start...die...start...idle great

[tazgn]

I know this has probably been covered before, but I can't find them. I have the annoying car start then die after about 3 seconds. Then when I start it again it idles great. This is ONLY when I initially start the car in the morning. Does anyone have any experience with this and where should I concentrate on looking to fix the problem (which parameters)?? I really don't understand a lot of the afterstart vs revs stuff and revs to run mode. Even after reading all the help files I'm still a little confused on how that all works.

Thanks for any help.
Derrick

 

[Spooled]

I kinda had this same problem. Not sure if this will help but try this...go into the aft start enrichment vs number of engine revs (or something to that effect) and in the cold temps, lower the numbers until it starts the first time. I had to take mine WAY down. It seemed to help mine. It will start the after start enrichment sooner and help keep the car running. Try it...it can't hurt.

 

[bobc455]

Funny, I was thinking the opposite, and I have the same problem. Maybe I'll try that.

Is it an instant transition to the running parameters, or is it blended somehow (i.e. interpolated)? To me it seems instant, because it just dies instantly. How come it doesn't die the second time I try to start?

What is the relationship between "engine revs to run mode" and "after start decay rate vs. CTS"?

-Bob Cunningham
bobc@gnttype.org

 

[Spooled]

I think it's instant. This is my theory...when you start the engine that first time, it needs alot of fuel to keep it running. In the c-com manual, it says it needs a little time to "burn off" the cranking fuel and this time between the start and when it starts adding aft start fuel. I think the reason it keeps running the second time is b/c it actually gets a few more revolutions and this enables the after start enrichment. Your # of revolutions must be set just over what it normally reaches on that first start. Then on the second start, it hits that # and the aft start enrichment comes in and keep the motor running. Therefore, if this is correct, you need to lower the number of revolutions it takes to envoke the after start enrichment so it surpasses that # on the initial start and the aft start enrichment is added into keep the motor running. I hope that's understandable...and helpful. Engine revs to run mode just lets the computer know when it can stop using the cranking values and switch to the rest of the tables. That's usually set at 400 rpm i believe. Decay rate is how fast it takes out the afterstart enrichment. If the decay rate is high, it starts taking out aft start enrichment fast and vice versa. At least that's the way I understand it. I think the c-com manual suggests keeping the # of engine revs before aft start enrichment higher when it's cold but I just tried lowering them one day and it helped me. Give it a try and let us know how it works for you. Like I've said before, if i've learned one thing about tuning, it's GIVE IT WHAT IT WANTS!

 

[bobc455]

This morning I got it to start and keep running the first time.

The changes I made, with my (faulty?) logic in parenthesis:

- Increased starting IAC position (rev the engine a bit higher at startup)

- Changed "engine revs to run mode" from 12 to 25 (give the engine a bit more time to settle out before transitioning)

- Increased the after start enrichment by 30% (in case the engine was leaning out and dying).

Whatever it was, the combination of them all worked. Temp was 28 degrees out this morning- usually when it's this cold it's always stalled at least once. Maybe it was luck and it will take several times tomorrow...

-Bob Cunningham
bobc@gnttype.org

 

[bobc455]

Okay, after thinking about this until my head hurts, it seems that the "off to hot" sequence goes like this

1) ECU uses cranking PW from starting table.

2) When engine exceeds 400 RPM (or whatever), it instantly uses the after-start enrichment.

3) After the engine turns 12 times (or whatever is set in "engine revs to run mode"), it transitions to from after-start enrichment to warm-up enrichment (at the speed dictated in after-start decay vs. CTS).

4) The warm-up enrichment slowly transitions to zero as the engine gets hotter (provided the table is set that way).

Is that right?

-Bob Cunningham
bobc@gnttype.org

 

[Spooled]

THat's the way I take it as well, provided one little detail. I dont' think it "instantly uses after start enrichment after 400 rpm (or whatever). After that 400 rpm (or whatever) is reached, then it waits for the # of revolutions specified in the aft start revs vs. CTS, and THEN it applies the aft start enrichment. Then it decay's out....and so on. I believe the engine revs to run mode is the 400 we're talking about. But yes, that's how it works.

 

[Craig Smith]

Spooled got this one.

