acliad

iTrader: (1)

Hello, I've got an 84 Camaro that has the original CCC Quadrajet and a rebuilt 350 in it. To make a really long story short, I've been battling this carb for about a year. Here's what I've done so far: complete rebuild, including soaking in carb dip; set the lean mixture screw with a 1.304'' spacer; adjusted the rich mixture stop screw to get 4/32nd (1/8th") plunger travel; replaced the float and set it to 11/32nds; epoxied the well plugs; and repeated about 4 times.

I have an old OCT live scanner that I use to see all the information (TPS voltage, vacuum, dwell, etc.). The scanner also shows if it's in closed or open loop, and it shows the rich and lean flags. So here's what happens — I take it out and get it warmed up, verify it's in closed loop with the scanner, and go to adjust the IAB screw. Now it just hangs out at 54 degrees, rarely dropping to 48-50. It does adjust, it'll run around 35-45 when cruising, and if I unhook one of the vacuum lines, the dwell will drop and it will change with the IAB screw, so I'm pretty sure it's getting too much fuel. I simply cannot get this thing to adjust down to 30º at idle. The only thing I can think that I haven't done is removed the idle mixture screw plugs and mess with those, but I was thinking that the factory setting should be close enough.

My problem seems to be just like the one in this thread, but that one apparently never got solved.

Thanks!

Damon

Hmmmmm....

If you pull a vacuum line at idle it will lean it out enough that the IAB will come into "sane" adjustment range, eh?

Well, I can't fault anything you've done with the carb so far. I'd ask how many turn up you have your lean stop (should be about 4- everything is "4" on a CC-Qjet). I set that first, then the rich stop for 4/32 travel (another "4"!) and then the IAB about 4 (!!) turns up. Idle mixture screws, should you decide to unlock them from their tombs, should also be about 4 turns out from lightly seated, as a baseline setting.

Anywho... there's only one vacuum leak I can think of that's DESIGNED to be there from the factory- the PCV valve. It can make a big difference in your idle mixture settings. If you're not running one, you need to. If you are, I'd check the valve, maybe replace it on general principle.

The other thing I can think of is a charcoal canister that's purging at idle when it shouldn't be (many reasons that could be happening). Basically, it's a matter of clamping off or plugging one vacuum line at a time that ends up at the charcoal canister assy and see if the problem goes away.

naf

iTrader: (7)

Put a few 350s under ccc Q jets and usually have to go a turn or so in on the idle mixture screws.

acliad

iTrader: (1)

Yep, a vacuum leak makes it go in to an acceptable range. The lean stop screw ended up about 3 turns out from lightly seated, and I double checked my spacer to make sure it was 1.304 inches. I then just adjusted the rich stop to get 1/8th of plunger travel, so I'm not sure exactly where it's at. The IAB is sitting right around 7 turns out right now (I read in another thread naf suggested not going above this), and it'll occasionally hover around 48-54, but it's usually stuck at 54.

The PCV valve is pretty new, and I'm definitely getting plenty of vacuum through it. I also checked it with the vacuum ports plugged at the carb, except the PCV, vacuum sensor, and brake booster. I also had the big port that runs over to the charcoal canister plugged at the time.

naf, sounds like that may be the next thing I try. It tends to run in the 30-40 range at cruise, and it just now occurred to me that it may be running on the idle circuit when it bumps up to 54.

Lastly, today I went to check the timing. I unplugged the 4 pin connector, and it was around 8º. I adjusted it to 6º, turned the car off, and plugged the connector back in. It was still hovering around 6º, but it does increase linearly with throttle (it doesn't "jump"). From multiple threads I've read through, I thought it was suppose to run around 20º advanced at idle? Maybe this is a separate problem, or not one at all? For curiosities sake, I advanced the timing quite a bit to see how it affect the dwell, and it didn't seem to make much difference.

Thanks, guys, for your info!

Damon

Yeah, I never cared where the rich stop ended up, either. It's 1/8" of travel over the lean stop. That's all that matters, as long as the lean stop is properly adjusted first.

I'm sort of scratching my head here because most of the "failures" that could happen in the IAB circuit cause things to go LEAN, not rich.

