Bugs in rebuilt 4.3

[shea1]

As many of you know I rebuilt my old '88 4.3 and put it in a '85 S-10 Blazer. It ran the first time I turned the key. (Well once I put the fuel pump facing the right direction.) The only major differences are that it is bored .030 over, has self ported heads, and Edelbrock manifold with the free chip, and a crane came with 107 lift 194duration on intake and 117 for 204 on the exhaust. I filled it with regular grade gas.

It idled and reved fine, but the valves tap under hard acceleration on the road.
I origionally thought that maybe I left a valve too loose, I did however fill the rest of the 20 gallon tank at this point with Sunoco 94 ultra. (36 dollars worth, ouch)
It runs alot better and taps alot less, but was that really the problem or is it hiding the problem.

Would timing cause this? I do know the timing is off. When I put the distributer in I set it to top dead center. To get it to run better I set it by ear. Where do I disconnect that stinkin wire that the manual says you have to dissconnect?

Any other guesses at the problem?

It runs great oter than that and the fact that it shifts just a little bit too soon. It goes up at 4000 under full throttle. I would like it to go to about 5 grand or five and a half. I kinda know how to fix it though.

[jrock262]

did u break it in properly , that the ing wire off an had a oil start ,
drive under 40 , with less than a half thorttle ,
sounds like u did something wrong with the heads or didnt break it in all the way or the right way

[Lvtrucks2000]

Your timing may need to be advanced or retarted. You can not run a modified 4.3 on the factory timing. as for shifting you may need to change your torque converter to a 3k stall

[MCOMEAU]

the wire you are talking about for the timing dvanced is inside the truck on the passenger sied. pull up the carpet and you should see that wire..... if its not there it is because it is an 85 body and it might just not be there. good luck.

[icemancomethe]

Did you change the valve springs as well?

[big dave]

You sure it's not detonation caused by timing advanced too far? Sounds similar.

[shea1]

Yeah I changed springs too, I am still in the break-in period, I am still looking for the wire. I am having it hooked up to a scanner. A friend told me it sounds like a TPS throttle position sensor.

As for shifting I think that is either a cable adjustment or vaccum leak.