My other thread turned into a blog since no one was responding, guess I took to long between compression tests.

Anyway, I am gonna order the stuff needed to do my leaking plenum very soon, just trying to fix everything I need to in one shot.

Last time I did a compression test I got roughly the same results as the first time, where 1 cylinder was much lower than the rest.

2nd test results (these are the values leading up to the final compression)

1 200 (150-180)
2 192 (120-160)
3 197 (130-160)
4 185 (120-150)
5 196 (155-180)
6 193 (130-150)
7 186 (150-170)
8 165 (70-130)

From what I learned in the other thread those values are kinda high, although thelocal Dodgedealershiptech thought they were fine with the exeption of the #8.

My question is, what are the chances my problem is NOT with the heads, and how can I test that.
I would rather not have to replace them if I dont have to, but would I want to do this right.

I have also recently discovered that I have a mis in the #8 cylinder, but it only appears to be happening when its cold, as the engine warms up its going away. Temps are obviously dropping rapidly now so I need to get this resolved asap.

Thanks everybody.

 

Those do seem alot for a stock engine. I would be somewhat concerned about #8 though. Does your guage hold it pressure awhile on #8? A shot of oil in the cynlindermight bring it up closer to the others if it's rings. If it's a valve leaking by oil won't change the reading. Hows the sprak plug look from #8? Oily?

 

#8 is a little oily, adding a teaspoon of oil did not change the results

I didnt leave the tester attached for very long, but after a couple of minutes it was still holding steady.

Thoughts?

 

Those numbers are way high. I don't know your mileage, but I would expect a 100K 360 to be in the 130-140 PSI range tested warm, 10 revolutions at WOT per cylinder. Anything approaching 200 PSI tells me you put oil in the holes, or your gauge is not accurate.

My fresh 10.7:1 moderately cammed 360 only hits the 140's. Now, there isn't a direct conversion from CR to cylinder pressure since cam duration and airflow of heads and intake will significantly affect pressure,but as a rule Higher CR=higher pressure.

Minimum spec for Mopar Small blocks is 100 PSI, and max variation is 25 PSI.

Even the tight tolerances and high compression of modern aluminum SOHC and DOHC engineswith variable valve timing (VVTi, VTEC, etc.) designed to optimize low rpm airflow for maximum torque seldom call for more than 200 PSI.

That said, when the problem lies with the heads, it's usually severe enough to cause a misfire. A cracked head or bent valve is going to drop compression enough to inhibit ignition. If you're not getting driveability issues, I'd leave it be.

 

Truck has 145k miles on it.
The guage was brand new, only been used 2x on this truck, not that it cant be bad but its worth noting.
And I do have drivability issues, cant tow for crap, and I have been pinging anditsmisfiring on that #8 cylinder for a while now.
First time it happened the plug preignited, and now it misfires whenever its cold and it goes away once it warms up, that could be a plugged fuel rail or injector though.
Funny, everybody here says its too high, but the Dodge guys and a machine shop guy said the all the numbers were fine exept that #8 cylinder was too low. Ill take the communitys word over theirs everytime.

 

So, I guess I am going to replace the heads.
Anything else I need to know or will have to replace besides the gaskets and bolts if I get into this project?

 

I don't think It's heads.
Although it not much more work to change them if the intake is off.
How many revolutions (pumps) did you do on each cylinder when you did the compression test?
I generally do 6 per cylinder.
I still think compression is too high on most cylinders and as far as I know excessive carbon buildup and worn camshaft exhaust lobes are the only things that will cause a high reading. Worn cam lobe generally cause back fires through the intake as I recall.
I know you seafoamed it and I expected that should have helped with the carbon. Ive never used seafoam so I can't comment on how well it actually works. How long did you let the seafoam soak in the engine?

 

After you fix the plenum gasket, run 2 cycles of MCCC thru the engine and let the first one soak overnight and the second soak for a few hours, then test it and see where you're at.
You could do it now, but with a severely leaking plenum you'll just be putting more oil, (which means more carbon when burnt) into the cylinders.

The heads could be expanding when they heat up, closing the crack enough to stop the misfires.

A misfire on 8 could be a clogged cat. I don't remember if that was gone over in the old thread.

You can pull injectors out and clean them with mineral spirits or even a concentrated fuel injector cleaner they sell at lube and tune shops. Valvoline makesthe "engine flush kit" that they run thru it and it works pretty well.I just bought a ultrasonic jewelry cleaner from Walmart (Haier brand) and puta whole bottle of Techron Plus inand ran 3 injectors at a time thru it.A fewcleaning cycles a piece andyou could wipe all the crud right off them.

 

If not the heads, what then?
I did 6 pumps per cylinder.
I think its excessive buildup also.
I did seafoam it, and it couldnt find ANYONE that really had anything bad to say about it.

 

Cat was plugged and has since been replaced, another reason to get this fixed asap, dont want to have that happen again.

I really dont want to fix the plenum, test it, and then have to possibly take everything apart again. As much as I dont want to, I would ratherreplace the headsand not worry about it, that have to do everything 2x.

I read about the ultrasonic thing, not sure if that was you that posted that you bought one at walmart for $35, but I do plan on buying that thing also.