Hey all. I did a compression test for the heck of it cylinders 1-6 were all 130. Cylinder 7 120 and cylinder 8 was 100. Wet test differences were miniscule. Barely any change. Unless i did something wrong. I followed the procedure in the Haynes manual. So do I have a major problem? Truck is a 99 1500 RWD 5.9 with 99xxx miles. Plenum done 2 years ago with no problems since except a little bounce in rpms at idle. So please let the comments fly. Thanks

 

That's a classic symptom of a cracked head. The most common cause of it is a blown plenum gasket fouling the catalytic converter -- #8 is closest to the cat, so it feels the most heat when the exhaust flow is restricted.

 

Thanks uu thats kind of what I was thinking. So it looks like a pair of clearwater heads are in my future.wooopie.

 

Don't forget to fix the root cause of the problem, and swap out the cat, and O2 sensors as well.

 

How long do yo guess it can last in this condition? It get driven 8 miles a week. I have to do some serious saving for this project.

 

do a wet compression test. See if the numbers jump up. No need to put new heads on worn out rings.


Ooops I see you already did that haha


You can drive it till it starts spewing a cloud of coolant and oil out the tail pipe.

 

Agreed, drive it till it won't drive it till it won't drive no more. Save your pennies until then.

 

Just wondering if I have the same problem. Started as a cylinder 8 misfire CEL light would come on and flash if I got it over 2500-3000 rpms. And shudder something fierce. Did plugs wires cap and rotor air filter oil change. All plugs looked terrible but #8 was by far the worst. After i changed all of that, the light went away and hasn't been back since (approx. 6 months ago) Question: Would this be the same problem? Also I've noticed oil burning around the top end of the motor on the left side, hopefully a valve cover gasket? And should I have made my own thread? Im new and Ive been creepin round here and getting awesome, helpful info you guys seem to know your stuff. Thanks!

 

Have you fixed your plenum gasket yet?

 

No. But after reading the plenum sticky, i think I will be.