New to the 3rd gen scene, just picked up an '86 305/Q-jet car off one of my g/f's friends at school.
Anyways, how much does the computer monitor and adjust? Does it just watch A/F ratio, and adjust the power piston accodingly?
What about ignition timing? Is there a good article giving a rundown of the CC system and how it works somewhere?

Also, for later on, do I have to worry about what camshaft I put in? Will too much duration/too little vacuum confuse the computer? Or would one just adjust idle, rejet/re-rod as normal?

 

Welcome aboard.

The computer controls fuel mixture and ignition timing. It uses imputs from throttle position, oxygen sensor, manifold vacuum, barometric pressure, and vehicle speed to make those decisions. '85-up (and all HO versions) also have a knock sensor to retard timing if detonation is detected.

The computer-controlled q-jets don't have a power piston per se. The mixture control solenoid pulses to lean out the mixture - more pulsing, leaner mixture; less pulsing, richer mixture. When the engine is cold, the computer is in open-loop operation, using pre-set tables to control mixture. At about 110 degrees F coolant temperature, it goes into closed-loop, using the O2 sensor to adjust mixture. It also goes into open loop at wide open throttle, with the primaries going full rich and the secondaries identical to the old mechanical q-jet system.

Some of the radical old school cam grinds with a lot of valve overlap will confuse the system. Companies like Comp Cams and Crane are making computer-compatible cams that work well. When I went from stock LG4 to the mods in the sig, I adjusted idle speed and choke pull-off (had already done secondary hanger/rods). It handled the rest on its own.

 

 

Well, I wouldn't run it any further advanced than where it just starts to get some knock counts. A scan tool, or some monitoring software on a laptop, will tell you this info.

Changing jets? On a Q-jet, you deal more with the metering rods. Most people leave the primaries alone and just let the computer handle things there, but most of us play around with the secondaries, as that is where you run it when you're loking to make power anyway.

On my car, I get about 15 inches of vacuum (LT4 HOT cam) and the ECM seems to do fine, even the torque convertor lockup is where it should be.

 

Okay, this system seems pretty dang good - how come I'm always hearing people saying to rip the computer out, and go with a mechanical q-jet?
any downside, aside from not liking low vacuum, and not having as much controll over timing?

 

I took mine out, and I think I'll end up sorry I did, because I foolishly thought it was the ecm being shot, when in actuality my timing chain was so stretched, it was causing such erratic timing.

I've gotten 19.68 all-purpose MPG on my CC Q-Jet motor before my timing went south. Highway, I'll see about 22-25 depending on weather, gasoline, speed, etc. It's a good system. Keep it as clean as you can (you could eat of my CCC if you had to) and give it a complete tune-up.

Plugs, Wires, PCV, Breather, Air filter, o2 sensor and spray that carb as clean as you can get it, then run some fuel injector cleaner through it on a tank of hi-test. Also, clean oil seems to help mileage as well.

I'll better be able to compare these the two (CCC vs. Mechanical) once I figure out how to mound my PS pump again and get it all back together later tonight.

 

Well, on my "84" the ECM must see at least 10" of vacuum (over 3 volts) from the differental pressure (vacuum) sensor or the ECM will set a code 34. The eng. must run at curb idle for at least (2) minutes berfore this code (check engine lite) will be set.

Auggie

 

That's one of the main issues, the CC carb doesn't like really big cams. Mine is doing well with my LT4 HOT cam, which isn't small by any means! The thing does have around 15" vacuum at idle though.

I had the baseplate off my carb a little while ago, I'm trying to figure out why the float bowl is empty after sitting for 3 days. I put a new fuel filter (second time in the past 1,000 miles, maybe the check valve in it was letting fuel out?) and I expoxied over the plugs in the bottom of the main body that are notorious for leaking, even though they didn't appear to be! I cleaned the carb off on the outside, and I checked to make sure all 4 throttle plates were opening all the way, and lo and behold, they weren't. The primaries were only a couple degrees off, while the secondaries were like 5 degrees, after fixing the primaries! Every little bit helps! These things aren't perfect from the factory, and they get a little out of whack after say, 216,000 miles! While I was at it, I gutted out the thermac that I noticed wasn't working anymore. Now my car will pull to higher rpm's than I'm willing to take it (afraid of belts flying again!)

To sum up my ramblings, there are some tweaks to be made to the Q-Jet, (CC or not!) to get some really noticable differences!

