How do I set the timing on a TBI 350 small block? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-16-2009, 04:16 PM
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How do I set the timing on a TBI 350 small block?

I've got a 86 S10 w/ a 350 throttlebodied and have had timing issues from the second I got the engine running. It also has a mild cam. I keep putting everything on top dead center and try to get the timing down, but it's never run quite right. So I need to know how to get RIGHT. Thanks!

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Old 08-16-2009, 05:54 PM
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What ignition system are you using, the stock distributor, and computer control, or aftermarket?
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Old 08-16-2009, 06:02 PM
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it's a stock ignition

Last edited by stewartfn1; 08-16-2009 at 06:27 PM.
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Old 08-16-2009, 06:07 PM
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Have you disconnected the check timing connecter, and set the base timing to zero?
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Old 08-16-2009, 06:09 PM
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yes, but I've that's as far as I've gone.
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Old 08-16-2009, 06:29 PM
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One thought I have, is the cam to crank timing.

The computer will control your timing curve, using the information from the PROM in it. By just disconnecting the battery to clear codes....etc. It will not reset the PROM to it's factory settings. In order to do this, you need to disconnect both battery cables, and touch them together for 30 seconds, or so.

This PROM is a programmable random memory chip, that learns as you drive. You can order performance programed ones of these, from places like this.
http://tbichips.com The best bet right now, would be to try to reset yours like I described, and see if it starts to run better after 50-100 miles, with your new setup.
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Old 08-18-2009, 11:56 AM
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Quote:
Originally Posted by stewartfn1
I've got a 86 S10 w/ a 350 throttlebodied and have had timing issues from the second I got the engine running. It also has a mild cam. I keep putting everything on top dead center and try to get the timing down, but it's never run quite right. So I need to know how to get RIGHT. Thanks!
Most likely the problem is the chip. It controls the fuel and ignition curves, but the cam changes everything. Manifold Absolute Pressure (MAP) managed EFI systems, of which TBI is one, are very sensitive to the relationship of manifold pressure (think vacuum to keep the approach simple) to throttle opening angle and RPM. A hotter cam changes these relationships which causes the computer to look in the wrong places of the fuel and ignition schedules. It doesn't take much of a cam or rocker arm ratio change a displacement or compression ratio change, a change to the CFM capacity of the throttle body, headers and duals, removal of the cats, etc. to start getting into trouble. Keep in mind that changes are additive to the problem, more changes, bigger the error of the PROM trying to match inputs against schedules to determine outputs.

This requires a custom PROM be made that redefines where on the schedules the computer looks for fuel and ignition values for the given references of manifold vacuum to throttle opening to RPMs to transmission gearing, etc . Also, if the overall final drive ratio changes, such as the effects of gear and tire size changes, the computer also needs to be reprogrammed for this. Just google "custom chips" and tons of shops will show up.

Note, there are people who will tell you the computer has learning capability, it does but it is very small. Block Point Learn as it's called is only intended to compensate for production line component variations from part to part, it does not have the capacity to deal with things like camshaft, header, compression ratio, gearing, etc. type of changes and it only works if you have a functioning O2 sensor and the computer is able to enter Closed Loop mode.

Bogie
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