When you're at curb idle, warmed up, choke fully open.... is the throttle pretty close to fully closed? You shouldn't have to back off the curb idle speed screw much to get it to literally stop touching the throttle arm (throttle plates fully seated in their bores). Also, are you getting any "nozzle drip" from the primary boosters at idle?

Has anybody mucked around with this carb before you? I've seen guys just start taking drills to things they have no idea what they're doing. The Idle Channel Restrictions are the main things I'd look at in that kind of scenario. From the factory they're around .052" give or take. I've seen them where somebody ran a 1/16" (or larger) drill through them which will make the idle go VERY rich.

Given you have the factory seals still over the idle mixture screws, there's no chance anybody drilled out the curb idle discharge ports, or that would be something else I'd recommend you check.

Oh, and.... how does this thing actually RUN at idle? Does it ACT like it's running way-rich?

How "aggressive" is this 350 that's sitting under it? Is it basically just a stock "pickup truck" 350 or is it got some cam, heads and stuff like that upgraded in it?

acliad

iTrader: (1)

Glad I'm not alone. I think you may be on to something though.

At curb idle, the throttle plate looks pretty close to closed, but the screw takes about 1 1/2 turns before it releases the throttle plates.

Unless I'm looking at the wrong part, it looks like I'm getting quite a lot of "nozzle drip" out of both sides. Here's a video of what it looks like:

and this is after I backed off the idle speed screw to reduce some of fuel coming out of the nozzle:

Interestingly, after I set it back to 750rpm, the dwell was hanging around 40º. All I touched was the idle speed screw:

I don't think anyone except for me has had this thing apart. All the adjustments were still plugged. I don't remember seeing evidence of anything being drilled, but then again I wasn't looking for it. If it were drilled, that wouldn't affect nozzle drip, would it?

The thing actually runs quite well at idle. It smells just a bit rich, but otherwise it hovers around 700-750 rpm with a little bit of a hunt to it. The 350 is pretty much just a truck motor; everything was put back to stock spec.

Damon

Yep. You got it. That's where your extra fuel is coming from at idle. It should ONLY be feeding from the idle circuit when you're at curb idle, full warmed up. For comparison, I have a QJet on top of my mild 383 blower motor with a mild cam in it, and it doesn't feed ANYTHING from the boosters at curb idle which is around 900 RPMs (in neutral, about 750 in gear). So something's definitely up with yours.

So now, here's the problem.... it's damned difficult to start diagnosing the difference between a carb fueling issue and an ignition timing issue, given that BOTH have the capability of causing nozzle drip.

Nozzle drip happens when there is enough airflow through the carb at curb idle to generate just enough vacuum signal at the primary boosters to have them start feeding fuel. And Qjet primary boosters are WICKEDLY EFFICIENT. You don't have to be far off at idle for it to start to happen.

Before you throw brick bats at the carb (don't ask- it's an ancient term only ancient people like me know about), you should really trace down that issue with the spark advance, or lack thereof, that you're seeing at idle even with the distributor computer control plug connected. I didn't say much about it before, but I agree with your recollection of how it's SUPPOSED to work. I recall it should be throwing a bunch more ECM-supplied advance at the distributor at idle, exactly the same as you remember. If I had ever mapped out the advance curve on one in the past (I have not on old computer controlled carb systems), maybe I could say for sure. But if the queen had *****, she'd be the king. I just don't know enough in that one particular area to advise you.

But if I was you, I'd start asking around and doing research. Lack of spark advance at idle will ALWAYS require more throttle opening (more airflow through the carb) to hold an idle. As such, it can definitely be the proximate cause of nozzle drip on a QJet.

Slowing down the idle speed to ~600 might help quite a bit, too (as a crutch or diagnostic tool, not necessarily a "fix"). If it's airflow-related lower idle speed always equals less airflow.

IF you rule out all spark advance-related problems, I can help with possible carb issues that could cause nozzle drip. Starting with the float height and the Idle Air Bypass system. No, NOT the IAB valve. The OTHER idle air bypass system that provides a path for air to be drawn from above the boosters directly to the bottom of the carb, bypassing the primary venturis completely. Yes, the factory knew all about nozzle drip problems with the QJet so they invented this system to fix it, but that doesn't mean yours is still active and functioning.

