Cold Start Stall After Injector Swap

[BrodyO]

Hi All,

This past offseason I swapped my truck from Snake Eater Performance 1000's to SEP Pro Series 1000 (genuine Bosch). Overall I'm happy with how my speed density tuning has been going and the truck is within about 4% everywhere once warm other than a few areas but one of the issues I've had since is worse cold starting. The truck is running a flex fuel tune and I'm normally running pump E85 but did the same with the old injectors. The old injectors would fire the truck up in the middle of Winter no problem, now I'm having issues with a cold start on a 60F ambient cold start.

Generally the engine will stall at least once, sometimes twice. After it does fire and start running, I normally have to give it a minute before I shift into gear (increase load) or it will die again. After the cold start, it starts normally. My initial assumption is that it's something around either not having cranking/idle VE dialed back in, incorrect injector data inputted, or something to do with how I fail the MAF as opposed to before.

Cranking/Idle VE is difficult because my wideband resets and goes through it's heater cycle as soon as you start to crank so that data is missed during a cold start (are all widebands like this?).

As far as injector data, I halved the flow vs pressure and set it to the 400kpa setting across the board (same as my last injectors) as I have a boost referenced FPR. Because of this I doubled the stoich AFR. The offset vs volts for LS3 was a direct copy paste but my short pulse correction was not. Not only does HPT not allow you to put your exact numbers in here but the neither provided scale from SEP lines up with the columns in my calibration so these were interpolated. Maybe something there?

With the new injectors I also wanted to fix a historical issue I had where I was failing the MAF incorrectly which would lead to me having to start the engine multiple times after flashing a calibration until it tripped the code and started running right. That issue seems to be fixed now.

Looking at the two starts in the log file, I don't see a ton of difference between the first start where the engine stalled, and the second start when it stayed running. One of the main things I see is ignition timing difference between the two. It was running high teens, low 20's on the first start, second was low teens into single digits. LMK if anything else sticks out to you.


[/ATTACH]GM HPT 1000 PRO-SERIES (1).xlsx

[ns158sl]

Give it some more fuel vs IVT. What is with the 30% LTFT?

[hjtrbo]

And halve your ivt terms

[BrodyO]

Give it some more fuel vs IVT. What is with the 30% LTFT?

Enlighten me, I'm seeing 7.8 LTFT in basically every cell that was hit in this short log. Is my scanner set up incorrectly?

Is "IVT Gain Gas" the correct table to add fuel vs IVT? Will this table still work properly with E85 or is there an alcohol specific table?

[hjtrbo]

No it is not the table. The open loop tables to the left. You can also increase crank fuel in the area you have trouble with.

Double check your ve table too. 15 - 20% lean in that log. Would need to see a longer log to see if that comes down with temperature.

[BrodyO]

No it is not the table. The open loop tables to the left. You can also increase crank fuel in the area you have trouble with.

Double check your ve table too. 15 - 20% lean in that log. Would need to see a longer log to see if that comes down with temperature.

Here's a log from today with the same calibration and the IVT terms halved. It didn't stall after startup today but I still had a long/backfiring initial start. This should give you an idea on idle trims at temperature. I just reconfigured my MAP zones in this calibration so I can fine tune as I'm turning the boost up so there's some adjustment needed under boost.

[hjtrbo]

You need to be using fuel trims not your wideband for closed loop.

[hjtrbo]

I wouldn't be turning the boost up yet

[BrodyO]

You need to be using fuel trims not your wideband for closed loop.

I will have to post up the log I took on Thursday last week, with a calibration I had been running for a while. All cell from 0-4% LTFT. I have been tuning off the trims in closed loop. It looks like I might be doing it differently than you so please let me know how I can do it better.

Right now I will normally start my log 5-10 minutes into the drive. That way I'm up to temperature and my adaptions have had some time to kick in. I've also read about a ~20 minute period after flashing giving bad data, not sure if true. Right now I will take my LTFT table into my VE table and multiply by half, then blend the zones in the best I can. I know that using STFT or LTFT is a bit of a debate, LTFT offers an output with more data input but can cover up hardware issues. I do filter my LTFT table in the scanner based on throttle position to try and make sure I'm not in PE, I use my wideband data for those zones.

It looks like you're using LTFT+STFT, can you give me some insight there?

[hjtrbo]

Please add volumetric efficiency and volumetric efficiency airflow to the scanner.

LTFT + STFT is your total fuel correction. You don't have to wait for LTFT data to be learned by the ECM. After a flash where you made a fuelling change you must reset the LTFT using the scanner functions. Do not turn off the trims to log. Wideband is solely for PE.

15 mins after a flash is true. Log injector tip temp. Below about 55 deg you're good to go.

Use the channel 'fuel trim cell' for filtering, gives you the ability to sense o/l, dfco & c/l with that 1 channel.

You are doing something very wrong, we need to get to the bottom of it and set you straight.

[hjtrbo]

ECM 4040, 4041 set those to not enable the performance test.

This is your current VE table state.

[BrodyO]

ECM 4040, 4041 set those to not enable the performance test.

This is your current VE table state.

Ok guys I see what's going on here. So on my truck I trim solely off of bank 1. This was due to an issue where when I hooked my 02 sensors back up, they seemed to be fighting eachother (they are in the same, single down pipe, slightly different angle, about 6" apart). So if you take a look at my STFT+LTFT B1 only, it looks much better. Really good advice though with the addition of the two. I've got volumetric efficiency added and I'll do a cold start/data log tomorrow for you. Attached you can see the difference of combined vs B1 only for my trims. If you have advice on how to stop the two fighting eachother so I can turn them both on, I'd be open to that. Otherwise just the B1 seems to be working. Great advice on that filter.

[hjtrbo]

Ah huh, that is important info! I'm not familiar with turbo set-ups and the accepted O2 sensor placement / combination. I'm also not sure tune wise what is required to make sure the 2nd bank is disabled correctly. Hopefully someone else will jump in.

[blindsquirrel]

Typically, that'd be Injector Bank Select. All that does is tie an O2 to a group of 4 injectors.

[hjtrbo]

Typically, that'd be Injector Bank Select. All that does is tie an O2 to a group of 4 injectors.

See, you do know what I told you.

[BrodyO]

There ya go. Blind Squirrel was the original person that gave me the advice. I added 20% to IVT Gain Gas. Will record a cold start in the morning.