1980 302 cylinder 8 not firing.

[Kai_Kraft]

I have a 1980 block with stock bottom end. Has edelbrock heads, intake, and carb, with a Lunati cam. The issue is that cylinder 8 is not firing. It has a new mallory distributer and new spark plugs and wires. I first thought it was spark, so I slapped a spark plug test light on their and I have spark. I then switched the spark plugs around and nothing changed. So it must not be spark. I then did a compression test and everything was 140psi while the engine was cold. So it has spark and good compression so I felt that it must be fuel. So I rebuilt the carb and nothing changed. So then I put my friends carb on it and still no change. So it's not fuel or spark or compression. I pulled the valve cover off and looked at the rockers while it was running and they look like they are moving properly. I have no clue what to do from here. If you guys have any questions or any ideas please let me know.

 

[CarMichael Angelo]

I have a 1980 block with stock bottom end. Has edelbrock heads, intake, and carb, with a Lunati cam. The issue is that cylinder 8 is not firing. It has a new mallory distributer and new spark plugs and wires. I first thought it was spark, so I slapped a spark plug test light on their and I have spark. I then switched the spark plugs around and nothing changed. So it must not be spark. I then did a compression test and everything was 140psi while the engine was cold. So it has spark and good compression so I felt that it must be fuel. So I rebuilt the carb and nothing changed. So then I put my friends carb on it and still no change. So it's not fuel or spark or compression. I pulled the valve cover off and looked at the rockers while it was running and they look like they are moving properly. I have no clue what to do from here. If you guys have any questions or any ideas please let me know.

I'm curious as to why you think it's not firing?

 

[Kai_Kraft]

The truck has no balls. Super slow and super underpowered. I took a squirt bottle amd squirted water on all the headers and cylinder 8 header was not evaporating the water. After running the engine for a little bit you can touch the that header but everything else will be screaming hot.

 

[Wayne Waldrep]

If you have compression and spark what's left? Fuel. There's not much of a chance that only one cylinder isn't getting fuel in a carb application. The squirting water test wouldn't be something I used as an accurate test but that's just me.

 

[Kai_Kraft]

That's the issue I'm having, I dont know why its not firing. When I pull the spark plug out it is not wet and does not smell like fuel. The plug also looks brand new. I'm honestly thinking it's a vaccum leak that is just effecting that cylinder.

 

[CarMichael Angelo]

That's the issue I'm having, I dont know why its not firing. When I pull the spark plug out it is not wet and does not smell like fuel. The plug also looks brand new. I'm honestly thinking it's a vaccum leak that is just effecting that cylinder.

Is the plug coloring? The only way that I'll believe that the plug isnt firing is if it comes out as clean as it went in.
If it has color on it, its firing.
The fact that you think it has no balls, is by far the most unscientific diag I've ever heard of.
A.Is the engine running like it has a dead cylinder?
B. Does the buck, cough, misfire, or do anything weird while under hard acceleration?
If the answer to either question is no,
You may just have to get used to having a ball-less running car..
I thought all of you n/a 5.0 guys were used to that?
Welcome to the society of the golden Geldings.

 

[Kai_Kraft]

It idles rough, it has open headers and if I put my hand in front of that header on that bank it feels choppy when compared to the other side. The engine also shakes at idle. It revs up slow but alright. 2 weeks ago i could spin the tires in second gear. Now it barly has any get up and go. Its slower then my stock Camry. And the spark plug looks brand new, exactly how I put it in. It also idles at 1200rpm and will stall if I try to adjust the idle down

 

[Wayne Waldrep]

Camshaft lobe on eight is gone. That or I agree with nothing being wrong with it.

 

[Kai_Kraft]

I pulled the valve cover off and all the valves look like their moving the same, and none or loose or doing anything weird. I think it's a vaccum leak that is just effecting cylinder 8. The cam and all the valvetrain is new. Just put on a couple weeks ago.

 

[Olivethefet]

Did it just start doing this all of the sudden or did you just do some work to the motor and then it started? Even if it had a vacuum leak I would think it would still at least smell like gas. It takes fuel, air, and spark to make the magic happen. If you just worked on it I hope nothing got dropped into the intake that is blocking the runner.... I just dont see how you could get air and fuel to the other 7 and leave number 8 dry.

 

[Kai_Kraft]

I figured out the problem. It was a vaccum leak. Runs great now.

 

[Olivethefet]

Where was the leak?

 

[Kai_Kraft]

Their is a port all the way in the back of the intake for a vacuum line for the trans and it was rotted out. I slapped a new vacuum line on and now all 8 are firing. The port for the vacuum line was right on the runner for cylinder 8. I feel stupid for not seeing it. I've been trying to figure this out for 3 weeks and I just found it... pretty sad. But happens, learned a lesson. The danger ranger is back! (For now)

 

[Olivethefet]

But happens, learned a lesson.

Amen to that! I know I've had to learn thing that way plenty of time....