Here are the options in the 200?-2004 JTEC+ PCMs with the current non-Beta version 5.2.2 of VCM Suite.
Tuning DFCO for better engine braking and fuel economy
- Thread starter Steel City 06
- Start date
Yeah that's not a lot of parameters to work with unfortunately... That said it is possible the JTEC software is simply more primitive and doesn't have the complexity of the NGC3.
What is it doing that is unusual?
So I turned the DFCO Enable VSS down from 32 mph to 12mph in part because I'm trying to get it out of this mode where it would high idle at about 1200rpm with the clutch in under 32mph. Instead it's just high idling at a higher rpm around 1500 until you come to a complete stop for a sec. There isn't a vacuum leak. Once you stop for about 0.5 sec it comes down to my programmed idle at 824rpm.
There are just fewer variables in just about any setting in the JTEC/JTEC+ than in the NGC3 PCMs.
JTEC+ on the left, NGC3 on the right.
Huh. I have had similar issues.
The first time that happened, it was my aftermarket exhaust header. It had only a very tiny clearance to the intake manifold. Had this nasty rev hang I couldn't figure out. Turns out, the exhaust header would expand due to higher temperatures and push the intake manifold up just enough to cause a vacuum leak. And then after 5-10 seconds the exhaust manifold would cool off enough, and the intake manifold would go right back to being sealed. Drove me nuts because I couldn't figure it out because every time I'd test for a vacuum leak it would be sealed...
I did find a random JTEC file on HPTuners. Perhaps the "Throttle Follower Decay" setting might do what you need? No such setting exists on the NGC3, so no idea how it really works.
Also I've found that an A/C request signal when the A/C clutch actually isn't being used does seem to slow down how fast the engine decelerates. It looks like there is a parameter for that as well on the JTEC.
How much spark advance do you see during these periods? If the spark is staying too advanced, the engine might not be able to cut airflow or fuel enough to let the engine slow down.
KennethS
TJ Addict
Also forgot to note, I do recommend using the latest Beta to read to see if there are any new parameters. Unfortunately the non-Beta is sometimes very slow to be updated. You'd have to do a fresh read of the ECM again with the Beta to see if any new parameters have shown up.
The beta version is usually stable enough for most purposes anyways. 5.3.60 is the latest at the time of this post.
You can have both versions installed, you just cant read/edit something in beta and then view it in the stable.
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Actually, you might not even need to re-read. I opened the same JTEC file in 5.2.2 (stable) and 5.3.60 (beta) and at least one new parameter showed up from the same file:
Beta on left, stable on right
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So it appears you might have some additional parameters to mess with if you use the beta
Beta on left, stable on right
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So it appears you might have some additional parameters to mess with if you use the beta
I'm using 5.2.2 which just came out with the MPVI4 in the last few weeks. I had been running beta versions up to that point because the main version didn't support Write to the JTEC PCMs. I've installed the Beta 5.3.x and didn't see anything obvious to make me think it would provide better options but will give it another try.
I'm certain I don't have an intake leak. It's all just been variance in behavior when I try different settings. I am using the throttle decay. At first I lowered the values thinking they were times, but it is actually stepper motor step sizes I guess.
I did actually see some improvement by steepening them. But then lowering DFCO threshold speed from 32mph to 12mph and reducing the Idle Spark Advance MPH threshold down to 8.0 mph seemed to drive the idle hang in the opposite direction from what I expected.
Idle Spark
Original
We posted across each other. I'll be taking a look at the latest, latest beta as I'd always done before applying an update in the past. I'd grabbed a beta release right after the 5.2.2 release came out and it looks like they've added some more stuff since then.
I'd recommend using VCM Scanner for a test drive and see if you can log what's actually happening during that time. It's possible it isn't going into DFCO even if it's going into open loop, and/or it may not actually be using the idle spark tables. When in doubt, test and log...
Agreed. I typically grab a log right after, but I think (I know) there is also a bit of PCM learning after a flash with the JTEC/JTEC+ like when you discharge the battery and I wanted to see if this sorted out with that. It hasn't.
You also have to get the engine fully warmed up to be certain with some of these settings, so it's not a flash and run around the block thing sometimes. There are ECT temp floors on a bunch of these idle settings relating to warm up.
You also have to get the engine fully warmed up to be certain with some of these settings, so it's not a flash and run around the block thing sometimes. There are ECT temp floors on a bunch of these idle settings relating to warm up.
