E38 6.2L Small Cam ? Needs Throttle to Idle

[FSAE_Junkie]

This thread could really be titled "How do I get my idle to hang" and that would probably answer my questions. Here's the details though.

I have a 2007.5 Silverado that I swapped the 5.3 out of with a 6.2 L92 from an Escalade. Unfortunately, after copying over most everything relevant from the 6.2 tune, I cannot get the truck to stay running without throttle. It's super easy to get to start, I just added 150% more startup airflow. It's just that after it starts up to 1300 RPM or so, it will plummet back down to 0 without throttle.

Everything is effectively stock (exhaust manifolds, stall, filter/intake) with the exception of adding a VVT Low Lift Truck cam. It?s a small cam at just 212/226 0.550/0.550 113. I was not expecting this to require much idle tuning, but apparently the E38 is more sensitive to these things than the E40 I?m familiar with. I'm using the L92 throttle body which should identical to what was on the 5.3, and so should be compatible with my pedals.

Also, I deleted DoD out of the tune and I do not have VVT enabled (or physically hooked up), so the cam should just be in the default (advanced) park position.

I have my idle RPM set to 950-850 to try and have a chance, but when it does idle, it runs between 700 and 800 RPM and will never hit 850 on its own. I would think this implies I need more idle airflow but I?m getting close to over 100% greater than stock and with such a small cam, that doesn?t feel right. I?ve also not really noticed much of a change over the last 12 lb/hr (1.5g/s) I?ve added.
I thought maybe the cryptic TB Percent Max (Effective Area) under the idle settings was limiting my idle airflow, but I moved it from the stock 2.97% up to 4% with little/no improvement.

Things I know:
At 70F ECT startup temp, I was able to get it to start and run without touching throttle using 67 lb/hr min idle air at 800 RPM. It was undriveable though as it would die after touching the throttle.
At 100F, it required throttle after startup to stay running using 83 lb/hr min idle air. BUT, after it warmed up, it was driveable and drove reasonably well with no stalls and would idle fine on its own when coming to a stop. It would not hot re-start however.

At 190F startup, I had to have 92 lb/hr of idle air for it to start and stay alive without pedal. After cooling down, to 70F it won?t start and stay alive though.

So, a consistent theme in 10+ hours of startup tuning is that approximately 2-3 seconds after starting cranking, it?ll be at about 1000 RPM?s and then the throttle % goes from 10% to 7% in 0.01s. Then the RPM?s come crashing down till it dies. No amount of idle air or throttle PercentMax prevents this. I was thinking that maybe it was the adaptives, so I turned off proportional and integral, and it still does the exact same thing. I thought maybe it was the 8s long startup airflow table which tapers off to lower airflows, so I set it to constant for those 8s and it still does the same thing.

In looking at what I?m doing when I ?keep it from dying? with the pedal, I?m essentially holding the throttle at 9%. So how do I keep the damn throttle from not going below 8 or 9%? Because apparently min idle air does not do it.

Latest Tune and Log attached. Here I tried disabling proportional and integral throttle adjustments thinking that was dragging my throttle down - without luck. Any other ideas what might do this?

[andyb756]

I?ll look your tune over tonight. It?s possible I could offer some insight

[FSAE_Junkie]

Well, this is interesting - I didn't notice this until I opened my log file on another computer where I have a different set of graphs. My Inj duty cycle(or ms) changes dramatically right around the time my RPM's begin their plummet. I mean it drops from 18ms injection time to 2ms - which is obviously massive. In looking at some of my successful starts, I see it only drop to 3ms or so and it does so more gradually. It's unfortunate my wideband (AEM 30-0334) doesn't usually start reading correctly until a few seconds after a start, so it's not easy to see exactly what is happing with fueling in these first few seconds.
001_ColdStart_FuelOddity.png

So maybe I've gotten hung up thinking this is a Throttle % thing and it's really a fueling thing? My VE airflow is only moving from 3.2 lb/hr to 2.7 lb/hr in this window where my injection time drops so I don't think that's doing it. I'll have to see what else could be causing this.

