2002 Chevrolet Malibu Sever Misfire

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%.