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Good evening, everyone!
To start off, I am new to posting to the forums here, but not new to ETCG and am excited to contribute to the community!
This may be a long post, but I do not want to skip any details that seem important, so here I go!
We have a 2002 Chevrolet Malibu with the well known Chevrolet 3100 V6 engine. For a few years now, it has had a slight misfire that we did not get to diagnosing due to financial reasons, it is the daily driver for my mom. Over the last few months though, the gas mileage has decreased dramatically, and currently it is a road hazard due to the misfire. There is no power, it bogs down, sputters, and it is unable to leave first gear or accelerate over 3,500-ish RPM, which is new over the course of it sitting the past week, I tried to take it out this morning. It was drivable for the most part before. Before It got this bad, you could at least make it accelerate very well at WOT if you needed the power, as if something kicked in at WOT. Once it began to overheat on her on the way home from work before last weekend, I decided it could no longer be driven and loaned her one of my cars. It otherwise starts perfectly, and idles pretty well with only a slight misfire, it runs okay not under load. Strangely, this problem is worse when ambient temperature outside is as hot as it has been.
These engines have a pattern issue with the ignition coils, ignition control module, intake manifold gaskets and the fuel pressure regulator failing causing a misfire. I connected my ELM scan tool and the PCM had codes P0300 (general misfire) and P1189 (Engine oil pressure switch circuit). I am not sure what the EOP circuit is about, the oil lamp is not illuminated when engine is on, and illuminates with key on-engine off. This car has no oil PSI sensor, just a switch. It also momentarily threw and EGR code being stuck open, but the pintle is not stuck and it does activate. I monitored the misfire counter and saw that cylinders 2 and 4 misfire the most. 3 and 5 misfire the least. This shows that it is not an ignition coil or ignition control module issue, however I have performed a spark test on each of the wires and spark showed great. Here’s info for the O2 sensors. Long term fuel trim bank 1 is -15.6% and long term on bank 2 is -100%. Short term bank one hovers around -1% through -20%. Short term bank 2 fluctuates like crazy between +50% and -99% once every few seconds. I am pretty sure this is why the car starts to overheat, it running VERY lean. I was unable to find any external vacuum leaks, and everything is tight to prevent pirate air with the MAF sensor. I tested the fuel pressure regulator with a handheld vacuum pump and it showed no broken diaphragm leaking fuel, and it held vacuum from the pump.
I rented a fuel pressure gauge today. Fuel pressure is between 40 and 50 PSI at idle, which according to the Chevrolet diagnostic manual it is normal pressure. I confirmed fuel pressure regulator functioned (pressure jumped to about 60PSI when vacuum was removed). I left the gauge connected and drove around the residence, and while the engine misfired the fuel pressure did not show any change, even when trying to accelerate at wide open. I am not sure if this rules out fuel volume issues, the gauge did not have a function for this. With engine off and the gauge still connected to the fuel rail for over 10 minutes, the pressure did not show any evidence of a fuel leak or stuck injectors. The fuel pump has been replaced in the past due to an unrelated incident in 2008. A stray piece of metal left on the road by some a**wipe was kicked up by the front tire and rammed into the fuel tank. destroying both the tank and pump and dumping 15 gallons of gasoline everywhere. The pump is not OEM though and may be some cheap POS some family member put in.
The intake gaskets were replaced by a professional mechanic in 2011 due to coolant leakage in the oil, coolant pooling on the driveway and overheating. This misfire issue did not occur before the replacement and there were no other noticeable drive-ability issues. In the last five years, the car has also received new spark plugs and wires for the 100,000 mile mark, fuel filter (done last summer by me for maintenance reasons) new cam sensor to resolve a crank/no start condition, alternator, MAF sensor, harmonic balancer, power steering pump pulley, water pump and a pressurized coolant reservoir and cap. To attempt to correct the situation, I have cleaned the EGR and its passages, cleaned the throttle body, checked all plugs/wires/grounds, and of course checked fluids.
Thank you for taking time to read about my problem! I would love to avoid paying for a tow as well as diagnostics and labor on top of the parts to repair. I am open to any and all ideas as I am currently out of my own, and this does not seem to be following along the “common fixes” for this car. Attached will be screen shots of my scan tool on my phone of the PID’s as well as CEL codes. The last image was taken after it began to overheat, with coolant temp at 223F and long term bank two pegged out at -100%.
![IMG_0363[1].PNG](http://new.ericthecarguy.com/wp-content/uploads/2016/06/media_kunena_attachments_14100_IMG_03631.PNG){kind=link}
![IMG_0370[1].PNG](http://new.ericthecarguy.com/wp-content/uploads/2016/06/media_kunena_attachments_14100_IMG_03701.PNG){kind=link}
![IMG_0372[1].PNG](http://new.ericthecarguy.com/wp-content/uploads/2016/06/media_kunena_attachments_14100_IMG_03721.PNG){kind=link}
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Replies
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First solve the overheat issue. This is not doing the engine any good.
Next with fuel trims being negative you are running rich. The o2 is reporting
to much fuel and not enough air or is stuck rich. What is the front o2 doing in
relation to switching voltage. Two things control fuel trim. MAF and o2.http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
My Brother has a 2001 Monte Carlo with the 3400.
It had the almost exact same issue(s) your stating.
But it completely died and would not start.
After pulling the plugs and seeing them carbon fouled (fuel mileage was almost none )
Checking spark, fuel pressure ETC which all appeared correct.
Replaced the fuel filter and flushed out the lines.
Finally got it to idle but barely and sounded like it had back pressure through the intake
It turned out to be clogged cats.
After replacing them, the engine was now running but still had a miss fire and the CEL would appear.
Checked the injectors all had signal and showed to be functional.
So before going in and R & R them.
Ran 2 cans of SeaFoam a week for a month.
The miss fire finally cleared it self so I had to assume the injectors were clogged/sticking/dirtyMight be something to look at on yours.
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.
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?
The Monte Carlo is running quite well.
A easy test you can try is remove the O2 sensor before the cat and see how the engine runs.
If the cats are clogged this will get the exhaust a place to go.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.
I would be looking at the fuel pressure regulator for a leaking diaphragm. Pull the vacuum line off (engine running)of it and see if fuel comes out of the regulator vacuum port. There should not be any fuel coming out of there.
Another way to test it is with a handheld vacuum pump. With the engine off, remove the vacuum line from the regulator and attach the line from your pump. Pump it down and see if it holds a vacuum. If it doesn’t hold a vacuum, you have a ruptured diaphragm.
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.
It is a bit high but I wouldn’t think it would cause that much of a rich condition where the PCM can’t correct it by injector PWM. Have you verified the upstream O2 operation? Unplug the upstream O2 electrical connector and then go drive it. This will cause the PCM to fall back on stored data and not use the O2 for air/fuel correction. If it drives ok, I’d say you have a bad O2.
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.
The common issues for your symptoms are bad upstream O2 (biased lean) leaky regulator and exhaust restriction. Less likely and harder to test without a scan tool are leaky injectors. Your fuel pressure could also be an issue. It’s hard to say. Any other info?
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.
[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=”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 think I understand what you’re trying to say but you said you had already pulled the upstream O2 out of the exhaust leaving the bung open and it still would not accelerate past 3500 rpm. This is why I suggested disconnecting it. It may be a bad O2 and falsely reading rich.
The fact that it takes so long to accelerate to 3500 rpm and wont fo beyond that says to me that you have a restricted exhaust. The rich condition also says this. Thus would also cause misfires due to excessive back pressure. It doesn’t make any sense that when you pulled the upstream o2 out that it didn’t run any better. Let me ponder this a bit.
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