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Discussion Starter · #1 · (Edited)
You probably have a missfire code and have been told to check your fuel injector. Maybe you have a crank but won't start situation, and want to see if you have power to the injectors. Here are a few simiple checks.

Caution... whenever you stick your head inside an engine compartment, make sure that you are not wearing any loose clothing, (hoodies with stings) long hair, or jewelry that can get caught in a moving part.

Often one may choose to use a mechanic's stethoscope to listen to the injectors clicking open when the engine is runnning or cranking.
Haynes says, one may use a long screwdriver held to the ear. I think that this can be difficult to say the least. If they are clicking, they are getting voltage, and are opening (although they may be clogged).

If they are not clicking, you can check for power at the injector with a volt meter, or a noid light. I've read that a noid light is much easier.

A noid light is an incadescent bulb that clips right into the injector wireing harness. It will blink/flash when the engine is cranked if the injector is getting power. They can be purchased as a set for a variety of injector brands, or individually.

One may also use a test light as a noid. Simply insert a stiff wire such as a paperclip into one side of the connector, and probe the other side, while cranking or running the engine.

For an individual cylinder missfire, one may move the injector to a different cylinder and see if the miss follows the injector.

How to test if the fuel injector is stuck open or leaking?


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Hi, anybody have any detailed info on replacing a fuel injector on a 2001 Expedition 4.6L Engine?
I have an elusive Cylinder 2 misfire (P302) Have already swapped COP, boot and plug. No change. Next step I would guess is to swap a couple of injectors to see if the problem moves. Also any cleaning tips while moving them about. Poppy, looks like you may have lots of the learning tools on hand. Also getting a too lean warning on both banks. Assuming this may be related and fixing Cyl 2 may resolve that issue?
Thanks in advance. Will check back later today and on depending when I get any responses.

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Misfire Detected in #2 Cylinder

Our emissions expert has put together the following information about the P0302 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the code.

OBD II Fault Code
  • OBD II P0302
Fault Code Definition
  • Check Engine Light flashing
  • Rough running, hesitation, and/or jerking when accelerating
  • In most cases, there are no adverse conditions noticed by the driver
  • In some cases, there may be performance problems, such as dying at stop signs or rough idling, hesitation, misfires or lack of power (especially during acceleration), and a decrease in fuel economy
Common Problems That Trigger theP0302
  • Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable)
  • Incorrect ignition timing
  • Vacuum leak(s)
  • Low or weak fuel pressure
  • Improperly functioning EGR system
  • Defective Mass Air Flow Sensor
  • Defective Crankshaft and/or Camshaft Sensor
  • Defective Throttle Position Sensor
  • Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems
Common Misdiagnoses
  • Fuel Injectors
  • Oxygen Sensor(s)
  • Power Train/Drivetrain problems
Polluting Gases Expelled
  • HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
  • CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
  • NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog
Want to Learn More?
Generally, the term "misfire" refers to an incomplete combustion process inside the cylinder. When this becomes severe enough, the driver will feel a jerking action from the engine and/or power train. Often the owner will bring the vehicle into a shop complaining that the timing is "off." This is partially correct because a misfire does involve a mis-timed combustion event. However, the base ignition timing being out of adjustment is only one reason for a misfire to occur—and not the most likely.
P0302Diagnostic Theory for Shops and Technicians
When the code P0302 is set in the Power Train Computer, it means that the Misfire Monitor has detected more than a 2 percent variance in RPM between the firing of any two (or more) cylinders in the firing order. The Misfire Monitor constantly checks the rotational speed of the Crankshaft by counting the pulses of the Crankshaft Sensor. The Monitor wants to see a smooth increase or decrease in engine RPM.
If there are jerky and sudden changes in the speed output of the Crankshaft Sensor, the Misfire Monitor begins to count the RPM increase (or lack thereof) contributed by each cylinder. If it varies beyond 2 percent, the Monitor will set a P0302 code and illuminate the Check Engine Light. If there is more than a 10 percent variance, the Check Engine Light will blink or pulse in a steady manner to indicate that a harmful Catalytic Converter misfire is occurring.

