P0300 Random Misfire 2.4L Quad 4 SOLVED!

[MDCole9761]

Well, drove myself nuts twice now solving my wife's 2000 Alero 2.4L Quad 4 ignition problems. I have always found forums to be of tremendous help and I wanted to share my insights to hopefully help the next guy (or girl) faced with this situation.

Both times, the engine was running fine and then PLOP! The engine will start running real rough and misfire- setting a code. Sometimes the computer can identify which cylinder is misfiring, but more often in these cases there are multiple cylinders misfiring (you'll see why later in this post) or it is too difficult for the computer to tell. Henceforth, you'll usually get a P0300 (Multiple/Random Misfire Detected) from the OBDII computer. Sometimes, you'll even get P0300 in conjuction with a more specific code like P0301-P0304 (Cylinder 1-4 Misfire Detected respectively). If you do, this may help guide you to the right place, but none the less, treat the ignition system as a whole because it all interoperates and is reliant on one another to a degree.

Known Failure Points:
1. Plugs- specifically Bosch Platinum plugs tend to self-destruct (1 year and 20,000 miles for me)
2. Ignition Control Module- Kinda a "go" or "no-go" type thing. When it fails, you most likely won't be able to start your car.
3. Coil Pack Housing (usually white, some aftermarket are black) - Seems like an unlikely part to go, but from what I hear the plastic can breakdown and cause crossfiring. My first ignition trouble turned out to be this and when I figured it out I said to myself "Huh? You've gotta be kidding".
4. Coil Pack- Haven't had a bad one yet, but it's entirely possible.
5. Plug Boots- If they're old, they might dry out and crack due to the high heat they are exposed to. Again, not very likely, but when all else fails.

Background:

This engine, in case you don't know, operates on a "waste spark" ignition system. It fires cylinders 1,4 at the same time and 2,3 at the same time. What affects one cylinder pretty much kills or significantly impairs it's companion cylinder. The ICM (Ignition Control Module) takes care of a lot of the work in processing the info needed to control the ignition. It communicates with the ECU (or PCM, or computer- whatever term you prefer) which helps direct the module when to "time" the sparks. On the output side of the ICM, there is three terminals. One is +12V with the ignition on, the other two are battery ground ONLY when the ICM pulls them to ground to fire the coil. The coils boost the 12v up to several thousand volts to create a spark. Grounding of the ignition cover is essential since it brings everything metal in the ignition assembly to the proper reference (ground).


Procedures:

First off, I've found that regular spark plug wires can usually be used to jumper the whole coil-on-plug assembly so you can troubleshoot without having to bolt and unbolt the assembly every time. This also allows you to use devices like inductive pickup timing lights and in-line spark devices to check for spark.

If your engine runs but misfires, you most likely have a problem with a spark plug, spark plug boot, or the coil housing. Inspect your plugs carfully and replace if you have any doubts- they're cheap enough to simply replace without much thought. Once your sure of them, check for spark. The recommended method is by using a spark plug jumper wire with an inline spark check device and place, if nothing else, a jumper from the companion cylinder coil terminal to ground. Remove the fuel pump relay or fuse so the engine will not start and crank it over (or have a friend) while you observe the spark. Make sure the spark is bright and strong- I've had a spark plug fire, but it was too weak to fire in the cylinder. If you have spark at all cylinders, next step is to replace the plastice coil housing. It's more of a trial and error because it would take a mega-ohm meter capable of several thousand volts output to properly check this cover (something most all of us don't own or have access to). It's not terribly expensive (under $50) and if all else is good to go, there's a better than average chance it's faulty.

If you car won't start, I'd look into the ICM, PCM, or maybe even the Crankshaft Position Sensor as culprits. Also realize that fuel is essential to start the car so be sure to verify operation of the fuel pump & injectors.

Hope this helps!

~Mark

[BNaylor]

Welcome to AF.

Thanks for sharing yor experiences.

[biv343]

I got bitten by the coil pack housing problem on a 2.3L engine a couple cars back. Didn't quite believe it myself at the time, but it fixed it.

Good info to share. I'm sure my number will be up one of these days as I keep piling the miles on.

[xeroinfinity]

Good write up !

But I would disagree with the Ignition system being the only cause for misfires.

Amost all the misfires I've seen(from the 3.4 & 2.4) are from the injectors shorting out, or just not pulsing the way they should due to being dirty or just bad.
Not all , but about 80%.

And any multimeter can test ALL of those ignition parts to make sure they are bad.
Makes no sense in wasting money on things that are not broke, unless your rich and have money to burn , in that case send me some

[benjdogg19]

I had the same problem on my 2000 Alero. It started yesterday and I checked everything else untill my friend found this thread and wahlah, it worked. It had me baffled. I even ohmed it and it looked fine. I checked fuel pressure, bought a coil and changed it, checked to make sure injector was firing, fuel filter, plugs, wires, checked cam sensor, checked cat, checked compression for bad valve. And to think all along it was this little plastic housing. geeeeeeez. Thanks alot, this post saved me even more headache.

