Understanding the Fuel Delivery system of Carbureted late 2nd and early 3rd Gens

If you have considered overhauling your computer controlled carb on a late (80-81) 2nd Gen or early (82-?) 3rd Gen, you could be forgiven for scratching your head and giving up due to the lack of literature on the subject. My Haynes workshop manual basically says "Don't bother, you are not smart enough to do this yourself", my manual is a little better in that it gives some specs and settings such as float settings and fast idle speed etc.

The Carb pictured in this article is one I obtained from a wrecker for the purpose of stripping down and examining, I dont know its origin but I assume it would be of the late 70s to early 80s in vintage. Although my Chiltons manual (Camaro 67 to 81) gives a year reference according to model number, this one was not listed, indicating it may have come from an 81 on model.

Before you begin to strip down and overhaul your carb you are going to need the following

1. A carb overhaul kit ( my 82 T/A took a Fuel Miser part no RT609A kit)
2. A tin or two of pressure pak degreaser
3. A couple of tins of carb cleaner
4. Some tape or tags to mark where vacuum pipes and associated plumbing go.
5. Some Ziplock bags to isolate carb components
6. T25 torx head screwdriver for some models
7. The model of the carburetor located to the rear of the Quadrajet name (see photo above)

Overview

The carbs used on computer controlled late 2nd Gens (80-81) and early 3rd Gens (82-?) are models E4ME or E4MC. The carb can be identified by a model number stamped into the external float bowl just behind the cast in lettering "Rochester Quadrajet". The model number of the carb shown in this article is a "17080530". The electronic function of the carb is to regulate the fuel/air mixture delivered to the engine at idle.
This is achieved by the ECM receiving input from the Exhaust Oxygen Sensor, the Throttle Position Sensor and the Distributor Advance Sensor. The ECM reads the signal from the O2 Sensor and depending on either a lean or rich condition being reported, pulses the piston driver solenoid at a higher or lower frequency.
This in turn increases or decreases the amount of fuel being delivered to the induction system at idle. It should be noted that the ECM only controls the idle mixture and has no say in the amount or concentration of fuel delivered at part to full throttle.

O2 Sensor info

Before proceeding any further, ensure that the O2 Sensor is operating correctly, it is a pointless exercise to strip down and rebuild a carb without verifying the O2 Sensor is functional. GM calls for replacing the O2 Sensor every 24000 miles or 24 months, whichever comes first. If you can't remember the last time it was changed, then you probably should replace it now. Additionally a good O2 Sensor may become contaminated and rendered useless if exposed to the following:

• Silicone (Silastic) always use an approved sensor safe sealant on gaskets.
• Leaded fuel.
• Excessive engine oil in the exhaust system.

Removal & Cleanup

The best method of approach is to completely remove the carb from the vehicle to work on it. Before removing the carb be sure to tag all vacuum hoses and pipes to ensure they go back where they belong when re-installing. Don't worry too much about the wiring bits as they can only go back one way.
Once the carb is removed from the vehicle it will be necessary to initially clean all grease and fuel dye from the external surfaces and linkages. A parts cleaner machine is most suitable, however if this is not available some degreaser will suffice. Do not use fuel or solvent to clean the carb as it presents a hazard in that a stray spark may ignite the solvent and cause serious burns to the repairer.
Once the bulk of the grease is removed use a pressure pak carb cleaner to remove the final residue.

Disassembly

Locate the 13 flat blade or T25 torx head machine screws (don't forget the two under the choke butterfly) and remove. If some screws are stubborn, don't force them, spray them with a substance such as WD40 and allow it to soak in. Once all the screws are removed, carefully tap the roll pin that retains the accelerator plunger pivot plate toward the carb body. Tap it in just far enough to allow the plate to slip out of its saddle but not so far that it is hard up against the housing. Next carefully remove the carb top and place it down carefully being sure not to bend or damage the metering rods. (it may be necessary to carefully pry the carb top up to remove it. If this is required be careful not to damage any of the carb top to base mating surfaces and be especially careful not to distort the carb top by applying too much pressure, if there is significant resistance go back and make sure you have removed all 13 hold down screws)

Once the piston retainer screw is removed the piston driver solenoid may carefully be removed and placed aside. Don't lose the small spring located in the base of the float bowl that the solenoid fits into.

Finally remove any remaining components such as pump plunger and brass jets, note the condition of the mixture solenoid wiring harness basket and replace if cracked or broken.
Proceed to soak the carb body in carb cleaner to remove gum and fuel dye, use compressed air to force contaminants from bleed holes and galleries. Once carb is spotless re-assemble in the reverse order using new gaskets and components supplied in kit and fit to vehicle.

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