I've been struggling with hot starts and finall got it just about right by copying this table from the ARAP code. Now it starts when hot but it takes almost exactly 3 seconds. The only downside is if I turn the car off and tr to start it within around 20 seconds. Then it will not start. But i I wait more than 20 seconds it starts fine again. My questions:

1. How man cells are 3 seconds of crankning?
2. What would you adjust to cut the cranking time?
3. Why is it hard to make a restart within 20 seconds?

My car is a Firebird 1987, 305tpi, APYM bin

 

UPDATED

1. How man cells are 3 seconds of crankning?

I am going to attempt an answer, but you might want to search the threads. It's in there because the info I am giving you I got it from TGO (most likely @RBob )

When cranking, if ecm sees DRP, the required fuel Base Pulse Width (BPW) is calculated and immediately (asynchronously, without regard to a fixed schedule) fired in the Interrupt Service Routine (hereafter “6.25ms ISR”)
Fuel is allowed every 6th pass through the ISR (every 37.5ms)
There are 4 DRP per crank rotation
At 250 RPM (for example), there is 1 crank rotation every 240ms (DRP/(RPM*(4/60))*1000), so 16.6777 DRP/sec
So, it would take around 1.4sec to go through the table (24/16.6777) at 250 rpm cranking
At 250 RPM, there are around 38 injections during 1.4sec (160/6*1.4)

Soooo... in theory, 3 secs of cranking at 250rpm is 50 DRP, 80 injections. Once the table has maxed out at 24, the ecm uses the last digit in table, in your case is ZERO from 19-24.

2. What would you adjust to cut the cranking time?
If your problem is with engine hot, remember that modifying your posted table will also modify when engine cold. It's better to use the other table Crank INJ PW vs CT IMO and experience. You can fine tune cranking at different engine temp.

3. Why is it hard to make a restart within 20 seconds?
I suspect, the ecm has no reseted, could take over 12 seconds. Your first hot crank does not work because there is not enough fuel, the table reaches 19-24 (ZERO) and shuts off fuel. If you wait longer before second start, ecm will reset and go back to beginning of table. There is already fuel in cylinder so it takes just a bit more to start up engine.

I don't known where you got your ARAP table but it does not match what I have (see attched BIN). ARAP is for a 350 AT.

Seems like you need more fuel when hot.

Here's what I use on a stock 305 TPI with MAF, no CSI

If your car is 5 speed and stock, you might want to check this out:

https://www.thirdgen.org/forums/diy-...89-camaro.html

 

Valuable info! I started with the ARAP table but moved the valuas up in thw table to remove the first empty cells. But my mistake was to add the empty cells at the end instead. But now I will try your values. Probably just right.

I read all I could about ref pulses and time but some say like you while others say that 8 pulses is about a second.

Will program another chip tomorrow. After that I might play with crank fuel vs coolant instead.

 

Who ever says “8 pulses is about a second” is missing some information. It’s like saying I do about 300 miles per tank. Well, how big is the tank?

For 8 pulses to be a second, the crank as to turn twice in 1 second. So you would be cranking at 120 RPM, a bit low.

“8 pulses per second” sounds like a fixed value like 60secs in a minute. Again, DRP/sec is constantly varying with engine speed.

Remember, distributor goes 360 degrees for 720 degrees of crank. It takes 2 crank rotations to complete the engine cycle. Each crank rotation is 4 pulses.

 

I like to vary the multiplier vs ref pulse in order to create a bit of a repeating ramp pattern and then level it out after about 3 ramp cycles to avoid flooding during extended crank events: https://datazap.me/u/tequilaboy/cold...11-114-116-119

Note: this is data is based upon $32B, so the multiplier vs ref pulse table is a bit different as compared to $6E. 17 rows in increments of 8 reference pulses per row rather than individual pulses per row.

In the data above: Looking at the approximate duration of the crank pw steps, 8 pulses appear to be about 300 ms while cranking at around 150 rpm. Tough to tell with the slow sample rate.

It typically fires in about 1 second of cranking, but there always is some variation in the cranking time.

 

Thanks to you guys I've sorted out the rich start. It doesn't smell fuel now. I'm really happy!

Next step is to get it to start faster when hot. I've played around with Crank PW vs Ref pulses. Not very successful.

I've done som reading. Add air och remove fuel seems to be the correct adjustments. Are these the correct tables? Does the IAC table adjust air during cranking? My idea is to add 5 steps at F 176

 

Glad you did sort it out.

Remember, the IAC always parks at same position when engine is off. It's determined by 0x527 scalar in $6E mask. For stock L98, APYP & ARAP = 160, for stock LB9 APYS = 145, ATNX = 120.
This is the position it stays at during cranking. This the steps count you are going to see on your datastream before and during cranking. Modifying the table "Warm IAC Park..." won't do anything for cranking. You have to modify 0x527 to add/remove air.

From ​​​​​@RBob , 22 years ago:

747 ECM IAC Control
Robert Rauscher
10/14/2000, updated 12/4/00
Copyright 2000, Robert Rauscher, All Rights Reserved.
This is specific to the 747 ecm. However, the methods and madness applies to many of the GM ecm's. (Use at your own risk, no guarantee that any of this is correct.)

With the engine off, the IAC will be at the park position. This is the position used upon cranking the engine. Once the engine starts, the ecm will start to move the IAC to another position. This position is from a table lookup of steps vs. coolant. However, the IAC does not move to the new position immediately. If it did, the engine would react suddenly, possibly stalling. The difference between the original park steps, and the newly desired steps vs. coolant, are lag filtered. These filters control the rate at which the IAC moves.

 

Ok. I think I will play around with that value. It’s 145 now. Maybe try 160 and see what happens. The engine i slightly modifyed but I don’t know exactly what the previous owners did.

 

By doing so, you will increase air across the board, not only when engine hot.

 

I understand. But only when cranking, right?

 

Yes when cranking only

 

I think I got it to a point that I feels it’s ok. I reduced fuel a bit more than what felt comfortable by table crank pw vs coolant. But it worked… Maybe something mechanical makes it rich during crank but I haven’t find out what over the years. So this feels better than continue to throw parts at it. Again, thanks for the support

 

Glad it worked out!