Feedback Carburetor Symptom Tests — Chevrolet Camaro II (1970-1987)

HOW TO USE THIS ARTICLE - TESTING

This portion of the article is to be used only AFTER you have checked that

The On-Car Diagnostics are working.
The ECM and "SERVICE ENGINE SOON" light are operating.
There are no trouble codes stored, or only intermittent ones.
The fuel control system is operating properly, by performing the System Performance Check.
A careful visual check found no obvious problems.

Verify the customer complaint, and locate the correct symptom below. Check the items indicated under that symptom. These procedures will normally lead you to a specific component or component system on the vehicle, such as EGR, EST, TCC, etc. These tests are covered in the FEEDBACK CARBURETOR COMPONENT TEST article.

Symptom Definition

"CHECK ENGINE" light comes on at all times, but does not stay on. A stored code may or may not exist.

Possible Cause & Correction

Check for poor mating of one connector to another. Terminals may not be fully seated. Check for improperly formed or damaged terminals. Check wire to terminal connections.
Check for poor connection from ignition coil to ground or arcing at spark plug wires or plugs.
Check wire from "CHECK ENGINE" light to ECM for short to ground.
Check for poor connections in wires from ECM terminals 12 and 13 to engine ground.
Check for loss of the trouble code memory. To check this: Ground dwell lead for 10 seconds with "test" lead left ungrounded. Code 23 should be stored and retained in memory after ignition is turned "OFF." If not, ECM is faulty.
Check for electrical system interference caused by a defective relay or an ECM driven solenoid or switch. They can cause a sharp electrical surge. This type of problem will normally occur when faulty component is operated.
Check for improper installation of electrical accessories such as auxiliary lights or 2-way radios.
Make sure that EST wires are kept away from spark plug wires, distributor wires, distributor housing, ignition coil and generator. Make sure that ground wire from ECM to distributor is connected to a good ground.
Check for open diodes across air conditioner compressor clutch.

This is defined as engine cranks properly, but does not start. Engine may fire a few times.

Perform «DIAGNOSTIC CIRCUIT CHECK»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-symptom-tests__diagnostic-circuit-check) .
Make sure proper starting procedure is being used.
Visual Check
Vacuum hoses for splits, kinks and proper connections, as shown on the Vehicle Emission Control Information label.
Ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs.
Remove air cleaner and check carburetor choke valve, vacuum break(s), linkage and unloader operation. See FUEL SYSTEMS Section. Choke valve should move smoothly and be closed when cold; open when hot.
Check for presence of fuel by noting carburetor accelerator pump operation. Look for gas squirt in carburetor bore while quickly opening throttle lever. If no squirt, check for: fuel in tank, carburetor fuel inlet filter dirty or clogged, fuel pump capacity, and float needle for proper operation. If there is a pump squirt, crank engine and check for flooding. If engine is not flooding check ignition system. See IGNITION SYSTEM CHECKS in the «FEEDBACK CARBURETOR COMPONENT TEST»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-component-test) article.
Remove spark plugs, check and replace as necessary.
Remove distributor cap and check for moisture, dust cracks, burns, and arcing to coil mounting screws.
Try to turn distributor shaft by hand, drive pin may be broken.
After starting engine, perform «SYSTEM PERFORMANCE CHECK»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-symptom-tests__system-performance-check)
In very cold temperatures, check that the oil is the proper viscosity and that the crankcase oil is not contaminated with gasoline.

Engine cranks, but does not start for a long time. Eventually, the engine does run. If the engine starts but immediately diesels (as soon as the key is released from the start position), refer to NO START - ENGINE CRANKS OK .

Perform procedures for both the DIAGNOSTIC CIRCUIT CHECK and the SYSTEM PERFORMANCE CHECK . Be sure the driver is using the proper starting procedure. Visually check the following

Vacuum hoses for splits, kinks and proper connections, as shown on the Vehicle Emission Control Information label.
Ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs.
Air leaks at carburetor mounting and intake manifold.
Wires for pinches, cuts, and proper connections.
Check the choke valve, throttle and fast idle cam for sticking. Replace any malfunctioning parts. If caused by foreign material and gum, clean with non-oil base solvent.
Check choke and vacuum break operation adjustment.
Check EGR valve system for faulty operation that could cause valve to stick open.
Check float level using external float gauge. Adjust float to specification if required.
Check carburetor fuel inlet filter, replace if required.
Check ignition system. See IGNITION SYSTEM CHECKS in the «FEEDBACK CARBURETOR COMPONENT TEST»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-component-test) article.
Check distributor for; Worn shaft, bare and shorted wires, pick-up coil resistance and connections, loose ignition coil ground, and moisture in distributor cap.
Remove spark plugs; check for wet plugs, wear, improper gap, burned electrodes or heavy deposits. Repair or replace as necessary.
Check ignition timing and adjust if necessary.

Perform procedures for both the DIAGNOSTIC CIRCUIT CHECK and the SYSTEM PERFORMANCE CHECK . Be sure the driver is using the proper starting procedure. Visually check the following

Vacuum hoses for splits, kinks and proper connections, as shown on the Vehicle Emission Control Information label.
Ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs.
Wires for pinches, cuts, and proper connections.
Check the choke valve, throttle and fast idle cam for sticking. Replace any malfunctioning parts. If caused by foreign material and gum, clean with non-oil base solvent.
Check choke and vacuum break operation adjustment.
Check EGR valve system for faulty operation that could cause valve to stick open.
Check float level using external float gauge. Adjust float to specification if required.
Check carburetor fuel inlet filter, replace if required.
Check for obvious overheating problems.
Check EFE valve or electric heater if applicable. EFE valve should be "OPEN," heater should be "OFF." See EFE CHECKS in «FEEDBACK CARBURETOR COMPONENT TEST»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-component-test) article.
Check ignition system. See IGNITION SYSTEM CHECKS in the «FEEDBACK CARBURETOR COMPONENT TEST»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-component-test) article.
Check distributor for; Worn shaft, bare and shorted wires, pick-up coil resistance and connections, loose ignition coil ground, and moisture in distributor cap.
Remove spark plugs; Check for wet plugs, wear, improper gap, burned electrodes or heavy deposits. Repair or replace as necessary.
Check ignition timing and adjust if necessary.

This condition is with engine at room or outside temperature, within three minutes after start. 1) Stalls after brief idle; 2) Dies as soon as any load is placed on engine (such as A/C turned "ON" or transmission engaged); or 3) Dies on initial driveaway. If symptom is present Cold and Hot, go to symptom "Stall After Start - Hot."

Perform procedures for both the «DIAGNOSTIC CIRCUIT CHECK»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-symptom-tests__diagnostic-circuit-check) and the «SYSTEM PERFORMANCE CHECK»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-symptom-tests__system-performance-check) .
Visually check vacuum hoses for splits, kinks and proper connections, as shown on the Vehicle Emission Control Information label.
Make sure hot air tube is connected to air cleaner.
Check for proper operation of THERMAC.
Check the choke valve, throttle and fast idle cam for sticking. Replace any malfunctioning parts. If caused by foreign material and gum, clean with non-oil base solvent.
With engine "OFF" check all choke adjustments, including vacuum breaks and TVS if used.
Check carburetor accelerator pump operation.
Check fast idle speed and curb idle speed if applicable.
Check EFE valve, or electric heater for proper operation. EFE valve should be "CLOSED" cold, electric heater should be "ON" cold. See EFE CHECKS in «FEEDBACK CARBURETOR COMPONENT TEST»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-component-test) .
Check choke and vacuum break operation adjustment.
Check EGR valve system for sticky operation that could cause valve to stick open.
Check ignition timing and adjust if necessary.
Check for poor or contaminated gasoline.

Perform procedures for both the «DIAGNOSTIC CIRCUIT CHECK»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-symptom-tests__diagnostic-circuit-check) and the «SYSTEM PERFORMANCE CHECK»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-symptom-tests__system-performance-check) .
Visually check vacuum hoses for splits, kinks and proper connections, as shown on the Vehicle Emission Control Information label.
Make sure hot air tube is connected to air cleaner.
Check for proper operation of THERMAC.
Check the choke valve, throttle and fast idle cam for sticking. Replace any malfunctioning parts. If caused by foreign material and gum, clean with non-oil base solvent.
With engine "OFF" check all choke adjustments, including vacuum breaks and TVS if used.
Check carburetor accelerator pump operation.
Check fast idle speed and curb idle speed if applicable.
Check EFE valve, or electric heater for proper operation. EFE valve should be "OPEN," electric heater should be "ON." See EFE CHECKS in «FEEDBACK CARBURETOR COMPONENT TEST»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-component-test) article.
Check choke and vacuum break operation adjustment.
Check EGR valve system for faulty operation that could cause valve to stick open.
Check ignition timing and adjust if necessary.
Check for poor or contaminated gasoline.