Anyway, that's work for another day. Go make sure your ignition advance is behaving "normally" first (or not).

acliad

iTrader: (1)

Awesome! This is the first real lead I've had, I think ever. I'll track down down my timing issue and report back. Thanks a bunch for your help so far.

naf

iTrader: (7)

Ensure that you've set base timing at a low enough idle speed so that the icm is not adding it's default advance. Usually around 1200 or so the icm will jump the timing up several degrees when the est is disconnected. This provides some limp home timing advance.

You can check this with est disconnected and observe the jump in timing.

Properly set and working you should see around 20ish at idle and linear advance.

acliad

iTrader: (1)

I just had an interesting time messing with it. I noticed that when the engine was cold, the timing appeared to be around 20 degrees, but as soon as it went in to closed loop (indicated by the scanner), it bumped back down to 6. naf, I set the base timing at 500rpm, so I should be good on that.

Here's the interesting bit — when I unhook the vacuum hose going from the back of the carb to the vacuum sensor (and plug the vacuum port), the idle jumps up to around 850-900 and the timing jumps up to around 20º. Now, with everything hooked up, my scanner is telling me that my vacuum sensor volts are around 1.5, and the pressure is 18 kPa. 18 kPa converts to about 24 inHg, as per this table.

With everything hooked up, I still get linear advance; it's not "jumpy." The timing just wants to hover where I set it when the 4 pin connector is unplugged. I guess I'll have to sleep on this one.

Edit: 18 kPa should be 5.3 inHg, not 24.

Damon

That's..... weird. One of those times I wish I had more experience with the spark advance curve prgrammed into the ECM on these old CC-Qet systems.

I seriously doubt you ACTUALLY have 24" of vacuum at idle. 18" would be about the lid for ANY stock-ish engine of that era. And that's even WITH 20*+ of advance at idle, which you ain't getting. With only 6* advance I seriously doubt you will be pulling more than maybe 14-15" of vacuum.

Moreover, I don't ever recall getting MORE advance with the VAC line disconnected than with it connected. That's just totally "backwards" from how I recall it operating from my informal observations over the years. I recall the VAC sensor operated somewhat similarly to how the vacuum advance canister did on an earlier non-computer controlled distributor. At least as far as spark advance is concerned. Supply vacuum, you get more advance.

You got a weird one here.

From the "pulling stuff out my backside" department.... Is your BARO (atmospheric pressure) sensor port open to air? Looks identical to the VAC sensor, but it has NO line of any kind attached to it. Everyone wants to put a line on it because there's a fitting for one, but it's supposed to be open to air.

Also, is there any chance somebody replaced your VAC sensor with a MAP sensor like on a later TBI car? They work IDENTICALLY, except that they read exactly OPPOSITE of eachother. One reads vacuum, one reads absolute pressure (the inverse of vacuum)

acliad

iTrader: (1)

Okay, so the Baro sensor (passenger side) has no vacuum hose going to it; it's open to the air. That did confuse my a while back.

It occurred to me this morning that I had to replace the vacuum sensor. I went to pull off the vacuum hose going to it and the whole thing popped apart. I remember not being entirely sure I got the right one. I must not have after all. The replacement sits at 4.46 (I believe) volts with the key on, engine off. I think I still have the guts of the old one; I should be able jerry rig 5v to it and probe around to see if the output voltage is reversed (I assume that's how it is reversed?). So now that you say that, it all fits. I would have thought I would've noticed a difference in the way it runs, but it had been sitting for about a year before I replaced it. Maybe I simply didn't notice.

That being said, how do you tell the difference between a vacuum sensor and a MAP sensor? All the references I've come across just talk about different BAR readings. I'll check around today and see if I can find a vacuum sensor.

naf

iTrader: (7)

I've never verified that the vacuum sensor and baro sensor are different parts. My assumption has always been that they are the same piece, the baro sensor is just open to atmosphere.

Were I not in Indiana this week I would be able to check some of this against my 84.

