Having trouble lately with higher IAT

[spy2520]

For some reason I have noticed during the hotter days I have been having trouble keeping the car running. This happens both on cold starts and hot, and frequently when coming to a stop IF the car hasnt moved much, i.e. slowly moving through a parking lot. Sometimes I'm embarassingly starting the car 3 and 4 times before making i out of where I'm at. Haven't really been able to get a good log of it, but what i do know is if i get up to speed, slowing to a stop isn't really a problem. And when the ambient temps ar 5-10*F lower i don't really have a problem. Which makes me feel like it must be related to intake air temps.

All i can imagine is when i tuned the car it must have just been too cold to translate to good summer behavior. Could this just be a situation of needing more/less idle air?

This is on a 99 LS1 auto.

[joecar]

Sounds like idle tuning needs to be revisited: Idle-Tuning-Helpful-Info-Inside (https://forum.efilive.com/showthread.php?4661-Idle-Tuning-Helpful-Info-Inside)

[spy2520]

Yeah i spent a decent amount of time on that thread. Everything was good up until we started getting some hot weather. I dont drive the car as much so at first it seemed like a one-off. But it has happened several times now. Wondering if maybe the VE table is just not good in that area and its too rich with higher IATs.

[statesman]

Is this the same vehicle you were having problems with winter idle a couple of years ago?

[spy2520]

Yep. Maybe I'm bouncing between getting it running well in winter vs getting it running well in summer. Seems I had partially corrected a problem and created another.

[spy2520]

Anyway to put in perspective. It rained yesterday, and the car ran fine yesterday and today. But I'm sure if it gets over 90* again, I will have problems. I'll try to get logs and see what is going on.

[statesman]

If I remember correctly, you zero'd out your airflow corrections. I thought that might come back to bite you later, and it looks like it has. You really need to have perfect desired airflow when doing something like that to your tune. Re-visit your desired airflow when the temperature gets hot enough to cause you problems.

[spy2520]

Yeah that zeroing was a temporary experiment. The tables have since been repopulated with stock data and then massaged based on the idle tips. I have attached what was ironically named "known good tune" which i guess i have to add "formerly known as" in front of that.

[statesman]

Okay... I've had a look at your tune file. I'm amazed that the engine actually runs at all on this tune. Can you give me a list of mods?

[spy2520]

Lol. Cam is 236/338 I think. 3500 stall converter. Fast 102. 102 throttle body. 1 7/8 headers. I think that's it.

[spy2520]

Also a 103mm MAF housing and card style MAF sensor.

[statesman]

Would you like to add fuel injectors to your list?

[spy2520]

Would you like to add fuel injectors to your list?

Ah yes. 42lb injectors. Apologies, this car has been modded over the years and doesn't get much attention these days. I should add no cats, 3" x-pipe, aluminum flexplate, bigger alternator and turn one PS pump.

[statesman]

Now we're getting closer to full disclosure.

Do you intend on tuning this thing properly, or do you just want a quick fix to stop it taking a dump everytime you pull up at lights on a hot day?... there's no right or wrong answer here, I just need to know what you want.

[spy2520]

Now we're getting closer to full disclosure.

Do you intend on tuning this thing properly, or do you just want a quick fix to stop it taking a dump everytime you pull up at lights on a hot day?... there's no right or wrong answer here, I just need to know what you want.

I'd like to tune it properly. Any advice is appreciated.

[statesman]

First thing you need to do is to get the B9021 cax file. It's somewhere in the cax section of this forum (I don't have a link to it so you're going to have to go and find it for yourself). Read the instructions carefully and put the correct cax file (renamed to your OS) in the calibration folder. When you next open the tune tool, it will appear under Injectors > Parameters.

Then...
Change {B9021} to 0.55
Change all values in {B4003} and {B4004} to 0.55
Zero out all values in {B4005}. (It will be wrong, but not as wrong as what you have now)

Then do a log for me. Include in your log...

MAF Frequency
MAF airflow
RPM
MAP
ECT
IAT
GM Volts
Short term trims
Long term trims
IAC counts
Wideband (if fitted and calibrated)

No need for any WOT pulls, just normal driving.

Post your updated tune file with the log.

[joecar]

See post #12: need-B9021-for-01250003 (https://forum.efilive.com/showthread.php?17699-need-B9021-for-01250003)

[spy2520]

Ok I'll get that set up. Don't know why I haven't read anything about the B9021 cax.

