DIY PROMDo It Yourself PROM chip burning help. No PROM begging. No PROMs for sale. No commercial exchange. Not a referral service.
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I'm going to talk about a generic engine, and the details may vary some, but this is some of the stuff to look at.
So what happens when you hit the key?.
The engine starts to crank, SLOWLY.
So slow, that there's a seperate fuel calculation for squirting fuel. There is a base PW (for cranking not what's used in the MAF or VE tables), and then a cranking rpm, and Distributor Reference pulse correction. In the GN code, where they use 30 PPH injectors the actual cranking pulse width can be like 4 msec.. So in a v8 with 19's your looking at like ~6msec.. Friends, that's alot of fuel.
OK, so not we got the engine cranking, and some fuel.
As the engine **starts**, and the RPM hits ~400, the ecm takes command of the timing, thru enabling the EST (in crank your just running of the initial timing, and ignition module). And the engine is starting to draw a vac.. Now in the MAF cars, the ecm can read the air flow very quickly, during this transistion, but in the MAP cars, it takes a .1 sec or so for the manifold to *pump* down. So the 400 RPM 100K/Pa *slot* has to be rather rich.
Just a something also to think about, in the SEFI cars, crank is batch fire, and run is SEFI, so while in crank you might see 4 msec, in first run after seeing a cam synch and 400 RPM you need alike 8 msec of fuel, to maintain about the same AFR.
Now once the engine catchs, the ecm looks at the cold run AFR correction, and Choke AFR correction. The Choke AFR is added in and then decays out rather quickly to help spin the engine to life. AND, AND to allow the IAC to decay down some.
Now, the Park / start IAC counts is EXTREMELY important. Changing the count alot, effects how fast the starter can spin the motor over. In really cold weather, the IAC plays a huge role in how fast the starter can first spin the engine over. While 20 RPM might not sound like much, but, when your talking a cranking speed of 200 RPM, that's 10%!. And if the motor is at 200 rather then 180, it's all the less time running on the EST.
So don't be surprised when you change injectors, that you might have to taylor things some. Seeing a hook at the end of the MAF or MAP tables at extreme lower end of things.
*Gentlemen Start Your Engines*.....
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Yeah, what he said. lol
People sometimes don't reliaze exactly what is going on when you go to start an engine. It's very complicated. Even at 200rpm that's still 3.3 revolutions a second and at such low engine speeds you will pull in a LOT of air so let's assume 5.5L of air on a 5.7L engine, that's over 15L of air ever second trying to go past your throttle blades. OPEN THE IAC and you'll start faster, or if you're like me and don't like the IAC, limit it to a low number and live with the fact that on really cold below freezing days you have to crack the throttle open with your foot . Hey, wow, I think I finally found a major limitation to the GM code for mild engines. Looks like it's time for us to hack the newest generation of OEM computers so we can screw around with more options .
Originally posted by 11sORbust Could you explain this process in greater detail?
Sorry, but not really.
Those several paragraphs took 50 chips, and about 10 hours on the ecm bench.
And the only reason that the bench was even helpful was that Lockers was able to show, The Choke AFR, and stay connected at 50 RPM, unlike may scanners that disconnect.
It's only when I was able to watch the PWs, IAC decay, and commanded Choke AFR correction, that it started to make sense.
Not to mention the spark added, and how it decays out.
Originally posted by Grumpy Those several paragraphs took 50 chips, and about 10 hours on the ecm bench.
You're not actually still burning individual changes to a chip and then testing are you? Thats so 1999! (I know, you're emulating too). =) Just kiddin' around.
This is *very* good info for me right now, as starting is something I plan to dig into very soon...
Now, the Park / start IAC counts is EXTREMELY important. Changing the count alot, effects how fast the starter can spin the motor over. In really cold weather, the IAC plays a huge role in how fast the starter can first spin the engine over. While 20 RPM might not sound like much, but, when your talking a cranking speed of 200 RPM, that's 10%!. And if the motor is at 200 rather then 180, it's all the less time running on the EST.
Seems to me that it MAY be useful to have a table that changes the IAC park based on Coolant temp.... Is this rational thinking?
Something else I'll have to look at when I finally get things together.
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Originally posted by JP84Z430HP Seems to me that it MAY be useful to have a table that changes the IAC park based on Coolant temp.... Is this rational thinking?
