Since I was having trouble getting a smooth idle on my mild 350 ( with CCC system ), I started playing around with some extreme setting trying to get it to run smooth regardless of what the dwell was.

I succeeded.

Basically, with the air bleed all the way down ( rich ) and everything else at roughly stock settings, my dwell maxes out at 94.7% ( that's max on my scanner ), the idle is very smooth, and...here's the stumper...the Check Engine light does NOT go on while ideling or driving.

Too soon to tell how the milage is, but appears to be about normal.

So how could this be?

 

You've got it running rich and the ECM is no longer in closed loop hence not making any adjustments to the mixture. You can achieve the same 'smooth' idle by unplugging the TPS. The CCC system attempts to maintain near 14.7 AF and, due to its feedback nature, the dwell will always 'hunt' a little at idle, especially if you've got a little cam.

How 'mild' is your 350? I've got a mild 350 in my camaro (vortec heads/XE262 cam) and it has a noticeable idle with the ccc system. It's set to idle around 700. My TA, on the other hand, has a 350 with LO5 heads/cam and it's relatively smooth (550-600RPM) -although I could pull the TPS connector on it and notice the diff.

 

Yes, it's definately a 'rich' thing going on. I get the same smooth idle by disconnecting the MC solenoid. However...

Accoring to my scanner, I'm in closed loop the whole time ( after the car warms up of course ). The dwell does in fact vary when I'm driving, it's just always very high or sometimes maxed out at 94.7% at steady cruise. It's about 85%ish on the highway.

So being in closed loop, with the dwell maxed at idle/cruise, I should get a CE light for being too rich no?

With correct carb settings, my engine will shake, miss, and general run rough. It can be driven like this, but it really sucks.

Engine is an Olds 350, 8.8 CR, and baby 207/213, 112 LSA Voodoo cam. Engine was built specifically to run well on the computer.

 

The dwell will vary in closed loop but it will be stuck on the 'last known good' data (or the default values) for TPS and VAC sensor readings. It won't be re-writing these values based on O2.

It takes some time and effort for the ECM to eventually trip the SES light for rich/lean conditions.

When carb is set correctly does it go open loop? Does the dwell then begin to vary in response to O2 sensor readings? Or are these just correct settings for IAB/Mixture screws and it's still in closed loop? How's the TPS voltage? around 0.40 at idle increasing linearly to around 4.0 volt at WOT? Timing good? Increasing with RPM like it should?

You should be able to get a relatively smooth idle AND open loop.

 

I had a whole detailed response that got wiped out do to a computer glitch. So here's the short version;

Everything you mentioned checks out fine naf. I don't know what you mean by 'does it go into OPEN loop with correct settings' though. If you meant CLOSED loop, than yes it goes into closed loop with ANY carb settings.

My friend thinks I should pull the intake because he thinks it's an internal vacuum leak. It's certainly not an external one ( doesn't reveal anything spraying starting fluid/carb cleaner anywhere ).

Should I set the air bleed to spec and just go for an extended drive to see if my ECM learns properly?

 

You want to adjust the IAB so that it is in open loop and the dwell is 'hovering' around 50% at idle. This may require some adjustments to the idle mixture screws.

I start (after setting timing and TPS voltage) at near spec settings: 4 turns out on IAB and mixture screws. If I don't achieve open loop (feedback) operation adjusting the IAB from 2 to 7 turns out-giving it some time to adjust to each 1/4-1/2 turn setting- I'll start over with the idle mixture screws 2 turns out. Back the IAB from 2-7 turns out in quarter turn increments then start over with the idle mixture screws 2 1/2 turns out.

You get the idea-run it systematically through different settings for idle mixture screws and IAB with the goal to keep each within 2 to 7 turns out. Find the setting closest to stock (4-4) that produces open loop operation and gets the dwell to hover nearest 50%.

Has your carb been rebuilt? I'd look towards that before an intake gasket.

 

Naf I think you have your terms backwards. Closed loop is feedback operation, and open loop is non feedback operation.

My carb has been set to proper dwell multiple times, and the results are always the same; crappy idle.

I've achieved proper dwell using the air bleed and keeping the mixture screws where they were ( about 4 turns ). I've set the air bleed with the proper gauge and used the mixture screws to get proper dwell. I even altered the rich/lean stop settings from proper specs too, all to no avail.

Carb has not only been rebuilt, it has been apart now 3 times to verify there's no funny buisiness going on inside. Everything checks out.

Basically I have an engine/carb when set up correctly runs like crap but will run great when adjusted richer i.e. air bleed all the way down or MC solenoid unplugged ( no, I do not drive it with the solenoid unplugged... ).

Top it off with no CE 'rich' condition triggered even though my scanner indicated constant high O2 sensor voltage ( rich ) and a constant 'rich' for 'rich/lean flag' at idle, this is a real stumper to me.

