I am having misfire problem with 2006 HHR with 2.2 motor. I filled up with gas and within 2 miles DTC P0301 came on. Found 2 spark plugs to be bad. Replaced the 4 plugs and then I got DTC P0303. Checked plug and boots and then I got DTC P0300(multiple misfires). I have replaced the coils and the boots. I have spark to all 4 plugs. Compression test was 195-200 so the cyl. should be good. I did not replace the ignition control module yet. The injectors have the correct ohms. I have used most of the gas from original fill up and filled up with 91 octane and put 2 cans of injector cleaner in the gas. Misses real bad when lugging the motor up a hill and it does not always set a DTC. Thanks for any help.

 

Welcome to the site, 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, check your MAF sensor connection , and get back to us with your results

Read more at: http://www.obd-codes.com/p0300
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So, now the ONLY code is P0300? If so, how many cold starts since it set? It takes a few cold starts to reset.

Did you check the compression in all cylinders? Sounds like you only checked the one.

P0300 means "random" misfire not multiple misfire. A fine difference, but meaningful.

All else being equal, I vote a vacuum leak or, maybe you forgot to re attach the MAF sensor?

 

All the cyls. had good compression. The DTC did not get set today, but it still missed badly under load going up hills. The MAF sensor was re-attached. The code reader that I have I think said Random/Multiple Misfire if I remember correctly. How do you check for vacuum leaks?

 

The most common is a split in the hose that runs from the valve cover to the rubber elbow at the throttle body to the left of the black tube in this picture

 

Today I used up a can of carb cleaner spraying the intake manifold from the top, side and bottom. I also did the vacuum hoses from the brake booster and any hoses that were attached to the intake. So I think I am okay with vacuum leaks.

I listened to the fuel injectors with my stethoscope and they all sound the same. Not sure that that means anything.

I also checked the fuel pressure and it was 58 PSI. Not sure how to check for volume to see if the fuel filter might be partially plugged in the tank.

Code P0304 was set when the fuel pressure gauge was installed as I let it idle for several minutes while watching the gauge.

The MAF code was set as well as I do not have it plugged in with the air cleaner assembly off the car. The only time I see this code is when I have it unplugged with the air cleaner assembly off the car while I am testing one the functions that might be the problem.

The spark plugs that I got from Napa when this started are AC 41-834 which replaces the original AC 41-981. The local Chevy dealer said I should be using AC 41-105 for the 2006 HHR. Any ideas if this would solve the problem.

So over the last 2 weeks I have had 1 P0301, P0303, P0304 and lots of P0300s on my code reader. When I was at a shop with a scan tool cyl. 1 fails the most, then cyl. 2 and then cyl. 4. Yesterday at the shop it stopped failing so I went home and then it was missing again.

This computer age is hard to get used to as as an old guy. I would much rather work on my 1930 Erskine with the Studebaker V8.

Any help will be appreciated and Thanks in advance.

 

You should be using the 41-105 plugs, the other years take 41-103. I got no idea where those others came from. The MAF being disconnected can cause misfires

You may be looking at a spark pack.

 

If I remember correctly the fuel pressure should be 65 PSI.

 

Yes only AC Delco 41-105 iridium spark plugs.
This could be the coil pack starting to pack it in!

 

I have installed the 41-105 plugs.

My chevy dealer says a stretched timing chain is most common fix for random misfires. Having a hard time wrapping my head around that, but I believe him.

How do you test for a stretched chain?. I have the cam cover and front cover off and have purchased the new designed tension-er.

The guide by the cam gears has no wear. I was going to check all the guides to see if any have the 0.045 wear without taking the chains out. Is that any kind of indicator that the chain has not stretched?

My wife's car has 165,000 miles on it, so how long should the chains last? I have used synthetic oil in all my cars since the 70's, so I don't ever expect them to wear out until 300,000 miles.

If I take the chains out how do I know if they are stetched?

Thanks