Well after weeks of trying to chase down a problem with a miss, I finally broke down and did a compression test on an engine that literally has just been rebuillt with new heads, new rings, new bearings, the works. The test revealed no compression on cylinder 3... Errrr. Here we go again... so I pull the head... flip it over and sure enough the exhaust valve is stuck open, open enough i could fit a penny in the gap. So here is my question for all of you....
Would that cause a total loss of compression? Second....
I drove it up the street to do a leak down test at a local shop before i tore into it... and it died at almost every stop sign.
One cylinder not working shouldn't cause it to die like that, and the truck has a hard time idling, every other cylinder has great compression, am i looking at an IAC maybe??? Need some help, I am running out of money to poor into this beast.

 

If the valve is stuck open of course it will cause that cylinder to have no compression and run crappy . That needs to be fixed first, because it will effect the way the pcm and sensors are reading things. In other words it's F'd. Not to mention the damage to that cylinder that's being done.

 

You sure it's the valve and not a spring or broken retainer?

 

Luckily no damage was done to the cylinder, the truck hasn't ran a total of 10 miles since the rebuild, i refuse to drive it unitl it runs right, no reason to cause more damage.

 

Haven't looked at valve assembly yet... I just pulled the head friday and noticed the valve isn't closing all the way. I will probably take it to a machine shop and have them fix it.

 

i'd think the truck would idle on 7 cylinders as long as it was the exhaust valve that stuck open - UNLESS, the fuel mix being pushed into the exhaust is screwing up the 02 sensor, and throwing the computer into a tizzy.

but, on 7 cyl, it would run like crap.

are you other compression readings ok. just remove/fix or replace that valve and try again. hang in there, you'll get it.

 

Yes, Every other cylinder is reading at least at 110lbs of compression. After doing a bunch of tests on it im thinking i might have screwed up a couple plugs too, Ill probably put all new plugs in this time too. I hope i get it soon... I'm moving and need my truck.