ECU cranks in cranking mode. When the engine fires and crosses the crank to run mode RPM **and** stays there for the number of revs specified in the Engine revs to run mode, off to run mode we go. Now that we are in run mode, it looks to the Number of Revs before After Start vs. CTS table. Once the appropriate number of revs have been detected, after start fuel is applied as per the After Start vs. CTS table and decayed out as per the After Start Decay vs. CTS table. Warmup enrichment is applied as soon as you go into run mode.

My old motorhome had the same problem and I never got it right. Every once in a great while it would stay running on the first try but for the most part it took two tries. I played with afterstart, cranking, VE, warmup, and anything else you can think of. Ran them up, down, sideways, nothing ever helped that piece of crap. It would hang with the 440/454 motorhomes in the hills though! (TPI 350)

 

[bobc455]

In an effort to keep things over-complicated:

Alright, but how much fuel does it use after it exceeds 400 RPM but before the 12 (engine revs to run mode) revolutions? In other words, what happens after the engine is running but the ECU isn't in run mode yet?

Once it hits run mode (after 12 revs), it sounds like we have the following sequence:

- We have the "base" (my word) PW as calculated from the A/F ratio table (per the VE table yada yada). In addition, we have add warm-up enrichment (but not after-start enrichment).

-Then after the engine has run for a while (the number of revs in the "Number of revs before after-start vs. cts" table), it immediately adds after-start enrichment. Now we have the "base" PW plus warmup enrichment plus afterstart enrichment.

- Then the afterstart immediately starts to decay away (according to the after-start decay vs. CTS table) linearly toward zero. (What is a step?)

-Now that the after start is decayed away, we're back to just the "base" PW plus warm-up enrichment.

- After warmup enrichment is all gone, the O2 sensor can start enriching or enleaning as appropriate. (Side note: seems like you can't have the O2 sensor active while you still have warmup enrichment, or the two will be fighting each other).

And we all know you were probably running 22# of boost on your 350...

-Bob Cunningham
bobc@gnttype.org

 

[Craig Smith]

Bob,

During the pulses above 400 RPM before run mode, it continues to run on the cranking fuel table.

Your understanding of operation once in run mode is correct.

The explanation of decay sounds worse than it is. The line in the graph sets the number of revs necessary to reduce the afterstart enrichment by 0.8% The higher you set this number, the longer the decay will take.

I'm not sure if warmup and closed loop fight or if the ECU knows not to do that. I suspect a fight. I'll hafta look into that one.

If these guys would just pay me what I'm REALLY worth I'd go get me a great big diesel pusher. THEN we'd see where 22# of boost would get me!

 

[bobc455]

This new learning amazes me. Explain again how sheep's bladders may be employed to prevent earthquakes.

So if my after-start enrichment is 20% and decay rate is 20 revs/step and I'm at 1000 RPM, the after start will decay from 20% to 19.2% after 20 revs, then to 18.4% after 20 more revs, then to 17.6% after 20 more revs, etc., and will be all gone after 25 seconds (500 revs).

Fascinating. (I guess the thing that confused me before was the difference between warmup and afterstart)

I think my problem is that I had too many revs before after-start enrichment- I was at like 170, probably should be at like 10... thanks for the help guys!

Derrick, since this is your thread, let us know if you can nail this down now. At the same time, I'll try to play with mine and see if I can get it to stay running.

-Bob Cunningham
bobc@gnttype.org

 

[ZBass28]

Sweet! This should help me with my similar problem that I experience with cold starts.

One other thing I have noticed with mine and cold starts. If I let the car sit for a month, I can go in there and fire it up and it will start, idle and run perfectly all on the first try. Any subsequent cold start on a regular basis after that will exhibit the crank, start, die instantly, crank again, start and stay running.

How in the world could not being started for a month have a "positive" effect on the initial start-up?

 

[tazgn]

Funny thing, After I posted this thread I went out and started the car up and ran fine the first attempt. Damn thing!!! First time in a month or more it did it. And it's been doing it still (with no changes in the program). I'm still going to fiddle with the afterstart and warmup enrichments as well to try and get it better. But, I figure since I'm posting this post, the car will now go back to it's old ways. Damn things more TROUBLE than the wife!!!!

Derrick