Cold start tuning
 

The moderator at EFILive (joecar) took a look at my tune file, and made some suggestions to me on some tables to take a look at for the rough cold start idle problems I've been having. Seemed like rather minor changes, but they made a world of difference when I loaded the tune that I modified with these changes.



Start up is MUCH better. Doesn't try to stall out on me and run extremely rough like it used to.

The changes made were:

• B3618 - increased richness of cells below 1600 rpm.
• A0002 - set percentage to 100%
• A0008 - increased commanded fuel multiplier at ECT values below 90 C.

OLD:
http://www.corvetteflorida.com/pics/B3618_old.jpg

NEW:
http://www.corvetteflorida.com/pics/B3618_new.jpg

==========================
OLD:
http://www.corvetteflorida.com/pics/A0002_old.jpg

NEW:
http://www.corvetteflorida.com/pics/A0002_new.jpg

==========================
OLD:
http://www.corvetteflorida.com/pics/A0008_old.jpg

NEW:
http://www.corvetteflorida.com/pics/A0008_new.jpg

I think A0008 was probably the table that really made all the difference, as at idle, power enrichment isn't even being triggered. I may take the car out for a spin to see if the changes to B3618 made any difference to throttle response. I'm thinking a bit more fuel might help, since from what I've seen of the logs I've taken, throttle blips tended to make a lean spike and the A/F ratio.

The cold start tuning has been coming along pretty well, so I made up a video showing the progression along the way.



I was feeling pretty good about the progress I made when I started up the car on Saturday morning to go along on a cruise up to Thomasville. In the past when I would start the car up, I would just leave my foot off of the gas pedal completely the entire time till I let the car warm up a bit, but this time I goosed it a little bit and the engine just fell right on it's face when the rpms came back down to what should have been idle speed. So yesterday I set up the laptop for logging and also had video running when I did another cold start to check out this problem. I then took video off of the laptop and merged that video with the audio of the car actually running so I could watch the log data while listening to what the engine is actually doing.



So apparently I still have more work to do in this department concerning the cold start process. The engine is running in open loop at this time, so I need to figure out what tables would be active when the engine is coming down from an abrupt blip to the gas pedal and try to compensate for this transition that allows the rpms to drop down into a stall.

Well, the most obvious event I can see when the engine stalls after the throttle blips is that the throttle blade opening goes from the normal 17.3 percent down to 14.1 percent, so apparently the engine is starving for air flow, which chokes the engine at the lower ECT (engine cooling temp) levels. Once the temps reach a higher level, then that throttle blade choke doesn't affect the engine as drastically.

So, I just need to find the table(s) that will get that throttle blade to come back down and STAY at 17.3 percent after the jabs at the gas pedal.

Sounds simple enough..... :crazy9:

I see a second career as a tuner in your future, Rich! You would probably
be better than 90 per cent of the guys out there........
Andy :wavey:

Thanks, but nah, not my cup of tea. I'm not about to pretend I know what the heck I am doing with this stuff.

Besides, I would need to have access to a dyno, and that certainly isn't going to happen. I only know of a two places with dynos around here and I'm not likely to ever step foot in their shops again.

Crawfordville Timing Association and Dyno Tuning Facility has a nice ring to it!
Just think of the sign........R. Zuchowski, Prop.
Makes you wanna jump right in there don't it! :D
Andy :wavey:

:lmao:

But no, not going to happen. I'm making a modest income off of my websites (well, not THIS one, of course) by doing practically nothing and I can spend my retirement just puttering around with whatever I want to. Why in the world would I want to give that up and then have the pressures and headaches of clients to have to deal with every day? Nope. I had my fill of retail sales with the snake business, so I'm done with that sort of thing.

That's not to say that I wouldn't help out anyone with advice (such that it is) if they need it. But no guarantees would be expressed nor implied other than the 2 cents it might be worth.

Man, that cold start problem is still beating me up. It's really a minor thing, but it just bugs the hell out of me. I've tried everything I can see in the tuning tables and so far nothing has had any effect. It idles real well at 17.3 percent opening of the throttle plate, but when I blip the gas pedal it will then settle at 14.1 percent and the engine acts like it is just starved for air and will either stall out, or oscillate the engine speed slowly for about 19 seconds. Then the throttle plate opens back up to 17.3 percent and the idle stabilizes. Once the engine cooling temps reach around 100 degrees, then it doesn't stall, and seems much happier when the throttle blade wants to be at 14.1 percent.

Well, it's GOT to be SOMETHING! Just damned if I can figure out WHAT..... :banghead:

Well finally! Something I did made a difference. I made changes to 13 tables that I thought might make a change to that stalling problem. Apparently one or more of them did the trick. Now this really isn't the recommended way to do tuning on a car, especially if you don't know what you are doing (like me) as most people will recommend only making a single change each time and then test the results. But this would take forever with the cold start issues. The iterative process is pretty drawn out because of the time necessary for the engine coolant to cool back down in between runs. So I can only get maybe two runs per day to check out the changes I make.

Anyway, here's where I am now...



The stalling has ceased, probably because the throttle blade doesn't drop down below 16.9 percent. But there is still a loping of the idle after the gas pedal blip. And apparently idle is revving up quite high as the engine warms up right before going into closed loop mode.

