Have a 90 Firebird w/305 TBI. All stock. New Timing Chain. Tried to time it to 0 deg TDC like it's supposed to be but when it is @ 0 deg it runs rough/lacks power and wants to die in gear @ idle. So I reset the timing to what "Sounds" like a well timed engine. The RPMs are at 1500 @ parked idle and drop to just below 1000 RPMs in gear idle. Runs great/power. But now I used a 1/2 tank of gas just to go 40 miles. That's only 5.33 MPG!!!!


Any Ideas? And yes I do disconnect the EST wire before timming the engine.
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Also want to point out that while ion the highway the SES light comes on after 15 min of driving @ the 70 mph speedlimit. But goes back off when I slow down to 45mph when I get off the highway.

 

I almost hesitate to suggest it, but it sounds a lot like the valve timing may be off. If that's the case, either the timing set was installed incorrectly, or was stamped/manufactured incorrectly. Did you use a three-way timing set, or a stock one?

 

Stock Timing Chain set up is what I put on. OK then, if the Valve Timing is off let me ask this: I know that when the cam sprocket is at 6 o'clock and the crank is at 12 o'clock it is set up with the #6 piston at TDC, What is it when the #1 piston is at TDC?

 

Dot to dot and both dots at 12 o'clock are TDC for both #1 and #6. It's a matter of which one happens to be firing.

Both dots at 12 are #1 firing, dot to dot is #6.

If the CEL came on, pull the codes.

 

That's really helpfull to know


And was going to do that today.