Survey- For those with misfire issues

[Rook82]

So something extra to add. I posted a few pages back as to my build info and that I was having the issues. My last tank of gas (previous one to what i am on now), the ASS error came on almost every start. Maybe 10 out of 12-14 starts during that tank. I got the tank to about 1/8 full, almost to empty mark. I got a new Tank of gas (87 regular unleaded as always). And the ASS error came on once, I think the second start. But has not re appeared again yet. And I am almost through that tank of gas. Probably over a dozen starts since last error. I am wondering if their may be something to some gas playing into the problem? Granted, the truck should be able to run it's suggested fuel from basically anywhere. It's factory tune should be able to compensate for what may be "less then ideal quality gas". I have not had any TSB work of any kind or any ecm flashes done yet. The truck is as it rolled off the production line. Other then the lift and wheels/tires and winch and whatnot.

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[mortuar]

Well, I managed to make it 47 miles before the 'service auto start stop' light popped back up on another rough cold start this morning on a trip to the grocery store. Felt the engine shudder while at highway speeds (60-70mph), so I know it's still struggling.

Can't wait to take this back to the dealer this week when it pops the misfire code again!

 

[Gijohn96]

Well, I managed to make it 47 miles before the 'service auto start stop' light popped back up on another rough cold start this morning on a trip to the grocery store. Felt the engine shudder while at highway speeds (60-70mph), so I know it's still struggling.

Can't wait to take this back to the dealer this week when it pops the misfire code again!

The CEL will most likely trigger on the 2nd consecutive cold start with cylinder misfire.

That is how mine went. The pending code will go away after a successful warm start. Kinda frustrating.

 

[mortuar]

The CEL will most likely trigger on the 2nd consecutive cold start with cylinder misfire.

That is how mine went. The pending code will go away after a successful warm start. Kinda frustrating.

How is your situation going?

 

[Gijohn96]

How is your situation going?

Ordered the replacement vehicle. Received the VON, no VIN yet.

They have ordered a replacement engine for Gladiator #1.

 

[DAVECS1]

The closed loop air flow model that controls the throttle body and fueling inputs, definitely has some issues with staying in bounds and under control. I have been logging this alot lately, and I can make it pop an ASS light on command. The throttle body can go into oscillation at steady state cruise or warm up. The pcm seems to have no answer for this, most controls will have an out of bounds on a closed loop control and do something to limit or correct the behavior. Those oscillations jump the timing all over the place, making the engine believe it has a misfire. I imagine if the engine does this enough it can be tuff on the variable cam timing components also, as it moves with input from the airflow model. I have a couple graphs of this on my PC, I will try an post of any one is remotely interested.

 

[ShadowsPapa]

The closed loop air flow model that controls the throttle body and fueling inputs, definitely has some issues with staying in bounds and under control. I have been logging this alot lately, and I can make it pop an ASS light on command. The throttle body can go into oscillation at steady state cruise or warm up. The pcm seems to have no answer for this, most controls will have an out of bounds on a closed loop control and do something to limit or correct the behavior. Those oscillations jump the timing all over the place, making the engine believe it has a misfire. I imagine if the engine does this enough it can be tuff on the variable cam timing components also, as it moves with input from the airflow model. I have a couple graphs of this on my PC, I will try an post of any one is remotely interested.

Sure - would like to see what you've captured LOL - bet Jeep would be, too! Seriously.
Some of this may be why they keep messing with the PCM code - what, 2 revs so far since the original?

 

[DAVECS1]

THe first picture is warm up oscillation. THis happened when I put it in reverse and then let the jeep coast out of the drive. THe bump in reverse is what started the oscillation. Once I shifted to forward and applied throttle it got out of the oscillation. The second is light cruise. If you have a steady throttle foot when the engine goes to light load, it will toggle map and then the airflow model takes off until there is a change or triggered ASS light. This behavior seems to happen when the airflow model has values for throttle position and actual mass airflow that are extremely close to real life life values. If you alter the air flow values to about 20% less than real life this does not happen but the throttle feels a bit jumpy. I imagine FCA is hamstrung by the fact that changing this model requires OK by the EPA. Notice during all of these there is no actual misfire. The timing is just super erratic, making it feel as if that is occuring.

 

[ShadowsPapa]

Not only the EPA - but California has their own regs, too - and Edelbrock smacks that brick wall now and then with their new product development.
You aren't kidding on the oscillations - that's obvious on first glance.
If it was slower, it might feel like a lean surge. At that speed, it's throwing things into a tizzy and would feel rough - rough running.

