2013 GT500 Coast Surging

[GHuggins]

Hi, so I wound up with this car that's apparently been tuned by 4 or so other people - car surged horribly during coast in neutral - rpms oscillated 1000 to 1200 or so up and down... I've got timing locked in now and throttle pretty well locked in - rpm's are still surging with fueling... I've tried injection timing, O2 tuning all among what seems like a million other things - nothing is working... What's really odd is when it's surging there is a significant bank to bank fueling difference, but in one log it's on one bank while in the next log it's on the other bank? Is there a test or something I've missed?

I've got throttle errors dialed into (.something) errors pretty much - tried adjusting the torque model, timing, idle air and so on to no avail - it says it's referencing dashpot during this time, but I can't figure out a way to make any changes to make things better - figured out how to make them worse though I've got it down to a 50 to 100 rpm surge for the most part - just need to figure out how to make that even less...

Build - unknown cams, unknown pulleys doing 16psi, Kooks Lt's with cat delete, stock mufflers, JLT CAI, Ford Performance Dual 65mm TB

Thank You

[BNA]

Try increasing the decel spark and increasing the decel cutoff rpm. Outside of tuning the camshafts can cause issues if not timed properly and a low vacuum bypass valve may be needed.

[GHuggins]

I changed the decel spark to help lock it in... I tried different levels of timing, but this one was the best I could come up with :/ I am worried about cam timing, but it doesn't "exactly" run like it's out of time, however the bank to bank fueling has me worried on that... BUT then again - the bank to bank shouldn't be changing which bank it goes rich on?

[GHuggins]

Would the bypass cause the fueling issues - I can see the surging from it most definitely...

[murfie]

Instead of zeroing out the bottom angles effective area, you should just raise the minimum throttle angle. Right now the way you have your TB model effective area below 3* is interpolated to 0 for any angle between 3 and .68, thats much too fast of a rate of change and dashpot is needing to be used to slow it down if its using an effective area in that range.

GH TB v3 model.PNG

[GHuggins]

What would you raise throttle angle min up to Murfie? The effective area is what the calculator came up with - I didn't even pay attention to that although throttle errors are near zero now...

[murfie]

I would try to keep it as low as possible for the best decel braking. With cams though having it open to a higher minimum makes it easier to get a strong idle. You definitely want your TB model to cover all possible angles the TB can be at.

My suggestion is try something like below.

GH TB model.PNG

[GHuggins]

Like this? I assume this might make me have to lower driver demand, torque model and possibly the min air tables too? Sorry min air = idle airflow tables... I'll give this a try Murfie - thank you... I assume getting the air to flow better through the throttle body or represent the airflow better in the tune is what your thinking to be the bank to bank changing fueling? I've got injectors ordered for it since it is long past it's duty cycle limits and the owner was wanting something capable of handling a bigger blower on a built engine setup, so I've got 1300's on the way... It already puts down 800 on race fuel - he's wanting something to handle 1200ish I think...

Thanks everyone - will give these settings a try...

[murfie]

Doubt you will have to change all that other stuff. You are defining a minimum airflow through the throttle body that is higher than zero. The model even being able to say zero airflow could cause strange fueling issues as it becomes totally dependant on keeping the DD torque value at 0.

[GHuggins]

Hi Murfie, so here's where I'm at currently - I've got it pretty nice - still not where I would like for it to be, but nice - except for at exactly 40mph it hits a tip out limit of some sort and then at that time timing dips then rpms dip and it goes back to driver demand then oscillation kicks in and the rpms kind of settle back... I may be causing problems with my changes, but right now it's idling the best during decal that it has so far... You can see this at the end of this log in the timing... For whatever reason I wasn't logging speed, but this happens at exactly 40mph every time?

[GHuggins]

Ok, so maybe not a mph switch, but instead a time period switch? Went up to 100mph in this one and it happened twice - once at around 60mph and once just below 40mph and then a few other times it didn't do it at all??? Thoughts one this? I want to believe this is a "test" or something else going on - just not sure what?

[GHuggins]

It's always tipout limit that causes the dip in rpm, then it goes back to driver demand after oscillation correction - I re-enabled the oscillation switch because I thought that was causing it's own issues... You can see the problem at 3:14:43.792 in this log... Am I just being too picky now that the worst of the surging is gone

[murfie]

I'm not able to review the logs right now, but is your indicated torque hitting the torque minimum ipc?

[GHuggins]

Can't say for sure when it does this at 1000rpms and 55mph because it's iffy, but it is higher than the IPC maximum table under torque management when it does this at 2300rpms and 94mph, but when it does this at 3000rpms it happens well within the max and min settings... It's even within the IPC max map settings in these zones as far as I can tell from the log? You think I should try raising the max tables some more and then possibly lower the min table some? Thanks Again Murfie...

