Just a question to throw out there. Have a 93 4 door Blazer with a 4.3l vortec. Have a misfire/skip on center cylinder/left-drivers bank of the engine. The tough spark plug removing cylinder. All other cylinders show 120 pounds pressure give or take. The cylinder in question shows 90. I realize this is not what the others have but I believe enough to carry it-in other words, not cause the misfire. Switched plugs, wires, the problem still remains with that cylinder. It appears to have good spark. I'm thinking(hoping) that it may be in the fuel angle-a possible injector issue which at this point would be great. Any thoughts-and what about the 90 pounds compression. Thanks all....[8D]

 

You have a problem if you have a 30psi swing in cylinder pressure. Either a worn/bent valve, bad rings, or a compression leak past the head gasket. If it is the rings, you can squirt some oil into the cylinder and then re-run the compression test.

And yes, this is enough to cause a misfire.

*Moving to 1st Gen Tech as this is a '93...*

 

Kyle-I believe I have good spark, am not totally sure on the fuel but put in a brand new GM injector last night and no difference. Couple of questions before I tear this thing down to the head and replace what might appear to be valve(s). Could a marginal fuel pump pick on a certain cylinder? Could a module possibly cause this-misfire to a certain cylinder? Have another 94 with a vortec in it and the fuel pressure is exactly the same although it does(on both vehicles) randomly bleed off quick but no perticular pattern. This has never caused a problem starting it(or the other vehicle up)yet. Squirted oil in the cylinders on the left bank-picked up no#3(the problem one) 10lbs, the other two(outside ones-front and rear) 30 lbs. Have heard a theory that a weak pump can pick on one cylinder but with a new injector I would think that that would put that theory to rest but...Bottom line-you feel that with the 120-90-120 readings, going inside deeper would be the plan. The truck has 80 k origional and appears to have had real good care but....the muffler appears to have had a backfire(out of shape)..I wonder if this could have caused the issue. And one last thing, when I bought this Blazer a month or so ago, it had a misfire at the auction that I purchased it at. I thought many things that could have been simple having owned probably 2,000 of these. After many things-plugs, wires, etc., I checked compression and had, I think the same readings on the left bank(threw away the records) but 35-120-75(in that order on the right bank-firewall forward). Did a valve job on that side only not suspecting any issue with the left bank. Sorry for the long post and there is a few more tidbits on this but I have to run for now but that is the most of it! Thanks in advance if you(or anyone) get a chance to respond. Bottom line-tear down??Sorry again for the length of this I will return later! JP BTW Kyle-hop on the thruway and head east-I'm right off it near Jordan(if you ever heard of it-25-30 miles east of Waterloo)