When diagnosing a P0302 code, it is important to record the freeze frame information and then duplicate the code setting conditions with a test drive. Pay close attention to the engine load, throttle position, RPM, and road speed because a P0302 (which is a specific misfire) can sometimes be difficult to detect. If the Engine System has a Misfire Counter for specific cylinders on the Scan Tool Data Stream, pay very close attention to the cylinders(s) named in the misfire code(s).
If there is not a Cylinder Misfire Counter, then you might have to switch components—such as coils, spark plugs, etc.—in order to isolate the root cause of the misfire. It is also important to note and record any other codes because the engine may be misfiring due to the failure or malfunction of another system or component.
Common Causes for an Engine Misfire and CodeP0302

Ignition Misfire
An Ignition System problem is one of the most common reasons for an engine to misfire. As the spark plugs, ignition cables, distributor cap and rotor, and ignition coil wear over time, their ability to transfer the needed spark to ignite the air/fuel mixture inside the combustion chambers becomes compromised. In the early stages, the spark will only be weaker and the actual misfire will be subtle. As the ignition components continue to wear, the misfire will intensify and the combustion process can be interrupted completely. This will cause a severe jerk or shock in the operation of the engine (the engine may even backfire through the air intake system, producing a loud "pop").
Carefully inspect all of the Ignition System components for wear and heat damage. The Spark Plug terminals should have a sandy color and not be blackened with soot, white from an overheating combustion chamber, or greenish from coolant. Neither the Ignition Cables nor the Coil(s) should have any signs of arcing. If possible, Scope Check the Ignition System to ensure that the firing voltages are even—about 8 to 10 kilovolts per cylinder. If there is a Distributor on the engine, remove the Distributor Cap and Rotor. Inspect their terminals and contact points for wear, signs of arcing, and/or any buildup from corrosion. Though all ODB II vehicles have computer controlled timing, be sure to verify that it is within spec, even if it uses individual coils.
Lean Misfire
The lean misfire is another common reason for an engine "miss"—this is due to an imbalanced air/fuel ratio (too much air/too little fuel). Since an engine needs a richer (more fuel) mixture for a smooth idle, this problem may be more noticeable when the vehicle is idling. The lean misfire may decrease or disappear as the engine speed increases because the efficiency of the volumetric flow into the combustion chambers increases dramatically. This is one reason why a vehicle gets better mileage on the freeway than in the city. An EGR valve that is stuck open, a leaking Intake Manifold Gasket, a defective Mass Air Flow Sensor, a weak or failing fuel pump, or a plugged fuel filter are some of the many causes for a lean misfire.

Pay very close attention to the Long Term Fuel Trim values because they indicate how much the Power Train Computer is compensating for an imbalanced air/fuel ratio. If the Long Term Fuel Trim is over 10 percent on one bank of cylinders and not the other, there might be a vacuum leak or defective/cracked intake manifold on that specific bank. It is important to determine what is causing this amount of compensation. Check the Fuel Trim "numbers" over the full range of operating conditions. A healthy engine should have Long Term Fuel Trim numbers around 1 to 3 percent, either positive or negative.

Mechanical Misfire
Mechanical problems can also cause an engine to misfire. Common causes of a mechanical misfire are worn piston rings, valves, cylinder walls, or lobes on a camshaft; a leaking head gasket or intake manifold gasket; damaged or broken rocker arms; defective fuel injectors (and/or the electronics that control them); and a slipped or incorrectly-installed timing belt or timing chain. Generally, this type of misfire has more of a "thumping" feel to it. It is usually noticeable regardless of engine speed; in fact, it may even intensify as the engine speed increases.
A Compression Test and an engine idle Manifold Vacuum Test are two very important methods of determining the mechanical condition of the engine. Compression readings that are consistent (within 10 percent of each other), and at least 120 PSI per cylinder and a minimum of seventeen inches of steady vacuum, are required for reasonably smooth and complete combustion.

Power Train Misfire
Sometimes, the engine has nothing to do with a misfire. One common cause for "jerky" performance that feels like a misfire is a problem in the transmission and its ability to properly up- or down-shift. If the misfire occurs during higher speeds, it could be a problem with the operation of the overdrive gear or a chattering clutch in the Lockup Torque Converter. If the vehicle jerks or feels like it is "missing" during deceleration, it could be due to harsh transmission downshifts, badly warped rotors, out of round brake drums, and/or sticking brake pads or brake shoes.
Vehicles can set misfire codes when badly warped and out of round rear brake drums violently jerk the entire power train when the vehicle slows from highway speeds. Make sure that you have the vehicle properly inspected in order to determine the root cause of the misfire. Entire engines have been replaced to solve a wrongly perceived mechanical misfire problem that was actually rooted in the transfer case, transmission, drive shaft, or front/rear differential.

