clemsparks

iTrader: (1)

Hi folks,

I'm just curious here as I contemplate a road-race project with an '83 (or so) computer controlled quadrajet equipped LG4.

What is the computer controlling and sensing? What I know:

It reads the O2 sensor.
It reads the throttle position sensor
It adjust the idle mixture solenoid
Controlls the timing in the distributor

I don't know much else right now...

What I'm thinking is...how much can I start to remove in the way of emissions and accessories and still have the CC Q-jet and computer operate flawlessly?

Can anybody give me a comprehensive list or link to what the computer functions are on an early thirdgen? I don't have a manual but it would probably help...wouldn't it?

five7kid

iTrader: (14)

EGR valve opening, A.I.R. diverter valve position, TCC lock-up if automatic.

It's actually the mixture control solenoid, not just the idle solenoid. Also gets info from the coolant temperature sensor, vehicle speed sensor, manifold absolute pressure sensor, barometric pressure sensor.

The system goes open-loop at wide-open throttle (actually some percentage of WOT). So, you can work over the secondaries without affecting the computer. Beyond that, it doesn't care if certain signals are received, like TCC lockup and A.I.R. diverter.

clemsparks

iTrader: (1)

Ok, thanks.

I would probably be dealing with a 5 speed car, but just incase, it's nice to know that the only difference is the TCC.

Thanks for the info on the mcs. I think I must have known better, but called it by the wrong name...was thinkinking idle control solenoid (rather than idle mixture solenoid) which our carbed cars don't have (right?).

Since I'll most likely be dealing with an earlier thirdgen, do I have a Barometric pressure and MAP sensor? Not sure about this.

If I go away from the EGR eventually (as things get more serious) is that going to give me troubles with the computer? If so, I would imagine it's just amatter of wiring in a resistor of the appropriate value or such to keep me out of trouble there.

The air diverter...that's just what selects whether air is being pumped to the manifolds or to the cat right?

thanks again for the help
Clem

five7kid

iTrader: (14)

The only CC carb car I've seen with an idle speed control (a stepper motor) was an '81 California Buick V6 car.

They do have both BAP and MAP. The rest of what you said is correct.

clemsparks

iTrader: (1)

So, the computer has the following inputs/outputs/controls:

O2 sensor, Throttle Position Sensor, EGR, AIR diverter, TCC, MCS, Timing.

It reads the O2 sensor directly, right?
Same with the TPS I think.

I imagine it direclty controls (electronically) the Mixture control solenoid, Timing advance (distributor) and TCC. Right?

How does it control the EGR, and AIR? They are vacuum actuated right? Are they controlled by a solenoid that is activated by the computer? Or are they just thermally operated (not by the computer) or a mix of both?

How about a shift light? My '83 5 speed car doesn't have one (that I know of). Did some have them? was this a seperate function that just wasn't wired up on an auto car? conversly, was the TCC function just not wired up on a 5 speed car? makes sense to me...

thanks
Clem

five7kid

iTrader: (14)

I think you've got it covered. On later models, the computer also took over the cruise control function (not sure what year, know the '86 was).

The A.I.R. diverter is just commanded for either manifold-directed or cat-directed flow (but vacuum powered, like you said). EGR valve is vacuum-actuated, the computer controls the solenoid that sends the vacuum to it.

The shift light is manual-only, as I understand it. I also understand the manual and auto PROMS were different because of the TCC lockup, but if you convert from auto to manual the computer doesn't care. If you go the other way, the TCC won't be commanded.

clemsparks

iTrader: (1)

In the early cars, is there anything else that the computer controls?

I did forget one output for the computer: the SES light

Could one seperate the wires from the chassis harness and have a stand-alone computer system for an early car...if it's this simple?

I know I'm asking wierd stuff. Just trying to learn more about my system.

thanks five7Kid

five7kid

iTrader: (14)

That's about what they did from the factory. The VSS goes to the speedometer in the dash harness, but most everything under the hood is seperated computer/non-computer.

clemsparks

iTrader: (1)

Ok thanks, It would be nice to seperate everytrhing out so that it would be totally divorced from everything else on the car.
but anyway...

As I research more, I'm learning more about the components of the system. So far I've got the following list:

The ECM (computer, pcm, whatever)
VSS (vehicle speed sensor)
O2 sensor (oxygen sensor)
TPS (throttle position sensor)
MCS (mixture control solenoid)
Distributor
Torque converter solenoid
EGR valve control
Air diverter valve control
SES light (service engine soon light...actually, I think it's "CHECK ENGINE" on mine)
BAP (Barometric Absolute Pressure)
MAP (manifold absolute pressure)
CTS (Coolant temp sensor)

Are these correct? If I have any nomenclature wrong, don't hesitate to call me on it. Do the early cars have a CST? It stands to reason that they should, though I haven't seen much talk of one (that's gotta be what the computer uses to decide when to open and close the EGR and AIR valves right?).

