Blinking check engine light

stew47 wrote:
Thanks gde trailer. I looked up harbor freight and was gonna go get one but autozone is so close. Po300 was the code.

I should also mention few weeks ago it blinked under hard acceleration but went off in less than a minute. This time it stayed.

P0300 Code Link

Text from above link..

P0300 - OBD-II Trouble Code

OBD II Fault Code

OBD II P0300

Fault Code Definition

Random, Multiple Misfire Detected

Symptoms

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 the P0300

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)
Powertrain/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 powertrain. 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.

P0301 Diagnostic Theory for Shops and Technicians
When the code P0300 is set in the Powertrain 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 P0300 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 P0300 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 P0300 (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 Code P0300

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 Powertrain 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.

Powertrain 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 powertrain 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, driveshaft, or front/rear differential.

How many miles on the plugs?

Have you changed the COPs and boots?

If so, did you use Motorcraft COPs or generic COPs?

Depending on mileage most likely you have a COP going bad..

But sometimes random misfires can be caused by a vacuum leak..

On some (not all) 5.4 and 6.8 modular engines there is a vacuum line that can crack and leak.. That line is known to cause random misfires. I am just not sure as to what years may have this line..

If it was a single COP, there should be an additional code which will indicate which "bank" or side the random miss was detected..

Hope that helps :)

Thanks gde trailer. I looked up harbor freight and was gonna go get one but autozone is so close. Po300 was the code.

I should also mention few weeks ago it blinked under hard acceleration but went off in less than a minute. This time it stayed.

Bobbo wrote:
A solid check engine light means check the codes whenever it is convenient.

A blinking check engine light means pull over, stop and call a tow truck.

No, not even close.

Blinking CEL is a DETECTED FAULT IN THE EMISSIONS SYSTEM, this MAY set a code but most of the time it will set a pending code if fault condition clears before the next cycle.

If the fault clears before the cycle then blinking goes out and no code is set (there may or may not be a pending code),

If fault persists into the next cycle then the CEL light is turned on (solid, no blinking) and the code is set..

IF code has been set you have two different routes, a temporary code and a permanent code.

Temporary code will clear it's self IF the fault no longer exists after 3 or more full ignition cycles (engine runs until it is fully warmed up then shut down and allowed to cool).

Permanent CEL code will not clear without the use of a OBD reader.

Just because you have a blinking CEL or full on CEL does not mean you must stop and have it towed.. It simply means there has been a emissions related fault detected and you should see about getting it serviced soon..

Now, continual operation with a lit CEL could cause damage to the CATS or Oxy sensors PROVIDED you have a over lean or over rich fuel condition..

The best tool to own now days is a full on OBD reader (I am NOT talking about those Blue Tooth dongles)..

A full dedicated code reader WILL not only read the codes but has built in dictionary of the codes it reads.. This makes troubleshooting much easier.

Those BlueTooth dongles will often give you a code, but then you will have to do an Internet search to find out exactly what the code means.

If you have a Harbor Freight store near you, they have multiple code readers.. They actually are a real good deal and work well.. With 20% coupon you can get the top of the line HF reader for about $112 and it reads engine codes plus ABS codes and the newest models also read the CANBUS communications codes as well..

If money is a problem they do have more basic models starting at $49 but be aware some cheaper models can not remove codes and reset to CEL light. Best to read the manuals before buying (hint, HF does have the manuals online so you can read them before buying!)

A solid check engine light means check the codes whenever it is convenient.

A blinking check engine light means pull over, stop and call a tow truck.

Are you saying it started blinking and then settled into a steady light? If it kept blinking I wouldn't drive it until the fault is known. It means severe damage can occur to converters. Go buy a $30 code reader.

I had an 86 Suburban that had the check engine light come on and then start blinking. I was coming home from snowmobiling on the NYS Thruway. I drove it the last 10 miles to my house. It was a malfunction in the distributor. It ended up needing both converters and all 4 O2 sensors because I kept driving it. Thankfully it had an extended warranty! A blinking check engine light is not a good thing.

What does your owner's manual indicate?