Have a 2.5 liter and number 2 cylinder exploded. I replaced the entire engine including head, valves, spark plugs and wires. new engine ran a little rough and had a check engine light for a o2 sensor. after replacing the o2 sensor, the new engine ran great. after two weeks of driving it, the engine started misfiring and running rough. are there any common problems with the 2000 jeep wrangler with a 2.5 liter engine and what could be my problem? any suggestions would be appreciated

Hello, this engine has 3 ignition coils on the passenger side cylinder head, each coil fires two spark plugs, the spark plugs on thew other side have plug wires connected to one of the coils on the other side, the #6 cylinder wire connects to the #3 coil, try replacing the spark plug wires

Mark the spark plug wires for the cylinder number using a short piece of masking tape on each wire. Remove all the spark plugs using the spark plug wrench. The engine will be easier to turn by hand with the spark plugs removed and it's a good time to replace them if required. Remove the valve cover from over the number one cylinder. On a V-block engine this is normally the valve cover on the driver's side. On in-line engines the number one cylinder is the one closest to the front of the car. Check your vehicle's specifications to be sure which cylinder is number one.

Rotate the engine clockwise and observe the valves on the number one cylinder. When both valves are in the up position, insert a screwdriver into the number one cylinder through the spark plug hole. Rotate the engine very slowly back and forth until the screwdriver is at the maximum height. This indicates the number one cylinder is at Top Dead Center or "TDC" on the compression stroke.

Locate the number one spark plug wire on distributor cap and make a tic-mark of this position with a marker pen on the distributor housing. Remove the distributor cap and observe the position of the rotor.

Loosen the distributor hold down bolt and turn distributor until the rotor is lined up with the mark you made in Step 3. Your timing is now set to zero degrees of mechanical timing.

Replace the valve cover using a new gasket. Replace the spark plugs and spark plug wires using the marks from Step 1. You may want to mark the harmonic balancer with a zero point referenced to a fixed point on the engine. A fixed point could be a bolt head or accessory bracket that does not move when the engine is running. Later on this mark can be used as an indicator for stroboscopic timing.

Connect a vacuum gauge to a manifold vacuum source. Most engines will have a port at the base of the carburetor or throttle body where a gauge can be connected. Start the engine and observe the vacuum gauge reading.

Turn the distributor until the maximum vacuum gauge reading is noted. Back off one inch of vacuum from the maximum reading. Tighten the distributor hold down bolt. Normal readings average from 14 to 21 inches of vacuum depending on the condition of the engine.

Test drive the vehicle and listen for pinging noises. Repeat Steps 5 and 6 if excessive pinging is heard, or if there is a significant loss of power. The timing is correct when the vehicle operates at maximum power without the engine hard starting, backfiring, or pinging on acceleration.

check that the egr valve is not stuck open remove it and cover the hole on the intake side and see if it goes away or with engine running remove the vac line from the valve and install a short length of hose and suck on the hose to draw a vac on the valve it only takes 3-5 inches of vac to open it the engine should stall or run even worse if it is not stuck and if it was stuck open you didnt change anything

Locate the spark plug wires in the Cherokee cylinder head. In the 4.0 liter engine, the spark plugs are below the coil rail assembly. On the 4.7 liter engine, the spark plugs are located under each corresponding engine coil.


Read more: How to Replace Spark Plugs in a Jeep Grand Cherokee ' eHow.com http://www.ehow.com/how_4484626_replace-spark-plugs-jeep-grand.html#ixzz27zi6736d

Code # 301??? That is NOT a valid Diagnostic Test Code (DTC) for the engine control system on a 2000 Mercury Sable.

Assuming that you mean P0301, that is a cylinder misfire code that is identifying number 3 cylinder as the cylinder with the misfire problem. MANY things can cause a cylinder to misfire including spark plugs, spark plug wires or boots, burnt valves, broken valve springs, blow head gaskets, cracked cylinder heads, bad or dirty injectors, faulty injector control circuits, Failed ignition coils...the list goes on....proper diagnosis required.

Your first mistake is thinking that the only thing that can cause a misfire is a coil or spark plug. Misfires can be caused by MANY things, including faulty fuel injectors, injector control circuits, blown head gaskets, vacuum leaks, burned valves, broken valve springs, low compression due to cylinder damage, worn piston rings, damaged or worn camshafts, etc..

I would recommend getting this problem properly diagnosed by a professional. Failure to fix misfire codes promptly can cause severe engine damage and destroy high-dollar parts like oxygen Sensors, catalytic converters, engine blocks and cylinder heads.

