GM 7pin module doesn't seem to be timing correctly?

[Blake]

I picked up an old GMC truck that came with a 350 and carb. So I naturally slapped a junkyard 7747 on it and it's running ok.

I'm running a GM 7pin module inside a stock GM HEI. When I put a timing light on it, the timing marks are rock solid and don't move. This is with the bypass plug connected or disconnected. When I rev the engine the timing marks do go up about 5-10 degrees and that's it.

Shouldn't the timing marks advance more than a few degrees? IIRC the marks should be 'jumpy' at idle with the bypass plug connected.

Running a stock ASDU bin.

[1project2many]

Did you shut off the key after reconnecting the bypass? IIRC once code 42 is set on a 7747 it won't try to control timing again until a power cycle occurs.

[Blake]

yeah - I even swapped ECM's and bin files.

I *think* I have it wired correctly, but it simply doesn't seem to time the engine...

[1project2many]

Used module or new? I've seen them fail, rarely, this way.

[Blake]

I'm using a module that was working great in another TBI project. It's about 2 years old.

So here is my question - Should the timing marks (as viewed by a timing light) move around erratically at idle with the bypass plug connected?

[1project2many]

They should be relatively steady with bypass disconnected.

[Blake]

yes

but what if the bypass is connected? Still steady?

I see no difference with the bypass connected or disconnected...

[1project2many]

You might see some changes at idle with bypass connected. It depends on the cam and how steady vacuum is. You should definitely see timing advance as rpm increases. You could also try connecting and disconnecting MAP, slowly, to watch timing change. Less MAP = less advance.

[Blake]

alright so I found TDC and discovered that this thing was way too far advanced. the engine has no timing marks for some reason, so I make 'em.

runs better, but now I'm seeing a part throttle bog (only when warmed up and in CL) that I need to tune out.

thanks for your help guys!