How about EFE? The valve in the passenger side exhaust to force exhaust through the intake to speed warm up? Is it controlled by the computer or just by a preset thermal vacuum switch?

Is there anywhere I could see the logic of this sytem? Would the factory service manual have it? Is it lost forever because no one cares? (likely)

I appreciate any input (still )

RB83L69

My factory service manual for 83 Camaro has schematics, which of course show all the things the computer hooks to. It doesn't really go into any detail about how it works though, it's written more like "if it does so-and-so, replace the such-and-such". It's a service manual for line mechanics not a technical manual. Bummer.

Not all 83 cars have a baro sensor, maybe even none do; mine doesn't. Later years seem to consistently have them.

Mine (L69) has a knock sensor in addition to what's on your list. AFAIK all L69s had it. LG4 that year did not, in some later years it did.

The EFE is not controlled by the ECM, only by a thermal vacuum switch.

There is also a ESC (elec spark ctrl) module.

There is definitely a VSS. It is a yellow box attached to the instrument cluster. I referred to this in your post on one of the other boards.

They all have a CTS. It's on the water outlet, has 2 wires, 1 yellow & 1 black.

Automatic cars have a connection to a switch inside the trans that tells the ECM what gear it's in, or more specifically, whether it's either in 3rd or 4th, or any gear other than those. The TCC only works in those 2 gears.

The way the ECM's wiring is run, every single wire under the hood that goes to the ECM comes out of the bundle that emerges from the pass side fender well. Every single other wire comes from the main bulkhead connector under the master cylinder.

clemsparks

iTrader: (1)

That's what I was looking for when I said "distrubutor." That's where the ESC is housed, right? thanks.

If anybody knows of anybody who's done much research on these systems...let me know. It seems though that everyone has just let them go by the way-side (rightfully so?). It seems like a fun challenge to me.

I guess I need to find a factory service manual...I hate buying stuff off ebay . Selling is more my style .

So if the L69s had a knock sensor...it wouldn't be a simple swap to an L69 (or ZZ spec) computer in an LG4 car (an early one anyway)...or would it?

thanks
Clem

five7kid

iTrader: (14)

I included BAP because my '86 has it, and that '81 V6 referred to earlier had it. End of knowledge base.

I know of one other wire that doesn't go through the two points RB lists (again on a later LG4, might also be on L69) - electric fan. At least for an AC car, there is a wire going to the heater control to the fan relay that passes through the firewall with the heater harness.

The system with the knock sensor is a little better than the non-KS type when you're running higher compression.

Overall, the CC-carb system is better than the bad rap it's gotten. I've even toyed with the thought of running the 396 with it when the '57 gets the 502 and the Camaro inherits the big block (that will only be after the Camaro is emissions-exempt, of course...).

RB83L69

The electric fan isn't controlled by the ECM in a carb car, it only connects to the A/C and the fan switch in the head. So that's one you won't have to worry about.

The ESC module is a flat thing against the firewall near the master cyl with a wide flat plug with about 4 or 5 wires in it. It isn't part of the distributor as such, but rather a separate piece.

I agree with five7 about the CC carb system not being as bad as some people think it is. The worst things about it are that re-programming the mixture and timing curves is next to impossible; and various systems within the carb (part-throttle, idle retrictions, etc.) that absolutely have to be altered to make the carb work on a modded engine, are inaccessible. I ran the CC carb system for some time on my 400, with a 282 solid cam; even that was too much for the carb to deal with. It would make plenty of pwer, no problems there, but driveability was terrible; idle was always way lean because the vacuum operated isle system was designed for a motor 3/4 that size, and the motor had less vacuum besides (so at any given vacuum, the carb only fed 3/4 enough gas, but the vacuum was low too, so it fed even less, and there was no way to compenstae enough for that). But on a near-stock motor, it's just fine.

five7kid

iTrader: (14)

Not to keep kicking a dead horse, but your 400 probably would have done better with a healthy compucam. I don't have any direct experience, but the "Stroke in the Desert" articles on this board indicated Jet can do a decent job recalibrating a CC carb for bigger cubes.

Sparks is going 5-speed, but another thing you said about the tranny - not all systems are the same, but mine has a normally-closed switch in the 4th gear port that tells the ECM it's in 4th when the port pressurizes and opens the switch, and a normally-closed switch in the 4-3 port in series with the TCC solenoid circuit that unlocks the converter when shifting from 4th to 3rd (to smooth out that down-shift - no interaction with the ECM for that one). AFAIK, the TH700's didn't tell the ECM when it was in 3rd. But, I don't know it all, and I only know about this issue because I've got my pan off right now installing a shift kit and trying to get that pesky TCC to finally work. I think the problem is a bad 4-3 switch (high resistance) that's keeping the solenoid from getting enough voltage, but I still don't know for sure.

five7kid

iTrader: (14)

For the sake of full disclosure, I finally discovered I don't have any power going to the TCC solenoid at the tranny. Live & learn...