Running Rich - Loop Fault

[ttanton]

Hey Guys & Gals,

 

I've got a problem with getting the fuel mixture running too rich - ECU can't settle into closed loop and fuel economy is pretty poor. It idles and runs pretty solid, but the vapors can be overbearing, and I would appreciate an improvement at the gas pump. I've done a lot of digging around the forum and elsewhere, but could use some advice on next steps for troubleshooting and determining my issue. I have a REM monitor. Here's what I know:

 

ECU stays in open loop ~95% of the time

REM Monitor Code: Loop Fault Rich

Fuel Economy ~11mpg (stock 4.0, stock tire size, 2wd, city)

Oxygen sensor pegged to ~0.3 idle & throttle, 4.92 in decel/DFCO

MAP ~13 inHg @ idle

CTS always maxes out between 150 - 180F (thermostat replaced with mopar recently)

IAC walks down to 0 and limits out.

New fuel pump ~ 6 months ago by a shop.

Idles fine

Grounds have all been refreshed following cruisers tips.

 

Oxygen sensor back probes and tests as accurate/operational as best I can tell.  When starting the vehicle, the reading starts around 4.9 then falls to 0.3 over the first 5 seconds or so, then is stuck around there unless in DECEL mode when the reading jumps to ~4.95 ish until ECU enters back into open loop.

 

As far as I can tell, the REM is correctly portraying an overly rich exhaust. So breaking this down out loud.... the engine is either getting too much fuel, or not enough oxygen. Since it seems to run strong, my guess is it's getting enough air - also I would think that MAP would be lower than 13 at idle if it wasn't getting enough air. 

 

I'm not real familiar with the injectors. The PO replaced them a couple years ago, but I'm not sure how to tell if sizing or other factors could be the cause. I also don't have a fuel pressure test kit, but I could also suspect that the fuel pressure at the rail is too high as a possible cause.

 

Any advice on next steps for troubleshooting or identifying where the issue lies? A lot of the reading I've done around here concerns the mixture being too lean, but not much to go on for investigating an overly rich mixture. Thanks in advance!

[fiatslug87]

So O2 does not bounce between a low and high value (which it should)? What is the Ω value when probing the A and B terminals of the O2 sensor? Should be 5-7Ω. Sounds like a bad sensor, I’ve only had luck with NOS Mopar sensors.

[ttanton]

Correct, the O2 sensor reading does not bounce at all, it falls to 0.3 ish and stays there. I’ve replaced the o2 sensor this week with an NTK and there is no change in readings. 

[fiatslug87]

I haven’t had luck with the “new” NTKs.

 

[cruiser54]

Gotta have power and ground to the sensor. 

Gotta test the sensor unplugged A to B terminals. 5 to 7 ohms as mentioned above. 

without verifying these 2 things you are peeing into the wind. 

[Ωhm]

Just as a quick check look for fuel at the vacuum hose between the Fuel Pressure Regulator (FPR) and intake manifold. Leaky FPR.

[cruiser54]

This also^^

[ttanton]

I’m going to check all of these shortly and follow up. Thank you all 

[cruiser54]

You better do that or you'll be in serious trouble.