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Discussion Starter · #4 ·
Hi, anybody have any detailed info on replacing a fuel injector on a 2001 Expedition 4.6L Engine?
I have an elusive Cylinder 2 misfire (P302) Have already swapped COP, boot and plug. No change. Next step I would guess is to swap a couple of injectors to see if the problem moves. Also any cleaning tips while moving them about. Poppy, looks like you may have lots of the learning tools on hand. Also getting a too lean warning on both banks. Assuming this may be related and fixing Cyl 2 may resolve that issue?
Thanks in advance. Will check back later today and on depending when I get any responses.
The injectors just pop out, and then back in. I'd move the #2 and see if the missfire code follows it.

A bad injector on ONE bank, will not give you a lean code on both banks.
I'd look for a vacuum leak, low fuel pressure (possibly clogged fuel filter, weak pump, or faulty fuel pressure regulator), or a dirty MAF sensor.
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Note: Most "real" auto parts stores can either test and clean fuel injectors, or can send them out and have them cleaned and tested. Most brands of injectors are designed to last a million (with an "M") miles so that injector problems are usually caused by a build up of fuel residue, or electrical connection/conductivity problems. NOID lights are easy to use and can visually tell you if the injector is gettig voltage. Listening to an injector will tell you that an injector is electrically activated, but it will not tell you if the pintell is clogged or only partially opening. Some scanning equipment will let you scan the injectors in real time so that you can determine if the pintell movement (opening) is withing specification (usually measured in miliseconds). If one injector needs cleaned they all need cleaned.

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Hi, everyone uel injectors are a key part of modern automotive systems, as they're responsible for getting gasoline into the engine in a precise, orderly and carefully engineered pattern. In general, they're expected to last a pretty long time. Both Bosch and Delphi, two major manufacturers of automotive components, say their fuel injectors have a life expectancy of 1 billion cycles. Essentially, that means that the fuel injectors should last as long as the car does.

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After 15 years of being an emissions mechanic, EEC-IV Cert, CA State Smog, injectors rarely did fail. On port injection, one injector on one side will only give you lean codes for that side.

Here's the catch, a leaking intake gasket will do the same thing. Lean codes only mean too much O2 at the sensor. This can be, low amount of fuel, vacuum leak, bad ignition, electrical, even an injector stuck open and dumping fuel into the cylinder. The O2 sensor does NOT check for raw fuel, only the amount of oxygen in the exhaust stream. Excess fuel (raw gas) will not measure, but the unused oxygen will, showing lean.

NOID lights are very helpful in troubleshooting injector DRIVER issues. These LED devices plug onto the harness and flash if they receive the signal from the ECM. No flashing means no signal. Harness or driver in the ECM. YOU will need to know if the engine uses Sequential Injection or Bank Injection. Sequential is all cylinders have their own firing time for the injectors. Bank is where a certain configuration of injectors fire together. If it's bank, it's highly unlikely that the ECM is at fault since the engine is running. If you lost a bank, then you would effectively be turning half the engine off.

One of the biggest culprits of injector failure is not replacing the fuel filter. The dirt will get by and clog the inlet filter of the injector. No amount of cleaning will fix this, replacement is the only choice.

Hope this helps.

Please note: do NOT use conventional test lights on the EEC system. The EEC requires a 10M Ohm resistance to keep from damaging the electronics with too much current. NOID lights have the 10MO resistor built in.

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Hey Guys. I have an 88 Bronco with the 302 V8 5.0, for some reason when the truck starts and is put under a load like reving the engine hard, I loose fuel pressure, and the engine wants to stall and sometimes it backfires, it seems like the engine is not getting the fuel it needs. My fuel pressure is very low to begin with so I thought it was a fuel problem. It's at 20 psi. I replaced the fuel pump, fuel relay, fuel regulator, fuel filter, sending unit and sending unit pump, and the fuel tank. I still have this issue and cant figure out what else it can be. Any ideas?
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