Random misfire this car origonally came in with a hard miss on cylinder 1. no injector pulse. we replaced the computer and it helped alot. but now i have random misfire but primaraly on cylinder 2. it has all new injectors, egr, plugs wires, no vaccum leaks, good compression, good ckp waveform but no codes. it has a hesitation and stumble at idle. my barometric pressure sensor is a little off. it runs at 152. i am at sea level i know it shold be at around 157. is this an issue and if it is how do i correct it. i want this nitemare to go away.

Is P0303 the only code?

Could be the injector but may also be wiring or ECM driver. Same goes for spark so verfiy spark at plug electrode. Remove, inspect sparkplug, and verify spark. Swap with another plug if nothing obvious. Try thumb test to verify compression or use a compression tester. Use "noid" lamp for visual indicator that injector pulses are present at suspected injector connector.

Some specialty tools are available zero cost under loan a tool programs at typical auto supply box store.

Also be aware cylinder misfires are sometimes (rarely) misidentified as to respective cylinder. You can disconnect fuel injector 3 electrical connector while engine running and if no notable change in rpms then cylinder 3 misfire confirmed. But could be missing spark instead of injection.

Injector pulses will be disabled on a cylinder with high misfire rates. Testing injector pulses on a misfiring cylinder may only be valid during engine crank or shorty after start.

Is the injector delivering fuel? New or not, use a pulse checker, cheap tool blinks if the injector is getting "pulsed" Also check the compression on all cylinders, any one that is 5% lower than the highest reading will cause a rough idle or miss.

replace no 2 injector

Hi Jason:
A Random/Multiple Cylinder Misfire Detected unfortunately doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.

A code Random/Multiple Cylinder Misfire Detected 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

Possible Solutions:
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.

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

For engine misfiring problem check the help links mentioned below. Click the link below to go through the troubleshooting procedure :---- No pulse to injectors? http://technoanswers.blogspot.com/2012/01/no-pulse-to-injectors.html
---------How to Test and Replace Fuel Injectors? http://repairhelpcenter.blogspot.com/2011/11/how-to-test-and-replace-fuel-injectors.html
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How to Replace a Fuel Injector
http://schematicsdiagram.blogspot.com/2011/07/how-to-replace-fuel-injector.html
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Engine misses and truck jumps? Hard to down shift? Issue with high gear only? http://technoanswers.blogspot.in/2012/02/engine-miss-and-truck-jumps-hard-to.html

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Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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Engine Misfire codes for car?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html
Engine Misfire codes?

http://schematicsdiagram.blogspot.com/2011/12/engine-misfire-codes-on-chevrolet.html

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Misfire on cylinder 4?

http://schematicsdiagram.blogspot.com/2011/12/misfire-on-cylinder-4.html

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Oil on spark plugs and car misfires?

http://technoanswers.blogspot.in/2012/02/oil-on-spark-plugs-and-car-misfires.html

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This will help.

Thanks.

It could very well be a bad coil pack,or you have low compression in that cylinder.If the compression is good then go with the coil pack,if not you may need a head gasket or an intake manifold gasket.

A misfire can be cause by several factors. here are a list of things to check check spark plug on that cylinder and check coil and wiring for coil. check cylinder compression on all cylinders if one cylinder is less than 10 psi different from the others that can cause a miss, last but not least check injector pulse using a noid light for injector pulse if pulse is good then injector is bad replace and that should solve your problem. Good luck and contact if you need more help. Thanks for using FIX YA

A misfire on this type of vehicle can be due to 2 factors if it missing spark it will trigger a misfire code and it you have a bad INJECTOR. Most misfires are due to missing spark but there are quite a few in my experience that were due to bad injectors or bad injector wiring. To check this you need a NOID light disconnect injector wire on suspected cylinder in your case #1 and connect wire to NOID light (engine must be running for this) Your NOID light should have a consistent flickering light going while vehicle runs at idle. If light its NOT flickering at a steady pace and flickers erratically. THE PROBLEM IS A BAD Injector wiring or a bad computer. If light flickers consistently and in a steady pattern then YOU HAVE A BAD INJECTOR. Replace injector and that will solve this problem. I know this is a lot of info but It will help you alot. Good luck and thanks for using FIX YA

If you have coils and spark plugs then you don't have wires. From personal experience these car's misfire because of coils and BAD INJECTORS. If you replaces coils and sparks plugs you need to check injectors. Get a NOID light and check injectors pulse to make sure it good. First you must locate the cylinder that has the misfire/Missing,this can be done by using a computer/code scanner or if can be manually by disconnecting each coil and see when there is NO change in idling or shaking. What you are looking for is when you disconnect the Eugine should shake more and when you reconnect it would smooth en out. If any cylinder when disconnected the engine doesn't change that the one with the problem. Check again for spark and make sure it good. Then check that injector pulse plug off injector connector and connect it to NOID light you should get a constant flickering of NOID LIGHT. If you do then BINGO that injector is BAD. However I must say this test is on valued if you have performed a compression test on all cylinders to make sure there are no BAD/Burnted valves. This can be done with a compression guage remember the reading should NOT be more than 10PSI difference between all cylinders example of a normal reading is cylinder 1 170 psi cylinder 2 168 cylinder 3 172..... abnormal is cylinder 1 170 cylinder 2 85 cylinder 3 172 ...etc. I know this is alot of info but read through and follow these step and you'll be ASE certified by the end of this job. Good luck and thanks for using FIX YA