P300 and P1174 codes on 2007 Pontiac G6 with 2.4L

[wtd]

Looking at this car for someone else and it has these two codes. I know the p300 is for multiple cylinder misfires and the p1174 is a fuel trim balance issue. Car has new Delco iridium plugs in it. Car runs fine going down the road with good power and it doesn't feel like it's missing.

When you come to a stop, the car will start running real rough and the CEL starts flashing showing it's misfiring. You can also watch the misfires on my scanner. It shows thousands of misfires in cylinders 2 and 3 and about 260 in cylinder 1 and none in cylinder 4.

When the car is idling and running rough, the pre-cat o2 sensor will only switch back and forth in the 700-800 range. When you give it gas and rev it up, it will switch back and forth normally from the top of the range to the bottom.

Does anyone know what else I should be looking at or has anyone had these codes before and got them fixed? Thanks.

Wayne

 

[Trav]

Gm has a TSB out for this. First unplug the MAF and see if there is any improvement.
Check for a vacuum hose broken, loose or off.

This is the TSB. Note this is with the Multec injectors which are known to cause problems.

http://engine-codes.com/uploads/gmc/03-06-04-030F.pdf

 

[wtd]

Trav,
Thanks for the information. In my research I did see that TSB as well as one that says to replace the stock injectors with a new part number and then have the ECM reprogrammed to work with the new injectors.

I did check for broken vacuum hoses as well as checked to see if any were off and everything looks intact and plugged in.

I also cleaned the throttle body as well as the MAF. If I unplug the MAF and it runs better, what does that mean? There are no codes for a MAF malfunction.

The owner had me order new injectors so I ordered 4 new AC-Delco ones. I got the #217-2907 ones which I believe are the stock replacements. He didn't want to have to take it to the dealer to get the upgraded ones reprogrammed. The stock ones should last for awhile anyway and I'm not sure how long they plan on keeping this car anyway.

What do you think about the O2 sensor behavior when the car starts running rough? Is that a symptom of something else causing the readings I'm seeing or is the O2 sensor actually malfunctioning?

Thanks again for your help.

Wayne

 

[Merkava_4]

First thing I'd do is check for spark - one cylinder at a time. I'd want to first determine if the misfire is ignition related or fuel related. In the meantime, I'd be using my nose to smell the exhaust. A rich smell means the fuel is getting delivered, but there's no spark to ignite it.

 

[wtd]

The CEL will flash at idle indicating it is misfiring. When driving, the CEL will quit flashing and the car drives smoothly with no misfires felt.

Doesn't this indicate that this is more fuel related than ignition related?

Wayne

 

[Trav]

If the CEL is flashing don't drive the car r keep running it, this indicates a CAT damaging misfire. The cat may or may not have already been damaged so don't be surprised if it goes out

Unplugging the MAF usually indicates a defective MAF or in my experience bad injector(s).
With no MAF code stored its probably the injectors.
It could be a lot of things, this is just a very general statement not to be used for diagnosis.

The updated injectors are a better unit and the Delco or Delphi ones need a flash but Bosch makes some that Ford and Opel just happens to use (making them a common item) that fit and work perfectly without flashing.
The next time you run into something like this let me know, i can either get you the injectors or give you the part# of the ones that will work best.

Just for your info the SMP# FJ718 is a Bosch or Deka USA or German made injector that uses the correct USCAR connector and fits this engine with no flash and no issues.

Anyway, after you get the injectors in i would suggest running Redline SI-1 at a rate of about 3 oz per tank continuously. It is easier to keep them clean and prevent the issue than trying to clean them up after they get dirty which isn't happening with these.
Amazon has it cheap enough and one bottle will last for 5 tanks of fuel.

 

[PF52]

Originally Posted By: wtd

The owner had me order new injectors so I ordered 4 new AC-Delco ones. I got the #217-2907 ones which I believe are the stock replacements. He didn't want to have to take it to the dealer to get the upgraded ones reprogrammed.


I've considering doing exactly this with my Cobalt (same engine). Replacing the injectors is a ten-minute job on this engine.

No misfires, but I get an occasional P1174 but its been a while since I've seen one. At least a month. Hardly seems worth seeing the dealer for.

 

[PF52]

Originally Posted By: Trav

Just for your info the SMP# FJ718 is a Bosch or Deka USA or German made injector that uses the correct USCAR connector and fits this engine with no flash and no issues.



Just to clarify, this is the correct injector for the 2.4 engine and requires no flash? 2006 Chevy Cobalt.

 

[Trav]

Yes thats one of them and they are one of the least expensive, plug and play job. The quality is good.

 

[PF52]

Excellent, thanks for the tip!

I see those are available on Rock Auto, which for some reason no longer has an AC Delco part listed under this application. Not sure why, except perhaps its because the new part numbers maybe haven't migrated down to Rock Auto's site just yet, but they've already run out of the old ones. Either way, though, I got almost 180K miles out of the original injectors, so I probably can't complain. A new set of SMP injectors is probably a wise investment.

 

[Trav]

It cant hurt at that mileage especially with these.

 

[wtd]

Originally Posted By: Trav
If the CEL is flashing don't drive the car r keep running it, this indicates a CAT damaging misfire. The cat may or may not have already been damaged so don't be surprised if it goes out

Unplugging the MAF usually indicates a defective MAF or in my experience bad injector(s).
With no MAF code stored its probably the injectors.
It could be a lot of things, this is just a very general statement not to be used for diagnosis.

