#6 not firing!

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4mulaSvaliant

4mulaSvaliant

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Hey guys I am in need of a little input. I just picked up an 81 truck with a /6 and the #6 cylinder is "missing". I have spark all the way to the plug. I pulled the plugs and swapped in new ones and thats when I noticed that #6 was fouled black. All the rest are nice and clean white. I them pulled the plug wire off to see if it changed anything and of course it didnt. So Im sure its that cyl. I havent done a compression test to check anything further but thats my next step.

Any ideas as to what it can be?
I am thinking
1. burnt valve
2. stuck/bent valve
3.flat cam
4. collapsed lifter
5. Bad rings.

If I come up with a good compression test, then what? Guess itll be valve train at that point yeah?
 
Nice find. Do a valve lash check with the engine hot. A valve cover gasket is cheap. You may also be able to tell if its a valve guide. Remember a slant doesnt pump too much oil to the top end so running it without a valve cover doesnt make as much of a mess as a V8.
Good luck and let us know.
Frank
 
I plan to pull the valve cover soon anyway because it needs to be replaced its leaking like crazy! Actually has created a sort of "oil cookie" on the crossover pipe of the exaust! LOL Oil is baked on the exaust pipe. Now that I think about it, it sounds like a fire waiting to happen!
Any how, Ill do the compression test next then Ill pull the vale cover and see what the valve train tells me. I was just wondering if there were something that is common to the slant 6 that may be the issue?
 
Your plan of attack sounds good to me, If I were to guess I'd say flat cam, but just a guess. Pull the valve cover and you'll learn a lot, along with the compression check.
 
Slants are usually good on cam lobes. I still think its valve related but could be rings. You would be surprised how much the lash will help the compression:)
Frank
:clock: Times a wasting
 
An 81 slant may be hydraulic, earlier slants had mechanical valvetrains. If you can't "light" the cylinder with a clean, dry plug, I'd bet zero compression. I'd also bet a fried valve due to a leaking intake gasket causing the cylinder to lean out. Typical for a high mile inline 6.
 
Thx for the input guys. Yeah Im pretty sure its hydraulic lifters, they switched to the hydraulic that year, but we all know how that goes, may or may not be! Just have to check and see.
I am thinking the same thing as fas as burnt valve. I had 3 burnt valves in my 170 from my valiant, seems to act the same. We shall see soon I am going to do a comp. check in the next few days. thx again
 
Ok so I check compression and it was great, 135 on every cylinder. So then I thought maybe a valve was stuck closed, but I have no knocks, or rattles indicating a lifter or push rod bouncing around in there. So I talked to "good ol' dad" (former certified mech) and he guessed at a vacuum leak at that perticular runner since mechanically it was seeming ok. Well I started by spraying starting fluid near that runner (I know not too smart near the exaust and all) and came up with nothing. So then I started digging around and see that there is a vacuum port with 3 plugged ports and one line that leads to the top of the carb. It seemed odd to me that this line went right to the top of the float bowl, but hell Im not the engineer of this carb! So the hose looked like it was in bad shape, I had some more in the garage so replaced it. Get this I start it back up and it runs crappier!!!! That was the only change I made at that point. So I removed the line while it was running and plugged the hole with my finger, WHA LA! it smoothed right out! NO MISS, NO HESITATION! NO NUTHIN'! As I am pondering what the hell the deal is I notice my fingers feel wet and I see there is a tiny bit of fuel on my fingers that has come from the vacuum line I am holding. Well I dunno what the point of that line was but it was sucking raw fuel directly into the intake. So needless to say it is disconnected at the moment and it runs great! I think I need to adjust timing and whatnot because it seems harder to start now but that seems to happen when it gets warm anyway. So I have it solved for now anyway. Anybody have any idea what that line does or is supposed to do? According to the sticker on the fender well it says it is supposed to be there. I hope I can get the hard starting under control because this thing runs like a dream now!
 
full manifold vacuum to the bowl vent isn't even close to right. Big hose off the vacuum tree should have gone to the brake booster. Post a pic of your engine compartment so we can help.
 
It wasnt a large hose it was the normal 3/32 or what ever it is. Also it was a braided rubbber hose, as if it were ment to handle fuel. Ill get a few pics this afternoon. Like I say the sticker says it is supposed to be there. I have been looking in my Haynes book to try to find some more info, but there are soooo many versions of the vacuum systems its hard to determine which or what combination I have. If it continues to run good, then the heck with it Ill leave it capped but I would still like to know what its ment for.
 
The hose in question is meant to go to your evaporative emissions canister. It collects vapors from the fuel bowl and stores them until you chop the throttle and the high vacuum draws the vapors into the intake manifold. Over the years they get full of crud and allow high vacuum to show up at the fuel bowl vent. When that happens, all the fuel is sucked out of the bowl and the car runs like crap. You can either replace the canister or leave the bowl vent open. This affliction was foisted on us in 1971. Good luck finding a new canister after 27 years.
 
What your saying makes perfect sence to me. However the sticker on the inner fenderwell indicates this vent going directly to intake vacuum. Like I said, your explanation makes perfect sence I just dunno' why the sticker wouls say this. The only thing I was thinking is that there was some sort of diafram or something that has failed and was letting fuel into the actuall hose. Ahhhh who knows but from your explanation I am thinking I should atleast uncap the vent and maybe put something to filter the hole so nothing big gets in it. I imagine that if the bowl isnt able to vent itll build up unwanted pressure.
 
Yep, a short piece of hose and an RC airplane fuel tank clunk filter is what I use. Works like a charm and the sintered brass filter is washable.
 
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