Topic: Help! Random Misfires (P0300), low power, both under hard acceleration

[slusamson]

Been wracking my brain over this one for weeks. Here's the facts:

2008 2.4L Solstice, about 65000 miles
Only mod is Solo Mach cat-back exhaust
Water pump replaced about 10,000 miles ago (dealership)
Fuel injectors serviced about 10,000 miles ago (dealership)

I started noticing that under hard acceleration my car was slow to get the RPMs up until about 3500 RPMs. After that they would come very quickly, but if I was in 1st gear (accelerating from a stop or from <20mph) , the car would not shift around 5000 RPMs like it normal would and if I continued to push it would reach 6000-6500 RPMs before I would let off the throttle and then it would promptly shift. Making the RPMs hover about 5500-6000 for a short while when these conditions were happening it would give me a P0300 random misfire code and depending on how many codes it had in it's memory would go into limp mode. Took it to the dealership and they give it back saying nothing is wrong. They said it was bad gas.

Of course something is wrong because it still does it even after two tanks of non-ethanol 93 octane. I decide to do some tune-up items since it's time for some of them and some of them wouldn't hurt to do anyway... certainly cheaper than letting the stealership do them.

1. New air filter
2. Changed the plugs
3. Changed the upstream O2 sensor
4. Changed the intake and exhaust camshaft position solenoids
5. Cleaned throttle body
6. Cleaned the MAF
7. Seafoam in the vacuum line
8. Seafoam in a fresh tank of gas
9. Tested vacuum and got 25 bar
10. Removed upstream O2 sensor and pressure tested cat, 0-1 psi
11. New battery

The problem still exists and has gotten worse. The code at first only appeared when I forced it to. Yesterday I hit the interstate and discovered that it is not a struggle to gain speed fast enough on the onramp to safely merge over. I also experienced a rattle/buzzing sound when accelerating followed by distinctive misfiring sounds and the deeded P0300 code again. I don't know what else to check at this point and plan to bring it back to the dealership in a few days. Anyone have any ideas? 

[Sly Bob]

A quick google search turned up these as possible culprits. Does the 2.4 have a fuel filter? I know that the GXP doesn't.

You changed the plugs? OEM plugs at the proper gap?

- Faulty spark plug (s)
- Faulty ignition coil (s)
- Clogged or faulty fuel injector (s)
- Intake air leak
- Fuel injectors harness is open or shorted
- Fuel Injectors circuit poor electrical connection
- Ignition coils harness is open or shorted
- Ignition coils circuit poor electrical connection
- Insufficient cylinders compression
- Incorrect fuel pressure
   
Read more: http://engine-codes.com/p0300_pontiac.html

[tman2000]

Check the catalytic converter. I had this similar issue, dealer replaced it for free.

[Sly Bob]

The first post said he checked the cat...

[Sly Bob]

You know what to do. Call DDM and talk to Dave. Tell him that you are a member here and ask him if there is anything he could suggest you check. He's a good guy and can likely steer you in the right direction.

[slusamson]

Thanks Sly Bob, I checked out the site you posted... don't know how I didn't see that one before. There is a TSB about cleaning the injectors which I'll bring with me to the dealership if necessary. I see some other things on your list that I can check that I haven't already so I'll give those a look tomorrow. I may give Dave a call as well and see what he may be able to tell me. If can't resolve this myself, I want to be armed and ready when I bring it back to the shop. I know I paid them a good bit to service the injectors and if that ends up being the problem, there's no way in hell I'm going to let them charge me for it because they obviously didn't do the work.

I'll update tomorrow!

[2kwk4u]

Just P0300?  (i.e. never P0301/02/03/04?)  Have you had any other electrical anomalies?  Check your grounds for corrosion.  Aside from that, check your ignition coils wire harness for poor connection.  On an older car, I'd think this is ignition coil pack related, but these cars have coil-on-plug with 4 individual coils.  If one were failing, you'd have a misfire in that cylinder (P0301, P0302, P0303 or P0304).

[TomatoSoup]

I wonder if it's simply excessive carbon build up?  You could try the GM top-engine cleaner, or just Sea Foam.

[POS VETT]

I had something like this in my '3 Z06. It turned out one of the coil wires rubbed on a bracket and grounded that coil. I'm unsure what caused the rubbing but it might be a broken engine mount, or both.

[elff]

I wonder if it's simply excessive carbon build up?  You could try the GM top-engine cleaner, or just Sea Foam.

I will bet this is the case.

Unfortunately the only real cure is to partially take apart the top of the engine and remove the intake manifold to get in and clean the carbon off the valves
It's a major issue with all engines that have Direct Injection.

BMW uses Walnuts to "walnut blast" the carbon off
It's like sand blasting with a vacuum using walnuts instead of sand
and
it is not covered in their warranty

[Jackknife]

I will bet this is the case.

Unfortunately the only real cure is to partially take apart the top of the engine and remove the intake manifold to get in and clean the carbon off the valves
It's a major issue with all engines that have Direct Injection.

BMW uses Walnuts to "walnut blast" the carbon off
It's like sand blasting with a vacuum using walnuts instead of sand
and
it is not covered in their warranty

First of all, a 2.4 is not a direct injection engine.

Next:  the telltale for me is the rattling sound with acceleration....classic catalytic converter behavior. I know, he said it was pressure tested;  but sometimes with different pressures the obstruction in the cat doesn't move out of position.