[MikeInIowa]

It was the coil pack housing for me too, 36 bucks and back on the road. I wanted to add in my case it is a quad 4 99 sunfire convet. that just turned 100k my wife was driving home and it just decided to run on 2 cyl. Being a shade tree mech. of days gone by if it does not have a set of points and a 4bbl its a shot in the dark. Funny thing is that I couldnt get a code from the computer so I started doing a keyword search that brought me here. Great job! I bet most people that take these in to get it fixed endup paying 1000+ for these gotya shops anymore.
Mike from By God Iowa.

[MDCole9761]

Hey! Great that my post was able to help- I'd all but forgotten about it (since I posted in back in 2006).

Yeah, it was such a headache to diagnose that it drove me to post that info in hopes that others wouldn't have to go through what I had to.

Thanks for sharing your experience!

~Mark

[craigon]

Hi. Good post. I have the same problem with a 2000 Alero 2.4L. It just started missing and throwing a PO300 Sunday. Tried plugs to no avail. I want to try the "coil pack housing" option but want to make sure I'm getting the right part.

Is this the part you all are talking about?

<Update 9/8/10: I replaced the below coil cover to no avail. I then picked up a new coil from AutoZone and that fixed my issue. I just did "brute force" part replacing and did not really test the parts. So with 1 new coil, a new coil cover/housing, and a new spark plugs, I'm hoping my 197k Alero (it's an ex-rental car I picked up for 2k a few years ago) will keep on chugging along as a commuter for a while longer! Thanks for this thread.>



Thanks!
Craig

[MDCole9761]

Yep! That's the one! The coils themselves and the ignition control pack, are also possible culprets, but I was able to thouroughly test them due to my backgroud in electronics, electricity as well as having detailed wiring diagrams and knowledge of how all the peripherial systems that "drive" the ignition work (such as the crank position sensor, etc).

Good luck!

~Mark

[reyesking]

I have hit the same wall. I just bought this alero. I have two codes.
P0302 for cylinder 2 misfire. and p0507 for high RPMs.

I have changed the spark plugs. Have gapped them to 0.060 as told by Autozone people. I have removed the coils and had the primary and secondaries checked out and they both were within the accepted resistance. So the Coils were good. I have changed the Throttle Position Sensor. I am seriously looking at changing the Idle Air COntrol Valve and the Topstream Oxygen sensor. I was actually shopping on EBAY for the parts when I decided to hold up and read more into it so hear I am. Discovering that for some people there problem has been the Coil Housing pack. Could this be my reason as well?

[MDCole9761]

Originally Posted by reyesking

I have hit the same wall. I just bought this alero. I have two codes.
P0302 for cylinder 2 misfire. and p0507 for high RPMs.

Possibly- it seems to be a REAL common thing with these Quad 4 engines. My guess is that the extreme temps it sees being mounted in between the cams and directly over the heads causes a breakdown of the insulating plastic.

In your case though, the codes seem to be pointing in a more specific direction. They have pointed to cylinder 2 only and it's recording a high RPM. Is it actually idling high? It should idle somewhere in the 500-900RPM range (that's off the top of my head- it can vary, depending on if the engine is warm, loaded down with the A/C, etc.). If it is idling high, I'd say check into the following:

Taken from http://www.obd-codes.com/p0507

A P0507 DTC trouble code may be caused by one or more of the following:

-A vacuum leak
-Leaking air intake after the throttle body
-EGR valve leaking vacuum (If memory serves, the Quad 4 engines don't have an EGR valve)
-A faulty positive crankcase ventilation (PCV) valve
-Damaged/failed/dirty throttle body
-Failed EVAP system
-Failed IAC (idle air controller) or faulty IAC circuit

Fixing the high idle should be somewhat easier than the misfire- and sometimes one problem makes others occur at random. Fixing the high idle might make the cylinder misfire go away. These are what we call "nuisance codes"- they only occur once in a great while and the vehicle seems to drive normally otherwise.

I've had IAC issues on other engines- they were due to carbon build up inside the throttle body- take some carb cleaner, remove the IAC, and clean up the IAC pintle and the throttle body to rule that out. If it's a cheap part, then just replace it (but I suspect it's not that cheap). Inspect all the vacuum hoses and fittings to be sure there aren't any vacuum leaks (that would certainly contribute to a high idle).

Anyways, fix the idle issue, clear all DTC codes, and then see how it runs and observe the "Service Engine Soon" light to see if it comes back on. If there is an ongoing problem, the light will turn back on within a day or two of normal driving.

**Remember- modern engine computers require a "drive cycle" to be completed before setting all but the most obvious/severe DTC codes. To complete a drive cycle will usually take a day or two of normal start/stop, accelerate/brake, warming up the engine, crusing at a speed for a minimum amount of time, etc. driving to complete.**

Sorry- there's just like 50 different ways to approach the idle air issue, let alone the cylinder misfire! My overall advice is to do all the checks, testing, cleaning and replacing you can that are free or cheap to do. Then work your way up to replacing expensive parts as your diagnosis points you in the right direction. Also, check with AutoZone to see what parts can be returned- something like an IAC doesn't really get dirty/used all that much during a 10 minute test to see if it fixes the problem, so you may be able to return it if it doesn't solve the problem.

