Repair And Fix it

Misfires are a common problem among cars, particularly older ones, when a lack of spark, fuel, air or compression occurs. Diagnosing and fixing a misfire takes skill because of the multiple components involved in the control of just one necessary element of combustion. Modern cars such as a 1996 Saturn have an on-board diagnostics system that can help find the source of the problem quickly if one is detected by a sensor. Misfires are characterized by a rough idle, reduction in power and poor riding comfort at speed and require immediate attention to avoid serious engine damage.

Instructions

1

Open the hood and disconnect the negative terminal from the battery using a wrench. Set it safely aside.

2

Hook up an on-board diagnostics scanner to the Saturns on-board diagnostics II port. This is usually located under the drivers steering wheel column on either side. Turn the car to accessory and enter the scan mode of the scanner. Search for codes indicating injector, fuel or air delivery failure and replace components as necessary. Also scan for oxygen sensor codes giving higher than normal readings; these indicate a possible spark delivery problem.

3

Remove the cylinder 1 spark plug with a socket set and check it for discoloration using a spark plug color chart. Dry plugs indicate a lack of fuel, while wet spark plugs indicate a lack of spark. Replace the spark plug with a new one, ensuring to coat the threads in anti-seize compound.

4

Inspect the cylinder 1 spark plug wires from the distributor to the spark plug for cracking and exposed metal. These change the resistance in the wire, causing spark failure. If replacement is necessary, order an entire set and replace all spark plug wires to maintain uniform resistivity to all cylinders. Also check the distributor for signs of wear and replace as needed.

5

Remove the cylinder 1 injector connector at the wiring harness and inspect for corrosion or wiring damage and repair as needed. Check the resistance of the injector by attaching multimeter clips to the injectors metal connectors and turning the multimeter to the 200-ohm setting. Compare with the manufacturers specification for that particular injector to ensure the electrical components are working.

6

Reinstall the cylinder 1 fuel injector clip. Remove the entire fuel rail with the injectors attached and coil wire. Turn the car over with the fuel rail off and inspect the spray pattern of the cylinder 1 injector. If a fine spray does not come from the injector, have it professionally cleaned or replace it.

7

Run a compression check whether the misfire continues. Use a compression tester specifically for car motors. Poor compression indicates a leak in the cylinder and will most likely mandate a check of the valve train or an engine rebuild.

The location of the vehicle in winter will affect the type of oil chosen during colder months. Hawaii, for example, stays relatively warm all year and therefore there is less need to change oil weight with the season. Consulting the owners manual for the specific vehicle will reveal what the manufacturer recommends (for instance, the owners manual for a 2001 Honda Civic recommends using 5W-20 oil year-round, but 5W-30 is acceptable if 5W-20 is not available).

Numbers and Letters on Oil

The numbers on motor oil show the oils viscosity rating and range from zero to 50. The oils weight is the "viscosity index" on a scale up to 100 degrees Celsius. The lower number, often followed by a W for "winter", corresponds to the oils ease of movement during colder temperatures. The higher numbers correspond the the oils thickness and ability to maintain that thickness even at higher temperatures. Numbers such as 5W-30 have a wide range, from below -30 degrees to over 100 degrees.

Age of the Vehicle

Older vehicles, whose engines have high mileage, are often recommended to use or switch to an oil that is thicker. This will help limit the noise produced by older engines, as well as reducing the overall oil-consumption by the vehicle and prolong its life. The improved lubrication of the engine helps protect it from wear due to long-time use and age.

Regional Differences

Many newer vehicles, less than 20 years old for example, are recommended by manufacturers to use one type of oil year-round, such as the 5W-20 in a 2001 Honda Civic. If the location, however, suffers extremely cold winters (temperatures below -30 degrees Celsius, for instance) local auto parts stores and mechanics will have regionally-appropriate recommendations for oil weights. Not all manufacturers will account for such temperature extremes in the owners manuals so consulting local experts will prove helpful.

The cylinder heads in the four-stroke combustion engine have valves and valve seats that must be machined to precise tolerance and fit. If the valves do not seat correctly with their seats, they leak and lose compression. Valves that do not match within specifications with their seats can also cause excessive overheating and valve failure. The valve seat takes a continual pounding from the action of the valve when it closes. Valve seats can crack and become worn. Several tools need to be used to check and repair valve seats.