Pull the exhaust off the cat and visually inspect its innards.

[elff]

You are correct, I missed the N/A part of the post.

[Sol Asylum]

It was up near the top of his post, you probably aren't tall enough to see it.

[TomatoSoup]

Doh      !

[Helios]

WOW! Just wow!

[POS VETT]

O lo blo ...

[LatinVenom]

You can have the carbon buildup taking care off by a professional without having to remove the head.
Someone on the BB had it done at the dealer.

[slusamson]

Update time! The problem had gotten steadily worse and I made an appointment to bring it in this morning... It got bad enough that misfires were happening during regular driving when trying to pass someone or accelerate from a light. On the way to the dealership this morning I got behind someone going 30 in a 55, so I decided to pass. It was really embarrassing that I couldn't get the car to go fast enough to pass an old beater truck, but it threw a code and I was happy that there was no way the dealership could miss this problem this time.

I got a call this afternoon and they informed me it indeed was the catalytic converter. A new one will be installed tomorrow and I'll be back on the road. I'm also having the transmission flushed and the differential serviced since it's overdue for both. I had a new set of tires sitting in the garage waiting to go on as well and I just finished dropping those off.

I checked on the car while I was there since I was in the shop unloading the tires and took a look at the cat to see how bad it was. It looked good at first glance, but after backlighting it with a flashlight, the middle about the size of a half dollar was all that was unrestricted. The new one would have been over $800, but the warranty was still in effect for the part. Something like 80,000 miles if I remember correctly. I told them an aftermarket hi flow cat would be cheaper, but they didn't bite on that one . The shop guys said I needed to test it with someone increasing the RPMs and I would have found it, but I didn't have an assistant so it never dawned on me to try that before.

Regardless, it's sunny, 70+ degree weather here in Louisiana and I'm ready to my car back and drop the top! Thanks to everyone that made recommendations!

[Jackknife]

Update time! The problem had gotten steadily worse and I made an appointment to bring it in this morning... It got bad enough that misfires were happening during regular driving when trying to pass someone or accelerate from a light. On the way to the dealership this morning I got behind someone going 30 in a 55, so I decided to pass. It was really embarrassing that I couldn't get the car to go fast enough to pass an old beater truck, but it threw a code and I was happy that there was no way the dealership could miss this problem this time.

I got a call this afternoon and they informed me it indeed was the catalytic converter. A new one will be installed tomorrow and I'll be back on the road. I'm also having the transmission flushed and the differential serviced since it's overdue for both. I had a new set of tires sitting in the garage waiting to go on as well and I just finished dropping those off.

I checked on the car while I was there since I was in the shop unloading the tires and took a look at the cat to see how bad it was. It looked good at first glance, but after backlighting it with a flashlight, the middle about the size of a half dollar was all that was unrestricted. The new one would have been over $800, but the warranty was still in effect for the part. Something like 80,000 miles if I remember correctly. I told them an aftermarket hi flow cat would be cheaper, but they didn't bite on that one . The shop guys said I needed to test it with someone increasing the RPMs and I would have found it, but I didn't have an assistant so it never dawned on me to try that before.

Regardless, it's sunny, 70+ degree weather here in Louisiana and I'm ready to my car back and drop the top! Thanks to everyone that made recommendations!

Glad you finally got it fixed.

Strange it never threw a code for the cat (mine did the same thing).  The muffler shop told me most often there's no code for a clogged cat.

[Jackknife]

WINNER!!!!!!

I have to ask though slusamson, when in the first post you said you checked the cat. How did you check it? Did you attach a hose with a guage to the upstream bung and watch the pressure guage as you drove the car?

Actually, Taylorman2000 got it first (in his FIRST post),but got brushed off.

Listen to the noobies...what is this, the Sky forum?

[slusamson]

Sly, I attached a gauge just like you stated but didn't have enough hose to drive it like that (basic Oreilly's kit)... Should have just gone and got some as I'd have solved this on my own weeks ago (with a Solo hi flow cat). I asked the dealership to test it the first time I brought it in but they said it was fine... Either they didn't test it or they tested it like I did.

I know the cat rattle sound and other symptoms now, so this will be valuable experience for the future for other cars.

Glad this didn't turn in to a more serious repair!

[Sly Bob]

Actually, Taylorman2000 got it first (in his FIRST post),but got brushed off.

Listen to the noobies...what is this, the Sky forum?

Sorry I somehow missed that post from Taylorman2000 and my name isn't Mike.           Tough crowd...   

[Gentleman Jack]

Sorry I somehow missed that post from Taylorman2000 and my name isn't Mike.           Tough crowd...   

SlyBob-
If you need some backup, call SHiNY and make some HamBacon. Everything is better with HamBacon.

[slusamson]

Just picked up my car and boy does it sound different. I forgot how loud and deep the Solo Mach exhaust really was. Shifts smooth as butter and accelerates nicely too. I never noticed it, but the car was idling much harder before, especially when the AC was on. Now it feels like it did when the car was new. Amazing how over time one doesn't notice the deterioration because it's so slow, at least in my case anyway... My only fear is that since it's another OEM cat, the same thing may happen again... Guess I'll know the symptoms next time and take care of the repair myself with an upgrade

Does anyone know if GM ever found out why this is so common on our cars and if it's been corrected?

[elff]

Just upgrade it and not deal with it any more