460 bbf has a dead cylinder

12681 Views 30 Replies 14 Participants Last post by Wicked Performance Boats, Jul 8, 2009

cguth

Discussion Starter · Jul 7, 2009

Long story short version. The #5 cylinder is dead. I have checked just about everything i know to check, and i am very well versed in engine diagnosis and repair. I have to be looking over something simple. Carbs are fresh predators on a tunnel ram. Head gasket is good, no cracks in the head, block, piston, or valves. I have not done a compression test or leakdown yet, i will do that tonight. But the old finger in the spark plug hole, the #5 cylinder feels just like the other known to be firing cylinders. Meaning that it is not a complete loss and even if it is low, it would have to contribute some to the engine. Valves are not sticking, and they are opening correctly. Valves adjusted on a solid roller, no flat cam lobe. Ignition is good, getting good spark to the cylinder at the correct time. When it is running, and i pull the #5 wire there is no difference in engine idle or rpm. You can tell on the over transoms that there is a dead hole on that side, and the #5 header tube is no where near as hot as the other 7. What else can it be? I need some ideas, because i know that i am overlooking something simple. Hopefully somebody will chime in.

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slowride

· #2 · Jul 7, 2009

Only way to tell for sure is a compression test. If the valves are good and no compression, you've got a ventilated piston. Burnt valves or blowing between cylinders (head gasket) should still show some compression.

cguth

Discussion Starter · #3 · Jul 7, 2009

slowride said:
Only way to tell for sure is a compression test. If the valves are good and no compression, you've got a ventilated piston. Burnt valves or blowing between cylinders (head gasket) should still show some compression.

head gasket was good, i had the head off yesterday to check it out. that is what i thought at first too, but i was obviously wrong.

snoc653

· #4 · Jul 7, 2009

The tried and true method of figuring out which of the 4 things you are missing would be the best route to go. It takes fuel, air, spark, and compression to make one run. You can check a lot of this by looking at the plug in that hole and figuring out if it has spark or not, too much fuel, ect.... If you get compression building when you stick your finger in the hole then it should be doing something when the plug wire is pulled. Hard to guess over the net, but I'd bet it's something like obstructed air path, or a bad wire. Easiest way to check the wire would be to move it to another cylinder and see if your dead cylinder moves with it. But if it's just no spark the plug should be fuel fouled when you pull it out. Good luck on the hunt.

cguth

Discussion Starter · #5 · Jul 7, 2009

snoc653 said:
The tried and true method of figuring out which of the 4 things you are missing would be the best route to go. It takes fuel, air, spark, and compression to make one run. You can check a lot of this by looking at the plug in that hole and figuring out if it has spark or not, too much fuel, ect.... If you get compression building when you stick your finger in the hole then it should be doing something when the plug wire is pulled. Hard to guess over the net, but I'd bet it's something like obstructed air path, or a bad wire. Easiest way to check the wire would be to move it to another cylinder and see if your dead cylinder moves with it. But if it's just no spark the plug should be fuel fouled when you pull it out. Good luck on the hunt.

cylinder is getting fuel, and the plug is firing. i checked resistance all the way from the cap to the plug and it shows up good. as far as too much fuel, i dont know, but the other 7 cylinders are getting enough to fire. i was thinking about obstructed air path but i am having a hard time seeing that because i just had the intake and head off to look for obvious problems. thanks for the suggestions.

2002CP19

· #6 · Jul 7, 2009

This is a dual quad motor correct?

Check your power valves, work the linkage by hand and make sure BOTH carbs are spraying fuel. This has happend to a motor I was working on before, the header was cool to the touch and the others were hot.

Wanna_be

cguth

Discussion Starter · #7 · Jul 7, 2009 (Edited)

Wanna_be_CP said:
This is a dual quad motor correct?

Check your power valves, work the linkage by hand and make sure BOTH carbs are spraying fuel. This has happend to a motor I was working on before, the header was cool to the touch and the others were hot.

Wanna_be

yes dual quad, but it dosent have holleys. i am going back to the drawing board tonight when i get home. i am just going to start from the beginning and double check everything. i have overlooked something, and it is going to wind up being something very simple when i find it. the only joy i get out of this is knowing it isnt my boat, its my cousins. my boat runs just fine.

1975sleekcraft

· #8 · Jul 7, 2009

tuliped valves ??

check your valves! if you already put the head back on, you can put a straight edge on top of the valve stems. they should all be sticking out of the head the same distance.
i only post this because it just happened to me!
your problem sounds like a dead plug!!

2002CP19

· #9 · Jul 7, 2009

Try flipping the dizzy cap 180* and rewire it. See if the same hole is dead. 1-5-4-2-6-3-7-8 Good luck!

cguth

Discussion Starter · #10 · Jul 7, 2009

1975sleekcraft said:
check your valves! if you already put the head back on, you can put a straight edge on top of the valve stems. they should all be sticking out of the head the same distance.
i only post this because it just happened to me!
your problem sounds like a dead plug!!

looked at the stems yesterday just to be sure they werent mushroomed. and when the head was off they were all closed. a sticking vlave should have shown up on the vacuum gauge.

cguth

Discussion Starter · #11 · Jul 7, 2009

Wanna_be_CP said:
Try flipping the dizzy cap 180* and rewire it. See if the same hole is dead. 1-5-4-2-6-3-7-8 Good luck!

now this i will try, but i have already ohmed the all the way from the cap to the plug and it is checking out ok.

2002CP19

· #12 · Jul 7, 2009

cguth said:
now this i will try, but i have already ohmed the all the way from the cap to the plug and it is checking out ok.

Ford ignitions do some weird stuff. Let us know!

scott foxwell

· #13 · Jul 7, 2009

Do a compression check, and not with your finger. You're wasting your time untill you do.

SS496

· #14 · Jul 7, 2009

A wire can ohm out OK and still be arching out to a ground.

Take a spray bottle of water and mist the wires/cap/coil (secondary system) with the engine running and see what happens (if the engine is back together). This is a very easy intial check that I do whenever an engine is misfiring.

cguth

Discussion Starter · #15 · Jul 7, 2009

SS496 said:
A wire can ohm out OK and still be arching out to a ground.

Take a spray bottle of water and mist the wires/cap/coil (secondary system) with the engine running and see what happens (if the engine is back together). This is a very easy intial check that I do whenever an engine is misfiring.

i was running it in the dark, it isnt arcing externally. when i pull the plug wire off, it arcs out of the boot at the cap to the dist. base.

cguth

Discussion Starter · #16 · Jul 7, 2009

steelcomp said:
Do a compression check, and not with your finger. You're wasting your time untill you do.

not true. there is no magic number that it has to have, but it has to have something. if it has enough compression to blow my finger out of the hole, it should be able to contribute to the engine output. but, i do plan on compression and leakdown checking tonight. i just didnt have my tools at the house for that last night. hopefully the brainstorming session can help me out. thanks for all of the suggestions so far.

76Elim

· #17 · Jul 7, 2009

Did you make sure the plug itself had spark?

slowride

· #18 · Jul 7, 2009

If you have spark, fuel, correct valve movement and timing, then obviously you have a shop rag stuffed in the #5 intake port.

sphss

cguth

Discussion Starter · #19 · Jul 7, 2009

slowride said:
If you have spark, fuel, correct valve movement and timing, then obviously you have a shop rag stuffed in the #5 intake port.sphss

sounds so obvious, but i dont have anything in there. tonight i am going to start all over. hopefully i will be back tomorrow saying i fixed it and be able to tell you guys what stupid mistake i made. just waiting on 5 o'clock

cguth

Discussion Starter · #20 · Jul 7, 2009

76Elim said:
Did you make sure the plug itself had spark?

yes sir i did. i even had all plugs out laying on the headers while rotating it over to compare the spark color. all light up nicely at night by the way.

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