So my thinking is this; my car wants rich. My car needs rich. What would cause an engine to need richer than 14.7 A/F ratio at idle but at the same time read everything's OK ( dwell 50%, O2 sensor flip flopping etc ) on the scanner? Vacuum leak? Exhaust manifold leak by the O2 sensor? I've checked for these and found no issues. Hmmmm.

 

Entirely possible, but if we talk feedback mode vs. non-feedback mode, we're good.

I've seen issues before where a problem at one bank or the other caused a rough idle. The ECM adjusted the mixture for the left bank and it was out of whack for the opposite. An overly rich mixture may also mask some other issues.

Where is your base timing at? How does the timing light look as it's idling? If it's bouncing around a lot, have you tried disconnecting the KS? Swap out the KS/Module with the bigger motor?

Air tubes still connected or do you have headers?

 

Timing is set about 2-3* over stock. Line on the balancer stays pretty steady. Air pump has been ditched long ago and I'm running the stock craptacular manifolds.

I know I'm going to slap myself after you tell me, but what do you mean by KS?

BTW I forgot to mention, with proper carb setting, it will idle great after a cold start....until the computer goes into feedback mode a couple minutes later then BAM, it suddenly idles terrible. I will have to verify if the rough idle happens exactly when it goes into closed loop ( feedback ) or if it the roughness happens at an earlier time than that.

 

Do you have a fresh O2 sensor in there?

 

KS = knock sensor... did you install one for a 350, or reuse the 305 part? You need one for a 350 for the system to work properly. One from an L98 car will work. A 305 sensor is basically 'deaf' in a 350 block, so the ECM will get no feedback from it, so it won't adjust the mixture and/or timing like it normally would.

 

The wrong KS/module might cause a problem if it sends false knock readings to the ECM, resulting in retarded timing. Easy enough to check, just disconnect it (the LG4 doesn't self test the KS like the later TBIs). A failing O2 will generally read lean resulting in a rich mixture. Craptacular running is more commonly (when not ignition related) a result of a lean mixture. Your idle problems are most likely a response to closed (feedback mode) operation. More later, maybe.

 

I agree. What's stumping me is why am I running so lean at idle ( in closed loop/feedback ) and if I'm so lean, why does my O2 sensor show everythings OK ( when my air bleed is set properly )?

I notice my engine runs a bit hotter with the air bleed set normal, which again points to it running too lean.

My O2 sensor is a brand new AC Delco and since I'm running an Olds on an Olds ECM ( I have an 85 442 ), I do not have a KS.

I won't be able to do this for a while, but when I get the chance I'm going to borrow a known good running CCC carb from my friends 87 442 and see what happens. Seriously can't see my carb being an issue though but since I'm running out of options, I mind as well swap em out and see for sure if it's carb related.

 

Vacuum leak on right bank could do it. Right after running it in closed loop compare plugs between banks.

 

This is what I originally thought but since I can't detect a vac leak anywhere, I suspected it was an internal vac leak between the head and intake somewhere on the drivers side bank ( where there's no O2 sensor ), hence why I was leaning toward removing the intake and resealing it.


I will give that try the next time I get a chance to work on my car. How long do you think I would have to let it run in closed loop/feedback to get an accurate reading on the plugs?

 

Just let it run for a few minutes and you should be able to see a diff.

 

The O2 sensor is on the driver's side.

 

No it's not. I have an Olds.

 

Was this issue ever resolved? If so, what was the solution? I'm having an issue with a rough idle and lean misfire while driving. I can't find a vacuum leak anywhere even after changing the intake manifold gaskets. I can't get a solid idle or smooth part throttle operation after setting mixture screws to 3.5 turns and IAB down most of the way for 50% duty cycle.

 

Lots of people don't check them properly, but I've always had to re-bush the throttle shafts on high mileage Quadrajets when I rebuild them. When I didn't, I got the same problems that the OP got with his CCC. I see no reason a CC Quadrajet wouldn't give the same problems since it uses the same parts.

 

Thought I would throw my 2 cents in here. I fought with a ccc quadrajet for 2 years that had similar problems to those in this thread (i.e. idle probs, part throttle probs, etc.) I had purchased the carb rebuilt and was assured by the rebuilder that the problems I was having could not possibly be due to the carb itself. He was wrong! I finally started changing float level and all settings and just as I got the thing working almost as I wanted it almost didn't get me home one day. Pulling the carb apart for the umpteenth time I discovered that a plug was missing from the underside of the quadrajet. Taking this along with all the evidence I had I deduced that this plug had been leaking the whole time dripping gas into one bank of the engine so that when the ecm tried to adjust for smooth operation it couldn't. The biggest telltale sign I had was that compression readings were approx 20 to 30 psi higher on one bank than the other. This being because one side was running rich while the other was running lean. Hope this might help someone.

 

Most of the carb stuff I read says to epoxy those plugs every time.

I bet a combination of this stuff is what ails the OP.