High Idle after Warm; Smells Rich; Code 44

[retmotor]

Hi. I like to figure things out by myself as I go, however I have gotten myself into a bit of a time crunch, so I’m asking for help. (I've been lurking for a few weeks. I'll post an intro when I get my act together.)

1991 C3500 Pickup, 2x4, 454, dually.

SYMPTOMS:
High idle (1100+ RPM) after warm.
Sooty exhaust.
Smells rich after parking (I have noticed an occasional miss at idle).
Under deceleration (like a long steep grade) engine surges from around 1100-1600 RPM.
SES light. And just recently a rapid flash SES light for a few seconds after a warm start.

HISTORY:
Recently purchased.
Occasional and temporary SES light
Cat was cut off before I bought it.
Plugs, cap, wires; 2-3k miles.
Previous thermostat appeared to open at 180 (replaced with 195).
Previous TPS showed low voltage at closed throttle. (replaced - shows within specs now)
After the above changes, gas mileage went from around 7 MPG to around 12 MPG.

This is the most recent scan from the MT2500, recovered from a movie a few seconds after a SES light:
Code 44 - Lean Exhaust
Open Loop
Exhaust Oxygen - Rich
TPS - .94v
Throttle 13%
Block Learn 134
O2 Crosscounts 6 (on previous scans within the past week crosscounts showed 17-21 at idle)
FT Cell - 5
IAC Pos - 114, IAC Coil - off, IAC Coil Enable - Yes, IAC Coil B - On, IAC Direction - Rev
Prom ID - 4251
MAP 39kPa 1.56v
Baro 97kPa 4.72v
Coolant 199 degrees
EGR Duty - 33
Air Control - Norm
Asynch PW - 0.1 mS
A/F Learned - No
A/F Ration - 16.0
Spark Advance - 43 degrees

I’m a very average novice wrencher and I am still learning my way around the MT2500 and many of the readings I don’t fully understand yet. So, if you see anything that jumps out at you, please let me know and maybe I can get ahead of my self-inflicted long ways to go - short time to get there problem.

 

[JDGMC]

I noticed your scan data was in the “open loop” mode with the engine warm. Do you ever get to a “closed loop”? Check the O2 sensor voltage directly. Check the wire(s) to the O2 sensor. Check the ECM temp sensor. Check your fuel pressure and fuel filter. Check for vacuum leaks.

 

[retmotor]

Yes, regarding the closed loop. Yesterday was the first day I had driven the truck with the scanner hooked up. It really didn't stay in closed loop until the return leg of a ~16 minute round trip.

 

[JDGMC]

Did it stay in the closed loop at idle after the drive? Did the SES turn on? Does the truck still have the air system operational? If so make sure the air isn’t diverted to the exhaust ports in the closed loop mode. Likely the o2 sensor or wiring to it. Do you have a manual to guide you through the diagnostics?

 

[retmotor]

I have downloaded the service manual (the link for which I found on this site - thank you very much). It's a bit cumbersome on the $100 refurbished chromebook, but it is useable.

I will have to research this air system you speak of.

I picked up an O2 sensor on a previous rockauto order. Considering the 6 crosscount I will replace it.

No SES light while in closed loop.

I did not idle for any length of time and I didn't look to see if it stayed in closed loop.

I should have that O2 sensor changed this morning.

Thank you.

 

[JDGMC]

Great! You’ll figure it out. Since you mentioned it’s a recent purchase and the Cat was removed, be on the lookout for other mods on your vehicle. You should have a single-wire O2 sensor. Look at the pigtail connection closely for splices or corrosion. Make sure there are no major exhaust leaks at the exhaust manifold or near the O2 sensor. A couple of charts that are pertinent to troubleshooting and info just in case.

 

[JDGMC]

Great! You’ll figure it out. Since you mentioned it’s a recent purchase and the Cat was removed, be on the lookout for other mods on your vehicle. You should have a single-wire O2 sensor. Look at the pigtail connection closely for splices or corrosion. Make sure there are no major exhaust leaks at the exhaust manifold or near the O2 sensor. A couple of charts that are pertinent to troubleshooting and info just in case.

A couple more regarding the Air and Fiel system.

 

[JDGMC]

Component layout for your truck (7.4L) I uploaded the 5.7 in the previous post.

You must be registered for see images attach

 

[retmotor]

Quick update: The O2 sensor is a single wire. I did find chafed insulation on the O2 harness where it runs over the top of the transmission. It's possible it was grounding out. That has been repaired. I don't have the proper tool to remove the O2 sensor and crosscounts are back up to ~20 now so perhaps I don't need to.

I may have figured out my high idle problem - the tach shows 1100 when the scanner show 800. In other words, the tach ain't right.

The SES light has consistently rapid flashed at start up since yesterday. It turns off fairly quick - faster than the scanner boots up.

Thank you, JD. I'll get busy.

 

[retmotor]

Another update: The rapid flash SES light had something to do with the scanner being plugged in and not powered up when starting.

I ended up taking the truck on a 1700 mile road trip. The SES light came on only once and that was on a cold morning on a cold start. She ran great otherwise and knocked down an average 11.7 MPG. The exhaust is no longer sooty.

I'm not going to say problems solved as it still idles just a bit high and it surges on decel, but other obligations are impinging. For the truck, the headlight relay upgrade is next.

I really, really like this truck. I'm going to sell my '03 Dodge Ram if you know anyone that swings that way.