Note, though, that my attempts to read dwell with my autoxray on my 84 were not entirely successful. A dwell meter was required to read true dwell on that model. With the later models, connection of the meter disables spark retard and none of the timing advance data can be read. The meter would read advance on the pre-ks models though. Limitation of the ecm I suspect.

I should be home this weekend and will be able to compare your readings to mine.

acliad

iTrader: (1)

This morning I went ahead and probed my old vac sensor. The circuit itself is still okay, it just slipped out of the casing and a couple of the leads broke. Anyway, measuring between output and ground (terminals A and B), I got roughly .5v. As vacuum increased (just sucked through a hose) the voltage went UP. This operation appears to be backwards from what the sensor currently installed does, and it's inline with Damon's description. It would be awesome if you could confirm or contest.

I realize that this is for a later model Astro/Safari van, but it appears to still apply (CCC): http://www.autozone.com/repairguides...00c152800a7f7f

Being Autozone, the reliability may be questionable, but they do list two different sensors — Barometric Pressure Senosr and the Manifold Differential Pressure Sens

I'll call around some dealers tomorrow and see if I can find a parts guy who doesn't need explaining that this is not a TBI car.

Could you elaborate on why you weren't entirely successful reading the dwell on your 84 with your scanner? I don't think my OTC shows any timing data, but I might be completely missing what you're saying.

Damon

Probably because the scanner threw it into "Check Engine" mode, which would completely hose up the spark advance the ECM would normally throw at the distributor. But I don't want to put words in his mouth.

I have a very old Diacom setup that I run on an old DOS laptop plugged into the cigarette lighter for these old OBD1 setups. It also acts "weird" sometimes, although I don't recall it messing with spark advance or dwell while connected.

naf

iTrader: (7)

Correct. The scanner throws it into check mode which disables spark retard from the ks on 85 and later models.

I don't know why my autoxray displays inaccurate dwell data on my 84. Dwell function was not disabled by the connection as I could simultaneously read dwell from the diagnostic lead with a dwell meter while the x-ray was connected. Likely an issue with my particular meter or a fussy car.

Wish I could brag about having an old DOS laptop.

acliad

iTrader: (1)

Ahhh, okay. I got it now.

I called around a couple dealers on Wednesday, and according to both the guys I talked to, the sensor has been discontinued. One guy showed two dealers in the nation who have them (3 in total). They were 102$. I'm fairly certain my local junkyard has a couple CCC setups, so I'm gonna swing by there when I get a chance and see if I can pick up a used one.

I believe I was doing my vacuum conversion calculations wrong as well. 18 kPa should be about 5inHg. This also means that it's reading 76 kPa, or 22inHg (4.64v) with the engine off. That sounds pretty backwards.

I once installed a DOS emulator to play a game.

acliad

iTrader: (1)

Well, I definitely owe you both a 12 pack.

I managed to pick up the proper sensor at a junkyard (with a few other small things I needed) for $5. For future reference, the part number the GM deal gave me is 16231141, for a differential pressure sensor.

I stuck the sensor on and that fixed my timing issue. Then I set the idle curb speed to 500 RPM (actually 525ish) in drive, which is what it's supposed be according to the sticker under the hood. It idles around 650 in park, which seems a bit low, but the nozzle drip is gone and it actually idles better than ever. The vacuum reads about 60 kPa (18 inHg) in park. I found ~30º dwell at around 4 1/2 – 5 turns out on the IAB valve. Thanks a bunch to both of you!

naf

iTrader: (7)

outstanding. weird on the behavior of your vac sensor. will keep that one in the back of my mind in case I see something like it in the future.

Damon

Excellent. Glad you nailed it dead-bang. I have to admit, you used up almost every bit of my "internet diagnostic ability" on this one. I also have to admit to a bit of a lucky guess on that VAC sensor idea- I've only seen that once, maybe twice before in the wild. If that hadn't fixed the spark advance issue, I would have had to admit defeat (or start blaming things on bad grounds and bad ECMs, per standard thirdgen.org operating procedure).

From idling rich to the wrong VAC sensor is one heluva stretch to diagnose over the internet without ever directly laying eyes, ears or hands on it. Definitely putting this one in my top 10 CC-Qjet hall of fame.

Enjoy the car.