Missing on the 6,8 I have done everything. Please help

[fire120ball]

So I have had a terrible misfire on the sixth and the eighth cylinder. It was worse before I did all of this stuff but its still bad enough. I have replaced the wires, the cap, rotor, points, I have replaced the condensor twice, Re-gapped the plugs (Plugs have under 10K on em), hit the plugs with some sand paper to clean them up. I checked if it has spark... It does, and then today I went to check out how the spark was.. And it was yellow, Which I know its supposed to be blue, and I THOUGHT it was a valve or needed to be relashed, now that I see the voltage is not good. What should I do!?!!?? replace the Distributor? all of the other cylinders seem fine. when I pull the plugs,. Please any help would be awesome!

[russgt]

you are running an HEI ignition and not points right? double check firing order and do a compression test to rule out a valve problem

[datguysaL]

i had a similar problem. i did all ignition checks and all. turned out to be the carb that was causing it. it was just dirty.


check the spark on the other cyllinders. are they all yellow or just 6 and 8?

[fire120ball]

Carb problem? Mine is pretty dirty, I never though about it, once my battery is completley started (from all the failed attempts), I will see if the spark is yellow, and post a update. Thank Guys!

[geezer#99]

Do a compression test. Sometimes a bad misfire on adjacent cylinders is a blown head gasket. 6 and 8 are side by side.

[Corts60]

I agree with above. Try all that stuff first and if you have played with the carb recently, check and make sure you didn't crack the base plate that contains the butterflys. I scratched my head for days trying to figure out a misfire and it was a cracked base plate on my Edelbrock.

[GMC Guy]

may be time to convert to HEI :]

[fire120ball]

Originally Posted by GMC Guy

may be time to convert to HEI :]

Greg trust me! I have had MSD on my mind... lol

[ElGracho]

You aren't numbering the cylinders like a F**d are you? For a Chevy...

[fire120ball]

No no no, ha, that is the first thing I checked. the order is correct, any other ideas guys? PLEASE

[gchemist]

Did you check compression? You can't go any further until compression is checked. A mechnical problem can only be found with a compression check.

[GMC Guy]

ya man, go down and borrow a compression gauge from autozone, unless you have one.

[billnorman]

Double righto on the blown head gasket. also, check the valves to see if they all move the same distance, if #6 or#8 has a tight intake or closed exhaust it may be killing the adjacent cylinder. How do you know those 2 are bad? Seems that a bad intake gasket could be causing this, spray the intake near the cylinders with carb cleaner see if the RPM goes up. See if you have a vacuum tap in the manifold that's leaking.

[fire120ball]

So I have now replaced everything that has to do with ignition, ran a compression test, highest number was 195 and lowest was 183. So thats good. I relashed all of the valves, put another new set of plugs in, all new wires today also, reset the timing, reset the point gap, and adjusted the dwell. So now im basically $200 into failed stuff. It doesn't sound bad at idle, you can hear a puttering noise coming out of the left side (driver) at idle, but once you give it throttle, you start hearing a little bit of clanking if you throttle it just rite, I cleaned my fuel filters all up, gave the carb a half tune-up/cleaning (Its brand new). next two things I can think of, is to replace the distributor itself, and purge my gas and put in fresh gas. The gas should not be bad, but who knows. Please fellas I mean ANYTHING that you think it could be just give me some ideas. the next thing after the dist. and the gas would be taking a look at the bottom end. And im very tight on cash rite now. but what needs to be done has to be done, considering this is my DD rite now.

[xrcr]

So do you have good blue/white spark on every cylinder, but 6 and 8? I'm sure you replaced the condenser, right? That wouldn't affect just 2 holes.

[wyattglock]

A friend of mine just went through a similar problem with his 78 Bronco. We replaced the distributor, carb gaskets, plugs, wires, and all the vacuum lines. Found out after doing all of that that the intake gaskets were dry rotted and falling down into the top of the engine while running. Replaced those and the misfire and advance problems went away.

