3.8TransAM

730 $8d mask 91 tpi


Wonderful cold weather in chicago area= lots of cold starting and cold/open loop driveability issues (most solved amazingly)

Somewhere around 0 deg to -10 deg i get a very hard starting spot. It will fire almost instantly hit 11-1200 rpm then just stutter and stall out. Will not refire unless i push the gas down and when it does fire runs incredibly rough for 15-20 seconds then calms down and all is good. This is only happening at one point and i believe the wind has something to do with it(colder temp, maybe icing tb(sholdnt but....))...

Anyone have some suggestions for me? I have serioulsy played with the startup SA, startup Fuel , open loop fuel, and the SA vs. coolant temp tables and have it starting instantly in almost any weather and only have some issues driveability wise when subzero at this point.

Trying to get mine completely worked out and starting correctly at all points before i share what i have found in regards to open loop starting and driveability...

thanks as always
Jeremy

87_TA

Maybe check TB adjustment / IAC Counts.
If not maybe add some timing for startup advance.
Then hit the cold start tables.

Grumpy

At really cold temps., gasoline gets really hard to light. If you look at the IAC park positions, you can see how they ramp up really fast at the lower temps, and often so does the first run fueling. You might try bringing down the IAC counts a little, and see if that helps or worsens things, just try 5 less and see if thta helps.

It was just a few years ago, that GM was able to get a first crank start and run routine for -20dF.

BTW, there's an SAE paper out, showing how waxy in appearance the injector spray is with cold fuel. Ask to see it next time by, interesting.

dankhound

You might be dumping too much fuel on startup. Cause flooring it while starting adds no fuel.

jeepguy553

Doesn't this put the ECM in clear flood mode? I tried to tell my sis-in-law this, but she refuses to believe anything a white man says. She will FLOOR her 5.7L, crank on it until it either bites or kills the battery, then cuss when her engine runs like crap. ???? WTF ????

dankhound

Yep its called clear flood mode and the injectors wont fire.

Morley

Your IAC may be freezing up atthose temps. May want to take it out and give it a good cleaning and let it dry overnight indoors.

Grumpy

Berfore stating that depressing the gas adds no fuel or that he's in clear flood mode.

You need to look at the TPS vs Crank settings.

There is/are some cals where opening the throttle some does add fuel, and there is usually just a range of TPS where clear flood applies.

And clear flood may be a 20:1 AFR, and the injectors do fire.

And this all aint to say that it can't be something mechanical.

3.8TransAM

Not in clear flood mode said i pushed the gas down, but not too the floor :-) or very far down

dropped alot of iac counts way down trying to get it out of the loop as much as possible.........may investigate that and give it a shot, at least add some counts back in in the affected temp range.

car does not reek of fuel when it does this, just kind of sputters and dies, crack the gas a little bit and refire and it runs rough and then clears up

definitely affected by the wind , almost identical conditions at home in driveway overnite, except for the direction of the car. Nose is pointing west instead of east(home)

Just trying to kill all the little things that annoy me :-) makes me feel like I've accomplished something
thanks for the input, anymore?
Jeremy

Grumpy

You took park IAC counts out?.
While the start up flair is somewhat annoying at the lower temps, it's hard if not impossible to get rid of completely.

Just park the car in the *right* direction, <G>.

3.8TransAM

Ive hacked about every table that i can think of relating to starting almost from one extrem straight thru to the other :-) Figured out how to relate most of them to each other now too... lol

but yes , am loading my other laptop and checking that out when i get home later........... more thinking on the flair got me to thinking about park counts and colder temps. that is my next logical place to start and restore the colder temp park counts back to stock... may be why it likes to start when i depress the gas slightly ............. stuff makes a lot more sense when other people chime in their 2 cents worth :-) and then u ahve time ti sit back and think about it
thanks
Jeremy

Morley

When you press tha gas part way you are puting the ECM into "fuel enrichment" mode, this adds a considerable amount of fuel (will usually flood the engine) When you press it all the way down it goes into "clear flood" mode, this supposedly shuts off the injectors for the duration of the cranking.
If you are having to open the throttle to get it started and it runs rough for a while after that, it may be that what you are needing is the extra air flow from partially opened blades but the rough running may be excessive gas from enrichment making it overly rich for a few seconds.
I would definately look into IAC counts and again look into the possibility that the IAC motor is freezing up.

