Dead on 2 and 4

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Blackhatguy

Blackhatguy

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I need to pick some brains here, mine is shot at the moment.

I'm getting no fire on cylinders 2 and 4.

I pulled all of the spark plugs and tested cylinder compression, every single cylinder is within 3 pounds of 140.

I have not done a leak down test yet, but the leak down tester has been ordered.

I put spark plugs in number two and four spark plug wires, grounded them and had my wife turn the key. I am getting strong spark from both.

Any ideas on what I'm missing? Other six cylinders run fine, just two dead cylinder side by side that have compression and spark. Any reason why those two cylinders wouldn't be getting fuel? I don't see any other signs of bad gaskets, no backfires, no pressure bleed between the two cylinders that I can see..

Got to be missing something here??
 
Curious, what is your indication that those two cylinders are dead ??? If they have hot spark, and good compression, what choice would they have?? Unless a rag went down the intake and plugged those two intake ports so they get no gas... I mean....
 
You are going to be asked to give a rundown of the engine combination and the details around the problem such as when it started and how the car was being driven. You may as well start with giving those details.
 
Blackhatguy said:
I need to pick some brains here, mine is shot at the moment.

I'm getting no fire on cylinders 2 and 4.

I pulled all of the spark plugs and tested cylinder compression, every single cylinder is within 3 pounds of 140.

I have not done a leak down test yet, but the leak down tester has been ordered.

I put spark plugs in number two and four spark plug wires, grounded them and had my wife turn the key. I am getting strong spark from both.

Any ideas on what I'm missing? Other six cylinders run fine, just two dead cylinder side by side that have compression and spark. Any reason why those two cylinders wouldn't be getting fuel? I don't see any other signs of bad gaskets, no backfires, no pressure bleed between the two cylinders that I can see..

Got to be missing something here??
Click to expand...
Have you pulled the valve cover to see if the intake valves are opening?
 
G70464 said:
Have you pulled the valve cover to see if the intake valves are opening?
Click to expand...
would the OP have compression on the cylinders in question if it they were not?
Blackhatguy said:
I pulled all of the spark plugs and tested cylinder compression, every single cylinder is within 3 pounds of 140.
Click to expand...
 
If you've got compression, spark and fuel, the cylinder should not be dead. Since you have compression, unless as mentioned above, you have a rag in the intake, I doubt that fuel is the problem, so....
I would start with either new plugs, or plugs that you know fire, cause they were in other cylinders of your engine. Then, I would either swap some wires from another cylinder onto 2/4, or new wires, and see what happens.
My bet is still an electrical problem.




(But pull the carb, and look for a rag, lol)
 
Maybe a bad vacuum leak by those two cylinders? When it's running, what does the manifold vacuum look like? Does dribbling a bit of gas down the carb smooth things out?
 
I had some errands to run and a kitchen faucet to put in for the wife, my payment for having her help me work on the car (turn the key ). That helped to take my mind off of the car for a minute and now that I'm a little less frustrated I want to thank you guys for jumping in so quick.

This is a magnum 5.9 engine that I built 5 years ago, 3 years ago I had a head gasket blow between 1-3 on that head in question, but it was on the odd bank at that time. Now that head is on the even bank so 1-3 has moved to 6-8, and the problem now is on 2-4.

Heads are heavily ported factory 2001 casting, floors have been raised with epoxy (thinking I should pull the manifold and check that it has not come loose)

manifold is the speedmaster air gap copy, also heavily ported with floors raised by welding.

Carb is Street demon 750.

Ignition is large cap HEI with pertronics module.

Since the last head gasket change, motor has run strong for 3 years until 3 weeks ago. I went on a little joyride, aerosolized a little bit of rubber off my tires, then made a 40 mile round trip to the hardware store. About 3 miles from the house I noticed it was running really rough and tried to die at the stop sign near the house. I pull into the garage and pop the hood, pulled spark plug wires with it running to check for dead cylinders and found that two and four make no change when I pull the wires. I then hit the tubes with a spray bottle of water and found them to be very much colder than the rest. I then inspected the distributor cap and found that it was loose because two of the hooks came undone. While I was pulling wires, a couple of them became damaged because they are older so I replaced them with brand new wires, cleaned all of the spark plugs, inspected to the contacts in the cap and found them to be clean so I put it back on and made sure it was on correctly this time securely with the hooks, and I still have two dead cylinders. As I mentioned, I still have yet to do the leak down test but compression is perfect. I did the compression test with all spark plugs out of the engine so it would not build pressure between cylinders in the event the gasket is blown out between two of them. In all of this, I never had the intake or a carburetor apart and it was running flawlessly until it wasn't.

IMG_20220806_005529.jpg
 
I don't know anything about the HEI type ignitions but is it posable that whatever triggers the HEI to fire on 2 and 4 is now damaged by the cap not being secured????
 
If the compression is good, the leak down test won't find the current problem for you. As mentioned, I'd pull that valve cover and watch the valve/rocker action first. If that looks fine, I'd then pull the carb and run an inspection camera down into the head ports to see if there's a blockage there somewhere. This is all assuming that there isn't a massive intake leak causing those cylinders to totally lean out.
 
I know this might sound crazy, but I read in a tech section of a magazine where someone had a miss like this, and the answer was that the distributor needed to be grounded. Easily tested.
 
Dana67Dart said:
I don't know anything about the HEI type ignitions but is it posable that whatever triggers the HEI to fire on 2 and 4 is now damaged by the cap not being secured????
Click to expand...
That was one of the thoughts I had, but they do have strong spark after I get it put back together..
 
cudamark said:
If the compression is good, the leak down test won't find the current problem for you. As mentioned, I'd pull that valve cover and watch the valve/rocker action first. If that looks fine, I'd then pull the carb and run an inspection camera down into the head ports to see if there's a blockage there somewhere. This is all assuming that there isn't a massive intake leak causing those cylinders to totally lean out.
Click to expand...
I did notice when I pulled the spark plug that it did not smell like gas, I have no idea why it would not have fuel, they are not even on the same plenum..
 
I'm thinking something in that distributor has gone awry. That's where the problem seems have have originated with a loose cap. The problem is deterministic, those two cylinders, which eliminates a carb or fuel problem unless you sucked a towel into the intake. There's no reason the other cylinders would be getting fuel and those two not. I don't think it would be a head gasket with good compression but I'm wondering if it could have let go in between those two cylinders?
 
It was suggested that I pulled the valve covers to check the rocker arms, and since I am out of my own ideas I went ahead and did so. Exhaust valve spring on cylinder 2 is broken. I guess that's why it took a couple of extra turns to get a good reading on the compression tester. Air pressure was closing the valve after a few revolutions. Still don't know about number four just yet, but I definitely have a good reason for number two not to fire
 
I bet the intake gasket took a crap, if the distributor checks out ok.
 
oldkimmer said:
Change the cap and rotor. Kim
Click to expand...
I certainly will before it comes back together, looks like I have to pull the whole top end off of the motor and run through the valve train. If I can have one broke spring I can have another sooner than later
 
cudamark said:
Check for coil bind on the valve springs.
Click to expand...
Got plenty of clearance on that front, they are good to .575 and I am at .555 at the exhaust.

Thinking back a few years, I installed the pushrod incorrectly on that spring once, push rod was sitting on the lip of the lifter, I cranked it up and bent the push rod. Turns out I must have damaged that spring back then and it just took 3 years to complain about it.
 
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