2000 Dodge 5.9L rough, rich, fumy idle, FTs leaning out heavily

Thanks, yeah, the upstream definitely looks odd after a long idle, right? As the FTs lean further and further out, the range of change is less, but still in the middle range. You can see that it oscillates higher and lower in voltage when it hasn't been idling as long and when I give it throttle. I'm not sure what to make of all this...

WIth higher RPM (1000 and up), FTs normalize and look good and LT comes back to zero, 02 voltages both up and downstream jump up and down the full range - so that makes me think that there's nothing wrong in the 02 sensor department, but maybe I'm missing something?

In open loop, with the 02s disconnected, the roughness and richness is still very apparent at idle. Makes me think that FT isn't part of the problem, but seeing the trims sure helps to understand what the computer is trying to do.

I can't find any exhaust leaks. Really not sure what to check next here...
Thanks again for the help!

Pinch off the vacuum hose from purge valve to intake.
See if fuel trims go positive.
Possible fuel leaking thru valve.

Ok thanks for the info.

I'm going to move away from the O2 sensors based on your response and the fact I can see the O2s switching in your graphed image.

I did look up the vacuum specs for your engine and they say you should see a minimum of 10 inhg of vacuum. So that eliminates the MAP sensor.

Here is a blurp from AllData

FUEL CONTROL
The PCM controls the air/fuel ratio of the engine by varying fuel injector on time. Mass air flow is calculated using the speed density method using engine speed, manifold absolute pressure, and air temperature change.

Different fuel calculation strategies are used dependent on the operational state of the engine. During crank mode, a prime shot fuel pulse is delivered followed by fuel pulses determined by a crank time strategy. Cold engine operation is determined via an open loop strategy until the O2 sensors have reached operating temperature. At this point, the strategy enters a closed loop mode where fuel requirements are based upon the state of the O2 sensors, engine speed, MAP, throttle position, air temperature, battery voltage, and coolant temperature.

Now I was going to suggest looking at the air intake temp sensor but according to that blurb, it may only use it for closed loop operation. Still, what does the IAT sensor read?

I'll think more on this later. We are eliminating things.

Does this truck of plenty of power under load?

The fuel pressure regulator is also mechanical it seems and is a fuel filter / regulator combination that does not require engine vacuum to operate. So that eliminates a possible ruptured vacuum operated fuel pressure regulator. Spec I find is 49.2 PSI

When you disconnect the upstream o2 sensor did you cycle the key off and back on to shut the PCM down for a moment?

Here is a far reach, but is it possible at all that the down stream O2 and upstream O2 harness plugs are reversed? I'm pretty sure, based on your last graph, they are not reversed.

Are you able to go to any misfire counters or cylinder contribution test in your tool?

Certainly seems vacuum related so, fuel or lots of vaporsl being sucked in from some where possibly. Only option I can think of which someone already suggested is the EVAP Purge valve.

I don't think a stuck injector would cause the O2 to read rich but you would certainly have lot of smoke, possibly white if bad enough out the exhaust and could hydro lock the motor. Since a stuck injector would wash the cylinder out, I would expect no combustion therefore more unburnt oxygen in the exhaust causing the O2 to read lean.

I am curious though, if its not actually rich and is now lean based on a bad input. I would expect the downstream O2 to read leaner than it is if that were the case.

Items Currently Ruling Out
- MAP Sensor - Engine spec @ idle is at least 10inhg
- Fuel Pressure - Your Test is within Spec of 49 psi
- Fuel Pressure Regulator - Mechanical, not vacuum operated

Another verification test is to put propane in the intake and see if the engine smooths out or runs worse. I'm guessing worse

If it runs better, than the PCM may be getting a bad input and we can rule out a rich condition

If its runs worse, than we can possibly rule out a bad pcm input and look for raw fuel or lots of vapors entering the engine from either a slightly stuck injector, or purge valve stuck open (which I find normally causes lean conditions) or raw fuel coming from the purge (Never seen it though)

Thanks much all!

Cutting the EVAP purge flow to the IM is a good idea - I've tried and no dice.

Thanks for checking the minimum vac. Good to know for sure 11.5/12 is at least ballpark.

IAT is generally around 150F at idle. Less while driving.

