replace the rotor and/or put all new wires on. The only way that cyl wouldnt get fuel/air is if you rolled the intake lobe on that cyl., or you sucked something up that severly lodged itself in the runner for that cyl., which is unlikely.

 

The plug for that cylinder had a nice coating of oil around it. I replaced all the plugs and now the engine seems to be running stronger than before and sounds a little better. Also now the paint on the header tube has started turning color, so it seems that i was running on 7 cylinders. Before I replaced the plugs i tested it by starting the car with the wire for that cylinder off the plug then restarted the car with the wire on. There seemed to be no difference. So now my question is where is the oil coming from? Valve guides, rings?? All of the other spark plugs looked healthy.

 

Probably all of the above, since there was no combustion pressure in the cylinder it was allowed to leak past and into the bore.

 

So does this mean I have to replace the valve guides an rings in order to stop this problem from happening again?

 

you may have just had a bad plug that wasn't firing properly or just quit firing. Check the wire going to that plug for high resistance and keep an eye on the plug for signs of oil fouling.

 

Run a compression test on yoiur cylinders, sounds like that cylinder isn't as strong as the rest. If you run the compression check and that cylinder comes back with low compression, you'll need some new rings. I did that on my Wrangler and had low compression in 2 cylinders, would've been bout $650-700 to put new rings in, so I went ahead and rebuilt the motor since they have to teardown the engine anyway, something to look into if you have to go that route.

 

You either have bad rings or a bad valve. Monitor your plug and see if it starts to foul quickly again. As mentioned above, consider a compression test as well as a leak-down test.

 

I pulled the new plug from that cylinder out and it had oil around the thread of the plug and showed signs of wearing much faster than compared to the other plugs installed in my car. I did a compression check on that cylinder and got 120psi. I didn't have time to check all cylinders but was able to do 2 more and got 120 for the #3 and #2 cylinders. I'm not sure where the cylinder pressure is supposed to be, but it sounds low. Any more feed back is appreciated.