Dead Cylinder

[Steves LX]

Well just as my luck would have it I figured out what part of the problem is. I pulled all my plugs out the other night and one of them was black and the rest were normal. So I replaced the plug and drove the car and it ran fine for about a 1/4 mile and then as soon as I stopped and took off again the dead miss was back. So I pulled that plug again and it was starting to get dark in color also that quick. So I did a compression test on that cylinder(#6) and the needle doesn't even move. So I moved over to # 5 and it was only at 70 best. So I pulled the valve cover off and removed the rockers for #6 and tried again and still nothing. The needle just jumps back and forth on zero. So I assume that means bad news now. I guess maybe a head gasket and if it is, why. Mind you I just got the car back together the other night and its been having this problem since I started it the first time. Stupid question for you also. The head gaskets I put on are 8548PT2. The block is .030, is there a certain head gasket I need for that or can I just use a stock head gasket like the one I am using. The other thing that confuses me is my oil is fine and so is my coolant. They are not mixing. Also this miss and running like poo is from a dead stop up to about 4000 RPM's and then the exhaust sounds more clear and crisp and the car seems like it want to go but anything under that RPM you can kiss that goodbye. Its an absolute pooch. I need some help here.

[ibstrokin]

I have seen leaking intake gaskets cause plugs to foul in one cyl. When you do a comp test you have to have the rockers on, otherwise you have no air in the cyl to compress. You should also prop your throttle body open to help fill the cyl.'s. Your head gaskets are for up to 4.100 bore, you are at 4.030, so they're fine.

[Steves LX]

I have seen leaking intake gaskets cause plugs to foul in one cyl. When you do a comp test you have to have the rockers on, otherwise you have no air in the cyl to compress. You should also prop your throttle body open to help fill the cyl.'s. Your head gaskets are for up to 4.100 bore, you are at 4.030, so they're fine.

Well either way with the rockers on or off I had no compression on # 6 cylinder. And I had the TB wide open on every cylinder we tested. I tested it 3 different times.

[ibstrokin]

Squirt a little oil in the cyl, if comp spikes, you could have ring trouble. Or with the engine running, squirt starting fluid or propane around the intake near #6 cyl, if your idle changes, that may prove if you have a intake leak or not. No compression at all sounds bad, that's odd, post up what you find.

[Steves LX]

Yeah I didn't squirt any oil in there. I will try that tonight when I get home from work. But yes I thought the same thing as far as no compression at all. That's why I tried it a few times and checked all the other cylinders out as well. I hope whatever it is it's simple. I actually have already hosed the the whole intake,TB,and vacume lines down looking for vacum leaks and of course my idle didn't change a bit. But like I said earlier my vacum is only at 8 in. at a warm idle. So I know I have something going on along with the no compression on #6 and fouled plugs on #6. And this cam is in straight up and its only a TFS stage 1. My f cam had more duration and lift than this thing and my vacum with it in was 12-15 in. at a warm idol.

[blacksn95]

maybe that nitrous caused some detonation and torched the piston or a head gasket .... hopefulley its something stupid keep us posted but man if your gonna spray i would invest in a wideband to tune with. Is your lower end forged ive craked a hypercrap piston before right at the ring glands.

[Steves LX]

I haven't sprayed this motor since I put it back in the car the other day. I dont even have my nitrous kit anymore I sold it and have yet to install a new one. I'm still trying to get it to run on motor much less nitrous. But good thought. Also all my internals are forged.

[Black Horse]

A couple of other things to check before you start pulling it apart. Make sure the valves are closing all the way. A bent valve could cause an issue like that. If you dont see anything like that, use your air compressor and the compression tester hose - roll the piston to the top and see if you can use the compressed air to cause the stroke. If it doesnt budge, you have a big issue somewhere. (You can use the compressed air into the cylinder to help check for leaking valves too - listen for the hiss).

Squirting the oil in the chamber is a great idea. If your compression comes up its rings..if it doesnt change its head/valve.

If this doesnt tell you anything, its time to pull the head.

Oh...and leaking intake manifold gaskets will not cause a drop in compression.

And...check that the compression gage is seated all the way and the plug threads are not pulling out (they are not heli-coiled are they?) It sucks to pull a motor apart to find that the o-ring fell off of the compression gage.

Good luck, keep us up on the status.

[RIXXX93GT]

Do a leak down test.

[Steves LX]

A couple of other things to check before you start pulling it apart. Make sure the valves are closing all the way. A bent valve could cause an issue like that. If you dont see anything like that, use your air compressor and the compression tester hose - roll the piston to the top and see if you can use the compressed air to cause the stroke. If it doesnt budge, you have a big issue somewhere. (You can use the compressed air into the cylinder to help check for leaking valves too - listen for the hiss).