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You are correct on the decay rate. The values are increments or steps of adjustment. Small number = small steps.
I mentioned in another thread idle rpm and timing. I still think there might be something here. If decreasing your vss idle spark threshold to 8mph raised the hang rpm, it may have a problem settling into idle rpm. Does raising the threshold from 12 decrease the hang rpm? If so it would lend credence to a timing issue, with too much advance not allowing the idle to drop until there is a more dramatic trigger event. Also I have seen when timing tables, (pt, MBT, minimum spark, etc ) get too close this doesn’t give the pcm enough headroom to control the idle speed well and it leads to instability.
Does lowering the idle speed to 650 affect the hang?
I am making changes going another direction - but just to show the sort of oddities that can develop.
I haven't modified the low end of the spark tables. I live at a relatively high elevation so my WOT throttle kpa is between the 79.1 and 92.3 kpa rows. And it goes down from there. I've only adjusted timing and fuel in these rows as it's only been the WOT ranges where I felt the jeep had especially poor performance. There are more opportunities for improvement
Here is an example of what it it doing in a log. AC is off and I have the vent running cold air. I've got the clutch depressed and decelerating coming up an exit ramp from the highway. The IAC remains in a more open state keeping the rpms high. The engine is fully warmed up, but my coolant temp has dipped a bit at this moment.
As I roll to a stop it is staying elevated and advance holds around 33 degrees until the speedo reaches 0.
And over 3 seconds comes down to 800rpm. Idle is set at 824, but I've noticed it rest on 800 pretty often. These are the 2 closest values HPT will allow.
I haven't modified the low end of the spark tables. I live at a relatively high elevation so my WOT throttle kpa is between the 79.1 and 92.3 kpa rows. And it goes down from there. I've only adjusted timing and fuel in these rows as it's only been the WOT ranges where I felt the jeep had especially poor performance. There are more opportunities for improvement
Here is an example of what it it doing in a log. AC is off and I have the vent running cold air. I've got the clutch depressed and decelerating coming up an exit ramp from the highway. The IAC remains in a more open state keeping the rpms high. The engine is fully warmed up, but my coolant temp has dipped a bit at this moment.
As I roll to a stop it is staying elevated and advance holds around 33 degrees until the speedo reaches 0.
And over 3 seconds comes down to 800rpm. Idle is set at 824, but I've noticed it rest on 800 pretty often. These are the 2 closest values HPT will allow.
The MAP seems fairly normal for that load and RPM. Maybe a tiny bit elevated, but not something that would give me concern.
Really it's the spark keeping that RPM that high. 30 degrees of advance with no load is almost certainly going to keep the RPMs elevated unless you really pull a lot of airflow out.
Looking at the random JTEC file I have, I wonder if it's related to this:
It's possible it's combining the maximum proportional spark gain with the minimum spark and causing it to be in the 30 degree range.
For something quick and dirty to try, perhaps set the MPH threshold up to something stupid high, like 128 mph, to basically force it into idle spark at all speeds. Not an optimal way to tune long-term but that will tell you if it's idle spark and corrections or if it's part-throttle spark and corrections causing the issue.
Looks like we posted on the same thing a minute apart.
That absolutely makes sense why this would improve the throttle hang. You're now forcing it to go to idle spark advance rather than running spark advance.
It might just be a matter of tuning it such that it doesn't fall in that window. Looking at your run log where you had rev hang, it never actually dropped below the 1,216 RPM threshold at that road speed. And with the amount of airflow and spark, it simply never dips below that because it can't get that low to begin with.
I guess the real question is why does it want to give you 30 degrees of spark at that RPM and MAP? Does that line up with what's in your part throttle spark or main spark table?
On the original one up above - yeah that RPM at that kpa was 32-33 degrees advance on the Main Spark map, but it was the IAC holding open keeping it there too.
Is this with the throttle decay rates lowered or stock? Did the hang occur with a completely stock tune?
I have the same behavior as Jugs with my JTEC PCM with the hanging idle, but I can also get it to stall at low speed maneuvering. Interesting additional symptom, it will idle normally, but if I push the clutch in and coast down my driveway, the idle will frequently kick up to the hanging idle speed without touching the gas. Been chasing this for a while and playing with the throttle follower settings to no avail. Subbed for the learnings 
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