Crack Checking Tools

Before any valve seat can be reshaped and ground within specifications, the vale seat area must be magnafluxed to reveal hairline cracks. An electrical transformer attaches to the head, where it delivers a a high voltage magnetic charge to the metal. Magnaflux, which consists of a powdered, reactive chemical, gets sprinkled on the valve seat area. The chemical power reacts to breaks in the magnetic lines of force (field), which shows up as horizontal lines or spider-webbing cracks in the metal.

Valve Seat Grinding Machine

The valve seat grinding machine consists of of a platform vice that holds the cylinder head in a fixed and upright position. The vice fasteners lock the head into a level and stable orientation. The overhead part of the valve seat grinder consists of a motor that drives a cutting bit, which can be adapted to cut out the old valve seat from either aluminum or cast iron. A machine bit then cuts the new valve seat face at a precise angle, usually around 45 degrees. Dial indicators determine the depth of the cut, while bits determine the seat diameter to be cut. Lubricant, fed by the machine, keeps the cutting surface cool.

Valve Lappers

Valve lapping tools must be used to attain final sizing of the face and valve seats for a perfect, sealed match. The most common valve lappers consists of wood dowels that have two different size suction cups on each end. After the valve has been inserted in the stem and abrasive compound has been brushed between the valve face and the seat, a manual twisting motion turns the wood dowel back and forth to cut the interface seat between the valve and seat. Valve lappers come in a variety of suction cup diameters for intake and exhaust valves of all sizes.

Motorized Valve Lappers

Instead of manual wood dowel lappers, motorized drills and air guns can be fitted with suction cup bits that attach to the top of the valve. Once abrasive lapping compound has been applied between the valve and seat, the motor or air tool is turned on to spin the valve at high rpm. The use of power tools for lapping reduces the labor time involved in cutting the final seat and valve face.

Valve Seat Grinding Compound

Valve seat grinding compound consists of a a thick paste that contains cutting abrasives. The cutting compound comes in fine, medium and coarse grits. The coarse grit takes the most of the irregularities and burs out of the interface surfaces, while the medium and fine cutting compound cuts the last finishing face between the valve and valve seat.

Cylinder liners are the interior metal components within the piston that protect it from the wear and tear of the operation of the motor. Three basic types of liners are used: hot, dry and finned. The purpose of each type is to protect the piston from heat and impurities using slightly different methods. Cylinder liners are expensive, precisely manufactured products and are primarily purchased from specialty shops.

Dry Cylinder Liners

Dry cylinder liners are among the basic piston protectors. They must withstand extremely high temperatures and guard against impurities, so they are constructed of high-grade materials, such as cast iron and ceramic-nickle plating. Dry liners are much thinner than their counterpart, wet liners. They do not interact with the engine coolant but instead provide a very close fit with the jacket in the cylinder block to protect the piston from heat and impurities.

Wet Cylinder Liners

Wet cylinder liners protect the pistons in a different way than dry ones, but they are made from the same hardy material. They come in direct contact with the engine coolant. Sometimes the wet cylinder liners are fitted with tiny openings to help disperse the heat and impurities. These types of liners are called water-jacket liners but are simply another type of wet cylinder liner. If the liner doesnt have a cooling jacket, one is created by the liner by interacting with the jacket present in the cylinder block.

Finned Cylinder Liners

Finned cylinder liners are constructed of the same type of heat and impurity-resistant metal. This type of liner is designed for the air-cooled engine, and in operation works much like the dry cylinder liner in that the cooling medium for the motor is air. However, these liners are fitted with tiny fins which allow the inflowing air to draw with great force around the cylinder to provide cooling.

Cylinder bores must fall within specific, factory-set tolerances to be considered useable. Check cylinders for visible damage and measure using precision measuring equipment such as micrometers and dial-bore indicators. Measurements taken at specific points of the bore indicate cylinder taper and out-of-round conditions that require machining to correct. Checking a cylinder bore requires knowledge of the proper use of the precision measuring equipment as well as the factory specifications as set by the manufacturer. Disassemble the engine to remove the cylinder head and pistons prior to checking the cylinder bore.

Instructions

1

Visually inspect the cylinder for signs of lateral scoring, galling and partial piston seizure.

2

Feel the top of the cylinder for a shoulder using your fingernail. The shoulder will form right at the top of the unswept portion of the cylinder bore above where the top compression ring ceases to travel upwards. Hone the cylinder to remove the shoulder, if one is present.

3

Install an arbor on the dial-bore indicator so the plunger on the indicator is roughly in the center of its travel when placed within the bore.

4

Set an outside micrometer to the small end of the cylinder diameter specification as indicated by the manufacturer. Record the micrometer setting on a piece of paper.

5

Place the dial-bore indicator in the micrometer and rotate the bezel on the indicator gauge until the zero aligns with the needle. Remove the indicator from the micrometer.

6

Measure the top of the cylinder on the X axis using the dial-bore indicator. Record the number indicated by the gauge and add that number to the micrometer setting number. Record the final sum. Repeat this process on the Y axis at the top of the cylinder. Record the final sum next to the top X axis number.

7

Repeat the process in the middle and at the bottom of the bore, pairing the X and Y axis measurements together.

8

Compare the X and Y axis number pairs. A difference in the bore diameter within any given pair indicates an out-of-round condition.

9

Compare the top, middle and bottom number pairs. A difference in the bore diameter between the position groups indicate a cylinder taper condition.

10

Measure the outside diameter of the piston skirt even with, and 90 degrees from, the wrist pin boss area. Compare the piston diameter to the largest and smallest bore diameter to determine the piston-to-cylinder clearance range.

11

Compare all measurements to the manufacturers tolerances to determine whether the bore is within service specifications or if machine work is needed.

The Jimmy is a mid-size sport utility vehicle that General Motors manufactured from 1983 to 2005. The 1999 model belongs to the second generation, which was in production from 1995 to 2005. These vehicles had a six-cylinder 4.3-liter engine with sequential fuel injection. The cylinder head in a 1999 Jimmy is a platform on the cylinder block that contains the poppet valves and spark plugs. The procedure for installing a cylinder head is generally the same for all versions of the Jimmy made between 1994 and 1999.

Instructions

1

Remove the negative battery cable with a socket wrench. Remove the filler cap to relieve the pressure in the fuel tank. Wrap a shop rag around the fuel pressure connection on the fuel rail and connect a fuel pressure gauge to the connection. Place the bleed hose of the fuel pressure gauge into a container approved for gasoline, and open the valve on the fuel pressure gauge. Relieve the pressure in the fuel system and drain the excess fuel into the gasoline container.

2

Place a sealable container under the radiator drain and open the drain plug with a socket wrench. Drain the coolant into the container and seal it for reuse. Disconnect the intake manifold and exhaust manifold from the engine. Disconnect the cooling fan assembly from the radiator.

3

Detach the electrical wiring harness and coolant sensor wire from the rear of the cylinder head. Record the positions of the electrical wiring for the spark plugs and disconnect them. Unscrew the spark plugs with a socket wrench and remove the spark plugs from the cylinder head.

4

Remove the bracket for the fuel line from the cylinder head with a socket wrench. Disconnect the cover for the rocker arm and loosen the rocker arm. Remove the push rods from the cylinder block.

5

Remove the bolts from the cylinder head with a socket wrench and lift the cylinder head from the cylinder block. Remove any dirt from the threads of the cylinder head bolts with a shop cloth to ensure you can properly torque the bolts later.

6

Mount a new gasket for the cylinder head on the dowel pins so that the side of the gasket with the words "This Side Up faces up. Install the new cylinder head onto the dowels and gasket. Apply a thin layer of sealer 12346004 to the threads on the cylinder head bolts. Record the length of each bolt and fasten the mounting bolts to the cylinder head by hand.

7

Tighten the mounting bolts for the cylinder head to 22 foot-lbs. with a torque wrench. Tighten the short bolts an additional 55 degrees with a socket wrench. Tighten the medium bolts to 65 degrees and tighten the long bolts to 75 degrees.

8

Connect the push rods to the cylinder block and fasten the rocker arms with a socket wrench. Replace the cover for the rocker arms and screw the spark plugs into the cylinder block. Connect the electrical wiring for the spark plugs using the notes you made in Step 3.

9

Attach the bracket for the fuel line with a socket wrench and attach the electrical wiring to the rear of the cylinder head. Connect the electrical wire to the coolant sensor. Attach the exhaust manifold and intake manifold.

10

Fasten the cable for the negative battery terminal with a socket wrench and fill the engine with coolant. Start the engine and check for fluid leaks.