95 S-10 4.3 TBI knocking to beat hell

If you are dealing with spark knock, the generation of knock control you have is limited on how much it can control it because it cannot retard below base line timing like new ones can. Secounf you are 30 over which means that you are running a even higher effective compression ratio than stock and 87 octane is very marginal at best in that engine (though some amnt to believe otherwise. When I bought my

89 4x4 burb new it wanted to knock badly at times on 87 and the only way you could get it under control was to set timing at 2 to 4 degrees ATDC but it was a slug and drank gas like no tomoorow was coming. I soon gave up on 87 octane for it and swithed to using 93 octane in summer and sometimes 89 in winter abd advanced static timing rto 8BTDC to. It ran great and MPG improved a lot and it still runs great today after over 180K miles now. People that ride in it are amazed at how well it still runs and how responsive it is and I have never seen below 16 MPG average on it in the driving it does today and on trips it is usually around 18 MPG give or take. You can keep fighting it but if it is spark knock, stop using 87 and your trouble will go away and it will not realy cost you more to drive (likely less) because engine will operate more effecently and use less fuel. I never get a knock signal using 93 octane on mine even with advance timing so it always has full sprak advance. When I take it to Colorado for a few weeks every few years I set timing at 14 BTDC (a old trick) while there and it runs much better than it would even think about doing with stock timing and 87 octane.

----------------- TheSnoMan.com

Umm....I will have to say no on the high octane for the simple reason that I run midgrade in that vehicle based off of the numbers we hammered out at the machine shop on the engine calculator program, it stated a minimum octane rating of 86 with a comp ratio of 8.7-1 but I run midgrade in everything just to stay consistent, cylinder head CC's and the CC's on the piston dish at TDC didn't justify feeding it any higher octane or even midgrade for that matter. I have done a few intake gasket replacements and timing chains on post 87 GM TBI V-8 and V-6 where distributor R&R is or may be necessary and have always set timing per book which usually states 0 degrees TDC with ECM control wire unplugged as per the book and have never had this rear up and bite me. To ensure that the computer ramps the advance and retard up and down as needed based off of load and temp with the ECM control wire hooked back up of course a little trick I learned to test knock sensor is to get engine to operating temp and to rap the side of the engine block 'carefully with a hammer' while running at idle or reved slightly and you will hear it stumble a bit and it can be seen on a timing light. The noise Im hearing is a distinct deep sounding knock but bearing to crank and rod tolerances are are still well below maximum allowed clearance. Just to make sure it was not sucking hot air all the time I bypassed the heat riser tube off of the air cleaner to exhaust manifold as well and it had no affect. I have the poor guys at the machine shop completely stumped as well as my self, it just doesnt make any sense why it ran perfect for a few days and then the noise came back after a long range test drive. I have parked it for the winter and figured screw it its getting what it really needs, a small block....have a good holiday gents.

Just a thought from an amateur:

You said that the timing chain was surprisingly stretched when you overhauled the engine, and that the new chain got stretched as well. Combined with your thorough testing of main, piston, and wrist pin bearings, this leaves me wondering if you might have a problem in one of the heads, which is heard as a knock, and places excessive load on the timing chain.

I think I'd go at it with a stethoscope to work out *where* it knocks.

-tih

I wish O could hear it to make sure it is spark knock or other source. (Does it knock with timing lset lead left disconnected?) Also do not beleive you shop program because that engine needs more than 86 octane if it is going to have any kind of timing advance in it. I have a old Jeep 360 V8 with 8 to1 CR and it will mostly run okay of 87 but that and a old tractor with 7 to 1 CR is all I use 87 in because 9 to1 and higher sufferes with it. You might check EGR function because it dilute incoming mixutre and make less oxygen availble and retards knock some (and power too). My 89 TBI 350 that I bought new runs so sweet with 91 to 93 octane aset at 8 BTDC I will NEVER go back to low octane fuel it it even if gas a $4 + a gallon because to do so would hurt its current performance and MPG. When I used stock timing and fuel when new it downshifted outof OD a lot of hills, want to knock at times and was a slug on hot days and a different animal than it is today. Also might consider pulling the pan to inspect bearings if disconnecting timing set lead does not change the knock and remove it.

----------------- TheSnoMan.com

You know when you thing of this the only thing that can cause this is a binding dritributor, oil pump or cam bearings.

----------------- TheSnoMan.com

Bad balance shaft bearing?

I'm beginning to wonder if I dont have a bad wrist pin in a spot I couldnt see on one of the front cylinders, and yea we ran a scope up and down the pan rails and on each cylinder at the head and its definitely not early spark or predetonation noise, the noise is most noticeable near the center and right of the timing cover. And the balance shaft bearings were good and the bore that the distributor sets into the block was kosher no wobble there and dist bushing were ok. Hehe if I keep over analyzing this thing it may be like getting M.I.T. involved here and who knows what the conclusion would be....laterz