My bro-in-law is dealing with very similar issues, well, he has no compression on 3&5 and bad knocking sound under load. We are searching around looking for others with similar issues. Originally we thought a bad cap/rotor/module or plenum gasket but codes said mis-fire on 3&5. Checked spark and it's good, but checked compression and both are at 0. At this point are left to believe it's a bad head gasket/head... Would a bad plenum gasket cause a loss of compression....???? I don't know how it would/could...... Have no signs of oil and pcv is good.

I know this is an old issues but hoping to hear from you that were involved with this and any help you can give would be appreciated.

Plenum gasket will not cause loss of compression.

If you have zero compression on adjacent cylinders, you can bet its a blown head gasket, or, a cracked head.

It ended up being bent valves and pushrods for me. Had to pull the heads and put in new.

Well, he has it in the shop right now, we didn't want to undertake pulling the head, at least I didn't. haha.... I'm sure it's the head gasket but could be valve issues too. I'll try to remember to leave some feedback when he gets the diagnosis....

Thanks for your alls input!

Did the engine re manufacturer cover it? If not, why?

They covered the parts and up to $30/hr labor. Labor rates are around $90 around here, so I did it myself and sent them an invoice from my shop. They paid within a month, although I didn't hear a peep from them until I got the envelope in the mail.

if u bent valves thats not a big deal. i just had 2 put a new set of heads on my truck. go to oddessa from clear water FL. a remand set of heads are 420 free shipping. it took me 2 days to do my whole top end of my motor. mind you i got out of school a 2 when i started. but just make sure TDC the motor before scrwing with it. and most likly if you bent valves you bent pushrods. so your lookin at 2 days to get it all back together. but that will fix your problem. no biggie

Time to pull the heads off and have a look-see. WEEEEWWW!