Trouble Shooting Procedure
WHEN ENGINE WON’T START
When the engine fails to start, when the ignition system is giving adequate spark and properly timed, the fuel system or the engine itself is at fault. Causes of fuel system failure are as follows:
1. No fuel in tank.
2. Choke inoperative or flooding.
3. Water in fuel system.
4. Clogged vent in fuel tank filler cap, filler pipe or tank gauge housing, whichever is provided.
5. Fuel pump failure.
6. Vapor lock.
7. Clogged fuel pipe.
8. Leaking fuel pipe or connection.
No Fuel in Tank
Determine by the fuel gauge or with a stick whether there is sufficient fuel in the tank. The fuel must cover the end of the suction pipe lead ing to the fuel pump. This is usually about one inch. If the fuel level is low, tilting the vehicle will cause the fuel to flow away from or toward the end of the suction pipe.
Carburetor Fuel Test
After determining that the fuel tank has suffi cient fuel, find out whether the fuel reaches or enters the carburetor float bowl. Do this by dis connecting the fuel line at the carburetor. If the carburetor fitting is of the elbow type, hold the elbow with pliers to prevent it from breaking while unscrewing the union nut.
Crank the engine with the starter (ignition off).
If fuel is ejected from the open end of the fuel pipe during this test, clean the carburetor screen at the carburetor. Be sure the opening of the fitting at the carburetor is not restricted and that the carburetor needle valve is not sticking.
Inspect the fuel ejected from the pipe to be sure there is no water present. Connect the fuel pipe to the carburetor. If the fuel fails to flow from the end of the fuel pipe on this test, inspect the fuel pump.
Choke Inoperative or Flooding
Examine the choke for free operation. Be sure the choke will fully close and that it will fully open. If the choke is stuck in the open position, remove the air cleaner and restrict the air passage to the carburetor with your hand while the engine is being cranked. This will enable the engine to start by providing a richer fuel mixture.
If the automatic choke is stuck in the closed position, or if the manual choke is used to excess while attempting to start the engine, or if the carburetor float level is too high, the carburetor and intake manifold will be flooded with fuel and the engine will not start. This condition can be detected by fuel seeping from between the car buretor float bowl and the bowl cover, or around the throttle shaft end in the carburetor body, or it may be evident by seeping past the gasket be tween the carburetor flange and intake manifold.
If the engine will not start due to overchoking, set the choke and throttle valves to full open position. Then as the engine is cranked with the starter, the excess fuel will be drawn from the intake manifold and cylinders, restoring normal fuel mixture in the combustion chambers.
A condition similar to flooding by overchoking is sometimes encountered when trying to start a hot engine. This is caused by “percolating” within the carburetor when the engine is stopped. This action is caused by the warming of fuel in the carburetor float bowl, causing it to expand and escape through the carburetor jets into the intake manifold. All modern carburetors have provision to prevent this condition by venting the float bowl to the atmosphere or by the use of mechanical anti-percolator valves. However, if this condition should occur, the engine can be started in the same manner as one flooded by excessive choking after the engine has been allowed to cool for a few minutes.
Should the inspection show that the fuel is reaching the carburetor and that the choke is functioning normally (not overchoking) and still the engine fails to start, examine the fuel system for water as outlined below.
Water in Fuel System
Water can cause engine failure by clogging the carburetor passages and jets. Allow a small amount of fuel to flow into a small container and examine it for water, which will take the form of a bubble or globule in the bottom of the container.
Another test for water in the fuel can be made by removing the fuel pump bowl or the fuel strainer bowl and pouring the fuel on the ground. The fuel will spread rapidly, but the water will remain concentrated in a bubble or globular form for a time. If there is only a small amount of water in the pump bowl, wipe the bowl clean with a rag. Reinstall the pump bowl and fill it by rotating the engine with the starter and again test the engine for starting. If water again appears in the fuel bowl, the entire system must be drained and cleaned as discussed under Fuel System Service.
In an emergency, remove the drain plug from the fuel tank and allow a gallon or more of fuel to drain from it. Install the drain plug and examine drained fuel for water. If a considerable amount of water is drained off with the fuel, repeat the operation until the drained fuel is free of water. Install and tighten the drain plug.
Disconnect the fuel pipe at the fuel tank and at the fuel pump and blow through the pipe from the fuel pump end to remove the water. Connect the fuel pipe to the tank and filter or fuel pump. Again drain the filter, or filter and fuel pump bowls. It is sometimes necessary to drain the carburetor.