Something else I'll have to look at when I finally get things together.
Yes, having the IAC go to a table defined position vs coolant at key on is helpful. Several masks do this, others do not. Difficult but not impossible to add.
During the transition from crank to run a lot of things are happening. The SA is being blended from crank (initial) to the table SA value, the AFR is being changed from crank (either PW based or crank AFR based) to the table values (VE or MAF), at the same time the IAC is closing down. There is also startup (pseudo choke) SA and fuel added that is then decayed out.
On the whole of it, each piece needs to be balanced against the other. And at each possible startup temperature from -20 c through a hot 115c restart (heat soak).
Originally posted by Mangus You're not actually still burning individual changes to a chip and then testing are you? Thats so 1999! (I know, you're emulating too). =) Just kiddin' around.
This is *very* good info for me right now, as starting is something I plan to dig into very soon...
For many things I still do things one chip at a time.
Emulating while doing research can let you buzz right on by the answer, or let you draw a false conclusion.
Originally posted by Grumpy For many things I still do things one chip at a time.
Emulating while doing research can let you buzz right on by the answer, or let you draw a false conclusion.
Have you the chance to play with the "modified" bench? BW
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Yes, having the IAC go to a table defined position vs coolant at key on is helpful. Several masks do this, others do not. Difficult but not impossible to add.
Do you know off hand which? I was referring to $8d, and it doesn't look like it does. The other code I'm considering is $58.
Interesting stuff...
So, what would happen to a TBI vehicle in START (like a few I have been reading about) on which the IAC has been disabled by running it all the way down and setting the steps to zero? In cold weather, it seems like this might be a problem.
Originally posted by JPrevost Yeah, what he said. lol
People sometimes don't reliaze exactly what is going on when you go to start an engine. It's very complicated. Even at 200rpm that's still 3.3 revolutions a second and at such low engine speeds you will pull in a LOT of air so let's assume 5.5L of air on a 5.7L engine, that's over 15L of air ever second trying to go past your throttle blades. OPEN THE IAC and you'll start faster, or if you're like me and don't like the IAC, limit it to a low number and live with the fact that on really cold below freezing days you have to crack the throttle open with your foot . Hey, wow, I think I finally found a major limitation to the GM code for mild engines. Looks like it's time for us to hack the newest generation of OEM computers so we can screw around with more options .
Yeah, thats one thing ive always hated about wet flow systems, they never start as soon as it cranks. After its been sitting and all the gas has dissipated in the intake it takes some time for the fuel to make its way into the runners and into the cyls. All the while, the ice cold gas is jsut being flung around onto the walls and floor of the intake and not really doing anything untill the motor finally starts and pulls it all in. The only wet flow system Ive ever had that starts on the first turn is the snowblower with a side mounted carb. Push the button, and it starts right up.
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Originally posted by dimented24x7 Yeah, thats one thing ive always hated about wet flow systems, they never start as soon as it cranks. After its been sitting and all the gas has dissipated in the intake it takes some time for the fuel to make its way into the runners and into the cyls. All the while, the ice cold gas is jsut being flung around onto the walls and floor of the intake and not really doing anything untill the motor finally starts and pulls it all in. The only wet flow system Ive ever had that starts on the first turn is the snowblower with a side mounted carb. Push the button, and it starts right up.
I've gotten my car to start right up almost instantanly but I watched my oil pressure and it wasn't pretty. I'm back to a few extra cranks and no surge but again I'm looking at oil pressure and I think I want the surge back. The little surge seems to jump kick my oil pressure up but who knows if the extra revs are doing more metal to metal on the bearings?
Grumpy, I haven't looked closely at my startup with lockers because every time the engine starts I get a lot of bad packets. What rate are you running in the PIC? I'm still at ~15fps (57.6kbs).
Sounds like you need a HP oil pump . The stock one that came with my motor generates 40 some odd psi while cranking and up to 80 psi when cold and idleing. Thats the only thing I like about taht goodwrench motor is it has oil pressure at all times.
How did you get it to fire instantaniously when cold. When its been around 10-15 degrees out sometimes overnight here it takes a fixed amount of cranks regardless of how much or how little park or run counts I give the IAC. I can even press teh gas pedal and open the throttle and it wont start any faster. Once its warm, it fires as soon as I go to start it.