Engine has no loss of power when under load.
Since I replaced the timing chain it's performing better than ever.

PCM gets reset (remove battery lead for a few mins then replace) after I do much of anything that could affect it.

O2s are definitely connected to the correct harnesses, there's only so much wire length to each to prevent that sort of thing, but important to be sure, thanks.

There are no misfire counts available in the PIDs or Mode 6 for this Chrysler year/model. If I'm wrong, it'd make my day - it'd sure be helpful to see what the PCM recognizes and how it counts misfires.

I've tried adding propane to the IM but I couldn't quite add enough to make any sort of difference with the little torch I have. I'll refill it and try again...

The two things that have me concerned now are the downstream 02 status and the injector timing.

The downstream 02 reads high and rich at idle. I don't doubt that it's telling the truth because the exhaust is so fumy. The fact that it mimics perfectly the upstream sensor when I give it throttle and the rpms increase makes me think the cat isn't doing it's job.

Also, there is a PID for downstream O2 fuel trim and it reads a constant 99.2% at idle and when under load. I know that it's been said that downstream is only for emissions, but if there's a PID for downstream O2 trims, it must mean that the downstream is contributing to the FT, right? Or at maybe the PCM is shot? Not sure what to think here... Thoughts?

That said, I know that in open loop it's still rough and fumy so I KNOW that the O2 and cat are not the underlying cause of my woes here... SO...

I'm suspecting that there is an issue with the injector timing. In this engine, it's a single coil conventional ignition system and the fuel sync is based on data from the CMP sensor in the dizzy. As you can see in the images posted previously, the fuel injectors are firing 3/8ths of a full 4 stroke cycle. E.g. the 1st cylinder's injector fires halfway through the exhaust stroke. That doesn't seem right to me. I'd prefer to see the injectors firing closer to when the intake valve opens - at or just past TDC of the exhaust stroke. But maybe I'm missing something?

The fuel sync can be set with the proper OBD tool and by rotating the distributor. Problem is, I don't have access to a better scan tool. Could this simply be a fuel sync issue?

I Don't know if you have fixed your problem but here is an image of a known good Jeep with the same engine.



This is at idle at 4200 ft in elevation. I had just replaced the MAP sensor due to it only showing 8 inches of vacuum at idle and my vacuum gauge showing 16 inches.

I don't know what your elevation is but it will effect you vacuum readings. Higher altitudes means less air to suck, so you wont have as much vacuum.

Man, it just seems like the thing can't breathe at idle. This one just feels like it's gotta be something silly that is right under our nose. A few thoughts/questions:

1. If I were you, I would be DYING to know IAC%, ESPECIALLY on a speed density engine. Plug in a different scan tool and see if you can find IAC %. I'm not sure what kind of DMM you have, but on a lot of them you can backprobe the IAC ground and read %. You will have to flip the percentage, because it reads the "on time" as when power is applied, not ground. Even better- you seem proficient with a scope, so just scope the ground at idle and calculate the duty cycle. Pulse width divided by wavelength, x100%.

2. What is your calculated load? I know someone said the vacuum was in spec, but I don't have the "warm & fuzzies" about 10". I feel like this thing idles a tad low, so it could be normal. Especially if you find an issue with #1 above.

3. Have you induced a vacuum leak to see what happens?

The 99.x% indicates that there is NO fuel trim from/by the rear oxygen sensors taking place. Don't be concerned about it, that's just a design flaw of early OBD2.

Thanks to Paul and all who had offered advice on this previously! It's been a while since I've been able to work on this engine - had to take a break for a while for sanity reasons, but it's STILL running rough and rich and leaning out heavily at idle. Getting multiple misfire codes again.

As for inducing a vac leak, with the evap purge pulled off for example, it runs smoother at around 1300 rpm and FT's begin to even out. I agree with TheTechWhisperer - seems like it can't breathe right at idle.

Scan tool tells me engine load sits around 4.3%.
Since I can't get scan data for it, here's what I was able to scope for the IAC at idle:

PCM ins at A10, 11, 19, 20, probed at the valve though:


Violet/Gray (Outer) wires:


Brown/Yellow (Inner) wires:


Here's a capture at startup (I think Gray/Brown)


I'm still not sure how to calculate this into steps to compare it to a normal 5.9L. Any thoughts?