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Good afternoon, everyone!
I thought I would post a quick update. The issue has mostly been solved. We limped it to a family trusted shop and to no surprise, they recommended replacement of the converter. Stated that it was so back-plugged that it was causing the engine to run rich. I am not entirely sure how this would be possible (maybe not enough exhaust flow for the 02 sensors?) but we replaced it because it was un-drive-able, and trusted in the accuracy of their diagnosis.
Got the car back last week and it has A LOT more power, more than it has had in years. But there is still a slight misfire when accelerating, which is how this issue started. Took it back to the shop today for another diagnosis and they said that the spark plugs we put in from AC Delco are the wrong type and claim this is causing the misfire. The under-hood sticker calls for AC Delco platinum, the ones in there are iridium. Plugs are gapped correctly according to the under-hood sticker. The iridium plugs were purchased new from autozone based on their parts system a month ago, but it was misfiring before using their cheapest line of plugs as well.
Could this be causing the misfire, having iridium plugs instead of the called-for platinum? Or is this shop calling BS? I don’t want to burn up a new converter. And the gas mileage is still crappy (about 8MPG with no hard accelerations), so I know it’s not running as well as it could.
[quote=”gginnj” post=168832]Our old Malibu – 1999 same engine. When it was misfiring like crazy – it was one of the spark plug wires arcing to ground.
Get somewhere really dark, and run the engine.
I was able to see the sparking – also heard the “popping”.
Replaced that one spark plug wire and it was good after that.[/quote]
Thank you for the suggestion! Incidentally, I actually replaced the spark pkugs and wires last night before discovering the plugged exhaust. Last time they were done 50,000 miles ago, we went cheap and got the autolite plugs and wires, I pulled them out of curiosity and while they had good wear, they were crappy. They broke when removing them, and they were not super tight in the cylinder head. The wires were also out of resistance spec for Chevy. So I got replacement wires and plugs. All new OEM AC Delco, the spark seems stronger. However the engine is still running super rich with the misfire.
On an odd note, I was at the pick and pull yesterday for another project, there were about 11 Chevrolet Malibu’s in there with the 3100 v6 that weren’t wrecked in any means. They were marked with “does not run”. I pulled the spark plus on most of them and they were either super black and fouled with carbon, or fuel soaked. Indicating they were running rich and the owner gave up on them. Seems to be a common issue.
Good news! I have determined the lack of power. You guys were right, the exhaust is clogged. But it is so clogged that removing just the upstream O2 sensor did not work, so I decided to remove the EGR tube (larger bung). Besides sounding like an old truck with a rusted exhaust manifold, the car has power again! Bad news, it needs new cats and it is definitely still running rich. I installed the upstream O2 (seems to breathe okay with only the EGR undone) and it showing a rapid fluctuation between .100 and .900 volts. The long term is pegged out a -99% still. The overheat is gone and the vehicle is no longer a road hazard but the exhaust fumes are so rich it is like smelling right out of a gas can. So it will just burn the new ones up. Any recommendations for good replacement converters/ideas for rich condition?
You’re correct, I did do this earlier today and experienced no improvement. Just a LOT of noise of course. If it were an exhaust restriction, I would figure it to be one so bad that leaving the sensor out could not relieve the back-pressure. But with that much restriction, I don’t see that the engine would even run. It does not seem backed up, or it would not be able to accelerate under wide open throttle when cold.
Ambient temp was a lot cooler outside today than it has been the past few weeks. When I drove it around this morning to warm it up for the O2 info, I was able to punch the pedal to the floor (wide open throttle). It hesitated for a few seconds, chugged, then it just came to life and took off without any issue. Engine sounded great. It was as if something “kicked in”. When ambient temp rose this afternoon, I would say above 80°, the condition got worse and it would hardly accelerate anymore. It puzzles me.
Would unhooking both sensors do anything useful? Downstream for the cat, if the computer didn’t see that would it default more fuel trims as well? Or just set a failed cat/O2 code?
Thank you for your assistance. I’m in no rush for ideas, the car isn’t going anywhere! 🙂
[quote=”ialmanza4″ post=168769][quote=”speedsterheitman” post=168768]I understand. No, this is all I have as of now. I’m stumped. If unplugging the upstream O2 solved the issue, I would not have had any idea if the converter was super clogged. [/quote]
Confused by this. By unplugging the O2 I mean disconnect the electrical connector at the O2 not physically removing it from the exhaust bung. Have you done this?[/quote]
Yes, I unplugged the electrical connector to the upstream O2 and then drove it around. It was located behind the alternator on the back of the motor. What I meant by that statement, is if the cat was plugged causing this, I would not know if unplugging the O2 sensor solved the rich misfire condition, if this larger misfire is caused by a plugged exhaust. If that makes sense.
I understand. No, this is all I have as of now. I’m stumped. If unplugging the upstream O2 solved the issue, I would not have had any idea if the converter was super clogged. Since it is running this rich, it is likely to have melted it up, if it is melted. The car has 147,000 give or take. Do cats have a certain “life”? Or do they only burn up with poor mixture or when burning oil?
I seem to be having more misfires on the front side of the engine (2,4,6) more than the back side (1,3,5) but it is a general misfire all around. Cylinder 2 has the most on the misfire counter, and got it’s own code today. I would certainly hope I did not have 6 leaky or sticking injectors, but anything is possible. And the ambient temperature factor. It can at least accelerate GREAT at WOT when the temperature is below 70°, which I found out tonight. Any higher temp than that and it is a three legged horse.
I think I will replace the fuel pressure regulator. It is only $45, I will also make sure the return line to the tank is not restricted since the whole deal it is a common problem with this series of engine. That will address the possibility of the fuel pressure issue, I am surprised it is not already leaking. They usually do multiple times by this mileage from what I have read. I will chalk it up under preventative maintainance. If that does not fix it, perhaps I can use a boroscope camera and look at the converter by removing the downstream sensor. It really sounds like a restriction is the issue though, especially since it is now starting to overheat if you try to push it.
Great suggestion! I just barely tried that. There has been no change to the situation, unfortunately. Oddly though, as it is getting cooler outside this evening, it is running better., but it still cannot be driven on the main roads. No idea what that is about.
Thank you for your response! I tested the pressure regulator as explained in more detail in the original post, and there is no leakage. It holds vacuum when pumped with a handheld vacuum pump. It also brought the pressure up higher when vacuum was removed from the engine and when the engine was revved at idle. However, is it possible that a SLIGHT overage in fuel pressure can cause thi bad of a rich mixture? Chevrolet supposedly specs about 41-47PSI for this engine. Yesterday when testing with the fuel pressure gauge, pressure tested as high as 55PSI. Can a failing regulator cause too much pressure? Being 8 PSI too high does not seem very negligible, but it did not hurt to ask. I want to be sure if so before just replacing it.
Good news! No plugged converters. Removed the O2 sensor and besides thrr horrible noise, there is no change in engine performance. It appears that the misfire is not due to exhaust back pressure.
This is what I fear now. The rich condition could easily burn up the converters. This issue needs fixed first before I replace them, or it will just burn up the new ones too. Seafoam is great! The Monte Carlo has no issues now?
Thank you for your prompt response. The overheating was not starting to happen until the misfire got this bad. Thank you for clarification, I had it backwards. As instructed, I pulled 02 sensor voltages. Sensor one bank one swings back and forth from as low as 0.49v to as high as 0.914v. It goes back and forth once or twice a second. Sensor two bank one hovers around the .300v-.700v mark, but it does fluctuate rapidly. I did notice that the higher the voltage was, the leaner the computer goes. What could be causing fuel to be dumped into the engine like this? Attached are images of the O2 sensor voltages in correlation with the fuel trims.
