Throwing codes...please help!

[License2Bill]

Started the car today and it was running unusually rough. Plugged in my scanner and it's showing a P0300 and a P1235 which are "random/multiple cylinder misfire" and "fuel pump control out of range"


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[fastblackmerc]

Started the car today and it was running unusually rough. Plugged in my scanner and it's showing a P0300 and a P1235 which are "random/multiple cylinder misfire" and "fuel pump control out of range"


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First lets reset the PCM, and Clear the Code. And see if it comes back on. Disconnect the Negative Battery Cable from the Battery. Keep it off for about 5 minutes, then reconnect it. Drive the Car again for a while. If it comes back on then pull the Codes again..Write them down, and get back to us.

OBD II Fault Code

OBD II P0300

Fault Code Definition

Misfire Detected in Random, Multiple Cylinders

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 theP0300

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

P0300Diagnostic Theory:
When the code P0300 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 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.

Common Causes for an Engine Misfire and CodeP0300

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.

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.

[fastblackmerc]

P1235 code.

When was the fuel filter changed last?

[License2Bill]

I'll pull the cable and report back. I've only had the car for about 3000 miles. No idea when the Fuel Filter was changed last.

Within the first month of owning it, I seafoamed it and P2197- Bank 2 O2 Sensor stuck lean showed up. I stupidly haven't replaced the 02 sensors yet. I think that may be my next course of action.

[RF Overlord]

Second what Jim said above about P1235 and the fuel filter.

This car has a returnless fuel system and as the filter gets more clogged the FPDM commands the pump to work harder until it runs out of adjustment range.

[fastblackmerc]

When I get a vehicle with an unknown service history the first thing I do is change all the normal maintenance items. At least your be starting with a clean slate.

[License2Bill]

I've put approximately 30 miles on it since disconnecting the battery. No shudder, rough idle, misfire or anything yet. Replacing fuel filter tomorrow

[License2Bill]

Autozone brand filter for 9.99 or Motorcraft for 12.99 from Advance Auto, I think I can spare $3 extra bucks for OEM

[fastblackmerc]

Autozone brand filter for 9.99 or Motorcraft for 12.99 from Advance Auto, I think I can spare $3 extra bucks for OEM

Go with a bigger filter.

[License2Bill]

I think I've read about doing that in another thread. Just can't remember the benefits or part numbers

[License2Bill]

I started the car this morning after clearing the codes and driving it yesterday, and it is idling really high between 900 and 1000 rpm. Normally it's right around 650. Could this just be the computer relearning everything or is something else going wrong?

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