[statesman]

Don't know why I haven't read anything about the B9021 cax.

It's a closely guarded secret... there's probably only a few thousand people in the whole world that know about it. :laugh:

[joecar]

Probably only a few thousand.

[spy2520]

It's a closely guarded secret... there's probably only a few thousand people in the whole world that know about it. :laugh:

Lol I meant as much as i bounce around reading threads on here I don't know how i let that slip by me. Log coming today.

[joecar]

People tend to find out about it when they try to tune idle.

[spy2520]

Makes sense.

[statesman]

Log coming today.

Let me know what part number is on your fuel injectors when you post your log.

[spy2520]

Definitely these from fuel injector connection https://fuelinjectorconnection.com/collections/ls-series-all-gm-ls-engine-series-fuel-injectors/products/fic-ls-series-42lbs-for-ls1-set-of-8

[spy2520]

Welp, i think i see where it all went wrong now. But attached are the files. It did stall while parking at the end but other than that nothing notable to me.

[statesman]

Welp, i think i see where it all went wrong now.

So, where do you think it all went wrong?

[spy2520]

At some point I reverted back to a stock tune and restarted the tuning process, with none of the injector data i should have been using except IFR. I have all the spreadsheets and remember doing it but it isnt in this more recent round of tuning files. That has to be a large part of the problem if not the entire problem. Still didn't know about the b9021 cax....but...

[statesman]

Let me tell you what I think.

I think that your drilled injectors weren't actually drilled... I think they're still flowing stock and the imbalance in your trims indicates that they're not even flowing evenly. Your MAF table is about 40% too high across the board and that's because your IFR table is about 40% too high. B9021 isn't going to make any difference to you because you're not using larger injectors.

Try this if you want to have some fun... put completely stock values back in for your injector data (stock IFR and stock voltage offset but leave Small Pulse Adjust zero'd out) and also set your MAF table back to stock values. See how much trimming you get with that... and see if the trimming is fairly consistent (with your new maf tube and card style maf, the MAF readings may be a few percent different to the stock MAF).

You need to get your IAC counts down at idle... you need to crack your throttle blade open a bit more and reset your TP sensor. Your IAC effective area table is a bit wild and needs some attention.

Getting the correct airflow readings is important. Your ECM calculates engine torque based partly on cylinder charge and your calculations are going to be way out with your MAF reading such high airflow. This affects your transmission, which determines line pressures from that calculated torque.

[spy2520]

Hmm. Interesting thought about the injectors. I never really doubted the numbers.

The IAC effective area was the result of some experimentation due to the bigger TB.

I'll start over and see what happens.

[spy2520]

I still have the stock injectors. In theory i would swap them and see no change right? Leaving everything as is.

[statesman]

If the stock injectors are the same part number then yes, you should see no change if you leave the tune as it is. If you go lean on the stock injectors then they are flowing less than your current ones and if you go rich then they are flowing more than your current ones.

[spy2520]

Got dirty. Part #0280155868. Not stock. Googling tells me anything from 36lb to 42lb I'm guessing those numbers come from different rail pressure. Don't know if I have the right injector data or not. Would post but it won't let me attach an Excel file. Could have sworn there were excel files on here before.

[statesman]

That's interesting. They should be flowing around 40lbs @4bar. Either your fuel pressure is really low, or your MAF is over-reading airflow for some reason.

We can test this if you want to run some logs for me.

[spy2520]

I can take some logs. First I should probably put the right injector data in there.i think I have b3701, b4003, b4005 and whichever the IFR table is I don't remember.

[statesman]

I'll set up a tune file for you to use. We need to be in MAF only mode for this test. The starting data is not important... I'll be adjusting the data from the logs.

[spy2520]

Also, I have not seen a lean condition at wot, cant imagine fuel pressure is low just based on that, but stranger things have happened so it's worth testing.

[statesman]

Flash this tune file in and run me a log. As well as what you were logging for me last time, add vehicle speed and commanded AFR.

[statesman]

Also, try to get me around 12,000 frames at full operating temperature. Avoid going into PE mode if you can.

[spy2520]

Added wideband lambda as well. The sensor is old, but hopefully atleast close to right. Calibrated it before putting it back in. I also notice the voltage seems low. Thats something I'll have to look in to.

