I been messing around with my motor today and realized No 1 cylinder is not firing....Pulling the plug wire while the engine is running has no affect on the motor...Pulling any of the other causes the engine to stumble a bit...I pulled the plug and checked to be sure it is firing and it is getting spark...Me and my uncle checked again to be sure the No 1 was at TDC...I checked for compression and it reads identical to the others..I took off the valve cover and I could see the the valves working properly. What could be causing this problem....

 

Bad wire, distributer cap or plug ? although you said it was getting spark? Maybe bad cam lobe?

 

I tried a different plug,,,plug wire,,,,same result,,,I pulled the dist. out several times to check timing and put it where no 1 would be using a different terminal,,,,same result,,,,I dont no what else to do..The plug is getting spark,,,Good compression,,,

 

Vacuum leak? What color was the plug?

 

the plug looked pretty clean,,and appeared wet...
If tdc is correct
plug good
wire good
what else could it be


Iam am only getting around 120 psi on each cylinder,,,,is this low

 

I assume you inspected the disty cap for a burned terminal.
Very odd problem...

 

So you had not noticed any problem with the running or performance of the engine, but you pulled the #1 plug and it didn't affect the idle speed, so you want to know if something's wrong?
You have a confirmed good spark to the cylinder, normal valve movement (does not exclude bad seats), and compression you can feel (did you measure it with a gauge, if so what were the pressures for all eight cylinders?).

Number 1: On a big V8, sometimes dropping a cylinder will have surprisingly little effect, but dropping 2 will be noticeable. It may just be that the change in idle isn't significant when that plug is pulled.
I would try warming it up and carefully watching a good tachometer and vacuum gauge, and writing down the readings before and after pulling the plug wire for each cylinder. See if there's a pattern. See what changes if you pull them in groups of 2. Last week I was working on mine and forgot I had pulled 3 wires. It started right up, but sounded a little wrong. Took me a minute to remember and reconnect them, but it wasn't running all that badly.

Number B: If you connected the spark plug wires to the distributor in the just the right wrong way, you could have most of them firing about right, but #1 firing on exhaust instead of compression. Double check that on compression the rotor is pointing to the #1 terminal (and not opposite), then double check that the other wires are connected in the right firing order (cast into the intake manifold) from there.

- Eric

 

In my experience, a wet plug isn't firing at all!
You didn't mention brand or heat range, but try switching that plug to #3, and see if your miss "follows"!
Could be a bad plug - -

 

I tried putting it in #3 with the same results....My compression test are as follows,,Are these numbers to low for a newly rebuilt 455,,,,I know i have the low compression pistons..
1-120
3-120
5-130
7-120

2-90
4-120
6-100
8-100

 

From research here on this website,,it appears the psi is way off...way 2 low,,iam going to talk to the machine shop tonite that did my motor

 

Engine fully warmed up, throttle fully open, cranked until numbers don't go up anymore?

 

with the engine warmed up iam getting around 120psi on each cylinder

 

That's way too low.

It doesn't matter if you have an 8:1 motor, or a 10:1 motor. Compression should be up around 180psi.

Is that the Cold cranking compression with the carburetor held at wide open throttle?

 

Unless you've a cam with overlap in it!

 

a cam with over lap in it,,what does that mean

it is cold cranking compression

 

Do you still have 90 in #2? That would indicate a problem.

In a newly rebuilt engine with a stock cam you should see 150-160 or so. But again the 90 in #2 is a problem.

 

I just went out and did a compression test again with the motor cold because i have the dist. pulled out from last night....Cylinder 2 was 90 psi with all spark plugs removed and throttle held wide open..

 

Squirt some oil into each cylinder and see if it goes up!!! possibly a a stuck or broken ring!!

 

Did you do this on purpose for laughs or just make a typo?

 

In Hi-Po cams, there is a longer duration that each valves open for air flow.
The degrees both are open at the same time, is considered overlap, which will reduce your cranking pressure.
If you've an aftermarket cam, all this will be listed on the cam card.
On the front of the cam, there should be a manufacturers name, and the numbers represent the 'grind' of the cam. Call them and you can get the lift, duration, etc. for that particular cam.

With #2 being low on the opposite bank, I can't imagine that affecting #1!
If you're talking about the cylinder next to it, #3, I'd suspect a head gasket problem.
Did the shop assemble the engine, or just the short block??
Who did the heads?

 

It was subtle commentary.

- Eric

 

they assembled the whole engine,,Mikes machine shop did all the work,,,

 

Me and my uncle pulled the intake off and found the valleypan gasket didnt seal the intake and head allowing coolant to flow into the intake valve and fouling out No 1,,,,

 

Well, that'd do it.

 

Iam glad i found it...It was driving me nuts..The machine shop seemed very releived..They ordered me a new valley pan and front rear intake seal...

 

should i use a valley pan or use the 4 piece intake gasket set...

 

Glad you got it figured out by all the comments the guys on this site are pretty darn helpful. I would like to bump this also and was wondering what the answer on using the valley pan or the the gasket set
________
CALIFORNIA MEDICAL MARIJUANA

 

I have had issues with the metal valley pan intake gasket sealing properly on engines that have had the deck milled or the heads milled. the metal gasket needs to have all the surfaces parallel and true for them to seal right. I usually use a composit gasket and they seem to seal better. at least for me they do.