P0300 Code with Flashing CEL

Hi!

I've reviewed numerous threads on here re: the P0300 issue, but to no avail. Here's some background:

Vehicle:

• 2005 Chev Aveo
• Manual Transmission
• 182,000 km

Symptoms:

• Idles fine when engine is cold or hot
• No noticeable missing when engine is revved and no load
• Noticeable missing when cold and under load
• Missing less noticeable as engine warms up
• After clearing code, CEL will illuminate and flash between 40 - 60 km/hr with engine between 2,500 and 3,500 RPM and stay flashing until code is cleared

In the last 1,000 km:

• New Alternator
• New Wires
• New Plugs
• New Coil
• New EGR Valve
• New Serp Belt
• New Thermostat
• New Timing Belt/Idler pulleys/water pump/Inner timing belt cover
• Replaced head with all new valves and seals
• New Battery

Troubleshoooting performed:

• Compression Test (#1 190, #2 175, #3 160, #4 180)
• Carb Cleaner Sprayed around vacuum lines and intake (1 Leak found and fixed)
• Misted new wires/coil (no issues)
• Vacuum Lines checked and compared against schematic (no issues)

Anyone have any suggestions for further troubleshooting or potential solutions before I give up and bring it to the *gasp* dealer??

Any help is appreciated.....

No mention of fuel, so I'll ask if you did a fuel pressure test. Can you borrow a real-time scanner which would give you fuel trim and TPS stats?

I have not done the fuel pressure test yet, but my cheap scanner does have some freeze frame info which I have attached.

Attachment 8453

The freeze frame posted above was from yesterday prior to the plug change and the resetting of the code. Here is the freeze frame from the code today.

Those S/T fuel trims indicate that it's running lean, so you should get a fuel pressure test done. Also in the mix for this is plugged injectors. Running lean can of course be cause by other things such as vacuum leaks, but it sounds like you've already covered those bases fairly well.

Thanks. I took a quick look last night and I noticed some moisture around the base of the #1 and #4 injectors. I have a spare set of o-rings lying around, so I think I'm going to remove them tonight, clean them, and replace the seals first since that will be the free option. If it still doesn't work, then I will lay out the cash to buy the fuel pressure tester.

One question I forgot about re: the vacuum lines..........

There is a small port circled in the attached photo and I cannot seem to figure out if it supposed to be hooked up to anything or not. I have seen some engines showing it attached to the intake manifold and some with it not hooked up to anything at all. Does anyone know what it is for?

I have that exact same stub on mine, also going nowhere.
Sounds like you may have a direct hit there with those injector o-rings. But if not, and you want to move along to the fuel pressure test, do you have Autozone in Canada? They have a fuel test kit in their loan-a-tool program, which would be just what you need to do this test.

After doing some work on the weekend I thought I would update the status of my CEL.....

I removed all the injectors, cleaned them up, and replaced both o-rings. Things were looking up during the test drive, but the light came back. It was later in the day on Sunday, so no stores were open to purchase a fuel pressure tester. In a moment of despair, I swapped ECM's.

The original problem with the vehicle was that it would stall and not start again. Let it sit for a few hours and it usually started up again. The mechanic diagnosed this as a faulty ECM. A replacement was acquired from an auto wreckers and the crankshaft relearn and programming was completed by a GM dealer. This solved the stalling problem at first, but the P0300 and flashing CEL problem appeared. Shortly after, the idler pulley seized (before the suggested PM mileage) which bent some valves and some other fun things. After putting everything back together this CEL was still there.

On Sunday night I put the original (supposedly fried) ECM back in the car and it started up no problem. It has been a couple days and about 100 km later and the car is running well; no codes and no flashing CEL. I have tried to research the replacement ECM part number to see what specific model Aveo it was from but to no avail. It looks like the original stalling issue was being caused by the idler pulley that would seize occasionally and not a faulty ECM. If I would have just replaced the belt/pulleys/pump from the beginning, all of this might have been resolved......

Quote:

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Originally Posted by AveoNewb

... It looks like the original stalling issue was being caused by the idler pulley that would seize occasionally and not a faulty ECM. ...

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Thanks for posting a follow-up to your problem - most never do.
We know that once something causes the timing to go off, such a pulley jumping, it's gone for good and it's curtains at that point.
So, in order for this to happen according to your theory, the idler pulley would have become a brake on the crank, and for just a small fraction of a second cause the crank, along with the entrie loop to be slowed down slightly. I wouldn't expect the belt to be strong enough to withstand the amount of force being applied by the crank, at the point it's momentarily restrained by the idler pulley. But I'm not an engineer and have no real life experience with anything like this. Perhaps the belt is actually strong enough to withstand a short jolt, transfer the force to the crankshaft, and continue to survive as long as the idler pulley doesn't continue to drag - IDK.
So if what you're thinking is correct, it would mean that it's possible for a misfire to actually be a warning that a pulley bearing is failing. Interesting concept. Was the idler pulley bearing completely seized, or nearly so when you looked at it?

Do be honest, I don't remember for sure. I do remember that it had broken up by that point and had burned plastic wear marks down the centre of the pulley. I am assuming this is from the drag on the belt as the bearings were seizing until the pulley finally exploded.

I would say the stalling is the warning. While the root cause is technically a misfire, I think a layman would recognize it as the engine just stopped running. I definitely didn't think of a misfire when it happened to me and there was no CEL or P0300 after the stall. I was driving down the road at 100 km/h and the engine just stopped. This happened 6 times over about 1,000 km of driving before the pulley finally gave up. The vehicle was brought to 2 different mechanics a total of 4 times and the problem could not be duplicated. That is when they diagnosed it as an ECM going south.

Edited to add: The CEL and P0300 started after the second stall incident; after I replaced the ECM. This sent me down the P0300 rabbit hole which lead me to delay the timing belt replacement, which in turn lead to the pulley exploding.

Certainly an ineresting adventure you've had there. But that's easy for me to say, and you obviously would have just as soon skipped the whole thing. One final question - had the belt and 3 other components been changed once previously around the recommended interval? (Don't know about Canada, but in the US it's 60K miles ~ 100K KM)

Sorry for the delay in responding. I just completed a 2,500 km road trip with the Aveo and I was not online very often.

Glad to say that everything went well and the CEL light stayed off. The mileage seemed pretty good too. Haven't crunched the final numbers, but it looked around 7.8 L/ 100 km.

Yes, the components were all replaced at around 91,000 km.