I was getting some random cyl 3 misfires in Yota last week after filling with gas out of toen. Started doing it within half hour so I suspected gas. With half a tank still left a bottle of techron poured in, it took care of it.

I think it is worth a shot!

 

So 9 gallons of 93 and 50 miles of driving and it only got worse. CEL finally came on, pulled a cyl 8 misfire. I tried another plug wire, no fix. I am starting to think i have a cracked valve seat. Any other suggestions?

 

Plenum been fixed? How many miles on it? Compression test? Leakdown test? (leakdown would be better...) Might try swapping the injectors on 6 and 8, and see if the miss moves.

 

If you ever disconnected the injectors from the harness, just take a looksey at the prongs to ensure neither of them got bent. This would make it useless. LOL Don't ask!

 

Have the cat pressure tested to rule out it being clogged.

I'd get rid of the Autolites as well. When I tried Autolites, my truck reported a misfire on #5 and performed like a sick dog. Engine performance returned to normal when I reinstalled the stock Champion plugs.

 

I pulled the 02 sensor, no change. Checked for injector pulse with a noid light and its good. Im getting consistent spark. Plenum does not appear to be leaking much if at all, no visible pools of oil and plugs are still clean and new. Compression test yeilded between 175-190 on all 8 cyl. I swapped injectors around but i wont know if the injector is the cause until the CEL comes back on, which seems to take forever on these things. With any luck the CEL will come on on my ride home and tell me that the miss has moved. If it has then i will be ordering a new set of injectors and a fuel rail cause mine is a little bent up.

 

maybe if you have to order some injectors you should look into those bosch 4 hole injectors. they can usually be bought cheap.

 

Cel came back on for cyl 8 miss. It got so bad I had to park it. Looks like it's time to build up the top end. I will be ordering a set of monster eq heads next week, followed by a cam and timing set. For now I'm driving my old '88 gmc 1500 but it's got some issues to, no rear lights and 2 bad tires.

 

Should find out what the problem is before just throwing money at it.... Your compression numbers are good... I would be tempted to yank the valve cover, and see if the valve springs are still intact.... that doesn't seem to be too unusual of a failure either....

 

I may do that but I was under the assumption that if it was a broken valve spring that the valve would be stuck open and I wouldn't build any compression. This weekend I will pull the valve cover off and give it a look anyways. It's got 210k hard miles on those original heads so I'm not too optimistic. Besides I've already got the ok from the wife to start ordering parts next week.