Need help with startup in SD

[irocbrninrubber]

The car is an 86 IROC with a 408. Whenever I set up the car do do VE tuning (SD mode), it struggles to start. I turns over really slow and then I have to "pedal it" to get it to start. Once is starts, I have to just give it a little throttle for about 5 seconds and then it idles and runs fine. I have attached the tune and the latest log of my VE tuning today. I tried to get a log of the startup, but because the car struggles to start, it disconnects from the scanner and wont record the log.

P.S. I have already added a bunch of air in the startup initial airflow table and no change.VE tuning after fuel pump VE tuning 5.hpt

[STR8BALLN]

What throttle body and IAC are you using?

[blindsquirrel]

Cranking VE table has been cut down a bunch from stock. Think about it, it will only ever use the cells from like 100-200 RPM and 90-100kPa MAP, you're at only 50% there. The slower the engine turns the more air can get in through the same opening (because longer time between events), cranking VE is usually very high (cylinders very well mostly filled even with the throttle closed). Gen 4's have that whole table just solid 100% everywhere and they start up just fine.

[04silverado6.0]

Im curious why earlier trucks had less cranking ve than the later trucks. I have copied from a 04 year truck and reduced from that table before.

[irocbrninrubber]

What throttle body and IAC are you using?

It is a fast 92mm

[irocbrninrubber]

Cranking VE table has been cut down a bunch from stock. Think about it, it will only ever use the cells from like 100-200 RPM and 90-100kPa MAP, you're at only 50% there. The slower the engine turns the more air can get in through the same opening (because longer time between events), cranking VE is usually very high (cylinders very well mostly filled even with the throttle closed). Gen 4's have that whole table just solid 100% everywhere and they start up just fine.

I forgot to mention that the PCM is from an 01 camaro. Regarding the cranking VE, I don't remember ever touching it. I will add to the cranking ve tomorrow and see if it improves. Ill report back on the outcome.

[blindsquirrel]

I compared against a stock 2002 Camaro with the same 12212156 OS, did I mis-read the Tune Details page? Is what it shows there not correct?

[irocbrninrubber]

You are right, I just compared against a 01 camaro with a manual and I have slightly higher VE numbers. I make small adjustments tomorrow and I will report back.

[abc]

I turns over really slow I tried to get a log of the startup, but because the car struggles to start, it disconnects from the scanner and wont record the log.

If it's cranking slow, solve that now. It's likely low on voltage if the OBD connector is kicking the scanner link off.

[blindsquirrel]

Main VE, or Cranking VE?

[ECM] 12360, 2002 Camaro M6 OS 12212156, shown is the amount yours is less than stock

screenshot.08-12-2024 21.18.35.png

[Alvin]

The car is an 86 IROC with a 408. Whenever I set up the car do do VE tuning (SD mode), it struggles to start. I turns over really slow and then I have to "pedal it" to get it to start. Once is starts, I have to just give it a little throttle for about 5 seconds and then it idles and runs fine. I have attached the tune and the latest log of my VE tuning today. I tried to get a log of the startup, but because the car struggles to start, it disconnects from the scanner and wont record the log.

P.S. I have already added a bunch of air in the startup initial airflow table and no change.VE tuning after fuel pump VE tuning 5.hpt

Your BRAF table is exceeding 40 g/sec. These have a "bug" where the IAC goes to fully closed when asking above 39.9g/sec. This is likely the cause.

Without seeing a log this is the first red flag I see.

[Alvin]

Cranking VE table has been cut down a bunch from stock. Think about it, it will only ever use the cells from like 100-200 RPM and 90-100kPa MAP, you're at only 50% there. The slower the engine turns the more air can get in through the same opening (because longer time between events), cranking VE is usually very high (cylinders very well mostly filled even with the throttle closed). Gen 4's have that whole table just solid 100% everywhere and they start up just fine.

I've always took the GEN 4 VE thing as 100% of the normal VE/VVE. Not 100% VE.

His cranking VE is more than his normal/primary VE. So if this was a comparison to GEN 4 stuff the GEN 4 table cranking VE would be >100%

Its normal practice for me to pull back cranking VE with a cam on GEN 3 and I use a tuned primary VE table to get the new cranking VE table.

[irocbrninrubber]

Your BRAF table is exceeding 40 g/sec. These have a "bug" where the IAC goes to fully closed when asking above 39.9g/sec. This is likely the cause.

Without seeing a log this is the first red flag I see.

Thanks. I changed it to 39.

[irocbrninrubber]

Thanks for all the help. I got it to start right up. I don't know if it was just one thing or a combination of things. Below is the list of things that I changed:
- Decreased BRAF to 39 g/sec
- Increased Cranking VE
- Added startup friction airflow initial

Now that I can get it to start, I will be connecting my wideband and fine tune the cranking VE and begin to reduce the startup friction airflow. Thanks again.

[04silverado6.0]

You can raise the startup airflow delay, start with 50 crankshaft revolutions.

[edcmat-l1]

If it's cranking slow and disconnecting from the scanner the battery is in bad shape. Need to charge, test, replace it. That's the very first thing you need to do.

Second, if you have a 92mm throttle body and your BRAF is maxed, you have other issues. Need to open the blade and do a TPS reset at a minimum.