It's a PITB, but tinkering with the start stuff will get you an instant start.
As far as wet manifolds and TBI's, they'll start as fast/easy as a car'b engine, if not faster. With a carb you have to wait for the starter to run long enough to pump down the manifold to start drawing air across the idle transfer port to get down to the cylinders. with TBI, once the ecm sees a DRP, the injectors *can* start metering fuel.
Here's a data log of an engine cranking, and starting.
Baro is reading 94 K/Pa and you can see it start to pump down as the engine first cranks. Then when it *catches* you can see the EST line go live, as the engine goes from running on the module to EST control.
Originally posted by Grumpy It's a PITB, but tinkering with the start stuff will get you an instant start.
How fast can you get it on your tbi vehicle? It takes me around 3/4 - 1 seconds worth of cranking at moderate temps to complete a full cold start. Very cold temps <10 degrees take about 1.5 seconds. It would be nice to have it start instantly like the newer cars but I suppose its not necesarily a bad thing given it gives time for the oil pump to prime and start circulating oil.
Originally posted by dimented24x7 How fast can you get it on your tbi vehicle? It takes me around 3/4 - 1 seconds worth of cranking at moderate temps to complete a full cold start. Very cold temps <10 degrees take about 1.5 seconds. It would be nice to have it start instantly like the newer cars but I suppose its not necesarily a bad thing given it gives time for the oil pump to prime and start circulating oil.
I wouldn't think that a 1 second or less crank time would be much of anything to bother with. From what I've seen, many of the newer cars take longer than that to start (and I work on them everyday!) Maybe I should pay some more attention to see how long it actually takes them to start.
I miss how my ole LG4 started. Just "bump" the starter and it was running. That was a warm engine, and sometimes the 355 starts like that with the carb on it still, but cold it cranks forever (I think it's taking a long time for the electric pump to get the fuel to the carb).
I do look at a slightly longer COLD cranking time as not such a bad thing when you think of oil priming, etc.... A nice quick startt is what I like when warm though. This is one area I'll be spending some time on, I'm sure!
Originally posted by dimented24x7 How fast can you get it on your tbi vehicle? It takes me around 3/4 - 1 seconds worth of cranking at moderate temps to complete a full cold start. Very cold temps <10 degrees take about 1.5 seconds. It would be nice to have it start instantly like the newer cars but I suppose its not necesarily a bad thing given it gives time for the oil pump to prime and start circulating oil.
All you need to do is reclearance the engine, use low tension rings, some 5-10W oil and your there.
1.5 sec is too long?.
You probably can beat that, but do you really want too?.
No, no... its not too long. Jsut people saying that they can get the cars to fire as soon as they turn the key. I was jsut curious as to how it was done.
Originally posted by dimented24x7 No, no... its not too long. Jsut people saying that they can get the cars to fire as soon as they turn the key. I was jsut curious as to how it was done.
I doubt this happens to very many on a cold start. My engine starts very quick on a warm restart, but most aren't so good on a cold start.
Im perfectly happy now with how it starts. At very low temps teh idle could be a touch better for the first few seconds but other then that its a turn the key and go affair. From the way they where talking it sounded as if they could go out on a freezing cold day, bump the key to the start postition, and have it fire right up on an ice cold motor. Its not like when I first got the car. With the stock engine id have to use starting fluid to get it to fire or deal with a bunch of floods. No fun when its snowing and all I want is to get ina warm dry car instead of playing around with the engine trying to start it up.
On the modified table, removing the 0 and just moving everything up a notch, drastically reduces the crank time. But, this is port not TBI. While I do have much bigger injectors, that difference is accounted for in the crank PW figure.
On my truck with TBI, taking the Crank AFR down one or two increments helped. As well as dropping the IAC warm park.
Again, for FWIW, the refence pulse tables just continue from the last crank, unless you key off for like 5 secs, and then that resets the DRP count back to 0.
. Hey, wow, I think I finally found a major limitation to the GM code for mild engines. Looks like it's time for us to hack the newest generation of OEM computers so we can screw around with more options 
. 
. The stock one that came with my motor generates 40 some odd psi while cranking and up to 80 psi when cold and idleing. Thats the only thing I like about taht goodwrench motor is it has oil pressure at all times. 