Clogged Fuel Tank Vent
If the fuel test indicates that the fuel does not reach the carburetor, examine the air vent in the fuel tank filler cap or in the tank proper, as out lined under Fuel System Service. If the vent is clogged, remove the obstruction, otherwise the fuel will not flow from the tank to the pump. If this is not possible, leave the filler cap off until a repair can be made. However, if the vent is clear, test the fuel pump as follows:
Fuel Pump Failure
To test a mechanically-operated fuel pump the type used on all passenger cars-disconnect the inlet pipe and operate the pump by cranking the engine with the starter. If fuel is ejected from the fuel pump outlet, the pump is working.
Vapor Lock
What appears to be an out-of-fuel condition is sometimes encountered in hot weather operation. It is apparent by a miss or skip in the engine, gradually slowing down or complete stoppage as if the throttle were being closed, or by failure to start after the engine is stopped.
This condition, known as vapor lock, is caused by fuel vaporizing in the fuel system and restrict ing the flow of fuel. When this condition occurs, the engine should be allowed to cool before at tempting to start it. Cold water may be poured over the fuel pump and fuel pipes to hasten the cooling of the fuel.
In exceptional cases, it may be necessary to insulate the fuel pipes and pump from engine heat. This may be done by inserting a metal
·shield, or wrapping the pipe with asbestos or tape at points where the heat may be picked up by the pipe or pump.
Clogged Fuel Pipe
To check for a clogged fuel pipe, disconnect the pipe at the pump inlet and remove the tank filler cap. Apply air under low pressure to the open end of the fuel pipe. If compressed air is not available, use an empty oil gun as an air pump, or blow into the pipe. Air bubbles venting through the fuel or a gurgling sound within the fuel tank indicates the fuel line is open and that the filter is not clogged.
If this procedure relieves the cause of engine failure, the obstruction has been blown from the fuel pipe back into the tank, and the tank must be cleaned as soon as possible as outlined under Fuel System Service.
Test for Leaks
When testing any fuel pump, bear in mind that air entering the fuel pipe will prevent the fuel pump from working. All fuel pipes and connec tions between the pump and tank must be air tight.
Examine the fuel pipes and connections for leaks. Test each pipe union nut with a wrench to be certain it is tight. Move the pipe back and forth by hand near each connection to determine whether it is loose at the connection. A pipe that is loose at the union nut or connection must be re paired as outlined under Fuel System Service.
WHEN ENGINE WON’T IDLE
When the ignition system has been thoroughly examined and found satisfactory and the engine fails to idle or fails to run smoothly at idle speed, the failure is probably in the fuel system or in the engine itself. The following checks should be made:
1. Carburetor out of adjustment.
2. Carburetor flooded.
3. Air leaks at intake manifold gaskets or in wind shield wiper tube.
4. Engine mechanical failure.
Carburetor Out of Adjustment
Start the engine and turn the throttle adjusting screw until the engine runs at a fast idle speed. Examine the choke to be sure it is fully open when the engine is warm. Then adjust the idle mixture and idle speed as outlined under Fuel System Service. If an idle mixture adjustment cannot be obtained, the carburetor should be removed and the idle system inspected for clogged jets or passages.
Carburetor Flooded
There are several causes for this condition. The float level may be adjusted too high, allowing the fuel to rise and run from the main discharge nozzle when the engine is idling. The float may be punctured, filled with gasoline and sunk, failing to close the needle valve. Dirt may lodge on the needle valve seat and allow an excess passage of fuel. The fuel pump may supply the fuel at too high a pressure and not allow the needle valve to close. The choke valve may be defective or (in extreme cases) stuck.
If one or more of these conditions are present, they can generally be observed because fuel will leak around the carburetor body. In extreme cases, fuel may even drip from the muffier tail pipe.
First, examine the choke to be sure it is in the full open position when the engine is warm. Lightly tap the carburetor body near the needle valve with a screw driver handle to dislodge any particles which may have lodged on the needle valve seat.
If the carburetor still floods it indicates that the carburetor is excessively dirty, or that the car buretor float is punctured. It may be that the fuel pump is building up too much pressure. For tips on carburetor and fuel pump service, consult the remarks under their respective headings.
Air Leaks at Intake Manifold or
Windshield Wiper Pipe
Air leaking past the intake manifold gaskets will mix with the fuel and air in the manifold, allowing the mixture to become too lean. As a result the engine will not idle smoothly or will not idle at all.
Test for air leaks as outlined under Fuel System Service. If leaks are found, tighten the carburetor flange nuts and the nuts holding the manifold to the engine. Tighten the carburetor body screws.
If the test indicates that leaks are still present at the intake manifold after the nuts are tightened, the gasket is probably broken or compressed and must be replaced.
Excess air may also enter the intake manifold through a leaking windshield wiper pipe or a power brake vacuum pipe.
To overcome the effect of a leaky intake mani fold gasket in an emergency, set the throttle stop screw so that the engine will run at the slowest idle speed possible without stalling. The gaskets should be replaced as soon as possible.
Engine Mechanical Failure
If the foregoing tests fail to correct the idling condition, the failure is probably due to a stuck engine valve, which is usually accompanied by a loud engine knock. It may also be due to a miss on one cylinder or excessive vibration.
WHEN ENGINE LOSES POWER
If the engine shows a marked loss of power when the ignition system is in proper adjustment, the failure is probably in the fuel or exhaust system, or in the engine itself. The following items should be checked:
1. Carburetor mixture too lean on acceleration.
2. Carburetor mixture too rich.
3. Fuel pump defective or vapor locked.
4. Muffier tail pipe clogged.
Mixture Too Lean on Acceleration
If loss of power is caused by a lean fuel mix ture, it usually is accompanied by a “popping back” in the carburetor when the throttle is opened rapidly. When this happens, test as follows:
With ignition off, remove the air cleaner and set the choke wide open. If the choke is automatic, it may have to be held open. Inspect the volume of discharge of accelerator jet by looking inside the carburetor past the choke valve. At the same time, open the throttle valve by moving the throttle rod rapidly. Fuel ejected from the accelerator jet should now be visible as a spray in the carburetor throat. (Do not open the throttle more than once or twice as flooding will occur and it will be difficult to start the engine.) If the spray is ob served, and the “popping back” still occurs, then the indication is that the accelerating pump has been furnishing insufficient fuel for quick get away, and the pump stroke must be adjusted to furnish an added amount of fuel.
If no spray is observed in the above test, the accelerator jet may be clogged or the accelerating pump may not be operating because it is discon nected or its valves are faulty.
A partly clogged main jet is indicated when the engine operates at low speed but fails to respond at full throttle. The main jet may be cleared by speeding the engine and closing the choke until the engine nearly stops. Repeat this procedure several times. If the main jet is still not cleared by this process, remove the carburetor and effect a repair.
Accelerator pumps are classi£ed as adjustable and non-adjustable. When adjusting the accelera tor pump, bear in mind that more fuel (longer stroke adjustment) is needed during cold weather at sea level than during hot weather or at a high elevation. If the car is to be permanently trans ferred from one area to another, change the accel erator pump stroke, if necessary, to correspond to the altitude and the prevailing temperature in the new area of operation.
One type of carburetor has an accelerating pump with a series of holes (usually three) drilled through the pump arm, Fig. 145. The adjustment is made by moving the connecting link from one locating hole to another. The second type has an accelerator link rod with a right-angle bend at the lower end. Adjustment is accom plished by bending the link.
If a carburetor with a non-adjustable pump provides insufficient fuel for acceleration, the car buretor must be repaired.
Mixture Too Rich
Loss of engine power caused by a rich fuel mixture can be detected by the tendency of the engine to “surge” at high speeds or on a heavy pull. This condition is usually caused by an execs-
, sive amount of fuel entering the carburetor. This may be due to a punctured carburetor float or a defective needle valve, or by an improper adjust-ment of the accelerator pump. It can be detected by the presence of fuel seeping around the end of the throttle shaft and by dense bl ack smoke ejected through the mufBer tail pipe.
Fuel Pump Defective or Vapor Locked
If the engine still h as a m arked loss of power af ter checking the above, indications are that the mixture is too lean, or that vapor lock h as blocked the flow of fuel. Examine the fuel pum p output and check for vapor lock as previously directed.
If the fuel pump is operating efficien tly and if the mixture is still too lean for effective power, clean the fuel pipe as already explained.
Muffler Tail Pipe Clogged
If the tail pipe is sharply kinked, or plugged with mud or clogged to a degree that the exhaust gas will not fully vent from the pipe, th e engin e power will be reduced . This condition usu ally can be detected by accelerating the engine to high speed, then closing the throttle. Th e exhaust gases passing through the restricted passage will pro duce a hissing sound as the engine loses speed . Unkink or unclog the pipe as describ ed under Fuel System Service.
Mechanica l Failure
If aWthe foregoing conditions have been elimi nated as causes of loss of power, the indication is that the failure is in the engine, cooling system or brake system.
EXCESSIVE FUEL CONSUMPTION
Complaints of excessive fuel consumption re quire a careful investigation of the owner’s driving habits and operating conditions as well as the mechanical condition of the engine and f uel sys tem; otherwise much needless work may be done in an attempt to increase fuel economy.