Squirting the oil in the chamber is a great idea. If your compression comes up its rings..if it doesnt change its head/valve.

If this doesnt tell you anything, its time to pull the head.

Oh...and leaking intake manifold gaskets will not cause a drop in compression.

And...check that the compression gage is seated all the way and the plug threads are not pulling out (they are not heli-coiled are they?) It sucks to pull a motor apart to find that the o-ring fell off of the compression gage.

Good luck, keep us up on the status.

Appreciate it Dave. I would assume that my vacum being low would be because the car is only hitting on 7 cylinders or is that not a safe assumption? I am going to do a leak down on it tonight. I will post up what I find later tonight.

[Black Horse]

Appreciate it Dave. I would assume that my vacum being low would be because the car is only hitting on 7 cylinders or is that not a safe assumption? I am going to do a leak down on it tonight. I will post up what I find later tonight.



Hard to say..It COULD be...or not.....you may have multiple issues...but it also may point to a intake valve not fully closing

Find anything yet?

[Steves LX]

Hard to say..It COULD be...or not.....you may have multiple issues...but it also may point to a intake valve not fully closing

Find anything yet?

Well here's the deal. I did a leakdown test tonight and started with #1 and went thru the firing order. # 6 is the problem child with black plugs and no compression. Well low and behold all the air is going straight into my upper intake. It's showing 30-60% loss. 30% or so if I leave the Throttle plate closed but if I open it it goes to 60%. You can feel the air coming out of the TB. Now if I loosen up the rocker it makes a woosh sound and no more air in the upper but if I tighten the rocker back down it makes that sudden woosh sound and starts blowing thru the upper again. I am assuming that means bent valve and if so I have the slightest clue when that happened. The car's been this way since I dropped the motor back in it last week. All my push rods to the best of my knowledge are all the same length. Stock length 6.243. On # 6 thats the only place you can hear it. I checked the dipstick tube,pcv,lifter valley,and the spark plug hole on either side of # 6 which would be 5 and 7 and you can't hear any air. It's all in the upper intake.

[dedpedal]

Sounds like that rocker is adjusting the valve off the seat. I would swap that rocker to another cyl and see if the problem moves. It could also be a frozen or collapsed lifter thats not allowing the valve to fully seat.

[Black Horse]

Sounds like that rocker is adjusting the valve off the seat. I would swap that rocker to another cyl and see if the problem moves. It could also be a frozen or collapsed lifter thats not allowing the valve to fully seat.


Good diagnosis! Also check to make sure the pushrod is seated in the lifter depression.

[Steves LX]

Well last night I decided to mess with the car agin and I started with a .060 shim under the pedastal and air was still leaking into the manifold on the leakdown. So I addede .030 more for a total of .090 and no more leakage. It was gone. So I am not sure what the deal is here. But my pushrod on # 6 intake is the same length as the rest of the. I also swapped that rocker out with a different one and that did nothing it still leaked. I spoke with a couple different machine shops and they said if the valve was bent it would be smaller and it doesn't sound like a bent valve. I have half the mind tonight to go ahead and start it and see what happens since I shimmed up the rocker. I just dont want to screw nothing up though. Any thoughts guys?

[kennebellcobra]

Lay a straight edge across the valve tips and see if that one is sitting higher than the others.

[12seclx]

Lay a straight edge across the valve tips and see if that one is sitting higher than the others.

X 2..... :rockon:

[Black Horse]

Does this head have steel valve seat inserts?

[ibstrokin]

If a shim caused you that much trouble, I would look into an adjustable valvetrain.

[dedpedal]

also, if someone replaced that valve, its possible that the replacement is too long. Check that. Im not sure on this next thought, but could it be possible that the valve seat is too deep in the head , allowing the valve to sit higher?

[Black Horse]

also, if someone replaced that valve, its possible that the replacement is too long. Check that. Im not sure on this next thought, but could it be possible that the valve seat is too deep in the head , allowing the valve to sit higher?


Or the seat insert is busted

[Steves LX]

Well as far as the heads go they are brand new. I dont know if they have steel seat inserts or not. I could call Ford Racing today and ask them. I am going to lay a straight edge across them this weekend. I will let you guys know what I find.

[Black Horse]

Whatcha find Steve?

[NXcoupe]

Sounds to me like a lifter is stuck in the up position, and it isn't preloading. Just a thought, but you might want to crank the engine a bunch with the distributor unplugged to let the lifters bleed down, if the intake rocker is still solid and won't move on that one, then the lifter plunger is just frozen.