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Performance Olds 307
Understanding The ECM & System
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Understanding The ECM & System
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This page is to help you get a better understanding of the ECM and system as well as a start on getting it running right, before you start modifing it. It is very important to tune it back to stock standards before you start changing things especialy if you are looking for better fuel economy it is also important to understand the basics of the system. This page will send you on the right track but sooner or later you are going to need a GM service manual if you dont already have one there's just to many little things about the 307s ECM and system to put on one web site Please invest in a manual to aid you in your studing. The article below was writen by Bob Powers, Akron, OH, he has did a great job at explaining the system.   

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The following is information on the CCC computerized carburetor systems used in many '80's GM cars.
I have seen a bit of talk on the Computer Command Control or CCC computerized carburetor cars recently, and wrote this to clear some things up.

The system uses a rudimentary computer to control:
- Ignition advance
- Idle to part throttle fuel enrichment
- Transmission torque converter lock up
- A/C compressor on/off (when it can run, not the exact pressure it kicks on and off at)
- Some other misc. emissions stuff, like Air Injection Reaction system function
That's it! The computer does NOT control:
- The secondary side of the carb
- The total advance (it has no idea where initial timing is)
- Transmission shifting
The computer needs a lot of sensors to know what is going on. The most important sensors are:
- Throttle Position Sensor (TPS) - inside the carb, senses how far the throttle is opened.
- Oxygen sensor (O2 sensor)
- Coolant Temp Sensor - engine temp
- Manifold Absolute Pressure sensor (MAP sensor) - engine vacuum
- Barometric pressure sensor (Baro sensor) - outside air pressure
- Senses RPM through the distributor
- Vehicle Speed sensor - it's built into the back of the speedometer cluster - senses vehicle speed
- 4th gear pressure switch - this tells the car when it's in overdrive. There may be a 3rd gear pressure switch, I'm not sure
- Later vehicles, '86 and later I believe have a knock sensor that detects pinging and detonation.

With these parameters known, the computer has a fuel and spark map. The computer operates in either "Closed Loop" or "Open Loop". Open loop means that the O2 sensor is not hot enough to work yet, and the computer is adding fuel and ignition advance based on the parameters in the computer with no feedback. Closed loop means it is getting feed back from the O2 sensor and is adjusting accordingly. Now the computer has a fuel and spark map that says for each sensor condition, the fuel and spark should be a certain value. On top of that it has a "block learn". It knows that the motor should need about a certain amount of fuel, but that could be a little off due to engine wear and tear, etc. So it can adjust that value based on what the O2 sensor says the exhaust Oxygen content is. This is why sometimes you need to disconnect the computer so it will "re-learn". If the computer is doing as much compensation as it can and the exhaust is still lean or rich, you will get a check engine light. Now the as I said in the beginning, the computer does NOT control the fuel delivery per se - it controls part throttle fuel enrichment. It does this via the MC solenoid. It is a solenoid that 10 times per second, can move the primary metering rods in the carb either up or down. But it still has jets and primary metering rods, similar to older carbs! Except you never really need to change them. Moving the rods up richens the fuel mixture. Down leans it out. It does this 10 times a second, so up-down-up-down-up-down-up-down-up-down would be half way between rich and lean. When you put the computer in diagnostic mode with the motor off, this is the ticka-ticka-ticka you hear.

The ECM makes all the decisions. Just like a person's brain, the brain gets info from all your senses. It takes all that input, and decides when things are right. For all of the computer's governed functions to work properly, the car must not be in "limp home" mode. Limp home is when something is wrong, and the ECM cannot make effective decisions. The O2 sensor could be bad, another sensor could be bad or disconnected, the ECM itself could be faulty, etc. The computer then goes out of closed loop mode, into open loop, and reverts back to a pre-set "limp home" setting with the carb rich, the converter un-locked, and the timing more retarded (less advance). These settings will get you home and the car to the shop with the least chance of damage to the car. Fuel mileage will be very poor in this mode.

Other than the M/C solenoid, the carb functions as any other Quadra jet. The secondaries are not computer controlled at all. All CCC carbs are 800CFM body castings. Their CFM is limited by the opening of those doors covering the secondaries, the secondary air valve. To cut the CFM down, they make the doors stop before they are fully open. If you increase the power of your 307 and need more carburetion, you can grind off the end of the metal stop that limits the opening of the doors. Look at an early non-computerized Q-jet and see how far the doors open - should be 'till the front part of the doors are vertical.

The secondary metering rods on most 307 carbs are "DD" rods with a very fat tip, calibrated for the stock 140HP engine. Fat tip = leaner, small tip = richer. If you swap a 350/403 into your Cutlass and use the CCC carb and distributor, of course it needs more fuel and air. First you should modify the secondary air valve doors, then you change out the DD metering rods for something like a set of AU's. Seventies 350 cars are good ones to get metering rods from.
Now, there are a LOT of vacuum hoses on the motor. If ONE of them gets a hole in it, the car may not run right as it will have a vacuum leak. Common causes are:
- Improper chrome air cleaner install. The extra lines should be removed and the open tee should be plugged.
- Lines bake hard and crack from age - especially near the hot EGR valve, and to the pass side exh manifold (the EFE or Early Fuel Evaporation valve).

The emissions tag on the radiator shroud does show the proper routing of all the emissions hoses. If your 307 has over 80k miles, replace them all (1 at a time).
The Air Injection Reaction system is widely misunderstood. It's job is to:
- Inject air into the cylinder heads and catalytic converter when the engine is in warm-up mode. Air is only injected into the heads at warm up. Think about it - how could the oxygen sensor tell what the air/fuel ratio is in the running engine with fresh air being pumped into the head upstream of the sensor? It couldn't.
- Inject air into the converter during various other times such as deceleration an full throttle when mixture is overly rich.
- The AIR system's main function is emissions control when cold.

The CCC system will work just fine without the Air pump, without the AIR manifolds, and without the 2 connectors that plug into the AIR system being plugged in. My '85 Cutlass has passed Ohio emissions several times without the air pump and air lines with a '78 350.

If you swap a 350 or 403 or even a mild 455 into one of these cars and want to keep the CCC system, do so! You will be rewarded with better miles per gallon, and more precise fuel metering, as well as still retaining tranny converter lockup. Although not technically legal, I like to delete the AIR System as it greatly clears up the engine bay, and makes service to the valve covers and fuel pump easier. I have a buddy who for several years had a '78 Caprice wagon with a 455 and a CCC carb from a 307. He richened up the secondaries as described above.

Another modification to the carbs - they come with 2 plugs over the area where the idle mixture screws are on Q-jets. With the carb off the car, and a small chisel and some care, with the carb flipped over you can knock these plugs out. With a larger engine, you can re-adjust these as needed. The idle mixture screws affect fuel metering up to 1/3 throttle. If the mixture screws are off, most of the time you will get a check engine light when cruising down the highway, and the code will be 44 - lean exhaust or 45 rich exhaust if you adjusted it too far rich.

The computer has no idea where initial timing is. On most CCC cars, the factory spec is 20 degrees BTDC with the diagnostic port grounded (car in diagnostic mode). Now this is not like an older car having 20 degrees timing. The CCC cars seem to run best (ET at the track and drivability wit h 87-89 octane) with 25 degrees to 27 degrees. I had mine set to 27 degrees in my '85 with the 350 when it ran 14.54 ET.

If you remove the computer carb, dist, wiring, sensors, and computer (Electronic Control Module, or ECM), the computer wiring harness is a separate harness from the alternator, gages, starter wires, etc. The CCC wiring all goes to the pass side on Cutlasses and behind the pass wheel well through the fire wall to the ECM. You can remove it all for a drag car and still keep all the other wires. If you do though you will:
- Need some other way to lock up the tranny lockup torque converter
- Re-wire the relay for the air conditioner as the AC will not kick on (this is easy)

The lockup torque converter is needed because the turbo 2004R and 700R4 trannies reduce the amount of pump output and coolant flow through the tranny when in overdrive locked up. This improves fuel economy. If you run the tranny unlocked in overdrive, especially with 2.xx series rear end gears, you could damage the transmission.

For lockup to occur, the vehicle speed sensor must be able to tell the computer the car is over about 40MPH (the computer actually reads in metric BTW - speed =kph, vacuum = pascals or kPa (I forget). You must be at light throttle. The rpm's must be low. The brake must not be applied (If you were to slam on the brakes and lock up the rear tires with the converter locked up the motor would stall). I'm a little foggy on the transmission pressure switches, but I think the ECM has to know that the tranny is in 3rd or 4th gear. If all these conditions are met, the computer will allow lockup and apply voltage to the lockup solenoid.

