No Fuel Trim Readings on SUPER Rich 5.7 Vortec

[LoCascio_Inc]

I'm super confused with what's going on so I'm going to lay out the situation in an "evidence list" format and would greatly appreciate any insight y'all might have.

Previous Details:

• 1998 K2500 was bought four months ago.
• Has a questionably rebuilt 5.7 Vortec (multiple, small oil leaks) and a used, Craigslist 4L80E of dubious quality...
• For a couple months I've been trouble shooting bad fuel economy (9mpg), slightly rich smelling exhaust, and sluggish but driveable performance.
• 59psi fuel pressure at pump prime and then falls to 50. Idles steadily at 50psi. Blips in throttle bump it to 59psi and then level off to 50.
• No CEL but canner revealed a P0175 (bank 2 running rich) and bank 2 long term fuel trim of +/- -15.
• Installed new plugs, wires, bank 2 upstream O2 sensor, and MAP sensor.

Current Situation:

• Truck suddenly and unexpectedly became un-driveable while driving through neighborhood (30mph).
• VERY rough idle between 500-700rpm and any input of throttle kills engine.
• Exhaust REEKS of gas.
• Gas gauge always read a little janky but now it's bouncing around like crazy.
• No fuel trim readings of any kind on the scanner. 0.0 on all short and long term readings.
• P R N D 3 2 1 bring no discernible changes to the current issues.

When it happen and while I was limping it(idling) home, I thought the trans or torque converter had grenaded, but now I'm thinking the fuel system might be drowning the 5.7 in fuel. Maybe an electrical issue? No fuel trims at all has me very confused as well...

Thank you everyone for any and all input.

 

[skylark]

What does your coolant temperature show on the scanner? Remove the air hat from the throttle body. Cycle the key off and on several times and with the engine off, open the throttle and inhale deeply at the throttle blade. Does it smell like raw fuel? Is it wet in the intake?

 

[LoCascio_Inc]

What does your coolant temperature show on the scanner? Remove the air hat from the throttle body. Cycle the key off and on several times and with the engine off, open the throttle and inhale deeply at the throttle blade. Does it smell like raw fuel? Is it wet in the intake?

The truck drove about .25 mile before falling apart so temp was only 100 degrees when I got back to the house and took readings.

Cycled the key a few times and the intake smells like fuel afterward. It has the MFI injectors and from what little I can see they “look” pretty new.

Intake looks shiny in spots but not WET. I want to suspect the fuel pressure regulator or injectors?

 

[skylark]

That sounds like a leaking spider. The reason for checking the temperature with a scanner is because if the coolant temperature sensor fails it defaults to -40f. It is pig rich if that happens.

 

[LoCascio_Inc]

That sounds like a leaking spider. The reason for checking the temperature with a scanner is because if the coolant temperature sensor fails it defaults to -40f. It is pig rich if that happens.

Leaky spider is kinda what I’m thinking. It just seems odd to be failing if it’s as new as the previous owner’s rebuild timeline suggests. Is there a recommended method to test it once it’s removed?

I’m also still wondering why ALL fuel trim readings were 0.0... I’d think unmetered fuel in the intake would set everything to -30 and throw codes for both banks running rich.

 

[LoCascio_Inc]

UPDATE:

I've done some more tinkering and I'm positive I'm having some kind of over-fueling issue.

Fuel pressure hits 60psi while the pump is actively priming and immediately falls to 50psi once the pump cuts out. Pressure slowly falls to 40psi over the next 10 minutes or so. Is that slow drop in pressure normal? Or indicative of a leak?

 

[LoCascio_Inc]

SOLUTION UPDATE:

Turns out the crankshaft position sensor was reading intermittently and causing the truck run totally out of whack.

Long story version:

• Disassembled upper intake to visually inspect spider.
• With upper intake removed, I reconnected fuel lines and pressurized system to check for leaks. None.
• Reassembled everything and decided to scan for codes again. Got a P0339 (crankshaft position sensor intermittent circuit) that hadn’t been there the day the truck started barely running and reeking of fuel.
• Pulled the CKP sensor to find it had been “self clearanced” by the crank. I’m guessing the leaky timing cover I recently replaced positioned the CKP a smidge too close to the crank.
• Not sure if the sensor suddenly got too close to the crank under normal, stop sign acceleration or if it had been whacked by the crank months ago after the timing cover job and just suddenly started reading intermittently or what...