[FSAE_Junkie]

For reference, here's a log and tune from a few iterations earlier where I had a successful start without throttle at 95F ECT. Conveniently, my wideband read this start. This log has a similar (but not as drastic) drop in injection time a few seconds after startup.

Interestingly, even as the injector ms drops from 9ms to 2ms, the wideband actually reports it going richer. I wonder if this is just part of the startup process (combustion efficiency is poor initially) or if actual fueling delivered is not changing that much maybe because fuel pressure is ramping up? I'll have to go see if fuel pressure is something I can directly log. Or, this whole fueling thing could also be a giant red herring and its really just an idle airflow/TPS thing.

[andyvillen]

I did the cam in my 07 escalade, kind of had the same problems.

Do Bigmike42's idle tuning, it worked for me.

https://forum.hptuners.com/showthrea...e-tuning-guide

[FSAE_Junkie]

Okay, I believe I found the solution a while back and its always annoying when people don't update their threads, so here goes.

Everything kept indicating this was a low airflow problem with the fact that I could trace the dying idle to the moment the TPS dropped from 10% to 7% about 2s after the start.

I was already sitting at about 100% more idle air than stock at 800 RPM. Stock 6.2 was 47 lbm/hr and I was up near 95 lb/hr. It bugged me knowing that when fully warm, this seemed okay and actually allowed for a start without the throttle. But then at low temps, this didn’t seem to have an impact. So, I got to looking at the Min Idle Air ECT Multiplier table. At 40F, it was a 0.35 multiplier. Thinking I maybe needed a little bit more air, I multiplied it by another 10% or so and went to a 0.39.

Unfortunately, this had little effect on the ability to cold start. Again, looking at the log, it looked like throttle went from 10% to 7% just as before and that the above ECT multiplier did nothing. I was a bit frustrated after this and said, “you know, F*** it, what if I give this thing 200% more airflow?” What’s the worst that could happen? So I bumped the multiplier up from 0.39 to 0.8.

Well, I loaded the tune, and went to start it at 40F and holy crap, it fired right up and idled great. So, in total (If that ECT multiplier is a straight multiplier on airflow), I now have 400% of stock idle airflow on a 40F start. It's still probably not enough as it consistently runs below the idle target, but it's been good enough for driving the past month or two.

I'm annoyed that it took 400% idle airflow as nothing I've read around online would indicate you need this much, but its the only thing that would keep the throttle from closing rapidly after startup.

[5FDP]

Did you forget to copy over the VVE data for the 6.2 swap?

Your VVE table is nowhere near what a 6.2 starting point is. Even with that camshaft the VVE shouldn't be that much different if you've even started tuning that.

Did you hook up the VVT yet?

[smokeshow]

Okay, I believe I found the solution a while back and its always annoying when people don't update their threads, so here goes.

Everything kept indicating this was a low airflow problem with the fact that I could trace the dying idle to the moment the TPS dropped from 10% to 7% about 2s after the start.

I was already sitting at about 100% more idle air than stock at 800 RPM. Stock 6.2 was 47 lbm/hr and I was up near 95 lb/hr. It bugged me knowing that when fully warm, this seemed okay and actually allowed for a start without the throttle. But then at low temps, this didn?t seem to have an impact. So, I got to looking at the Min Idle Air ECT Multiplier table. At 40F, it was a 0.35 multiplier. Thinking I maybe needed a little bit more air, I multiplied it by another 10% or so and went to a 0.39.

Unfortunately, this had little effect on the ability to cold start. Again, looking at the log, it looked like throttle went from 10% to 7% just as before and that the above ECT multiplier did nothing. I was a bit frustrated after this and said, ?you know, F*** it, what if I give this thing 200% more airflow?? What?s the worst that could happen? So I bumped the multiplier up from 0.39 to 0.8.

Well, I loaded the tune, and went to start it at 40F and holy crap, it fired right up and idled great. So, in total (If that ECT multiplier is a straight multiplier on airflow), I now have 400% of stock idle airflow on a 40F start. It's still probably not enough as it consistently runs below the idle target, but it's been good enough for driving the past month or two.

I'm annoyed that it took 400% idle airflow as nothing I've read around online would indicate you need this much, but its the only thing that would keep the throttle from closing rapidly after startup.

Seems like you're pretty fed up with this lol, so I'll just make this into a list with some rough values:

1) Put your min airflow back to stock plus maybe 25%. (set the ECT mult back to stock too) I'm sure you figured, but this isn't the table to be ratcheting up. 25% should be enough for that cam for the time being...you can fine tune later.

2) Double your Park and Neutral throttle follower torque values below 1200rpm. (NOTE: it says Reverse on the bottom row, but this is PARK...at least in my version of HPT) The throttle follower is the magic surface that's going to 'catch' your idle rather than letting it stall. Looks like you've reduced it, and this is basically never necessary with a bigger camshaft. Without touching virtual torque, doubling those values should make a noticeable difference. Don't be afraid to try more if need be. This is an important table, probably the most important one to idle quality on a gen4 with a bigger cam.

3) Put all adaptive idle airflow values back to stock for now. You need these for stable idle. Disabling them will only make things worse. Stock values are typically fairly robust to even decently sized camshafts, but there is a method to the madness with these adaptives and I can address that later if necessary.

4) Set startup airflow back to stock. You can add a gram or two in there if it makes you feel any better, but it looks to be just worsening the problem with the values that high. Reasons being, #5 and #7. Start airflow shouldn't need a whole lot of adjustment unless you've changed the throttle body. The manifold is already full of air before you start it, so a stock throttle should fire up just fine with little to no changes here.

5) The reason that start air is making it worse is because it's heavily triggering startup flare control spark retard. That's trying to come in and prevent a super high start flare and is contributing to the RPM drop. Multiply that table by 2/3.

6) Back in the idle airflow tab, multiply startup time overspeed by at least 1.5. That throttle cut you're seeing a couple seconds in...that's where its coming from. As you get cranking spark and start fuel dialed in, you can bring this back down later to rein in the idle speed quickly after a start...but for now, it will give the RPM time to settle a little more slowly before idle control takes over. The throttle follower and adaptive idle air will be helping out here now.

7) That extra start air keeps MAP/load too high while it transitions from crank fuel to open loop run fuel. You'll notice the sharp drop in IPW as that happens...and then a fall in RPM shortly after. Fuel doesn't like to vaporize as well in cold, high pressure ports. You can't do anything about the cold, but you can bring the MAP down with lower start air to help it evaporate. While you're looking at fuel, open up the OL IVT gain table and progressively increment the multiplier starting in the 75? column and adding to the lower temp columns. I might add 2% to 75f, 4% to 60f, etc. 15-20% total by -40 should be plenty for now. This table and the OL EQ tables are something you may want to spend quite a few starts dialing in...they make a big difference.

8) Soften up the misfire diagnostic thresholds. You may have noticed that it looks like random enrichment coming in after about 30 seconds of run time...that's due to the misfires from the camshaft. Easing up on the misfire detection window (I usually just double them to start, since we can't really calibrate them) will help prevent the cat protection enrichment.

9) Last step...high octane spark. Where crank spark ends and before idle spark begins, the high octane surface briefly fills in the gap. Problem is, you've got high air mass at low RPM, where the stock cam would be more knock prone...and the HO spark is lower there as a result. This doesn't play well with a bigger camshaft during starts, especially when its approaching negative values. So you'll need to add some spark in that area. I'd start at 1200rpm and 0.32g, select everything down to the bottom left corner of the table and add a degree. Move to 1000rpm and down to 0.36g and do the same thing. Repeat until you've added 4-5 degrees.



Give this list a try and see how it responds. It may actually be too much and flare excessively, but at the very least you'll notice an improvement to cold start and idle. Tons of other stuff to tweak, but that's a start.