#4 and #6 miss

[apgnos]

I had the car on a scope last month and #4 and #6 cylinders
we not firing well. Looked like the top of the wave was clipped
on the scope. Anyway, I did a valve job, replaced timing chain, and put new valve springs in. Also, I had the injectors checked, and put in a new injector harness. New wires and plugs, too.
Guess what--still misses. The only think that concerned me was
the top 3/8 of an inch of the 4 and 6 cylinder bores. Seemed like
some carbon--yet the compression in all cylinders is 140 cold--
I know, but I don't go near this thing when it is hot!!. I'm not burning any oil, but I do have low vacuum with 12 lbs at idle with
A/C on. Heads were planed, valve guides replaced. Any ideas??

 

[Dave85]

How do the plugs look on them cylinders? How about coilpack/module? I had a module go and I did more work then I needed to thinking it was else where.

Dave85

 

[Buick From Hell]

this is a tuffy

hard to diagnose!

#4 and #6 are NOT opposite each other in the firing order, nor do they share the same coil in the coilpack...

and 12 inches of vacuum isn't necessarily all that low of vacuum, especially with the AC on! What's more important, is the vacuum needle bouncing at all while idling? Have you done the carb-cleaner spray test? You may have an intake leak.

The one other thing I can think of, is a cam/valve problem (flat lobe, bent pushrod, bad rocker, etc)

 

[apgnos]

Yea--this is driving me nuts! BTW I put in new pushrods, but I did
not check the cam/lifters for flatness. Does anyone think that the
waste spark could be the problem? I've checked the plugs, and
put in new wires. Since one and four fire together, perhaps the
ignition module is bad--of course I have no SES light. The other thing that is interesting is the bad cylinders are right under the
turbo. I was very careful to get all of the intake surface clean, but I did not get it surfaced at the machine shop. BFH--thanks--I will try the carb cleaner trick--maybe I do have a vacuum leak.

 

[alb84]

Did you use the same injectors in the same cylinders when you put it back together. Did you clean the injectors while it was apart?Just a thought. Later...Danny