Greetings everyone. I finally ( after numerous spark plugs, wires, rerouting of wires, caps, rotors, and sensor changes) found out what was causing my CEL Cyl 6 misfire code. I checked the compression in all of the cylinders and the no. 6 was lower than the rest at about 115 - 110( I don't know the normal for a 360 V-8). My question is this will running Mobil 1 or Royal Purple ( I only use those 2 types of motor oil ) 10W-40 help or hurt. I put a bottle of the Rislone stuff in and it helped for about a month then it went back again. I have 157K on the motor and I have another motor with 92K on it I could drop in but I need suggestions of " What would you do ". Thanks!

 

The oil you use won't help that, I think that was just coincidence. What you want to do is use some Techron+ or seafoam to clean out the chambers, could just be some carbon build up on the valves.Or a cracked head,blown plenum and bad cat. And did you pull all the plugs when you did the compression test? 115 is not all that bad really.

 

Yes I did and when we squirted a bunch of WD-40 in the sparkplug hole and tried it again the compression came back up which would eliminate the head thing. Cat has been check about 5 months ago and was fine. Plenum was redone about a yr ago.

 

Stock plenum fix? And how does that plug look? Did you try swapping an injector or replace it? And you know what I'll say next, if squirting oil in there raises the compression you pretty much have a ring problem. But I would try the seafoam first before getting totally pissed. May just be a sticky/carboned up valve.

 

I recently swapped out plugs even though the others were relatively new. I was more fouled than the others and had a different smell. The injectors have been swapped replaced etc. I have a friend who rolled his truck which was exactly like mine and I bought it for $500. So I pulled his entire fuel rail along with injectors and cleaned them out and replaced mine with it. I seriously doubt it's an injector. We did the WD-40 thing to rule out the valave. My best friend has been an ASE mechanic for many yrs and that was one way to make sure it wasn't the valve. I'll try the SeaFoam again and see if that helps. I drive my truck 125 miles round trip everyday Mon-Fri at an avg spped of 70 MPH and it's all highway miles at a constant speed. I use the middle grade gasoline from either Exxon, Chevron, or Shell. I went up a grade becuase I started getting a rattling sound under accekeration with the regular grade. Once I upgraded it went away. I could swap the motor for the one I bought but it has 92K miles on it.

 

If your hearing a ping on regular fuel it may me your plenum gasket again... One way to check that besides pooling on the plenum pan is disconnect the hose where it goes to the pcv valve and the blow by hose where it enters the the stock air cleaner and rev the engine and feel if its sucking air from both sides.. If so its probably blown..

 

Sounds like a cracked or broken piston ring and the only fix for that is to rebuild that engine or put in the other engine but with 92k on the other engine you would benefit yourself by doing a rebuild on that one as well before dropping it in and end up having to pull it for a bad component that fails shortly after installing it. Preventative maintenance will be your savior here. At the very least I would do the plenum,intake,oil pan, and front and rear seals on the 92k motor before dropping it in.

 

Ok I'll check on that. Thanks!

 

Well after pulling the spark plug this weekend it was not fouled. A buddy of mine sprayed the tip with carb and choke cleaner ( why I have no idea ), anyway after reinstalling the plug the miss wasn't as bad. Also he said the same as ZMAN17 did, that the current compression would not make it run that bad and that it's probably more valve than ring. Yeah I guess that's what I could do but alot of people don't like " cracking open " engines they would rather install a new one.

 

If the plenum is bad , maybe there is just a lot carbon on the valves in that cylinder. Maybe a Seafoam treatment or two might clear it up. But you have to fix the plenum.