[murfie]

From that log I would be checking the passenger side exhaust manifold for leaks or a bad O2 sensor.

The tip out limit, my guess is idle airflow values need to be lowered in the higher RPMs. you have 3 while its in gear, you could probably do 3.5-3.25 while its in neutral and get a nice RPM drop, 7 is much too high and will slow the drop considerably. As long as it isn't so low its causing the engine to stall or stumble you should be ok. This is where tuning it to have a strong idle helps as you can have aggressively low numbers and the strong idle recovers no problem.

[GHuggins]

You talking about dashpot min or idle airflow? AND when you say tuning for a strong idle - are you just referring to the min throttle settings or do you have a more involved process? I did forget to order the O2 today - was actually going to do that this morning as it's either an injector issue, exhaust leak issue, O2 issue or cam issue on that bank... Changing injection timing - retarding it - helps a lot, but I have to retard it a whole lot more than I like and it still shouldn't be causing this excessive of an issue... At times it will be out 10% bank to bank then others be within 3 or 4 percent, so believing more likely that it's an exhaust leak issue or O2 - just have to get it back off of the dyno to check... When your setting up the TB min, how do you typically do it? I went up to 3 without problems, but of course too high causes the engine to free rev and I didn't want it changing altitude or anything and winding up with a self running condition...

[murfie]

The idle airflow tables.

For idle tuning: Have the engine in proper working order, have your MAF curve tuned well, Have torque model/ TB model accurate. AC off
Goals:
Fuel is going to be Lambda
Air is going to be maximum for target idle speed
Spark is going to be minimum. Piston speed is low compared to flame propagation so its best to have the majority of pressure build as the piston is going down not up. Idlely working it up to MBT spark value in the idle region.


Increase the target rpm 200-250RPM so you are in the 800-900 range. For race only you can go up to 1100-1200 or higher depending on driver preference. This is solely to increase the engines air moving ability.
Open the hood and let the car idle for five minutes to ensure its at temperature, you are not in any transient fueling mode, and VCT (if it applies) settles into its mode. With the hood open IATs should remain constant and not at any extremely high values.

The goal after this would be to increase the idle airflow values at the target RPM until the engine can not maintain the RPM. This opens the TB and this gives you the maximum airflow at idle. Usually you can decrease that 5 % and tweak the spark values up or down as you want.

In a perfect world above your target idle speed would be zero airflow and below would be your max airflow or slightly higher to help prevent stalling. The engine does not react this fast you you have to give it a "heads up" in order for it to respond the way you want it to.

You could probably modify the axis of those tables so that below your target Idle speed is not lower values than your target idle speed, that would help as well.

Once you have all the airflow values figured out you are going to want to lower the minimum throttle angle to get the fastest engine decel.

[MRRPMBRP]

Good info above!
This is exactly what I needed to know about throttle settings, wasn't sure what all it meant.
Now if I had a good explanation of how to set the torque values, I'd be good. (I think)
Or does anyone have any info about a book that teaches how to do this? The book I bought doesn't show this on GT500.

[Thatwhite5.0]

Logging throttle angle and throttle angle desired helps since that's pretty significant in throttle body tuning. Very hard to do without.

Make sure your columns flow in order.

The column axis in ETC Predicted needs to correspond with the column in ETC area, it will define it. I tend to choose choose a number that I know the throttle body flows through. The oval throttle bodys do not like zeroes. I tried and tried with the twin 67. It would not give. When correcting based on ETC error. You have to change fractions of the error. The error will sometimes show -4 when you're already at 2. it does not want -2, it needs smaller fraction, the throttle body was oscillating so it will sometimes pick up numbers that are too much.

TB_t.JPG

hpt_tb.xlsx

[murfie]

When tuning the throttle body model, to avoid what Thatwhite5.0 pointed out, you can set up the scanners graph ignoring the ETC Vacuum axis. Just get an average angle error for the respective effective area axis. When you apply the error you can apply it to the entire column to shift that part of the model at that Effective area up or down and maintain the order. Most effective areas will have about a 2* difference in throttle angle between high and low vaccum values. You may need a higher difference in parts of the model where minimal vaccum is seen and lower where high vacuum areas. This way the calculator also returns a good effective area table as well, and thats the value that really matters.

So Instead of applying large error in the diagonal pattern that its usually seen in graphs, just move all the angles in the direction the average error usually a 1* or less is until the scope of angles are where they return the least error. Depending how far off your TQ model is you should be able to eliminate angle error completely. If you find moving the angles up or down only increase error or do not reduce it, then you can be sure your TQ model needs to be adjusted.

TB model EZ error.PNG

TB model error.PNG

If you do end up having to adjust the angles more than the difference, I suggest modifying the axis of the effective area so that you don't have an offset between the tables and values from one axis falls in the other tables values. More for a visual thing as the calculator compensates for any offset.