 

[mortuar]

@JeepCares reached back out, so I updated them on my situation. I really don't want to keep doing this song and dance. I went through this with my 2012 JKUR with the head issues.

 

[DAVECS1]

I need to increase the resolution on the airflow so I can capture startup issues. I was actually working on surge during cruise when I uncovered this behavior. That is why you cannot see the airflow oscillation during warmup. The rpm physically bounces at warm up not as much at cruise. My guess is there are a number of parameters that get you here and they are not all understood, and it deals with environment, driving style, and engine variation and damage.

 

[ShadowsPapa]

I need to increase the resolution on the airflow so I can capture startup issues. I was actually working on surge during cruise when I uncovered this behavior. That is why you cannot see the airflow oscillation during warmup. The rpm physically bounces at warm up not as much at cruise. My guess is there are a number of parameters that get you here and they are not all understood, and it deals with environment, driving style, and engine variation and damage.

When you say the RPM bounces - can you define - range, for example? When I start mine, unless the AC is on, it's rock-solid. The tach stays up for a few seconds, then smoothly drops back to "curb idle" and stays solid as a rock.
AC on is another matter. In fact, I thought it was running rough. I could feel it and hear it, just wasn't right - I turned the AC off and the thing smoothed out. I was feeling the compressor and belt. The 3.6 isn't exactly a 400 hp steam engine at idle - it can't easily handle the load and even modern compressors aren't smooth like spinning an alternator would be.

I'm not an electronic genius - I've built basic circuits, I came up with a voltage regulator replacement circuit for our older alternator systems - something I could pot into the original aluminum housing since you can't buy the originals any more - but even that took me time. I scope the alternators I work on to determine what is needed before tear-down and restoration, and again after to ensure things are right under load, watch the pattern for indications of failure or uneven output, too much ripple. but it seems to me that if that throttle body goes into oscillation, they could resolve that with a simple fix. What's up there, some sort of resonance? How about a filter for that?

 

[DAVECS1]

I would guestimate about 150 rpm bounce. There are many ways to fix this issue the problem is they have relied on the closed loop control for airflow into the engine via throttle body, to govern itself based on the number of inputs they are feeding it. The problem arrives by were do you begin. From my limited view there are three control feeding this control all with modifiers. The airflow control is a variable into the torque control and transmission control. On top of that there are torque limiting models for the drivetrain, that step in at various times to Interrupt the airflow control. You change the wording thing or not enough things and the fix is not robust. Probably the result we are seeing, from FCA. Personally I would use PID limiting strategy (similar to a filter) to normalize the output of this model. In the long run someone has implemented an extreme complex way to control the throttle body and engine response, and that strategy is paying dividends. My guess is the closed loop system has been reliable across most product lines, but the gladiator presents some new load factors that cannot be pinpointed.

 

[1JeepFamily]

So something extra to add. I posted a few pages back as to my build info and that I was having the issues. My last tank of gas (previous one to what i am on now), the ASS error came on almost every start. Maybe 10 out of 12-14 starts during that tank. I got the tank to about 1/8 full, almost to empty mark. I got a new Tank of gas (87 regular unleaded as always). And the ASS error came on once, I think the second start. But has not re appeared again yet. And I am almost through that tank of gas. Probably over a dozen starts since last error. I am wondering if their may be something to some gas playing into the problem? Granted, the truck should be able to run it's suggested fuel from basically anywhere. It's factory tune should be able to compensate for what may be "less then ideal quality gas". I have not had any TSB work of any kind or any ecm flashes done yet. The truck is as it rolled off the production line. Other then the lift and wheels/tires and winch and whatnot.

I notice significant differences when I put in 89 octane fuel or higher—it idles better, shifts smoother, and accelerates faster. It sucks, but I'm not putting in anything less than 89 into this engine ever again.

 

[ShadowsPapa]

I notice significant differences when I put in 89 octane fuel or higher—it idles better, shifts smoother, and accelerates faster. It sucks, but I'm not putting in anything less than 89 into this engine ever again.

The reason for that is that the PCM can push the envelope farther with higher octane fuel and still avoid detonation. Timing can be advanced further, combustion temps kept higher (unless cooler is needed for emissions), you may notice a bit more pulling power if towing a load.
Idle should not be impacted as idle mixtures are necessarily more rich anyway, and timing is at a minimum in most cases.

This was a big discussion deal before RENIX and OBD came along - "I can run higher octane fuel and do better" - uh, not on an engine with no computer running the mixture or timing - UNLESS you tune based on the fuel you put in! That means recurving both mechanical and vacuum advance, base timing, and other fun stuff.
These days, though, running over minimum could help. The computer can push things farther without detonation or ping.

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