4-cylinder:

Firing Order: 1-3-4-2

3.1 liter:

Firing Order: 1-2-3-4-5-6

Rocker Arm (Valve) Cover REMOVAL & INSTALLATION 2.3L 4-Cylinder Engines

1. Disconnect the negative battery cable.
2. Label and remove the spark plug wires.
3. Remove the attaching bolts for the valve cover.
4. Remove the valve cover from the cylinder head. If necessary, lightly tap the valve cover with a soft hammer to aid in removal. To install:
   
5. Thoroughly clean the valve cover and cylinder head gasket mating surfaces.
6. Install the valve cover on the cylinder head using a new gasket.
7. Tighten the valve cover bolts to 14 ft. lbs. (20 Nm) in a crisscross pattern.
8. Install the spark plug wires.
9. Connect the negative battery cable.
10. Start the engine and check for leaks. Fig. 1: Valve cover and gasket assembly
    

2.8L 6-Cylinder Engine

1. Disconnect the negative battery cable.
2. The following steps are necessary if your car has A/C and if you are removing the passenger side valve cover, if you do not need to remove the passenger side valve cover, skip them.
   1. Remove the A/C compressor belt and the compressor from the mounting bracket located on the passenger side of the engine. Do not remove the lines from the compressor.
   2. Place the compressor with the lines attached on the passenger side front shock tower and secure.
   3. Remove the compressor bracket.
3. Remove the air cleaner-to-throttle body hose.
4. Label and remove all necessary electrical and vacuum connections.
5. Remove the attaching bolts for the valve cover(s).
6. Remove the valve cover(s) from the cylinder head(s). If necessary, lightly tap the valve cover with a soft hammer to aid in removal. To install:
   
7. Thoroughly clean the valve cover(s) and cylinder head gasket mating surfaces.
8. Install the valve cover(s) on the cylinder head(s) using new gaskets.
9. Tighten the valve cover bolts to 11 ft. lbs. (15 Nm) in a crisscross pattern.
10. Install all necessary electrical and vacuum connections.
11. Install the air cleaner assembly.
12. Install the A/C bracket (if removed).
13. Install the A/C compressor and belt (if removed).
14. Connect the negative battery cable.
15. Start the engine and check for leaks.

2.3L and 2.4L 5-Cylinder, and 2.9L 6-Cylinder Engines The 2.3L and 2.4L 5-cylinder, and 2.9L 6-cylinder engines have a two-piece cylinder head, the upper half and the lower half. The upper half is basically the same as a valve cover, except that it incorporates the bearing caps for the camshafts into the underside.

1. Disconnect the negative battery cable.
2. Remove the spark plug access cover.
3. Label and remove the ignition coils and vent hoses or the distributor cap and wires if equipped.
4. Check the cam alignment before removing the cylinder head.
5. Remove the bolts attaching the upper cylinder head.
6. Remove the upper cylinder head, lightly tap with a soft hammer if necessary. To install:
   
7. Thoroughly clean the upper and lower cylinder head gasket mating surfaces.
8. Apply liquid sealing compound to the upper cylinder head mating surface. WARNING
   Use a roller or your finger to spread sealant, do not use an excessive amount of sealant, or the oil passages could become clogged.
   
9. Place the upper cylinder head onto the lower cylinder head.
10. Check the cam alignment before tightening the cylinder head.
11. Install Volvo tool number 5454 or equivalent to the upper cylinder head.
12. Tighten the nut on the tools to seat the upper cylinder head.
13. Tighten the upper cylinder head bolts, beginning from the center out to 13 ft. lbs. (17 Nm).
14. Install the ignition coils and hoses or the distributor cap and wires.
15. Install the spark plug access cover.
16. Connect the negative battery cable.
17. Start the vehicle and check for leaks. Fig. 2: Remove the clamp and detach the vent hose
    Fig. 3: Remove the spark plug cover and the plug wires or ignition coils to access the retaining bolts
    Fig. 4: Remove the retaining bolts
    Fig. 5: A light tap with a soft-faced hammer is usually required to loosen the valve cover
    Fig. 6: Carefully lift the upper cylinder head up and off the lower section. Note the integral camshaft bearing caps in the casting
    

There can be several causes for low compression.
Chck the obvious first. the spark plugs must be checked that they are all in good condition. not burnt, the gap must be good( for your engine).Check the wires and coil so that good spark is obtained. Blue spark , not weak yellow spark. After everything is good. Check the cylinders to see if they have compression. To test the cylinders do the procedures shown below.

If the cylinder shows little leakdown or holds good compression when a little oil is squirted into the cylinder (wet compression test), it would tell you that the engine needs new valve guide seals and/or guide work. Most late model import engines have positive valve guide seals. Often, the guides are fine, but the seals are worn or cracked. The seals can be replaced on some engines without too much effort and without having to remove the head.

compression test will help you determine if the oil is getting past the valve guides or the rings. If the cylinder shows little leakdown or holds good compression when a little oil is squirted into the cylinder (wet compression test), it would tell you that the engine needs new valve guide seals and/or guide work. Most late model import engines have positive valve guide seals. Often, the guides are fine, but the seals are worn or cracked. The seals can be replaced on some engines without too much effort and without having to remove the head.

finally if the rings on one or more of the pistons can caus compression leak. It must be located and fixed.

A P0303 code means that the the car's computer
has detected that one of the engine's cylinders is not firing properly. In this case it's cylinder #3.
Symptoms may include:

• the engine may be harder to start
• the engine may stumble / stumble, and/or hesitate
• other symptoms may also be present

A code P0303 may mean that one or more of the following has happened:

• Faulty spark plug or wire
• Faulty coil (pack)
• Faulty oxygen sensor(s)
• Faulty fuel injector
• Burned exhaust valve
• Faulty catalytic converter(s)
• Running out of fuel
• Poor compression
• Defective computer

If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors
.