[reyesking]

REmoved the IACV and cleaned it with some carb cleaner.

Last night I changed the hose right underneath the Throttle that enters the intake manifold and connects to the MAP sensor. It seemed all cracked and beat up. I replaced it with a new one. The new one fits on the sensor nice and tight but the enterance into the intake fits slightly loose but not too loose.

Cleared codes. Right away, I'm talking not even 5 minutes the P0300 is showing up as pending with a Random Misfire. WHen it is pinpointed, it has been zeroing in on Cylinder 2 misfire with the P0302 Misfire and the p0300 goes away.

I already replaced the TPS as mentioned before as it was turning off at idle and accelerating on me while on 1st on occassion and the new TPS took care of this problem. However, a rough idle still occurs, but not as rough as when the old TPS was on.

My next bet is to purchase the IACV. I found it on EBAY for 23 bucks. I have a 10 dollar coupon so I really only pay 13. I should get it within 4 days. Hopefully this takes care of the erratic idle. and clears the p0507 code.

This will still leave me with the p0302 problem, I took the coils off and autozone checked them and they were good. From what I have read, I am leaning towards the Coil housing causing the misfire. I see its selling for 42 bucks at Autozone here in Los Angeles. Is there a way to check if this coil housing is the issue or if it is the Ignition Control Module. Can they be tested prior to me dishing out the money?

[MDCole9761]

Ah....very good info. That helps quite a bit.

I too, had the P0300 as well as a code that identified the cylinder- basically it sounds like it's catching cylinder 2 misfiring more than the others, but the fact that there are others is what's throwing P0300. At this point, I would bet that the plastic housing is to blame.

The only other likely causes are a bad ignition control unit (expensive, would probably prevent the car from eve starting), a faulty crank position sensor (might be a pain to get at, and again would likely prevent it from even starting), or a bad ECU (not terribly likely).

The tough part is that you can't really test the plastic housing- the problem is occurring under conditions where several thousand volts are being carried through the ignition pathways that are molded into it. With normal test equipment, you'll find that the resistance between these pathways is essentially infinite. But several thousand volts can jump through even the tiniest cracks or weak spots in the plastic which causes the spark to jump to another pathway (and therefore, another cylinder) which means the cylinder that it was intended for receives a weak spark- if any.

When I worked as an electrician, we had special meters that could test wires designed for several thousand volts- but they were expensive and I doubt you have access to one of them (I think it was called a "Hi-pot"- short for Hi-Potential"). So unfortunately, $42 might be the cost of trial and error. On the bright side, after this many years of engine heat it's probably not a bad part to replace- even if it's not the source of the problem.

[reyesking]

Changed the coil housing. Deleted codes.

both the p0300, p0507, reappeared and I am sure that it will end up as identifying the cylinder 2 misfire.

The car fires up everytime without a problem so that should exclude the ICM if you say it wouldn't start because of it.

Here are some other things that could be the cause.

1. When I open the Engine Oil cap, smoke is coming out, which leads me to believe I either have a bad gasket, or a loose Piston ring. (I have been reading about Lucas oil treatment, and Engine Restore to see if this is an option vs. opening the Engine)

2. I am unable to accelerate to above the 4000 RPMs. I am not racing or anything but I read somewhere that this could be due to a bad TPS. I changed the TPS but the same problem occurs. Once I get to 4000 it just loses the push I was giving it and sort of bounces around 4000.

3. After the downstream oxygen sensor there is a second cat converter. This second converter appears to have a slow drip of black engine oil. I am figuring that this has to do with oil being spit out of the misfire into the exhaust and contaminating the CAT CONVERTER. This might be what is making the car so shaky, if there is a hole, or a bad CAT converter, I believe this is a symptom.

4. I seem to be hearing a hissing sound coming from around the throttle. I was playing with the acceleration cable a bit to rev it up, and as I go from bout 2000 to 1000, back and forth, I hear a slight hiss, but I can't find the leak. I am thinking it is from the wide hole in the Throttle that connects to the resonator.

5.Also, there was quite a bit of oil in the resonator and I believe this is due to the misfire. I also messed up and put 5 quarts instead of 4 plus motor honey so I am not sure if this led to the oil being there.

6. I was also thinking that maybe a new Oxygen sensor might help but at this point I was thinking of taking it to the dealer to give me the 411 analysis. I fear that I will hear, "oh yeah your car needs a new engine"

[reyesking]

is there such a thing as an Idle relearn process since there doesn't seem to be a screw to adjust the idle on this Alero. I will double check but I don't think I saw one when I removed the throttle to clean.

IF there is an idle relearn process, what is the proper way to teach the Computer to get back to normal idle speed at 700-750 rpm.