 

Well, you sure are right on about the throttle plates. I did get them to open all the way on the bench but they would not open all the way when mounted on the eng. To determin if the plates are wide open have someone press on the th. pedel. If the th. plates are W.O. you should not be able to move the sec. linkage down. I had to drill another hole in the throttle cable to to get that done which also raised the throttle pedel in the car. I did expoxie the pri. welsh plugs for the same reason but I also expoxied the small welsh plug for the acc. pump passage. So far so good. My eng. will only pull 14" of vacuum at idle so I had to add a Crane vacuum canister to help my power brakes in stop and go traffic. The idle was hard to adjust so I sprayed WD40 on the pri. th. shafts when the eng. was idling and the eng. rpm changed. I rebushed the carb base plate and that was that. Anyhow thats it for now.

Auggie

 

I haven't tried to see how the throttle plates look when opened from the pedal, and I'm sure they're not opening all the way! I'm usually working on this after work, when everyone has left. I suspect that if they aren't opening all the way, the cable may be stretched. I'm going to EFI within a year (I hope!) so I may not put a new cable in it until then. I'm sure after 216,000 miles, it has stretched some, just like the shifter cable had about 10,000 miles ago!

As for the plugs, I epoxied the 2 for the primary metering rods, the one for the accelerator pump, and just to be sure, I also hit the 2 where the secondary metering rods are. I'm not sure if they are common leaks, but since I had it apart that far, it didn't hurt anything!

On the topic of vacuum, the 14-15" range seems to be right where the power brake issue comes into play. I have 15" and the brakes are fine, but not perfect all the time. After the car is warmed up completely, I don't have any issues, but as it warms up, the pedal feels just slightly harder, barely noticable. I think the ECM would be able to deal with down to 13 at idle, although I haven't personally verified this.

Vacuum leaks? I can hardly believe it, but I couldn't find any! I put a new base gasket on it tonight after putting the carb back together, then I started it. It didn't want to idle, so I sprayed it down to check for vacuum leaks. I couldn't find any, and after it finished warming up it was fine.

Just one last note, if you're having a problem, check everything! That stupid ThermAC on my car wasn't opening, so I gutted it, and it made a HUGE difference. I'm now thinking about finding a good drop base open element air cleaner, or just cutting mine up for more flow!

 

Add another snorkel to it. See tech articles for more details.

 

Well, you might want to look at www.ramairbox.com I put one of their air cleaners on my brothers 406 Monte Carlo because I cut off the sec. air valve stop (installed a set screw for adjustment) which allowed the sec. air valves to open all the way. This turned the Q-Jet carb into a 750 cfm unit and we felt that the stock air cleaner wasn't cutting it. Man did that make a diff. I kocked the plugs out of the carb air horn for the rich and lean screws so we could get at them to make adjustments without removing the air horn. We used an Air/Fuel Monitor to adjusted the air fuel ratio of the pri side first with the sec. disabled. Then with the sec's working we set the air fuel ratio at 13 to 1 at WOT using metering rods and hangers. After that we made a few WOT run's and checked plugs and they looked great. Well, thats it for now.

Auggie

 

I wanted to update the link that Auggie posted, because for some reason, it kicks you to some european telecom site!

www.ramairbox.com

It looks the same, but there's not a dot on the end of it! Weird thing on the net!

Wow! Those air cleaners look awesome! One downside, I don't think I can part with that kind of money, when it will get replaced when I go to fuel injection. If I was planning to leave it carbed, or TBI, I would probably get one!

 

Man you are right. Sharp eye. That dot at the end is the period at the end of the sentance

Auggie

 

Yeah, I've seen the ram air box people, and geez they want a chunk! I think I'll rig up something with dryer ducting or something on my own...

Thinking of fitting ram air under all there with all the cr@p the LG4 came with - how much stuff can I remove without setting "check engine" lights? Any way to make it look like there's actuaslly an engine in there, and not a bundle of wires and hoses?
I was looking at the AIR pump system, and it looks like there's an electrical connector going to the diverter valve or something? Would removing that screw with the computer? I'd really love it if I could ditch the smog pump, then move the AC compressor there, more out of the way... No, Idaho doesn't have any form of emissions inspection (or safety inspection, either!) but I'd keep the hardware around just in case.
I'd leave on the EGR, because I assume the timing curve the computer has assumes EGR to be working, but is there anything else that can be removed?

 

The AIR doesn't affect the ECM, it's just controlled by it. If you remove it though, the Catalytic convertor doesn't work as well, and therefore MAY cause problems with it. Althoug I ran mine for a couple years like that without the first problem, and even when I pulled the cat off, it was clear and I could see right through the honeycomb! My EGR also has been disconnected for even longer than the AIR because the vacuum line broke and I never fixed it. Just keep an ear out for pinging. I don't have that problem anymore with the new engine, as the aluminum heads tend to help keep down on the detonation.

