cylinder misfire

hey guys i think i put some bad gas in my jeep... i am just getting to where it will run and not knock and ping too much... i now can give it gas and it will not die... i put some stp gas treatment and some more superconcentrated stuff to help plus a gallon of 93 octane (i have about 2 gallons in there now)... on the OBD II i get this

PO300, PO302, PO303 --> multiple cyclinder misfire...

i know i need to change the plugs becasue they are probally fouled up... what else should i do now? will i know if the o2 sensor is bad through the odb? it still smells a little funny and does not accelerate 100 percent... any thoughts about what to do next? should i add somthing else to the gas to help clean it out? acetone? also i am installing a new catalytic converter, car sound magnaflow 2.5 universal b/c my random cat is all banged up- too but it ran fine before i added the foul gas

what are my next steps?

oh yeah at first i thought it was the fuel pump becasue it would even stay running but now it will run fine but the check engine light is still on... now it runs and is getting gas but obviously the obd is picking up the cylinder misfires

You can use Seafoam. Works good. Also, ohm the injectors, if one is way lower than the average, it may be bad. Check the wires too. Check out cap and rotor for corrosion.

I'd take the car back to the gas station and demand it be returned to normal.

well it was a bp down in east atlanta... it was 3 gallons of 93 just to get home! man anyways well i will try and flush it out with seafoam... do i need to change the oil after the seafoam runs through the engine? i will be changing the plugs b/c they have to be fouled with all the cranking and misfires that i have put them through... i will check the cap and rotor along with the wires to see if they have corrosion... they are the accel from the tune up kit i put in a year ago... thanks i will report back i reckon

how should i ohm the injectors? stupid q- should i use a volt meter if so where should they be and where should i test them? 1999 cherokee 4.0 L... any other way to test injectors with out taking too much off the engine?

add seafoam to gas or oil? both?

Remove the wires, Use a volt/ohm meter, set it on ohms, and one on each side of the metal connector prongs on the injector itself.

aparke4 said:

add seafoam to gas or oil? both?

Click to expand...

The can will give good directions on how to use it. I used some in my oil, gas tank, and right down the throttle body while running.

sweet i appreciate it i will get on this tomorow and hopefully it will clean and get rid of the misfires and hesitation and restore acceleration and get rid of the check engine light...

just found this:

Basically this means that the the car's computer has detected that not all of the engine's cylinders are firing properly.
A P0300 OBD 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

A code P0300 may mean that one or more of the following has happened:

• Faulty spark plugs or wires
• Faulty coil (pack)
• 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 computer

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.

this is pretty much what yall said so i will also check all ignition components...

well just checked the obd 2 again got a PO302 so its down to one cylinder

Mine would throw a code and run poorly when it was really hot out. Theres a TSB for it somewhere.

it is still running funny probally i tune up issue still wont really even get out of the driveway

Yeah my xj just had the same issues as yours where there was multiple cylinder misfires. I had had several issues regarding the cylinder misfires and it turns out my fuel injectors' are shot. My third fuel injector is out and all the other ones are weak.. according to the mechanic.. :squint: heh, the ride does have 95k on it though.. and so I assumed the best thing to do was to replace all six fuel injectors.. idk if this helped..

good luck with your issues

yah thanks i replaced plugs and had fuel pump looked at and injectors... fouled plugs as a result of bad gas or some combustion problem... anyways did a whole tune up with oil change, plugs, accel cap and rotor and its clean now also a bottle of super conc stp and half a gallon of 93... its runs great now except for my rear end might explode... its having issues...anyways thanks for the help! luckily it was only some minor tune up components that needed replacing1

I had the jeep idling in a driveway chatting with a friend when it started sputtering and running goofy out of no where. I shut it off, and later restarted, still ran goofy, but not as much, and after I backed it out and hit the gas, it stopped misfiring. Pulled the codes today and got:

300 Misfire detected in multiple cylinders.
301 Misfire detected in cylinder #1.
302 Misfire detected in cylinder #2.
303 Misfire detected in cylinder #3.

This is an 01 XJ with coil packs. Check engine light obviously came on, and remains on, but no issue with running or acceleration since that one short moment. I imagine it is not just a coil pack, since cylinder three also misfired, but not cylinder 4. Am I wrong to think I just had some random bad gas?

Try the SeaFoam or other gas treatment, this will work if it's water. Doesn't sound like trash since you can accelerate.
I don't think you have a coil pack problem.. it does go when you floor it,
Me thinks a water droplett may take a few injector cycles to clear through a nozzle.

mike71800b said:

Try the SeaFoam or other gas treatment, this will work if it's water. Doesn't sound like trash since you can accelerate.
I don't think you have a coil pack problem.. it does go when you floor it,
Me thinks a water droplett may take a few injector cycles to clear through a nozzle.

Click to expand...

I am under the impression that most if not all US gas is now around 10% ethanol (?), or at least has a considerable amount of ethanol in it.

That being the case, I suspect that some (not huge amounts, but some) water in the gas is no longer an issue we should be concerned about, as the water would disolve in the ethanol and the ethanol in the gas thus dispersing the water. After all products like Seafoam, at least ones that disperse water in the gas, all use alcohol in the formula to disperse the water.

Thoughts????

I think the Seafoam is mostly disolving cured hydrocarbon gum and varnish these days.