SOLVED Please help, engine runs very poorly!

[los341]

The first clue is that it runs good until the PCM has fuel control -- but we need short term fuel trims. At hot idle, what is the MAF reporting in g/sec (please don't bother posting the value in lb/min; change your scanner settings)?

Graph the upstream O2 sensors to see how they compare and if they're moving appropriately. Age? Mfr? (that's "manufacturer," not mother-f'er...)

What ethanol % fuel is in the tank? What does the scanner say the alcohol % is? (compare)

When was the fuel filter on the rail last changed, if there is one.

While it's warmed up run a CASE relearn if nothing else to rule it out.

Could do an injector balance test.

Hello Fless, thank you again for your suggestions. I tried pulling all 4 oxygen sensors and the engine still runs bad with near continuous misfires on bank 2, especially cylinder 6. I'm just running regular 87 octane fuel with no ethanol. Fuel pump / filter assembly is brand new and verified constant 62psi fuel pressure. I did clear all codes and pulled the battery for a while and it's still doing the same thing.

Any other suggestions are appreciated!

Thank you Carl

 

[rockola1971]

Theres quite a few grounds and hots that would cause just 2,4,6,8 problems. The wiring harness to your 2,4,6,8 coils get a ground at splice S157 to G102. Check your black wire at each plug of your coil, check resistance to ground. Should be low at each coil. Also check each pink wire for 12v at each coil plug. All coils are fed power from your INJ2 Fuse and so are your injectors for that side. Your coils are fed via a splice (S160) via the INJ2 Fuse. Check that fuse for 12v both sides to rule out corrosion on the fuse.

 

[DodDel5-3-6L80e]

Thanks DodDel, I'm just curious, since the engine has a single camshaft wouldn't a cam timing issue affect both banks equally?

Thanks, Carl

Yes, improper engine timing, especially if affecting only one side of the engine, can lead to spark plug fouling on that side, but other factors like fuel mixture, ignition system issues, or even coolant leaks can also contribute.

 

[bodabdan]

Is there any chance you have a leaking exhaust/broken exhaust manifold bolts?

 

[los341]

Problem Solved! I figured out what was wrong! In my original post, I mentioned that I checked the pre-cat exhaust pressure as less than 1 PSI. When first I checked it, I had to hook it up to the O2 Sensor 1 hole (pre-cat) on each side. Since the gauge hose wasn't long enough for me to see it while in the driver's seat, I had to start the car and then get out and get under the car to look at the gauge, which would read about 1 PSI. I did this several months ago.

Recently, I was thinking about this and decided to go back and check my work. This time, instead of starting the car and then getting underneath to look at the gauge, I had my wife start the car while I watched the gauge. It was connected to Bank 2 Sensor 1 port. To my complete amazement, the gauge started at zero and went ALL THE WAY AROUND PAST 8 PSI, but kept going around the bottom before finally setting on 1!!!!!

So yeah, it read 1, but the real pressure was probably at least 12PSI.

Hmmm, Houston, we have a problem.

I cut the cats open, removed the cores, welded it back shut, and now it runs great! I noticed that Bank 2 cat was black, while Bank 1 cat was white.

Why did bank 2 cat go bad? Well, when replacing the fuel injectors earlier, I noticed that Injector 6 (bank 2) pintle cap was half hanging off, but still attached on one side. So it was hanging at a diagonal, potentially interfering with the injector's spray pattern. So my best theory is that fuel droplets were forming and dripping off the pintle cap. These droplets would theoretically not burn correctly or completely, sending some raw fuel into cat 2, causing it to overheat, melt, and clog.

Has anyone else ever had something like this happen?

Carl