I have done a bunch searches and haven't really come accross this topic.

I had a 87 LG4 with a CC-QJet, but swapped it out for a 383 with Vortec heads and about 10:1 compression. The engine has a Comp Cam that is streetable (I will look at the Cam card tonight and post it). I have a Carter block pump that flows 120 gph and have it regulated to about 6 psi. The distributor is stock, but I have a Crane Fireball ignition and coil. This is multi-spark and similar to MSD units. This problem below was actually a little worse with the stock ignition setup.

The problem is the car seems to 'hunt' for a good idle. The tach swings about 50-100 rpm's at the 750 rpm range. I have set the idle screws at the front of the car 7 turns out and adjusted the dwell to 30 on the 6 cyc scale. But while adjusting the dwell, the dwell meter kept slowing oscillating never staying on a set point. I adjusted it so the mid point of the oscillation was at 30.

Does anyone know how to make this idle smooth out and stop this constant varying? Also, while in park and listening to the idle, I can here a slight miss out of the exhaust every so often. The timing is about 36 total, but I am not sure what the base timing is, I think it is close to factory setting.

Thanks for the help, it is much appreciated. I know somebody can answer this.

P.S., top end acceleration is not perfect yet, but I am mostly concerned about the primary circuits right now.

 

The only way you can set CC system timing is by base. Disconnect the ECM connector from the distributor, set the base timing (probably somewhere between 6 and 10, most likely), reconnect the ECM for operation. I'd guess you're running really retarded right now.

As for the cam, "streetable" and "computer-compatible" are completely different. Not saying yours isn't computer-compatible, just that you need to be specific about the computer part when choosing the cam.

 

Here are the Cam specs:

Lift = .460/.480
Duration at .050 = 218/230
Lobe Separation = 113
Intake Centerline = 108

This is Comp Cams NX262H-13
The part number is 12-556-4

Is this too much cam for a smooth idle when using a CC-Qjet?

Also, I will have to double check the timing, I didn't think I had it that retarded, but you know what they say when you assume.

 

Your cam specs are very close to my Crane compucam. Mine idles smoothly at 500 in D. But, Crane claims things like ramp rate have a profound effect on how the computer will handle it. I think that applies more to EFI than it does to CC carb, though.

Checking total timing at high RPMs with a CC system is like checking it with the vacuum advance connected on a non-CC system. The system will provide a bunch of advance, which you are going to back off by setting it at 36 degrees. The result is base timing that is probably AFTC. You'd have to open the throttle blades so much to get an idle that it'd probably drive the ECM nuts.

Just a guess.

 

Well I was wrong. The base timing was set to 0 degrees. I bumped it up to about 8 degrees and I will see how it does tommorrow. Hopefully this will fix the problem.

Having bumped the timing up, is it possible that my full advance curve would now be 40+? I was getting about 36 total timing with the base set to 0. So now would the car be at 44 degrees total since I moved the base 8 degrees? 8+36=44.

I understand vaccum advance and weights, but not sure how the computer advance works. Is it a fixed timing curve, or does it limit total timing based on engine and ECM parameters?

Thanks

 

Advancing the timing seemed to help some, but not completely. Another issue is that the tach seems to be jumpy, moreso than just 100 rpm. The tach will jump under load just before a downshift. The engine does not change rpm but the tach is all over the place. Do you think this could be a pick-up coil going bad?

Also, sometimes when under load, the engine will have a miss and sparatically losing power. When I let off, the miss goes away.

 

Are you using the tach lead on the Fireball, or off the distributor? It needs to be off the Fireball or the tach won't work correctly.

But, that shouldn't be affecting your idle. So, sounds like there is still something not quite right there.

"Total advance" when discussed in the context of 36 degrees on a non-CC distributor is the initial plus mechanical advance only. On a CC distributor, the advance is controlled by the PROM, so the base is all you can "adjust". So, total timing doesn't really mean anything like it does to non-CC distributor applications. Most people with CC will try different base advance settings to see what gives the best performance. I have mine set at 10, for instance, but I'm also compensating for altitude.

 

Well I was about to change just the pickup coil, but then noticed how rusty the rest of the distributor was. Therefore, I swapped to a new unit from Advance Auto. Unit looks really nice and a little different design. Anyways, the swap cured the problems. The car is set to about 8 degress advanced base timing and it runs perfect! No more hesitation, jumpy tach, or misses at idle. I AM HAPPY!

Thanks for all the help:hail: