Something amazing maybe? How does ECU know about 'valve float'!?

[kingtal0n]

So I got a new boost controller that I haven't used before. started turning it up without a boost gauge (lol). I knew the valves would float at some point, I just wanted to experience it for myself. I've only heard about it, never had an engine actually do it.

So bit by bit turning it up but didn't realize the "high" knob was actually starting off higher than "low". So what I thought was 1 click higher on "high" turned out to be around 3 whole marks (about 30% higher) putting the engine from 7~psi to around 15+ psi. Me not having a boost gauge didn't let off, even though I felt it fall on its face I was interested in the log of "valve float" having never done it before.


So This was extremely interesting to compare with all the 7psi runs I had made before. I took a picture and made it easy for you to see:
lolboost.jpg

Question is
I thought the ECU used the VEmap, and air in lbs/hr to determine torque production. I thought that by using larger number in the VE table for example would increase 'torque' the computer thinks the engine is making.

This must be incorrect. If you look carefully at the picture you can see that at almost double the airflow, literally WAYYY higher VE from the VE map (which is fairly accurate) nearly DOUBLE the amount of fuel injected (engine didn't even hiccup just felt a little slower), yet the computer accurately determines that there is LESS TORQUE somehow? I thought it was a coincidence at first, but after attempting other boost levels and opening/closing the cutout (which reduces exhaust gas pressure thus reducing valve float allowing higher boost) I see the same trend over and over for it to be a mistake.

Buggles my mind. It must have some kind of rate of change algorithm? But it would need to know vehicle weight for that. How on Earth does it know I made less power with twice the airflow and fuel from the model??!

Setup is
all stock 5.3 turbo + 4l80e in a 3000lbs 240sx, 'test engine'
93 octane only
Actual A/F is very close to Commanded A/F. I command 12.7 I see 12.4~ for example. I leave it a bit richer in the base map because I dont have an IAT yet and other reasons.

And one other question as an aside. Why when the valves float don't the pushrods jump out of the rocker arms and send the whole engine into a bent up twisted pile of rubbish? I was kinda hoping for a catastrophic failure so I can swap in this gen4 4.8 I have lol. But it seems pretty indestructible... Not even a hint of oil flow from the crankcase vent at 16~ psi makes me really happy.

[Ben C]

The ecu doesn?t know about valve float.
That?s not really an apples to apples comparison you posted, different revs and timing being run.

[kingtal0n]

The ecu doesn?t know about valve float.
That?s not really an apples to apples comparison you posted, different revs and timing being run.

Since when does timing factor into torque calculation for the ECU?

Or RPM.

Torque and timing can be set independent of RPM. You can have the same torque at the same airmass at every RPM. Torque changes (presumably) based on VE which is given by the VE table.

The ecu doesn't know how much air the engine uses unless you tell it. And I did tell it, it shows double the air going into the motor.

But it consistently shows less torque for more air whenever the valves float.

Theres no way the ECU is subtracting 30 ft*lbs of torque at double the airflow rate, double the fuel flow rate, because of 3* less timing

I am missing something. If I get more time Ill find a log comparing apples as you put it.
Its a very fine line and I am not going to do much more testing though. This was just for fun. I'll put 1218's in the engine in a week or so.

[Ben C]

The ecu has to use timing to calculate torque.
About halfway down is an explanation.
https://forum.hptuners.com/showthrea...ng-table/page2

Change values in that table and see why happens.

[kingtal0n]

Heres two shots from the same run.

boostsamerunwtf.jpg


It shows more/same torque for half the airflow and half the fuel input.

You're telling me that its predicting torque solely based on timing now? Wahhhhhhhhht

So why does it shows low torque during cruise when theres a ton of timing? If I got 500 ft*lbs at 15* I must have 1000 ft*lbs at 30*?
Also when I open the cutout at the same timing I show more torque when the valve float stops.

Something else is at work here. You are def onto something though. I might simply reduce my 7psi timing to equal 15psi timing and compare.

[kingtal0n]

Thanks for the link

The max torque timing table is used by the ECM to determine the amount of torque the engine is making. The torque calculations are usually referenced to a "Mean Best Timing" table (the table you are asking about).

So if your engine is running at 22deg spark and the MBT table says 24deg it uses this 2deg difference to offset the calculated torque values. Note that the MBT is often a theoretical number.

There's really no need to modify this table, we only ever really added it for the LS1 V8 engines for infomation and that got carried over to the V6 during that development.

On Fords the MBT is actually enforced as a maximum allowed timing, but for GM it is not.

Chris...

So I have some experimenting to do. Interested to see what happens when I stop the valve float and raise the boost back to 15...

[scoob8000]

Do you trust what the scanner is telling you about injector duty cycle? (I don't know how accurate it is on some platforms) Seeing it at near 100% caught my eye though. Whats your WB showing when that happens?

[Frost]

I was going to mention the other things used for calc'd tq; the same dyn cyl air / cyl fill stuff but...


Back in 2006 I was present at a small shop with a dyno and a kid was tuning his own car on there. I had only been doing this for a few years at the time, and I wasn't there to "help", just there with other friends. That kid made one pull that, on the dyno graph, was clearly floating the vales up top; right at 6K. I didn't recognize it that first time, and put my nose in their business never-the-less and advised them to pull it off now; as this issue isn't tuning (mixture at 12.7ish, 26-27 deg spark at 6K) but something physical. The kid balks, makes a second pull and absolutely famously destroys the whole motor on the dyno... It floats, piston touches valve, valve pops up and drops it's locks and goes right into the cylinder; up there over 5K RPMs. I've been conducting, or present, for ump-teen thousand dyno pulls. I never, have ever, seen anything like that before, so it was pretty well stamped in my mind. I would call intentionally running an engine into float past-reckless behavior. If parts leave the car, even if they are yours, they could harm person or property.

He re-used NOTHING but the rocker arms.... and guess what his new motor did on our dyno? Yep; same thing. It took over an hour to get him to own up to having used the rocker arms over. They were Harland Shapre orange garbage. Also to his protest, OEM rockers and trunions went back and the car did what it was supposed to up top.

This is the graph, attached, of the car floating the valves on the dyno. For reference, this was (again 2006ish) Thunder Racing TR 224 cam on a 112LSA, some mild heads like PRC ported OEM castings, Comp 918 valve springs and Harland Sharpe rockers.

[kingtal0n]

Do you trust what the scanner is telling you about injector duty cycle? (I don't know how accurate it is on some platforms) Seeing it at near 100% caught my eye though. Whats your WB showing when that happens?

When I first put the motor in I noted that the more stuff was going on in the scanner the less accurate the injector PW per bank was. It would have two different numbers.

However the duty cycle seems fairly accurate. Some injectors will still work at 100% it just isn't reliable. I think they can over heat or something. Its why you shouldn't static flow test them.

I wasn't watching the wideband that time. But I am sure it was simply rich or the engine should be toast or at least would have had a hiccup. It just kept going though. I was pretty amazed.
Those injectors are FIC 58lb/hr so that was a LOT of fuel. However, to conserve pump life and reduce fuel system wear, I only run 35~psi of fuel pressure atm, so it was like half of what they are capable of. When I need the extra fuel in the future it will be raised...

I was going to mention the other things used for calc'd tq; the same dyn cyl air / cyl fill stuff but...

I've never really looked hard for it but I did read alot about people saying their valves floated, and nothing happened to it. They just change springs and go on the way.
I think its a different kind of float from high exhaust pressure. I know if the bounce on the seat due to uncontrolled momentum that is perfect for destroying the engine in a manner you speak of. But for whatever reason slight opening with stock camshafts at reasonable rpm due to high exhaust pressure don't seem catastrophic at all.
I knew something catastrophic could happen but I didn't think it would be an issue around 5k. Although part of me wonders what keeps it together sometimes when I make these mistakes.

Thanks for the post. I've never actually seen valve float or had an issue with it before ( this is my first LS motor ) and most JDM engines won't do this either because the OEM springs are good at 7k or 8k sometimes, or that we simply change them as easy as they are to access. It was because so many people reported it happening to stock truck motors at 8-10psi and nothing bad happened that I was willing to experience it. I won't be doing it again though as much as I wish I could capture it on a dyno myself. springs and on my way from now on. I look forward to more of your posts, they are always exceptionally well tuned ;D

[kingtal0n]

I'm curious also if anyone knows,

1. when uploading a new tune and the fuel pump re-primes, I must be also getting another prime pulse to all injectors maybe? So if I key on, I get prime, then Upload, another prime happens after upload. 2x primes. It means I could essentially flood the engine if I kept re-uploading tunes without cranking. Is this correct?



2. Before cranking, inj pulse reads 19ms. During cranking, as high as 38ms. Was the 19ms the prime pulse or from the FA table or from the first pulse mass? Also can anybody explain the "FA Mult Stage 1 vs. Time" or "Cranking FA Mult Stage 1 vs Cranking Time" Table. My FA table says 0 to 32 but there is no unit given. I assume it is milliseconds. Can anyone confirm the table reads in ms? Also how does this work exactly, for example at 0 the first row, coolant at 86*F says 2.165ms, is this added to the "first pulse mass" which is in grams of fuel from the other table?

Having trouble figuring how they interact


3. I know I asked this before, but what the heck is with the injector running during DFCO? Has anybody ever defeated that? I am on the verge of putting a little switch that I can flip off my injector harness during a decel. I tried putting minimum injector PW to 0. I don't think the short pulse adding .2 or .3ms adds up to 1.2ms I see during DFCO.

Would I be better off just zero'ing out the VE map in the decel regions? I hate doing that though because then it sucks to hit those cells when you need them. Plus I like a little fuel on the subtle re application of the throttle (just barely touching the throttle at the top of the map I prefer it rich, like 13's, to cool the motor. But not during a full DECELERATION thats just a waste of fuel...)