misfire

[levi15]

Hello been searching a while for the problem of my 86 chevy c10 with a 1990 350 converted to carb..did not personally do the conversion but problem i having is the misfire....so things i have changed are manifold distributor new plug wires and coil...ok so i did a leak down test because i had noticed there was some blow by out of the valve cover breather , so the results are cylinder 2 was the lowest at about 22% leak and the rest were at 15 to 10% and spark plugs seem to be wet with oil could this be bad rings cause of the misfire?

[levi15]

Well drove the truck today and seem to run perfect...i do remember buyin spark plugs for an 86 350 and this engine is a 90 tbi 350 converted to carb i believe, could that cause a misfire, wrong plugs??4

[Slammed84]

Not sure man, but I would assume the TBI heads take a different plug. I know the vortec heads do because I ran some on my 84 a few years ago and had to buy the same plugs as my 97' takes.

If the taper is different they wont seal right.... if the length is too short they are getting shrouded in the spark plug hole..... if they were too long they could get smacked by the valves but youd probably know that by now.

Theres really only one way to have oil on plugs and thats blowby due to the rings being worn. But im no master mechanic either

[Shifty One]

Same plug, one step heat range change (hotter in the 91).

I'd inspect cap and rotor thoroughly, and check all your wires end to end....


You could jump to say for example a 26 Autolite in place of the 25's that should be in a 91 TBI motor, whereas the 86 plugs would be a 24. You could run the 26's in the cylinders with the oil foul problem to help a little, or just a full set-just watch for pinging.

[levi15]

heres me driving it and pics

[levi15]

nope here is the pics having trouble uploading a video

[levi15]

Dont mind the oil stains dropped a big 5quart full of oil all over... so cant upload a vid so here it is link through youtube

http://youtu.be/KsqrtiH7zUY

[levi15]

So can a bad coil cause this random misfire....bought one brand new from msd and accel distr brand new and summit racing plug wires....so i guess how can i check the coils and plug wires

[86c20]

she sounds a little off to me but not sure if its the laptop of the motor.

when you did the leak down where was the leak coming from? oil fill carb pvc? weak cyl will cause a misfire also do a vacc test and see if a vavle is bad. i know in my 86 that is what my problme is.

pull the plugs that are oil soaked and post a pic lets see what the bad vs the good is. is this a high miles or hard run motor?

[levi15]

So tried again and here is a video of how it sounds....
86 c10 misfire?: https://youtu.be/f46nkMGaqyo

I will try to get some time to check the plugs soon thanks

[Liberty]

Sounds like my truck, which as far as I can tell isn't misfiring. Unless its that kinda hallowish clanking sound I'm hearing in that video.

[levi15]

Yea i might have to drive it a bit like that but its hard to hear it through the vid

[cadillac_al]

I can hear it but I can't place it. I think I would run the valves again

[levi15]

Well here are the pics of the sparplugs first pics left to right: 1 3 5 7

Sec pic right to left: 2 4 6 8
look at 6 and 8 they seem to be really dirty....

So i cleaned them and ran the teuck and worked fine , even pulled another truck

[levi15]

Most of the leak came from the valve cover breather hole 86c20

[86c20]

well looking at the plugs i have seen worse go hotter as it looks like oil on there. if the leak is in the cover its vavle giuds. or rings. mainly rings. best thing is to do a wet leak test same as wet comp test just helps to seal the rings

[levi15]

Wet leak test, how do i do that?

[86c20]

spry a little wd or what ever in the cyl it helps to fill the gaps and leaks that the rings will have. then when you start it it burns off. only thing i do is crank it over with the plug not in there just to make sure that it will not hydrolock on me. prob over kill but i do it any way.