[46flatty]

So I have posted this over on mud but I figured Id post it up here and see if anyone has any ideas.

My 2f is missfireing on cylinders 5 and 6. If I remove wither of the two spark plug wires the motor will actaully idle better. It seems that 6 affects the idle the most. It will actually kill the engine if it is hooked up. I had the head rebuilt and installed and had the truck running great, smooth idle and decent power. I I drove the truck for a while and while backing into the driveway last week it started miss firing. I replaced the cap, rotor, plugs, plug wires, adjusted valves and even removed and re insalled the distributer to ensure proper timing. The compression has been checked and is 140 across the board. The plugs come out nice and wet so I know Im getting fuel.

I had installed a new cat and have even removed it make sure its was not blocked forsome reason, it made no difference.

 

[Pighead]

You sure you don't have the plug wires crossed? (going to the wrong plugs?)

 

[46flatty]

im sure of that. Had the cap off and everything is numbered

 

[Pighead]

I was afraid of that....

 

[46flatty]

I was afraid of that....

any other ideas?

 

[DHONDAGOD]

When mine did that (happend like a light switch) I ended up with a blown head gasket between cylinders....


Might be time for a compression check....


Chris:cool2:

 

[Pighead]

Blown head gasket was my other idea...

 

[46flatty]

i thought that as well but have checked compression multiple times. its 140 across the board. The head gasket is only a few weeks old and all the head bolts are properly torqued.

 

[Pighead]

Yeah, I noticed that in the OP...which moved head gasket out of first guess.
But, is it possible, to have an inter-cylinders head gasket leak and still generate enough compression to fool the compression tester?
And this bit about hooking up #6 sparkplugwire and having a worse idle...it's gotta be either miss-hooked up sparkplugwires or a headgasket leak between 5 and 6. Or you're badly out of time.
How many times did you re-torque the head after rebuild? And 5 and 6 are famous for burning valves due to vacuum leak at the brakebooster take off. Probably not applicable in your case though....
How do you test for an inter-cylinder headgasket breach? maybe with sparkplugs out, force compressed air in to each cylinder and listen/feel for where it comes out?

i thought that as well but have checked compression multiple times. its 140 across the board. The head gasket is only a few weeks old and all the head bolts are properly torqued.

 

[46flatty]

I am totally baffeled as to why hooking number 6 up will actaully kill the motor. I went ahead and checked for vacuum leaks at the brake booster and I am good there. On a side note the intake manifold bolts where a little loose. I tightened those up but wasnt able to get the carb back on before I had to run. Ill get it all put back together tomorrow and see what happens. FWIW I put the old cap and wires back on and the same thing. I also noticed that if I put my timing light on the number 6 wire I can see the 7 BTDC mark at the pointer. Is this nomal?

 

[Rockzar]

did you take out the plugs for those two cylinders and check they are okay- and the right plugs for your motor? Gap and all?
I would even try taking out a few plugs, including those two, and make sure everything is firing in the order you think they should- turn the rig over with the plugs in the wires- make sure the plugs fire in the proper order, and are firing at all.

 

[Pighead]

I also noticed that if I put my timing light on the number 6 wire I can see the 7 BTDC mark at the pointer. Is this nomal?

That made me think. And I almost insulted you further by asking if you were SURE you weren't 180 degrees out of time...
But, remember you can adjust both #6 valves with the line on the pointer...therefore I'm thinking that is normal.

 

[46flatty]

I think Im going to pull the head and take a look to see if the gasket is trashed. I cant imagine it is but wierder things have happened. I have had all the plugs out quite a few time and am sure Im getting spark to ALL of them. If the motor was 180 out of timimng would it even run? I dont think it would. At this point the only thinkg that makes sense is head gasket. There is not water in the oil and Im not burning coolant as far as I can tell. Im stumped.

 

[Rat70FJ]

I don't have my shop manual handy, but is #6 the third cylinder in the firing order? In my thinking that's the only way it should be firing at 7btdc. Unless maybe I'm full of shit!

 

[46flatty]

#6 is fourth to fire 1,5,3,6,2,4

 

[72fj40]

I think Im going to pull the head and take a look to see if the gasket is trashed. I cant imagine it is but wierder things have happened. I have had all the plugs out quite a few time and am sure Im getting spark to ALL of them. If the motor was 180 out of timimng would it even run? I dont think it would. At this point the only thinkg that makes sense is head gasket. There is not water in the oil and Im not burning coolant as far as I can tell. Im stumped.

Yes it will run w/the dizzy 180 out. If you installed the dizzy 180 out then #1 is at the top of the exhaust stroke and its companion cyldr will be @ the top of its compression stroke. I dont know which cyldr on your motor is #1's companion, but it would be the 4 cyldr to fire in the firing order.


Double chk the position of the rotor when #1 is @ TDC on the compression stroke. Good Luck.