[statesman]

Okay, I've run your first log and it indicates that your fuel injectors are flowing around 41lbs with your fuel pressure. So why is your MAF table so high? I had to think about this, but then I realized that I had forgotten something you told me... you have a 103mm MAF housing. The larger housing means that you flow more air per unit of raw frequency. Mystery solved... and my fault for not paying enough attention to your list of mods.

Do a log of this tune update and I'll finish cleaning up your injector data. Try to get a hard decel in your log. You might have to lock the transmission into a lower gear to achieve that. Also, get at least 12,000 frames again.

[spy2520]

Hard decel with dfco enabled or no?

[statesman]

I've disabled it this time in your tune. Just use the updated tune file as it is.

[spy2520]

Oh ok gotcha

[spy2520]

There is a pause somewhere in the middle. had to stop for gas.

[statesman]

Fueling is pulling in a bit slower than I would expect. Do you have short or long tube headers?

You opened your throttle blade and got your IAC counts down, but now they're too low. At the end of the last log your counts get down to 6. Try to close your blade around half of how much you opened it (if you can remember how much you opened it). You'll have to reset your TP sensor again too.

Your fueling should be looking better now, so go a bit harder in your next log... it's alright if you get into PE now. Do another hard decel again too.

[spy2520]

I have longtubes.

[spy2520]

Here is the latest log. Its warmer out today. I got the throttle blade closed a little.

[statesman]

Okay, I've adjusted for the longtubes. Fueling is pulling in nicely now. This update should be very close to what I'd call good injector data. Still log at least 12,000 frames incase I need to do one more adjustment.

[spy2520]

Here is the latest log.

[statesman]

Your injector data is now good. I'm adjusting your O2 switch points which will affect fueling a little bit, so flash in the attached tune file and do a Calc.VET using trimming for CL and wideband for PE. When you get that done, let me know and we'll move on to your airflow.

[spy2520]

Long work week. Finally got to the car. Attached is the "BEFORE" log and the resulting tune from the CALC.VE process. The VE table i just hit smoothing once after pasting. MAF table needed some hand blending and smoothing above 7000hz. I have not taken a log after.

[statesman]

Okay, now let's look at your airflow. Log the same parameters as you were logging in your last log but add the following to your list...

GM.IAC
GM.IAC_STD_DMA
GM.IAC_STPN_DMA
GM.IAC_LTD_DMA
GM.IAC_LTPN_DMA
GM.IAC_SUM_DMA

Don't worry if you go over 24 channels... fast frame rate is not important for this.

Do this log with your a/c off. Log a warm up in gear from a cold start. Just sit there in gear with your foot on the brake. When the engine is fully warm, shift into park and then blip the throttle once (that's just so I have an easy to find marker when you shifted into park) and let it idle in park for a couple of minutes. It's easy to log, but painfully boring.

[spy2520]

Log attached.

[statesman]

I asked you to log GM.IAC_SUM_DMA but you logged GM.IAC_SUP_DMA instead. Do another warm up log in gear like the last one, but this time include GM.IAC_SUM_DMA in your log and get up to full operating temperature before shifting into park.

[spy2520]

Ah crap

[spy2520]

Finally got the log with correct pids.

[statesman]

It's looking better already. Airflow should line up reasonably good with this update.

Do another warm up log in gear, like you've been doing.

[spy2520]

Alright got the latest log right here.

[joecar]

Ah, you're running a GenIII... I was looking for GenIV and/or GenV logging the pid SAE.LAMBDA

( sorry for not be clear )

[statesman]

Winter cold starts should be a lot easier to dial in now that your IAC effective area table is in better shape.

When you log this update... start logging before you start the engine so I can see the engine start-up in the log.

[spy2520]

Latest log. Looks like the IAC is going to zero steps again. Don't know why it would do that on this log. Nothing else has changed. I don't know if i can close it much more than it is.

[joecar]

there's now too much physical air causing the PCM to drive IAC all the way down to zero (i.e. and now PCM can't reduce/control the amount of air)...

[statesman]

Latest log. Looks like the IAC is going to zero steps again. Don't know why it would do that on this log. Nothing else has changed. I don't know if i can close it much more than it is.

Your idle trims are very consistent now... which makes me think that your IAC valve has just lost its way. Try doing an IAC reset.

[joecar]

Good point.

[spy2520]

Hmm I'll give that a shot.