This is defined as a momentary lack of response as the accelerator is pushed down. It can occur at all car speeds. Usually, it is most severe when first trying to make car move. Occasionally, this condition may cause car to stall.

Perform procedures for both the «DIAGNOSTIC CIRCUIT CHECK»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-symptom-tests__diagnostic-circuit-check) and the «SYSTEM PERFORMANCE CHECK»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-symptom-tests__system-performance-check) .
Visually check vacuum hoses for splits, kinks and proper connections, as shown on the Vehicle Emission Control Information label.
Visually check ignition wires for cracking, hardness and proper connections at both distributor cap and spark plugs.
Visually inspect wires for pinches, cuts, and proper connections.
Make sure hot air tube is connected to air cleaner.
Check for proper operation of THERMAC.
Check float level using external float gauge. Adjust float to specification if required.
With engine "OFF" check all choke adjustments, including vacuum breaks and TVS if used.
Check carburetor accelerator pump operation.
Check fast idle speed and curb idle speed if applicable.
Check EFE valve, or electric heater for proper operation. EFE valve should be "CLOSED," electric heater should be "ON." See EFE CHECKS in «FEEDBACK CARBURETOR COMPONENT TEST»(/chevrolet/camaro/ii-1970-1987/remont/testing-diagnostics/#feedback-carburetor-component-test) article.
Check vacuum hose to MAP sensor for leaks, restrictions and proper connections (should be manifold vacuum).
Check EGR valve operation.
Check TPS adjustment.
Check canister purge system.
Check for open ignition coil ground and for intermittent ECM ground.
Check engine ignition timing.
Poor or contaminated gasoline.

DIAGNOSTIC CIRCUIT CHECK

Diagnostic Circuit Check determines if: 1) the "CHECK ENGINE" light works, 2) the ECM is operating and can recognize a fault, and 3) any codes are stored. It also checks to see if stored codes indicate an intermittent problem. This is the starting point for any diagnosis. If no codes are indicated, go to the System Performance Check. If no additional checks are called out from the System Performance Check, go to the Driveability Symptoms.

Check operation of the "CHECK ENGINE" light. Key "ON", engine not running, light should be on steady.
Grounding test terminal will flash a Code 12 and any stored trouble codes. The light must go "ON" and "OFF" to indicate a code. The light going from "Bright" to "Dim" is not considered a code. See CHART A-6.
This step will determine if any codes, other than Code 12, are still present or were intermittent and are no longer stored. Clear memory. Run vehicle for 2 minutes. See if trouble code(s) reset.
If the light is "ON", fault is still present. Go to the applicable trouble code chart. Refer to the appropriate TESTS/CODES article in this section. Press the light pen to the lower right corner "F10" to exit to the section menu. Locate the appropriate TESTS/CODES article. Press the light pen to the title and then scroll to find the test associated with the code.
If the light is "OFF", the fault is either intermittent, or it is a code that cannot be set with vehicle stationary. For codes that cannot be set during the Diagnostic Circuit Check, the applicable trouble code chart will determine if those codes are intermittent.

Note. The following flow chart may refer to test steps that are found at the end of this article or in other articles in this ENGINE PERFORMANCE section. Refer to appropriate TESTS W/ CODES, SYSTEM & COMPONENT TESTS, or TESTS W/O CODES articles in this section.

Diagnostic Circuit Check. Scheme 173

Scheme 173: Diagnostic Circuit Check

( * ) - To clear codes, remove power to "R" terminal of ECM for 10 seconds by removing ECM connector with ignition OFF or ECM/BAT fuse, or disconnect ECM power feed at battery. Verify codes have been cleared. The System Performance Check should be performed after any repairs to the "System" have been made.

( ** ) - It is possible to set a false Code 42 on starting, but the "Check Engine" light will not be ON. No corrective action is necessary.