[bctom]

Replace the plugs that are sparking yellow. I've had brand new plugs that were bad right out of the box.

I read that you cleaned them but didn't see any mention of replacements. If not then change just the two that are acting up and see it that helps.

To check for a vacuum leak around the intake gaskets - pour some water around the suspect area while the engine is running.
The vacuum will suck the water into fuel air mixture and the motor will make a definite missing sound that will quickly stop when the water is gone from the cylinder.

For carb cleaning I use a product called Seafoam that you spray into the carb while the engine is running. It's cuts out the gum and carbon in fuel system. They make a fuel additive as well. There are lots of brands of 'tune up in a can' out there but this is the one that works best for me.

Good Luck

[fire120ball]

Originally Posted by bctom

Replace the plugs that are sparking yellow. I've had brand new plugs that were bad right out of the box.

I read that you cleaned them but didn't see any mention of replacements. If not then change just the two that are acting up and see it that helps.

To check for a vacuum leak around the intake gaskets - pour some water around the suspect area while the engine is running.
The vacuum will suck the water into fuel air mixture and the motor will make a definite missing sound that will quickly stop when the water is gone from the cylinder.

For carb cleaning I use a product called Seafoam that you spray into the carb while the engine is running. It's cuts out the gum and carbon in fuel system. They make a fuel additive as well. There are lots of brands of 'tune up in a can' out there but this is the one that works best for me.

Good Luck

Ya man I replaced all, and there all firing blue, I checked my vaccum lines previously, there all good. And I just ran Seafoam through my carb last night....

I also just replaced the intake gasket about 4K ago? ish...

and for the condensor, yes I have replaced.

And yesterday I sprayed starting fluid all the way around the carb, and the intake.. No differences.

Now this is one thing my friend and I found weird, When I would get the motor to about 4K, the upper radiator hose will literally just about go flat, like something inside of the motor is sucking it so hard to make it basically flat... (maybe water is getting into a piston somehow?)

[geezer#99]

.

Now this is one thing my friend and I found weird, When I would get the motor to about 4K, the upper radiator hose will literally just about go flat, like something inside of the motor is sucking it so hard to make it basically flat... (maybe water is getting into a piston somehow?)[/QUOTE]

Dang!! Another sign of a blown head gasket!! Go figure.

[hotrod_991]

i just went through something similair. I was getting a small pop sound from my left pipe and when i would get into it would make noise also. ended up tearing it down after doing everything i could think of to ignition and timeine even bought full MSD including box and still pop sound. well ended up finding out that I have 3 glazed cylinders and really bad detination on to pistons. Make sure you have good gas and good octane level so its not detonating

[hotrod_991]

yea im going with the head gasket. does it smoke at all?

[bctom]

Starting to sound like a head gasket, especially if it smokes.

Is your truck using coolant with no sign of leaks or drips on the ground? How's the oil look when you change it? If it's a bad leak coolant will end up in the oil (very bad for bearings).

How's the temperature when the truck is warmed up? If it's sucking coolant then it may run cool (ie. water injection).

Drive it and see what the plugs look like with a few miles on them, that might give you some more info.

Didn't you just rebuild the heads? Were they checked for staight and flat?

I'm running out of ideas!

[fire120ball]

I just replaced teh head gasket about last year, That would make perfect sense though because my truyck is running really cool. I will run it for a while nd check if the coolant is low. It does not smoke, but that really doesn't mean to much. I had my aluminum heads redecked when I did the head gasket about 2 years ago. But what about my compression? Wouldn't it show if the Gasket was busted? Thanks a lot guys!

[fire120ball]

looked in the radiator, it doesn't look like any oil, and I pulled the dip stick for the oil and it looked normal...

Should I drain the coolant and the oil to really take a look?

[xrcr]

I'm going to echo on the head gasket. Might be a PITA but get a good set ( I use felpro blue or cometic) spend a couple hrs and pop the head off. This eliminates the guess work. Have to get some intakes too. If the gasket is not burnt between 6 and 8 I'm out. Don't re torque the old gasket if this is the case