The updated injectors are a better unit and the Delco or Delphi ones need a flash but Bosch makes some that Ford and Opel just happens to use (making them a common item) that fit and work perfectly without flashing.
The next time you run into something like this let me know, i can either get you the injectors or give you the part# of the ones that will work best.

Just for your info the SMP# FJ718 is a Bosch or Deka USA or German made injector that uses the correct USCAR connector and fits this engine with no flash and no issues.

Anyway, after you get the injectors in i would suggest running Redline SI-1 at a rate of about 3 oz per tank continuously. It is easier to keep them clean and prevent the issue than trying to clean them up after they get dirty which isn't happening with these.
Amazon has it cheap enough and one bottle will last for 5 tanks of fuel.


Trav,
Thanks for the info. I will keep you in mind next time for parts. Just to clarify, are the injectors I got the ones that don't need to be flashed to work?

The guy is bringing the car over tomorrow so hopefully I will know something then after I replace the injectors. I will give the owner the info about the Redline Sl-1. I have used it in the past as well.

Hopefully the CAT doesn't go out but I think the owner has had this problem going on for awhile. I know the car has at least 2,000 miles on it since the last time I worked on it for something else and it was doing this then and he said the light had been coming on for awhile before that.

Anyway, thanks again for the info.

Wayne

 

[Trav]

Yes no flash needed. Just disconnect the battery for about 10 min, then follow the relearn procedure. Don't sweat the scan tool #2

GM procedure.
Quote:
1. Start and idle the engine in PARK for 3 minutes.
2. With a scan tool, monitor desired and actual RPM.
3. The ECM will start to learn the new idle cells and Desired RPM should start to decrease.
4. Ignition OFF for 60 seconds.
5. Start and idle the engine in PARK for 3 minutes.
6. After the 3 minute run time the engine should be idling normal.
Important: During the drive cycle the check engine light may come on with idle speed
DTCs. If idle speed codes are set, clear codes so the ECM can continue to learn.
֜ If the engine idle speed has not been learned the vehicle will need to be driven at
speeds above 70 km/h (44 mph) with several decelerations and extended idles.
7. After the drive cycle, the engine should be idling normally.
֜ If the engine idle speed has not been learned, turn OFF the ignition for 60 seconds
and repeat step 6.

 

[wtd]

Thank you very much for this information. I'm keeping my fingers crossed that this will fix the issue.

Wayne

 

[wtd]

Well, installing the new injectors did not fix the problem at all. Car runs the same. Since unplugging the battery, all of the misfires are now in cylinders 2 & 3 with roughly 4,500-4,600 in each cylinder.

Pre-cat O2 sensor acts normal when increasing rpms at idle but as soon as you bring it back to idle and the engine settles down and starts running rough, the CEL starts flashing again and the O2 sensor parameters only move back and forth between .700-.900 volts.

When driving down the road, the CEL will stop flashing and the car runs smoothly with no misfires felt.

Why is there no misfires at higher RPMS and why does the O2 sensor act normal under these conditions but as soon as the car is at idle, these things are no longer normal. What else would cause this behavior?

Wayne

 

[Trav]

What is the STFT at idle?

 

[wtd]

Originally Posted By: Trav
What is the STFT at idle?


I don't remember but I think I found the problem. I did a compression test on the engine and here are the results. I let the engine turn over around 5 to 6 revolutions and had someone watch the gauge. The highest readings in each cylinder was as follows.
Cyl 1 was 150 psi
cyl 2 was 90 psi
cyl 3 was 95 psi
cyl 4 was 175 psi

I didn't have time to put any oil down in the cylinders of 2 & 3 to see if they came up any but the two lowest cylinders are the ones with multiple misfires at idle. Cylinder 1 had a few misfires detected when I first looked at it but none after installing the new injectors. Cylinder 4 never showed any misfires. If I remember correctly, the minimum in any one cylinder should not be less than 70% of the highest one and none of them should be less than 100 psi.

I didn't get to do a more detailed diagnosis of whether or not these readings pointed to a valve problem or a ring problem so I'm really not sure of that at this point.

Could this be a possible blown head gasket since both of the low cylinders are next to each other? Thanks for any additional insight.

Wayne

 

[wtd]

I just looked at the scanner that I used last week that saves the live data info and the STFT was showing 3.1%. This is an AutoXray 6000 scanner. The scanner that I used today is a Craftsman equivalent to the Innova 3140d which for some reason doesn't save the live data info after you disconnect it from the vehicle.

I also forgot to mention that when I went to replace the the injectors, I didn't get any fuel out of the schrader valve on the fuel rail. I didn't have my fuel gauge at the time so I wasn't able to see what the pressure was then. Some fuel did come out when I removed each injector but not with any force.

After the injector replacement and driving the car, I hooked up a fuel gauge to the schrader valve and had 60 psi at idle and fuel did spray out the schrader valve for a second when hooking up the gauge so I know it was not plugged.

So I guess it was possible some of the original injectors were leaking down.

Wayne

 

[Trav]

You could have had a leaker or two, send them to me if you want instead of tossing them and i will check them for you for laughs if your curious.
It could be a bad head gasket between cylinders do a cyl leak down test on them, that should help pin point the compression loss.

 

[wtd]

I will have to ask the owner what he wants to do with the old injectors since they are not technically mine.

As far as the compression issue, I don't have a leak down tester and I don't have the time to tear into this engine if it ends up being a mechanical problem. I'm going to suggest that they take the car somewhere to get another opinion and to fix whatever is wrong with the car.

I was hoping it was going to be something fairly basic but it doesn't seem to be the case. Thanks for all of your help and if the owner doesn't want the old injectors, I will get with you on testing them.

Wayne