Choke - Initial Start Help

[srgould41]

Hi all,

I have been working on getting my initial cold start to smooth out. This only happens once a day at the first start. The engine surges and bounces off the stall saver for about 15 seconds then smooths out. I raised the stall saver enter/exit values by 100RPM which helps a little. My engine did NOT like 425 RPM.

I have a 7747 $42 ECU. I have been told it is probably lean and I should fatten up the idle area of the VE table. Not only did that not help, but then I was running very rich at warm idle. I only want to richen the initial 15 seconds of cold running. In other words the choke area.

I am leaning towards working on the choke settings.

I tried Open Loop - AFR vs. Temp. Lowered by 0.5. No help. I think this is the wrong idea anyway. I put it back.

Next I think I should try "Choke - Time Out AFR vs. Cool" increasing the -7c through 31c cells by 1.0.
Would this work? The comments say this is subtracted from AFR which would mean more lean.

Suggestions?

Thanks

Steve

[RobertISaar]

you may be targeting the right problem the wrong way....

it's possible you just need to get more air into the engine when it's that cold rather than feeding it more fuel(though both could be the solution as well).

[ony]

look in scalers and see what [engine start up rpms are]

[srgould41]

The engine does run well when I advance the throttle a little so the idea of needing more air could be valid. The question then becomes "how"?

Ony, I don't see any scalar for engine start up RPM. Can you tell me what scalar you are thinking about?

I do have one idea. There is a scalar "IAC - Pk to Run Delay Sec's". Mine is set to 2. I am thinking this means the IAC moves from 90 (my park position) to about 20 which is where I idle at when warm, over a 2 second period. This could maybe be set for 15 seconds so the IAC keeps the RPM's up over a longer period?

[RobertISaar]

there are probably a few different ways to get the IAC count up(or move the throttle-stop, should that be helpful), but i don't know enough about $42 to recommend much.

[lionelhutz]

I doubt the ECM will ramp the IAC steps. I would expect it to just stick at 90 steps for 15 seconds and then go to the IAC position that will give the correct idle rpm. Try it but you may find the engine races for 15 seconds if the IAC is left at 90 steps.

I don't fully understand your 425rpm comment. Is that the idle rpm you're calling for?

You could just step-up the idle rpm vs temp table in the lower temperature range.

You were correct that modifying the VE table was the wrong approach.

[joegreen]

Not sure if this is helpful but after i reset my iac valve i got a much better idle.

IAC reset/min idle speed- This sets the throttle plate on the throttle body to a specific rpm. I recommend about 500 rpm for most engines. Procedures- Go to sheet 7 of the pinout diagrams. At the top is the ALDL connector. You need to put a jumper between pins A and B of the connector. These are pins A9(wht/blk) and A12 (blk/wht) on the ECM. This puts the ECM into aldl mode. Turn the key on (not start) and the IAC should drive completely closed. You will normally hear a buzzing from the IAC. If you have the winaldl up and running on your laptop, you should see the IAC went from 145 to 0. Now unplug the IAC connector. turn the key off. Remove jumper. Start motor. If the idle is too low you may have to keep it running. On the front drivers side of the throttle body is the adjustment screw. It may be behind a silver plug. If so just use a nail or punch to poke it and remove it. Then use a #20 torx bit to adjust the idle speed to at least 100 rpm less then your warm idle speed. if 600 then set to 500 rpm. You are looking for the lowest consistant idle your motor will do. When set, turn off motor and reconnect the IAC. I try to keep the IAC count to at least 40 with the motor warm and idling.
This is a good time to verify the operation of the IAC. When the jumper is in and the key is on the IAC is driven closed. So while it is idling to set min rpm put a finger over the IAC port just above the IAC. There should be no air being sucked in and you should be able to see the pintle on the IAC.
When the IAC is connected and operating there should be a small amount of air being sucked in the port at idle and should increase as you apply some throttle.

[srgould41]

Sorry, 425 is the stall saver RPM. I idle at 675 warm. The engine cant get much lower without being at 0 steps.

I doubt the ECM will ramp the IAC steps. I would expect it to just stick at 90 steps for 15 seconds and then go to the IAC position that will give the correct idle rpm. Try it but you may find the engine races for 15 seconds if the IAC is left at 90 steps.

I don't fully understand your 425rpm comment. Is that the idle rpm you're calling for?

You could just step-up the idle rpm vs temp table in the lower temperature range.

You were correct that modifying the VE table was the wrong approach.

[ony]

the engine start up rpm is all most at the bottom of the scalers. all so I have seen weired spark tables for cold engine compensation. post your bin file with your next data log.

[srgould41]

I see it now. What exactly does it do? The comments are not that helpful. "ENG Start Up DRP Periods. Setting affects idle spark."

Mine is set to 561.

I changed the scalar "IAC - Pk to Run Delay Sec's" from 2 seconds to 10 seconds. I fired it up yesterday and it did not act as I predicted. The IAC closed down within a few seconds, not 10 seconds for sure. It seemed to help, but the engine had already been started once so I will test when I get home tonight.

I wonder if "IAC - Position vs. Temp" might work. The comments say it acts like a fast idle. The current values seem appropriate to achieve what I want, but I don't think they are being acted on, it seem like the steps are much lower than this table. I need to pay more attention to TunerPro when starting. With the computer being so slow I don't really get a good look at what is happening.

Joegreen, I have walked through the IAC reset procedure already. I believe it is good.

the engine start up rpm is all most at the bottom of the scalers. all so I have seen weired spark tables for cold engine compensation. post your bin file with your next data log.

[ony]

supposeable that is how fast it will run at first start up,i would set it 100 rpms above your warm idel and see what tunerpro says your timming is at as you are have the surge. did you apply the bpw hac to your bin?

[srgould41]

I did apply the BPW hack.

I'll look at my notes tonight and email my bins and notes to myself so I have then off my laptop. I made one change to test when i get home. If it doesn't work I will try the RPM setting. I'll post my results and bin tonight or tomorrow.

supposeable that is how fast it will run at first start up,i would set it 100 rpms above your warm idel and see what tunerpro says your timming is at as you are have the surge. did you apply the bpw hac to your bin?

[srgould41]

It looks like I might have solved it. I need to start the engine a couple more times to be certain.

This is what I did:
Choke - Time Out AFR vs.Cool- added 2 -7c through 31C cells

The original is on the left and new table on the right.

I did apply the BPW hack.

I'll look at my notes tonight and email my bins and notes to myself so I have then off my laptop. I made one change to test when i get home. If it doesn't work I will try the RPM setting. I'll post my results and bin tonight or tomorrow.

[EagleMark]

This is to add fuel when cold right?

Keep us up to date on changes!

[srgould41]

Mark, yes this is to add fuel when cold. The thought from others was that I was running too lean at cold start. I can really only test once a day since it only does this on first start. I would love to do it before heading to work, but my neighbors would complain about the racket at 4:30 am. Getting home at 6:30 the garage is already in the upper 90's. Not quite a "cold" start, but the engine would surge anyway. Last night I fired it once and it started correctly. I will try again tonight. This weekend I will start it in the morning at a more reasonable hour :) This winter might be a better time to verify that this really works.

I liked Ony's comment on the Engine Startup RPM scalar, but I have not altered the original value of 561. I don't know what this object would do or not do. I can tell you that the engine won't idle that low unless I have the dizzy bypass wire disconnected. Even then it's on the edge of a stall.