I don't know how you would get the A/C pump mounted down lower, but it does sound like a good idea! Maybe part of the bracketry from an '93 or newer LT1 would help? Although the mechanical fuel pump may be in the way in that case.

 

Well, I had all that stuff hooked up because MN did a tailpipe test for a few years but the air around here is really good so they stopped the testing. Anyhow a lot of people said that they never needed it in the first place. So I disabled the EGR valve, removed the charcaol canister (EEC),removed the air pump/diverter valve (AIR) and removed the cat converter. I have SLP headers so the EFE system (heat riser) is also gone. I have a home made 14" x 3" duel snorkel air cleaner with a K/N filter so I also don't have the THERMAC system working. I converted my trans (700R4) over to a non-lockup tq. converter so the TCC system is gone. I don't know what year your car is but mine is an "84" and the computer did not seem to care so it never set any check engine lites. I haven't removed the AIR tubes going to the headers yet but when I install the 406 I will do that. I have everything stored away in case I need it. I did not have all that stuff removed but I did disable everything before my "Last" test and I failed. CO2 = .77% and spec is 1.20% HC (ppm) = 363 and the spec is 220 (ppm). I installed the cat and I passed. CO2 = 0.00% and HC (ppm) = 27. I have a 355 with a cam that has 222* @ .050 for both INT. and EXH., .467 lift on 110* lobe centers. Runs pretty clean. Well thats it for now.

Auggie

 

Cool, sounds like I'll be taking a few things off then Might actually be able to see the engine soon (not that that's a huge plus, it's covered in grime)

I actually spoke with a guy in Spokane recently who passed emissions without EGR, or even a cat on a '76 with a mild 350. Of course, I'm sure that car has looser regs to pass. But, he said his '02 didn't even come with EGR...
I've heard that the cars didn't even really need the AIR pump to begin with anyways, and no new cars seem to have them. Improvements in cat design, and engine controll? I can't see GM spending the money to put them on if they didn't think they needed them! With the CC keeping the A/F stable and optimal, I guess it shouldn't be a problem though.

What stuff is involved in the TCC system? I definately don't want to give up lockup - there are alot of highways around here and it gets HOT in the summer, so less trans heat, and lower RPM are a plus.
BUT, I wouldn't mind just having to flip a switch in the cabin. My '77 will be the same once I rebuild a 200-R4 for it.

I'm going to have to look at moving the AC some more. Hadn't thought of the fuel pump clearance, hmmm...
My main worry was that the AIR brackets wouldn't be strong enough - they certainly put enough bracing to hold the AC on! I was thinking that the demands on the AC system might put alot of torque on the brackets?

 

Some engines don't need EGR. Many setups don't NEED the AIR to keep things functioning properly, but they may need it to pass emissions testing. In order for the cat. to work properly, it needs to have enough air to burn the fuel. Without getting knee deep in teory of operation here, that is why the O2 sensor needs to switch back and forth from rich to lean.

As for the TCC system, there are many aftermarket lockup kits available, or you can wire up your own with a vacuum switch and harness out of an early 80's S-10 with a 2.8 carbed engine.

A couple issues with the AIR brackets holding the A/C pump, they aren't strong enough, the A/C requires a decent amount of power to turn it as it is compressing refrigerent to around 150-200 psi. The second issue, the AIR pump is much smaller in diameter and just wouldn't line up. THe other thing is the cost of getting custom lines fabricated for it. Now if you could use some other brackets, you may have something.

 

Well, I am not a fan of extra toggel sw's to control TCC or elect. cooling fans ect,ect. I think that not to many third genner's let other people drive there rides but just in case that does happen I like everything to be automatic. I don't like handing out an operators manuel when I let someone drive my car. As far as the TCC goes I had to have my trans overhauled (it was getting tired) and the lock-up tq. conv. was making a rumbling noise at hwy. speeds. Drove me nuts. I knew that I had to replace it anyhow and I didn't like the lock, unlock feature so I bought a conversion kit from TCI that redirects the oil flow in the trans to keep the oil temp down. I bought a rebuilt 700R4 diesel tq. conv. with a 1500 stall speed. I know that sounds odd but I drive my car 99.9% on the street and just have street tires. With a high stall conv., say 2500rpm the HP is much higher then at 1500 rpm and over powers the street tires very easy. If the tires are spinning your not going anywere. I can leave the lite at almost WOT and no tire spin and to top this off does that trans without the TCC system drive nice. I installed an oil temp gauge (i had to know) on the oil pan and the trans oil temp ran so close to coolent temp that I removed the gauge. So with out the TCC system trans oil temp is not an issue. Anyhow back to what controls the TCC sy. The ECM does that by looking at internal trans fluid pressure, VSS, CTS, TPS, gear select sw., and the brake sw. The ECM lookes at all of these and if everything is OK it will ground the TCC sol. compleating the circuit. I think that the sol. moves a valve or check ball allowing the conv. cl. to apply. I am not sure if I got that right or not but mabey someone else could help us out here.