Driving habits which seriously affect fuel economy are: high speed driving, frequent and rapid acceleration, driving too long in low and second speed when getting under way, excessive idling while standing.
Operating conditions which adversely affect fuel economy are: excessive acceleration, frequent starts and stops, congested traffic, poor roads, hills and mountains, high winds, low tire pressures.
High speed is the greatest contributor to low gas mileage. Air resistance increases as the square of the speed. For instance, a car going 60 miles an hour must overcome air resistance four times as
great as when going 30 miles an hour . At 80 miles an hour the resistance is over seven times as great as when going 30 miles an hour. Over 75 per cent of the power required to drive a car 80 miles an hour is used in overcoming air resistance, while at 30 miles an hour only 30 per cent of the power required is used to overcome air resistance.
Gas mileage records made by car owners never give a true picture of the efficiency of the engine fuel system since they include the effects of driv ing habits and operating conditions. Because of the wide variation in these conditions , it is impos sible to give average mileage figures for cars in general use. Therefore, any investigation of a mileage complaint must be based on an accurate measurement of gasoline consumption per mile under proper test conditions.
Gasoline Mileage Test
There are a number of gasoline mileage testers commercially available that measure fuel con sumption precisely. Manufacturers of these de vices furnish full instructions for their use. How ever, an inexpensive tester can be made with a quart oil can, suitable fittings and a tube to con nect the can to the carburetor.
Drill or punch a hole in the bottom of the can and solder a fitting to the hole. The fitting at the carburetor end should be the same as the existing fitting at the carburetor inlet. Arrange a suitable handle or wire hook to the can so it can be mounted either under the hood or in the driver’s compartment.
Before making the test, disconn ect the fuel pipe at the carburetor and plug the pipe opening with a small cork so that the fuel will not spurt out during the test. Run the engine until all the fuel in the carburetor is used up. Then connect the tester tube to the carburetor.
With the can mounted at a higher level than th e carburetor so fuel will flow into the carburetor by gravity, pour exactly one quart of gasoline into the can.
Make the test on a reasonably level road, at fixed speeds, without acceleration or deceleration. Test runs should be made in both directions over the same stretch of road to average the effect of grades and wind resistance. Test runs mad e at 30, 50, and 70 miles an hour will indicate the approxi mate efficiency of the low speed, high speed and power systems of the carburetor and show whether fuel consumption is actually abnormal. Under the conditions given, the fuel consumption in miles per gallon, based on the normal economy of a car capable of giving 20 miles per gallon at 20
miles per hour , should be approximately as follows:
| Constant Speed | Miles Per Gal. |
| 20 | 20.0 |
| 30 | 19.7 |
| 50 | 15.9 |
| 70 | 8.0 |
If it takes 5 miles to empty the can, it means that the fuel consumption is 20 miles per gallon, since there are 4 quarts to the gallon.
If the test indicates that the fuel consumption is above normal, check the following before deciding to take the carburetor apart:
1. Check all gasoline pipe connections, fuel pump bowl gasket, gasoline filter gasket, and carburetor bowl gasket.
2. Check for low tire pressures.
3. Check for dragging brakes.
4. Late ignition timing causes loss of power and increases fuel consumption. Dirty or worn out spark plugs are wasteful of fuel.
5. Use of gasoline of such low grade that igni tion timing must be retarded to avoid excessive detonation will give very poor fuel economy.
6. Check for sticking manifold heater valve or improper setting of the thermostat.
7. Check for dirty or clogged air cleaner element and for excessive oil in the crankcase.
8. Check for sticking choke valve and improper setting of the automatic choke thermostat.
9. Check for insufficient valve operating clear ance or sticking valve.
10. Check for excessive fuel pump pressure.
11. Check for carburetor idle adjustment. On Car ter carburetors, the metering rod setting may be checked without removing the carburetor. For all other corrections to high speed and power systems on all carburetors, the car buretor must be removed and disassembled.
Changing Carburetor Jets
Under no circumstances should leaner than standard jet sizes, metering rods and other cali brations of a carburetor be changed from factory specifications. The specified calibrations must be adhered to unless these are later changed by a bulletin issued by the carburetor manufacturer.
Carburetor calibrations have been determined by exhaustive tests with laboratory equipment and instruments which accurately measur e overall per formance and economy. Besides, the leanest pos sible mixture obtainable by the use of smaller jets, etc., will not increase mileage as much as 10 per cent, and will often impair engine performance.