1997 C1500 hydrolocked after MPFI

[Tataocb]

I finished putting it back together today. I cranked it before I installed the plugs, with the ICM and coil disconnected to flush out excess fuel. Not much came out though. The oil still feels "oily" but I will be changing it along with the filter.
I let it get up to temp and stayed with it the whole time. It did not shut off, but what was disappointing was that the fuel trims still showed at -30 for the short term and -17 for the long term. I disconnected the battery for 20 min to reset the system, and the fuel trim went up to -25ish on bank one and stayed at -30 on bank 2.
I started it after 20 min (to simulate the trip to the store I mentioned in the original post) and started it again and it fired right up, it did not crank for a few seconds like it did before. So at least there is some improvement.
I will probably drive it a bit after changing the oil and see if that helps get the fuel trim closer to zero.
The O2 bank 1 sensor 1 behaved normally, but the bank 2 sensor 2 stayed within 0.8-0.9 volts, it never dropped to 0.1 like on bank 1. Sensor 2 acted similar to bank 2 sensor 1. My truck only has one sensor 2 (only 3 O2 sensors in total, which I found strange). All 3 sensors are new so I doubt it is a bad sensor.
As for the fuel pump, I can hear it running when I am standing next to the truck, but if the pump is going out, I don't see how it would translate to it adding extra fuel causing the negative fuel trims, but I will go to AutoZone to rent the fuel pressure tester to check the pressure.
Any thoughts on what else might cause the negative fuel trims?

 

[stutaeng]

I would say just extra fuel that got washed into the intake causing the fuel trims being lean? Probably needs more driving...

In this kind of case, it's actually not a good idea to disconnect the battery, as you want to see the system making corrections by itself.

You only have 1 downstream O2 sensor? I think some trucks came like that from the factory. The upstream are the ones responsible for providing data to the ECU for fuel management.

 

[Tataocb]

Took it out for a 20 min drive today. It felt normal. One improvement I noticed was that when coming to a full stop it no longer stumbled like it did before right before it completely stopped. There was a slight hesitation at idle before which is now gone.

After I got back, the fuel trims had gotten closer to zero. The short term fuel trim for bank 1 was at -7ish and bank 2 was around -15ish (both up from -30). So maybe a little more driving is all it will take to get them closer to zero.

 

[someotherguy]

If there's significant fuel dilution of the oil, not only is it a danger to your bearings and rings, it will also effect other systems - having too much fuel in the oil is enough to make one fail emissions, so I can *imagine* it might affect LFT's. Maybe. It's worth paying attention to once you change the oil, which should happen, oh.. yesterday

Richard

 

[grey wolf]

Nice work on diagnosing that problem!

As for the fuel trims, I'd try changing the oil again and see what happens. Odds are that the engine oil got heavily diluted by gasoline during the initial problems. Changing it once may not be enough to get all the raw fuel out of there. As the engine runs, it is drawing in crankcase vapours (in this case, heavily laden with raw fuel) from the PCV system, and causing the ECU to cut back fuel (the negative fuel trim numbers) in order to compensate for the additional fuel being supplied by the vapours from the PCV system in the air intake stream. I'd also maybe take it for a good test drive in low gear, get the RPMs up high and steady for a while to burn out any raw fuel or residues that formed and got trapped in the catalytic converter during the time when raw fuel was just dumping into your engine. The old "Andretti tune up".

I work at a local dealership, and we've seen that problem happen with our direct injection vehicles, which have known issues with fuel washing out the cylinders especially when the engine is cold. Over time, the engine oil gets so diluted that it affects fuel trims. The engine oil level actually goes up on the dipstick in some cases, we call it "oiling up". One of my coworkers did a bit of an experiment on one of these cars, he changed the engine oil and filter three separate times, monitoring trim levels each time. Sure enough, those trim numbers came closer and closer back down to zero with each oil change.

 

[Tataocb]

Thanks for the input. I have not changed the oil yet because I will be replacing the oil pan gasket (leaking towards the front of the engine). Maybe having the pan off will help it get some of the fumes out of the crankcase.
I need to make room in the garage to pull the truck in so I don't make a mess in the driveway. I don't plan on driving it until I change the oil.

 

[HotrodZ06]

As far as sensor 2 goes there is always at least one per catalyst if you only have one catalytic converter then usually just one sensor 2 regardless of the number of banks.