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p0300 code

6924 Views 5 Replies 2 Participants Last post by  96 FSB
I dont know if this is related to the six litre tune up or not but I did this tune up a few months ago and lately my engine has been idling rough. Today is the second time it has thrown a p0300 code (multiple cylinder misfires) since I did the tune up and it never did this before. I read another thread that someone had misfiring codes and it was an issue with regular plugs and there problems were fixed going back to the motorcraft. I had removed the original platinum motorcraft plugs and put in cheap autolites and regapped like the 6 litre recommends. not sure what to do now. just figured I'd just wait and see what you guys have to say before I go and spend more money on plugs. oh and also I used the MSD replacement coil in the tune up which I later read some people had some problems with.
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A P0300 diagnostic code indicates a random or multiple misfire. If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.

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

Causes; A code P0300 may mean that one or more of the following has happened:
Faulty spark plugs or wires check each wire for connection integrity first. Ensure that routing is ok;
Look at that VECI Label on top of radiator; look at the spk plug wire routing diagram carefully.

Test coil before pulling plugs to inspect again and re-gapping to save your time & $
Re-gap Plugs
Faulty coil
Faulty oxygen sensor(s)
Faulty fuel injector(s)
Burned exhaust valve
Faulty catalytic converter(s)
Stuck/blocked EGR valve / passages
Faulty camshaft position sensor
Defective Powertrain Control Module (PCM) (aka Electronic Engine Control (EEC), computer) - check for capacitor leaks, see how to remove PCM & check by JOWENS1126 @ )
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.

Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.
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I added the MSD Coil Test Link

and included doing the EZiest and cheapest DIY testing/inspections first based on probable Causes for da Code
Hey thanks for the reply. I have already read the code possible causes. the msd coil i am using is just a factory replacement and not that msd-6a box in your link. today Im going to pull the egr and have a look to rule that out. Its not that old either. This seems to be more of a problem when the engine is warming up. once its up to temp it dont seem to be an issue.
Do you have the Ford Bronco Electrical and Vacuum Troubleshooting Manual (EVTM), Powertrain Controls and Emission Diagnosis Manual (PCED), Service Manual CD from Steve83 or E Bay?
If not, suggest you get under $20.00 thang you'll ever get to repair the Bronco!
well I pulled the egr off and it seems to be clean and working just fine. I put it all back and go figure it ran good, atleast for now anyway. tomorrow we'll see what happens when i warm it up again.
Im kinda hoping someone with a 96 that has done the 6 litre tune up would chime in. have you did this 6 litre tune up??
I need to find out how to test the coil output and what it should read.
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