Lockup actually happens simply by applying 12 volts to the lockup solenoid. You can control the lockup with a toggle switch if you delete the computer. Crude, but it will work. The B&M lockup kit uses a speed sensor in line with the speedometer cable, so it can be adjusted as to what speed it locks up at. Downside to it is that if it's set to 50MPH, it locks up at 50 no matter what the throttle position. Very annoying when you are getting on the highway at 1/2 or 2/3 throttle and the motor is revving nicely waaaaaaa- then it bogs down because of the lockup bwwwwuhhhhhh. I am trying the following out on my car out this spring - For applications that need control over the lockup torque converter without an ECM, use GM P/N 14032087, "Switch" came in '83-'84 Chevrolet pickups. This is a vacuum operated switch that when wired in line with the lockup solenoid, will only allow current to flow to the solenoid at high vacuum (light throttle). It comes with a 2" x 2" zinc plated steel mounting bracket. If the tranny is re-wired such that it only locks up in 4th gear, this works out nice; you don't need any speed sensor because it will only lock up in 4th, which with 3.23 to 3.73 gears will be like 35-40 MPH.
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Wiring changes for a TH200-4R to allow Lockup only in 4th Gear:
- Leave the red wire from the TCC solenoid to the case connector.
- Splice the black ground wire from the TCC solenoid to the (usually) blue wire running from the 4th gear clutch switch.
- Cut off and remove any additional internal wiring.
- Not all 4th gear switches will work with this wiring setup. It will only work if you have a normally Open (N/O) switch. You can check this with a meter. If it shows zero resistance when you measure across the contacts, it's the wrong kind. To correct this, get a switch from a GM dealer, part number 8627332.

See photo, above right
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Many people hate the CCC system, only because they don't understand it, and it has been neglected! It is a reliable and efficient system! If everything is hooked up correctly, you should rarely have a problem with it. Generally when there is a problem, you read the diagnostic code, and replace a faulty or worn out sensor.

If you build a motor or change a cam in a motor and are using the CCC, keep the cam duration mild. RV cams work well. If you were building a race car, you wouldn't have this system on there. There are several cam makers that make a cam with the following specs:
204/214 degrees duration @ .050"
.448/.472" lift
114 degrees Lobe Separation Angle
I have used this cam with stock non-adjustable valve train for 150k miles. The car has good power from 1,500 to 5,000 rpm, and respectable fuel economy with this camshaft.

I would say that with a 350 or 403, the largest cam you would want is in the range of:
214/224 degrees duration @ .050" (int/exh)
112 degrees LSA
You definitely want a wide Lobe Separation Angle. This is not to say a larger camshaft would not work with the CCC system; I have no personal experience with larger cams and the CCC system. All the cars with larger cams I have worked on are primarily set up to go fast, and the computers have been deleted.

If the manifold vacuum drops too much, the fuel/spark map will be off at low throttle. Now you can replace the PROM (Programmable Read Only Memory) chip in the computer with a fuel/spark map corrected for your engine modifications. Replacing the PROM is the easy part. Getting a corrected fuel/spark map is the tough part. You either need to speak with a company that specializes in replacement PROMs, or find someone who has de-coded the air/fuel map program and knows which areas of the coded correlate to which functions. In the do-it-yourself fuel injection circles, the programs for certain cars have been broken down and modified already. A good place to start may be http://www.diy-efi.org.
Does your check engine light come on?
If it does, you need to remedy that. Some people think that if the light comes on and then goes off, it was just a temporary problem. This is not so. If during driving, the light EVER comes on, the ECM will log a fault code and store it in the computer. For most problems, the check engine light will come on for a little while and go out. To adjust the ignition timing or to check for trouble codes, take a paper clip and jumper the 2 top right terminals on the ALDL connector, terminals "A" and "B" (see diagram at the top of this page). This is the diagnostic connector; it may have a cover on it. It should be under the dash between your legs, or somewhere nearby. It is black and has 2 rows of 6 pins. Jumper the 2 top right spots, and turn on the key. (If you are setting timing, have the motor running, then jumper A to B, then check timing, then when you are done pull out the paper clip.) The MC solenoid should start ticking (ticka-ticka-ticka). The check engine light will blink out a code. First should be a (flash) (pause) (flash-flash). This is code 12 - no engine RPM signal. This should ALWAYS come up first, as the motor is off, so of course, no engine RPM signal. It will do each one 3 times, so you will see the (flash) (pause) (flash-flash) two more times. THEN it will flash out any stored trouble codes (3 times). If there are none, you will see code 12 again. The Haynes manual has them all listed. Click on the thumbnail at the right to see the codes and explanations.
Bob Powers, Akron, OH
www.robertpowersmotorsports.freeservers.com
Street HOF#255
'86 Cutlass/461/TH400/3.73 8.5"

Arrow Now that you have a basic understanding its time to do is a simple tune up. Change the plugs, cap, rotor, wires (if needed) air filter and changing the engines oil if you feel extra nice change the transmissions fluid and filter also If you need instructions on doing that then its best if you just close your hood and find a mechanic because this is basic stuff. Its is very important to check the ECM for errors, check out the page on my site called "ECM" to learn how to check and repair. Everyone knows how to change plugs but you might want to read my "Ignition & Spark" page under the subject "Indexing Plugs" for a good modification tip before changing them also on the same page is a article on ignition timing and how to check it. The TPS sensor should also be checked and adjusted if needed, find out how to do this on page "Carburetor & Intakes 1" it is also important to adjust your Q Jet, check out the page "Tuning The Q Jet" for info on this!

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