I threw up a video of whats going on with my 2001 Dodge ram 5.9L, 4spd auto, 4x4.

around 1:10-1:40 is the issue, I was not letting off the gas.

After a fresh start, the engine will rev and hold RPMs just fine. After the Short Term Fuel Trim kicks in and starts to adjust, the engine will hesitate and the rpm's will vary. STFT will go from 8-13%, then back down in relation to the RPM shift. Sometimes under slow-moderate acceleration I will feel this shift, but at speed (any gear, 1,2,3/OD OFF, or 4) the RPM's and power seems to remain constant. Long term fuel trims were at 32% when I checked them today before resetting the PCM. It is behaving like a vacuum leak, but I don't have one so I think it might be my intake.

I have checked for vacuum leaks. There are none. I pulled and plugged all Vac connections on the manifold individually, and checked downstream like at the transfer case and front axle, as well as checking all connections with carb cleaner and propane.

I did receive a P0171 code at one point a couple weeks ago, which is a lean code, but it hasn't come back. Thinking it was my new headers, I re-torqued them and the down pipes. I have not lost a drop of oil in the last 1200 miles or so since the initial break-in oil change and there has not been any pinging, so I do not believe it is the plenum plate. But could the seal between the log intake manifold and heads be leaking? What would be the signs of this? I know I torqued everything down as per the factory service manual. Edit: About the only thing I haven't replaced were the injectors, which were in spec, but were split about 50/50 on the extremes of being in spec, so those are on my list to replace.

Here is a list of new parts (probably missing a few):
360 crate motor
IAT (intake air temp)
CTS (Coolant Temp)
TPS (Throttle position sensor)
MAP (manifold absolute pressure)
NTK o2 sensors, front and rear
Coil
Fuel Pump
Distributor Cap+Rotor (wires in good shape, no arcing)
NGK plugs
Aluminum plenum plate (like the hughes kit)
Water Pump
Power Steering Pump
Magnaflow Cat/y-pipe
SCT Tuned

 

Where are you getting the numbers on fuel trim?

 

Using a scan tool (for VAG cars like VW/Audi ect..., but it has basic OBII functions that I have found work on Dodge, Mazda, Honda, Ford and Chevy)

On my VW it shows Fuel Trims as digits with 1 decimal place (because it has direct access to the ECU's engine module), +/- from 0, on the dodge the OBDII function shows it as a percentage, so I'm not exactly sure if the percentage it gives is accurate to interpretation as +/-10 being out of spec. I'll grab a screenshot of what I'm seeing.

Edit: Album here

Current codes:


Pending Codes: (p0171 popped up again!)


Idle vs 2k RPM vs 3k RPM


Mechanical gauge reads 20 inHg. Scan tool reads ~44kPa abs, whchh is about 18 inHg gauge at startup and settles to around 27 kPa abs (22 inHg gauge). I was converting the map reading of kPa to inHg, which was incorrect, It should have been kPa absolute to inHg gauge.

This is what I can log either as a graph of cvs to import to a spreadsheet:


After letting it warm up, idle fuel trim was bouncing around 0, when I give it some throttle, past about 1500 it will start to jump around, by 3000 its obvious. I'm beginning to think my headers are leaking, I don't hear the tick they made at first, but its possible I crushed the gasket too much and its not sealing properly. I had removed the bolts I used one by one and replaced them with ARP bolts so I could get at them more easily. Could an exhaust leak cause these bouncing trims?

Edit2; Didn't record the logs, but Intake air temp was around 145-153F (63-67F), coolant showed 188F (87c). I watched them come up to temp pretty smoothly, so I don't think I should have to pull those sensors to check them again.

 

Makes sense. Just wondering. I do not know what the numbers should look like under normal circumstances, so I can't tell if what you are seeing there is correct or not. Wish I knew.

 

Tomorrow morning I'm going to pull the intake and redo all those gaskets (plenum, intake, TB). It has to be there. I tried spraying TB cleaner around where the intake meets the heads, but didn't notice anything. I spent the better part of the day re-installing my headers with fresh gaskets. This is insanity. And I thought my VW as a PITA.

Edit: Oh yeah, while I had the down pipes off, I looked in my new cat, looks perfect, almost brand new still.

 

EDIT: I ended up talking to someone that had extra sensors from the dealer laying around. After swapping things around, it was the MAP sensor.

The newish factory sensor works perfect, the more expensive of the NAPA sensors gives the surging, as does the MAP out of a 2wd 5.9 Ram I also have. But in that 2WD, it runs perfect, gets 15-17MPG empty, 13-14 when I have tools/loads in it.
The original one on the surging dodge was giving sporadic readings so I replaced it with the NAPA one. Go figure. I can't believe a dodge is more picky about its sensors than my VW.

So:
Old factory MAP: Sporadic readings, caused rough idle/bad gas mileage in 4x4-10MPG, Seems to run OK in the 2wd-no surging, smooth idle. Replaced with the NAPA sensor below.
NAPA expensive sensor: Surging, smooth idle in the 4x4. Runs perfect in the 2wd.
2wd factory MAP: Runs perfect in the 2wd. Surges in the 4x4, like the NAPA sensor.
New Factory: Runs smooth in the 4x4, didn't try in the 2wd.

It makes my head spin. I bet there is a short somewhere, either in the pigtail or the line. We'll see if the surging returns. I drove around for 20 miles and it was fine with this new sensor.

Long Term Fuel Trim is now 8-9%, short term is bumping around 0 +/-5 depending on throttle. Its up around 8-10% at startup till long term kicks in and it reset to 0 a few times then worked its way up to around 8% (on my VW, long term is a stored value and stays pretty constant once it is 'learned'). Factory MAP also reads ~18-22 inHg at idle, which is what it should.



While I'm at it, I re-tested my injectors.
Injector resistance is:
1-12.9 2-13.4
3-12.9 4-13.2
5-12.9 6-13.4
7-13.2 8-13.1

Are some or all of these worth replacing (even if it doesn't relate to the surging issue)? I never had them flow tested so I guess they could be partially clogged. They all seemed to spray well when I did the motor swap when firing them with cleaner running through them like this: