tuning/timing a 307

[techg8]

Ive been running my 1986 307 for a little bit now, it drives real smooth in my 83 Cutlass. Stock ECM and PROM chip.

I have been tinkering with timing a little bit and thought Id share what Ive noticed. Maybe you all have had similar results?

The emissions sticker says to set timing at 20 degrees BTDC at 1100RPM.
When I do this, I cannot hold an idle. It appears that the ECM pulls so much timing at 550 or 600 rpm idle, that the engine just quits.

Messing around with it some more, I found it started well cold or hot with what I consider a "normal" amount of timing at idle - 8 to 12 degrees BTDC. Throttle response down low in the rpms, right off idle, really wasnt great. once the rpms got above 1100 or so more timing came in and the engine felt good.

Today I went to an initial setting of 20 degrees, just for the fun of it. Engine starts right up cold or hot. great response down low. No audible detonation under load. Just all around much more "peppy". I took a look at total timing at higher rpms and it looks like 43 or so degrees all in.

any thoughts on this? Whats the farthest you have pushed your initial setting on an Electric timing control 307?

 

[DoubleV]

First off, are you disabling the ECM before checking your timing? If not, then you need to.

I don't know why your car ran like crap with normal timing then suddenly now runs good, but it could easily be non CCC issues like a vac leak. My friends 87 442 ran like *ss sometimes and ran great others. It ended being the throttle shaft busing on the carb causing a vacuum leak. When it ran good you could apply pressure on the throttle shaft and suddenly it would run like sh*t. Curiously it was a 'sometimes it was leaking and sometimes it wasn't' problem.

I usually ran 22 base timing on mine and know many others have too. Some have even run more.

How are you verifying 43 total timing? For one I can tell you the ECM alters the timing advance if you're not in gear, so even if your 43 total is correct, that isn't what your engine's getting when in gear and under load.

 

[techg8]

I make the initial setting with the test lead grounded

The carb may be a little off but not much. i rebuilt it with the engine. Dwell adjusts right in but I do have to put the idle air bleed further in than the gage would like.

the 43 degrees I mentioned was just in P or N revved up a ways to see what kind of timing the ECM was adding. Interesting about in D and under load, though it makes sense. It would be great to see a graph of the timing curve "contained" in the prom chip. Any ideas if its out there?

 

[DoubleV]

It would be great to see a graph of the timing curve "contained" in the prom chip. Any ideas if its out there?

There out there. I've seen some posted before on Oldspower a long time ago.