Auggie

 

You got it really close, except the ECM doesn't look at anything inside the transmission for determining the lockup. It looks at CTS, TPS, MAP, and VSS to determine lock and unlock. In all reality, the ECM strategy tries to KEEP the TCC engaged, and basically uses inputs to unlock it, such as below about 35 MPH and WOT, etc.... nad it WILL lockup in any gear other than reverse and first, where it is hydraulically prevented. The pressure switch that is inside the trans is for determining when it is in Fourth gear. Th ECM uses this for some reason, but I'm not into things far enough to know why!

Auggie....What sort of cooler setup do you use? Do you use the stock cooler in the radiator? Just curious. I plan to run an aftermarket cooler myself, maybe even one with it's own fan! Since you have a street only car, the lower stall convertor is fine, but one thing to consider, the 1500 stall and a gas engine is likely going to be lower than on the diesel because the diesel makes a lot more torque at 1500 RPM's than your gas engine. A towing/RV convertor would be my choice, but if it is how you like it, I don't see any problem!

 

Well, I just use the stock rad. cooler. I thought about installing an aftermarket trans cooler but what if i didn't need one so I opted to buy a oil temp gauge insted because I also wanted to check eng. oil temp. Your right about the diesel stall rpm's but I was thinking of the future. One of these days I will finish my 406 and it should have enough ***** to increase the conv. stall rpm slightly. The 406 that i built for my brother had 423 hp with 467 lb. ft. of torque, idles at 650 rpm in "D" and flew through emissions when they were testing.

Auggie

 

Wow, 423 HP and passing emissions! That's about where I will be when I get my car finished, but I'm glad we don't have emissions testing here, I know it would fail!

 

I have a CC Qjet I just rebuilt. I've set the lean mixture stop according to the directions from a mixture kit I bought. You know, take out the primary jets, put in the metal spacer, tighten the screw until the plunger just touches it in the down position.

Then I assembled the airhorn with the rich mixture screw fully up (fully rich). The directions say I should adjust the rich screw until I have 4/32" of plunger travel. Well, I didn't even touch the rich screw and I have about 7/64" of travel. Is this right? Shouldn't I have to turn the rich in at least a little bit? How do you guys set your lean and rich stops?
thanks

 

Well, I set my rich and lean mix. settings using an Air/Fuel Monitor gauge. I have knocked out the alum. plugs in the air horn so I don't have to remove it to gain access to the adj. screws. I taped the hole for the lean mix. screw and plugged it. After a lot of testing here is what I ended up with. The rich mix. screw is set at full rich or all the way up. The lean mix. screw is set at two turns up. Turn the screw all the way in and back it out (2) turns. I don't know what the measurement is for the sol. plunger movement? Too do the testing on the pri. side only you will have to disable the sec's so your A/F readings will not be influenced by the sec's. I used a real heavy spring (small) so the sec. throttle plates will not open. After that is done you can put the sec's back into the pic. and start all over. Have fun :lala:

Auggie

 

Solenoid plunger movement is based on the rich and lean stop screws. The higher up you put the rich screw and the farther down the lean screw, the more room the plunger has between them and the longer the travel gets. I always wondered why you wouldn't simply open them up all the way to give the computer the largest range of fuel mixtures to pick from. I'm glad someone did the real-world test to figure out that this really is true.

Not having access to the equipment that you have, I'm gonna just copy your settings. Qjets are adaptable enough that as long as I set the idle screws and IAB, it should probably work quite well.
Thanks Auggie,
Homer

 

Well, as you know Homer there are trade offs. The extra travel of the sol. plunger will cause more wear on the plunger rod and there is a possabilty of the plunger sticking in the down position. I have had these settings on my carb for years and two years ago my eng. started to idle rough and would die sometimes. After awaile the check eng. lite came on and set a code 44 (lean).
Anyhow I made it home and removed the carb air horn and found the sol. plunger stuck in the down pos. I removed it and did notice some sratches on the plunger rod. I polished the rod with #600 wet paper and put some light grease on it. So far so good. So when you go to start your car move the key to the on pos. and listen for the clicking noise that a happy plunger makes. I think that you could remove the IAB (count the turns) and gain access to a stuck sol. plunger to free it up with out removing the carb air horn. Thats it for now.

Auggie

 

the clicking noise that a happy plunger makes

I was just gonna ask what that clicking noise was when I turned on my key! I'm glad my plunger is happy- one less thing to check out.