Some of the difficulties of this stuff is trying to figure out whether the chicken or the egg came first when looking at the results seen in the log data. You can see the RESULTS, but what is the actual CAUSE of what you see? Is airflow, or the AFR mix causing the timing to change, or visa versa?

So I'm going to make changes to each of those 13 tables mentioned above, in order, to try to get the idle to come back down to a more normal speed. The engine loping is still an issue, but it's not really a killer like the stalling issue was. I may or may not spend time trying to track that down and fix it immediately, as I want to move on to throttle response as soon as I can.

But at least now I feel that I am moving forward...

Well, apparently one or more changes I made to fix the stalling issue at cold start brought back another problem I had earlier. While driving and coming to a stop light, when I would push in the clutch pedal, the engine would rev up to around 1400 to 1500 rpm until coming to a dead stop. Then at a dead stop, the idle would drop down to a more reasonable 1000 rpm. Still a little higher than I would like it to be, but better than 1500 rpm.

The data log shows that timing is apparently causing this to happen by staying too high, as the throttle plate doesn't move during that time to change the air flow. So I went back to tune #20 (I am now on iteration #25) and pulled the two base spark timing tables (B5932 & B5933) from that tune into the new tune.

I'm hoping that this isn't a tradeoff whereby I have to choose between having stalling at cold start when I blip the gas pedal, and having the engine rev up higher than I would like when the transmission is taken out of gear coming to a stop. If they are tied together, I will have to see if I can figure out a compromise point between the two problems.

Other than that, the car ran really well today when I took it out for a drive. Throttle response feels improved from the last time I took it out, which is on the plus side. Cold start is much improved, but that rpm oscillation is still there, as I could hear it when backing out of the garage.

Arghh... I took the car out for a drive today with test tune #25 loaded in. Still had the problem with high idle speeds, regardless of the changes I have made. Pulled into the local Walmart parking lot and made a few more changes in a new tune, but they didn't change anything. Soooo, I went all the way back to tune #12 and loaded that one in. Idles fine now coming to a stop. But I'm sure I'm going to have that cold start stalling issue back, and I felt the lope back a bit at slow speeds. But I guess I'm going to have to just make one change at a time to tackle each problem. Going to be damned tedious, but the way I've been doing it is obviously producing unintended consequences that are then harder to figure out and fix.

But at least I can look over the tunes I've done since #12 and have a better idea of what I need to change that MIGHT have the effect I want.

Got some better results today by modifying table B4307 (Desired Airflow). I copied the table from a much earlier tune into my current working tune and reducing the values in the ECT (engine coolant temps) regions of 90 degrees and above by 10 percent. I also increased the airflow 10 percent in the lower ECT cells. Idle RPMs dropped down to a much better 925 to 950 rpm when I would take the transmission out of gear to coast to a dead stop.

I made some of these changes while out on a drive to log data, so I need to do a cold start up in the morning to see how everything reacts to a gas pedal blip. I made other changes to this same table last night, and noticed that the recovery time after blipping the gas pedal was greatly reduced. Went from 18 seconds to just 2 seconds. So that told me that I am likely on the right trail.

My guess is that the changes I had made to this table a while back were allowing too much air at idle, and when I would blip the gas pedal, the airflow and timing were fighting each other trying to keep the engine from stalling. Another obvious sign was that the RPMs were revving too high coming to a dead stop, which apparently was being caused by the throttle blade being open too much because of the commands from that B4307 table.

Just guessing, but I'll know more with more trial and error testing.

Haven't done one of these boring videos of me taking the car for a test drive for a while. Just fiddling with the tuning to iron out some minor issues. Startup is much improved. Unfortunately I left the wideband plugged in over night, so it started up kind of sluggish. But at least it didn't have to crank over a bunch of times before starting up. Still getting a little bit of instability after blipping the gas pedal, but it's gradually getting better. And the coasting to a stop when out of gear is much improved too, as the RPMs drop down to a much lower level than before.

Cranked it out in second gear a little bit when I got out onto the highway. Only hit 52 percent throttle in second gear and it felt like the rear tires broke loose. One of these days I've really got to try 100 percent throttle to see what happens.

SWEET! It's going to be very interesting seeing the trees going past the
windshield when that beast goes sideways....:D I'm looking forward to seeing THAT
video! Do you have any intentions on putting it on a dyno when you get the tune
where you want it to be?
Andy :wavey:

I wonder if there are some tweaks I could do to the suspension to keep the rear end from wanting to swing around to the passenger side when the tires lose grip? The suspension is real stiff, as the car doesn't even budge when I get in and out of it. I don't know if that stiffness makes things better or worse for that problem. Stickier tires would help prevent them from breaking loose of the pavement so quickly, but that introduces additional stresses on the drivetrain. I guess I'd much rather have the rear tires be the "fuse" in the drivetrain instead of the driveshaft popping under load.

As for the dyno thing, Mike Carnahan said I can bring the car up to him whenever I'm ready (and his schedule permits) and he'll put it on the dyno for me and fine tune the WOT tuning. I'm just not ready to trust the car for that long of a trip quite yet, though. If I get more familiar with creating MAPs in EFILive, I might be able to get some of that done myself. But when boost kicks in, I don't see how I'll be able to hold it there for very long to get some good data collection for the MAP cells.

I must say you exercise restraint better than I could Rich.....:rolleyes: