astro engine timing

lack of power - further investigating with obd analyzer i have found that i cannot generate advance greater than 22 deg, in coast mode the advance does jump up to 30 or slightly above, and typicaly under idle its around 19 deg and still the thing runs, starts, idles like a dream. When i consulted the manufacturers manual, it specifies that the advance timing is extracted primarly from the crank pos. sensor and the cam pos. sensor. To this, other sensor data information is added to obtain final result. The other sensor data ?? i am interested in, which sensors ??. Can exhaust backpressure keep timing retarded? It also seems that when cold, the van has better timing advance than when engine is at temperature. I have still to conquer my re-occuring po420 code, and still not getting any other codes except that one. There must be over 100 codes for that vechicle listed and i get the one that is so general that i might as well change the whole thing. Once again thanx for any help. Andre.

What year?

There are a lot of factors affecting timing. Coolant temperature, intake air temperature, MAP reading, throttle angle, RPM, whether in power enrichment mode or not - The tables are a base, and the multipliers are affected by lots of variables. Exhaust backpressure is not one of them, except as it may affect MAP amd MAF flow readings.

sorry - the year is 99, and looking at various points, they mostly look normal, the other strange thing is that i am not getting any other code except for po420 once every other day, in accel mode the advance never crosses 24 deg. In maintain mode it climbs to 26-28 and in coast it will go over 30. But if i hammer on it the adv sits about 22,23 and the van will rev till it cant scream any higher but will not shift up till i release the pedal. What makes it frustrating is that i do not get any codes, oh ya except for missfire at super hi rpm rev. And i think that i can attribute this code to hi rev because under normal driving up to 4000 rpm it will not miss at all, and give no missfire codes. Every time i accelerate it is smooth but a super turtle, its getting kind of annoying because there is no certainty of speed increase which makes passing impossible.

One thing to look at a carbon, the carbon is a killer.Right from the throttle plate trough to the exhaust manifold.Carbon slows the flow through the plenum and transfers all the way down.Cause detination which in turns causes a knock,the knock sensor picks it up and turns the timing back.Not saying this is it but it NEVER hurts to do a REAL carbon clean.None of this in tank crap.

how do you clean carbon deposits, other than a additive solvent ?? , thanx for info.

The timing is not adjustable on the 1996 and up vortec 4.3.You set the distribitor with a scan tool not with a timing light,look for cam sensor retard in the engine data and the spec is 0 degrees