87_TA

I would not totaly rule out Timing either. EI: cold start tables and coolant correction tables.
If you have a heated 02 - heat it up first then watch MV. when started. (Not sure if that will work or not) initial cold air charge may cool it back off.

3.8TransAM

have my laptop at work to play with iac counts vs. coolant and park counts as well compare them to a stock file and move them back if needed . i was basically thinking alonmg the lines of what morley said cracking the blades let in xtra air but extra fuel as well till it cleaered itself up

should no more alte t-nite t'row am
thanks
Jeremy

3.8TransAM

reset the lower temp, below 20deg C back to stock for the idle step counts and the warm iac park position :-)

hopefully this cures the starting blues for me :-)
should know late t-nite or early am what the results are
(at work so no chip or romulator)
thanks
Jeremy

TRAXION

BTW - I have the same problem on my car and am still trying to rectify it. I changed both my idle speed timeout steps and the warm park position back to stock. I also changed my idle speed table in order to bump it up for the lower coolant temps in order to be in line with the general global increase of that table due to my lumpy cam. Still no success. These changes made things better. The car fired right up ... but then stumbled and died. I immediately started the car again and it fired up ... stumbled but cought and kept running solidly. If I crack the gas slightly when starting the car then it won't stumble and die.

I need to track the startup routines in the hac to figure out what is happening. There's either not enough air or not enough fuel on initial cold start. Next time I'll have the wideband hooked up and have Datamaster running in order to try to track down the problem.

Tim

Grumpy

Then, I'd try taking adding start up timing.
My hac shows a straight 5d all the way thru the temp corrections, on the 749 I'm running I go up to 9d at the lower temps.

;--------------------------------------------------
; START UP ENRICH vs COOLANT
; *** CHOKE ***
; TBL = 2.56 * %CHG
;--------------------------------------------------
ORG $0431 ;
; %CHG Deg c
;----------------------------------
L8431 FCB 243 ; 94.9 -40.0
L8432 FCB 192 ; 75.0 -28.0
L8433 FCB 154 ; 60.2 -16.0
L8434 FCB 154 ; 60.2 -4.0
L8435 FCB 128 ; 50.0 8.0
L8436 FCB 64 ; 25.0 20.0

;--------------------------------------------------
; START UP ENRICHMENT DECAY DECAY AMOUNT vs COOLANT
; TBL = 6.5536 * %CHG
;--------------------------------------------------
ORG $044F ;
; %CHG Deg c
;------------------------------
L844F FCB 255 ; 38.9 -40
L8450 FCB 229 ; 34.9 -28
L8451 FCB 82 ; 12.5 -16
L8452 FCB 82 ; 12.5 -4
L8453 FCB 66 ; 10.1 8
L8454 FCB 118 ; 18.0 20
L8455 FCB 118 ; 18.0 32
L8456 FCB 66 ; 10.1 44
L8457 FCB 66 ; 10.1 56
L8458 FCB 66 ; 10.1 68
L8459 FCB 66 ; 10.1 80
L845A FCB 164 ; 25.0 92
L845B FCB 164 ; 25.0 104
L845C FCB 164 ; 25.0 116

;--------------------------------------------------
; OPEN LOOP AIR/FUEL PCT CHANGE vs COOLANT
; TBL = \(PCT CHG * 2.56\) * SCALAR
;--------------------------------------------------
ORG $045D ;
;
L845D: FCB 221 ; SCALAR,
; ARG = 256 - VALUE, \(35d\)
; %CHG Deg c
;----------------------------------
L845E FCB 242 ; 94.5 -40
L845F FCB 153 ; 59.8 -28
L8460 FCB 76 ; 29.7 -16
L8461 FCB 50 ; 19.5 -4
L8462 FCB 38 ; 14.8 8
L8463 FCB 25 ; 9.8 20
L8464 FCB 25 ; 9.8 32
L8465 FCB 25 ; 9.8 44
L8466 FCB 25 ; 9.8 56
L8467 FCB 25 ; 9.8 68
L8468 FCB 25 ; 9.8 80
L8469 FCB 25 ; 9.8 92
L846A FCB 25 ; 9.8 104


Looks like there's alot stuff that knees over at certain low temps..
Also a couple oddities.

87_TA

TRAXION

Thanks for the heads up Bruce. But - you know me - just call me "Mr. TIMing". I play around with the timing a lot and the timing hasn't had much of an affect on this problem. I'm fairly sure that it is a fueling adjustment based on coolant temp. I just need to go to some extremes at -4d C and 8d C. My main point that I am currently playing with is the Start up enrichment vs. Coolant temperature. Let me explain my reasoning so far ... and, if you have the chance, maybe you can comment on my logic?

My cam is much much LESS volumetrically efficient than the stock cam. In fact, my VE at idle is HALF of the stock VE at idle. Well - my startup enrichment is currently the same. 100% stock. I don't seem to have the problem at warmer coolant temps. My main problem is when temps approach 8 degrees C. Well - haha - the stock AUJP file has a HUGE change between the 20 degree point and the 8 degree point. 20 degrees C has a 25% change to the AFR. 8 degrees C changes this value to 50%! That is a huge difference and a lot of extra fuel.

In short, I think the problem is twofold:
1) My car needs less startup enrichment because my cam is only 50% as volumetrically efficient as a stock cam.
2) The stock startup enrichment tables are very aggressive when going from 20d C to 8d C.

I'm going to startup the car with the wideband attached and try to see if I can determine if it is dumping way too much fuel into the chambers on startup.

Tim

Grumpy

Might look at what the Voltage is during crank. also.....

TRAXION

Will do. But, no comment on my logic and thoughts?

Tim

87_TA

Is it?
I just looked at my VE vs. stock and @ 900 RPM / 60 KPA my value is 59%. (where my car idles)

Stock VE @ 900 RPM / 30 KPA is 55%. (where a stock cammed acr would be @ same rpm) (Guessing on thet map value) but I am sure yo see my point.

So basically you are using same amount of fuel you just shfted VE because of vacuum.
Which (if this makes sense) you still pull same amount of air just less vacuum, same volume with less negative pressure.
Hence the reason guys with large cams need to open Throttle body blades at idle - to allow same amount of air.
To back that up - have you ever put your hand behind your cars exhaust at idle? pushing out a heck of alot more air than stock.

But I am sure cranking vacuum still plays a role even though inj. are right at port.

If it helps at all - My cranking tables are 100% stock and car start instantly (as a matter of fact too fast sometime I think for a car with a gear reduction starter)
The coldest its stayed outside was close to 5* F / - 15 c

The car does omit a pretty rich smell on initial fire in the cold, Granted I am using a 406 pulling more vacuum than you, also my initial timing is set @ 20*.
Maybe try reducing the Problem area by 25% the difference in size of our engines..
If you would like me to take initial back to 6 and try I will.
Hope some of that helped.

TRAXION

Good point concerning comparing my idle VE to the actual idle region of the AUJP. I didn't do that. However, I'm still close to what I originally said. My VE at idle 70kPa / 900RPMs is 35%. Stock VE is 55% ... still a fairly large difference. I'll run some testing with the widband and such and see what I get. I really think it is related to fuel ... but, we'll see.

Thanks for the info!

EDIT: Just a point of note that my car fires right up on a cold day. It's just that it stutters and dies immediately. It's amazing that it fires up as quick as it does ... especially since I just tried it yesterday after letting it sit for almost 2 months!

Tim

87_TA

Hmm, Possible its the lower VE table?? IE: 400 - 700 RPM ,When car just starts to pick up and is refencing those areas ...
Hopefully the WB will tell the story..

11sORbust

You might just need to raise the cold idle speed. Is the engine stock? I had the same exact problem. I just needed to raise my cold idle speed ALOT.

TRAXION

Tim

11sORbust

what did you bump it to? My fat cam needed ALOT higher cold idle speed.

Another idea is the "open loop change to fuel air vs map". Since my car idles in the 65-75kpa range that table seemed to richen me up....

Grumpy

Well, I think I know more of what you mean.
We had a low overnight of in the single digits.

The truck's always been a first twist start, until this morning, and it acted just like Jeremy's. An instant run of like 20 engine revolutions, a stall, and then on restart ran fine.

I think it was that with the ice cold engine the cranking voltage was seen as extremely low for a moment, and the look up for crank vs V was extreme enough that when it first started, it ran just long enough to flood out, and then with that little extra fuel the next crank cycle's voltage reading was high enough to prevent the excesive rich start.

Least that what it felt like, so I'm gonna try changing a few things to see if I can clear it up.

RBob

iTrader: (1)

There is something else that can also happen: if the battery voltage drops low enough the ECM will shut down and the RFD takes over. I've seen this with the '747 TBI 305 the past week or so whenever the temperature dropped below 0°C.

RBob.

87_TA

Well you can test that easily..
Hook up to another vehicle when trying to start and see if that does it.

3.8TransAM

yeah! Im not the only one , thanks bruce :-) lol

All fueling, open and startup are as stock . Ive slightly increased the park counts at low temps(+5 or 10) and have added a large amount to my startup SA to see iff that will change anything. When cold this car has always appreciated any timing sent its way and I have never touched the startup SA.

Chip is on the seat in the car and im going to try it directly after work(burn and run in am lol)
LAter
Jeremy

Grumpy

Dunno if it's all fixed by my cold start is alot better.
I couldn't fine the inj vs voltage table just off hand, so got my notes out.

Got looking at what I'd said about when first starting the engine how it takes a .1 sec or so to pump down the vac in the manifold, and got looking at the VE and spark tables.

Then looked at the IAC park positions.

The IAC counts jumped from 90 to 145 at -4, and then stay at that number for the remainder of the table.

So I dropped the -4, 145 count to 125, and then the next entry to 135.

I then took 2d of timing out of the cold start spark adder.
Added 2d to the 70-100 K/Pa at 400 and 800 RPM levels.
Added 3% more fuel in the VE Table in the 70-100 K/Pa range.
Took out .2 in the cold run AFR table.

After 6 hours in 12dF temps since last run, it was almost scarey how fast it lite. Will know more tomorrow, am, but none the less at 12d this is the best it's been.

On the 8D code
when you tickle the gas during crank you're probably going to the main spark table instead of the throttle closed, you might look at the difference in timing at those two spots, and if there is much difference lean toward the main spark settings.

Just what works for me.

Grumpy

While it was almost balmy with a wake-up temp of 12dF this morning, I like the new extreme cold start-up settings. The engine cranked just slightly longer, but started with less rpm flaring, which I really liked.
So I'm dropping the IAC park posistion a little more, and leaning out the cold enrichment slightly more.

Grumpy

My final numbers.
Notice no large steps in values.
I'm not sure what the GM's strategy was, maybe that on the older cars with weaker batteries, it'd be better to have the engine do a deliberate no start on first crank to get the oil moving, and then with the IAC well opened and the fuel from the no start, have the engine *race* to life. Mine actually starts fairly quick with the lower IAC and has no rpm flare. Just starts and runs at about 900 RPM even this morning at 9dF.

Start-up Spark Advance
11.6
10.9
10.5
9.8
6.7
6.7
4.9
4.9
4.9

Start-up AFR
9.5
11.0
11.7
12.0
12.1
12.2
12.3
12.4
12.5
12.6
13.0
13.0
13.0
13.0
13.0
13.0
13.0

IAC park steps
135 was 145
120 was 145
110 was 145
100 was 145
90
75
60
50
35
20
20
20
20
20
20
20
20

HTH

3.8TransAM

took everything back to stock AUJP settings on all fueling for open loop and startup. Slighlty increased my neg C park positions(+5)(IAC) and made the majority of my changes to the start up spark table, actually made quite an increase there. Tryed to keep the same relationship to stock (14 d difference(stock) to my hotcam and 25-26d at the same point).

so far has worked well in 2 below 10 deg F cold starts and slight flair up to maybe 12-1300 rpm and then settles to 1100 or so(set at 1100).
Later
Jeremy

JPrevost

My battery is getting old and having a hard time cranking at these low Ohio temps.
Still, this was the extream today and with 4 inchs of snow on the car it took only a couple seconds to start to life and no flair. It's all about limiting that darn IAC . It's a love hate relationship, most of the time it's hate until it saves my life. That time when the car seemed fine but was way lean, then it warmed up and almost died.... thanks IAC .
Hey Bruce, you should have a cold pow wow. This way we could all trade tricks and tips on how to get a car to run well at such low temps.

Grumpy

LOL
Have a cold start contest. Use a stop watch off the crank posistion to see who can get the fastest cold start......

Maybe a TBI, vs TPI contest?.

<G>

RBob

iTrader: (1)

This sounds like a fun contest. Is burning charcoal under the oil pan allowed? Or is that a cheat ;(

RBob.

RBob

iTrader: (1)

My first vision of this was bunch of folks out in front of Grumpy's huddling around a 55 gal drum and throwing in whatever will burn. "Here, I just striped the carpet and underlay out for less weight, it'll provide some heat. . ."

Then, one-by-one, someone goes out to crank their engine for the time-to-start contest. But, the stop watches aren't working. It appears that the seconds hand are frozen to the dial. As someone strips the tail light wiring from their car and throws it into the 55-gal drum of heat.

Wow, I hope winter ends soon. . .

RBob.

P.S. Forgive us Trax as we are under the stress of no clear roads and weather bearly suitable of polar bears (oooh, bad pun).

JPrevost

lol, I'm stuck here at C.A.R. until the roads get plowed. Columbus is the worst city I've been too when it comes to clearing icy roads. I'd like to see how many accident reports get filled tonight alone .
If later tonight my car doesn't start then so be it. I just hope when I get back to my appartment that the poor kid with a Honda got his car towed. He had left a note on my hood asking me to call him when I move so he could get a tow truck out to pull his car in to get fixed. I guess those Honda's just can't hack the winter. It was funny because he was standing there this morning while my camaro fired right up and drove off with a rumble .

11sORbust

I think I would win the contest. My 406 HSR starts up within the first rotation. It has only gotten to around 10*f in stl this winter

On a side note, I'm thinking about increasing the crank time....maybe work to kind of pre-lube the engine...

3.8TransAM

Dont hold your breath 11'sorbust, Since i raised my startup SA and the rest to stock/near stock im crnaking and firing on the first rotation as well....(4 times under 10d F and fires right up)

20 car lengths and fire, duel to the death
LAter
Jeremy

11sORbust

Maybe we can meet half way between stl and chi-town for the contest,lol. Anywho, nice to see you have fixed the problem!

3.8TransAM

lol

I hate the IAC grrrrrrrrrrrrrrrrrrrrrrrr

car was starting at 5f and up....

droppped to near zero and whammo, same thing again lol

should be fixed and finalized now spent 1hr in the garage freezing my beeheegies off resetting the IAC using Diacom :-)

It just does not like being set the "factory" way ... cheated and got the step count that i wanted and then reset it to see if it measured up..... hot in gear I'm at 13 counts and with fans on etc. im at 18 counts...

I believe(first mistake) this is the final chapter in the sage(we shall see)

LAter and thanks
Jeremy

Morley

Seems really odd that everyone is having such problems getting their cars to start when cold. When I bought mine I was stationed at Grand Forks AFB, ND, I never got the block heater installed (I knew it was only going to see 1 winter up there) and it always started up on the first flick of the ignition, even when the temps were -25 F and lower.

TRAXION

Stock for stock my IROC always started up when cold. It's the freaking huge cam with tons of overlap that is screwing me. If I could just get a solid hour or two with my car I could fix it. But, my IROC across town in a borrowed garage until I get my garage built in the spring.

Tim

Grumpy

It would be interesting to compare the fuel sold there to what's around here. I'd bet ND in temps like that gets a full-on Artic brew.

3.8TransAM

grrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr

Did it this morning think it was less than 5 deg F out and the car sat nearly 8 hrs...........just cheated at work today and barely cracked the throttle when i started it and it lit and went just fine .........


Thinking about possibly taking some park steps out at lower temps? My TB blades have been opened quite a bit over stock and im wondering if its too much air incoming to match the fuel?

Opinions and suggestions please?(that means u bruce lol)

Trying one thing at a time to eliminate it..............starts on first turn of the key in all other weather unless its been sitting for days then it might crank over twice and fire
thanks
Jeremy

11sORbust

I'm not bruce but how old is your IAC It sounds like you just need to open the throttle blades and/or raise the cold idle speed more. I know this sounds like a dumb post but sometimes it's something simple. My 406 did that exact thing when I first started it after cam/intake swap. I didn't have to change much to fix the problem. Just trying to help...

Grumpy

Does the closed throttle spark, match the main spark table?.
And at 0 and 400 RPM read about 10d, at 100 K/Pa?.

BTW, the truck will take on all comers now <G>
3dF overnight, and 12 hours sitting fired off really quick, idled at about 875 for 2-3 secs, and then to the proper commanded 900 rpm.. EVEN, Doc, was impressed.