Got that L31 stuffed into my 91 Z28 w/ an HSR. It started! And ran! Yay! Running the L31 cam for now. I set the timing dead on the notch on the plastic cover and reconnected the EST for now. I have no idea where it SHOULD be for this setup. The L31 comes with that plastic timing cover with the one timing notch. So I used it, LOL. A little advice as to how far out from it, if at all, would be awesome. And please specify clockwise/counter clockwise. All the fumes in the garage right now are making me sleepy...... zzzzzz. TIA!

 

Setting the timing is ROCKET SCIENCE. So, prepare for some SUPER DIFFICULT stuff here.

Put your timing light in the drawer and fuhgeddaboutit. Loosen the bolt. Turn the dist a little. (well, maybe, alot) Yes you should turn it clockwise or counterclockwise although I'd suggest counter based on your description of where it is now. Tighten the bolt. Drive the car. Do you feel like it's better, or worse? "Better" would include some combination of snappier throttle response, more power, better gas mileage, less pinging, runs cooler, starts easier; worse would be the opposite of some combination of those things.

OK, here's the hard part: if it got better, do it some more. If it's worse, turn it back. If it's ALOT better or worse, turn it ALOT in the appropriate direction.

Note the precise and intellectual wording here: ALOT. Note also that the opposite of that is, A LITTLE.

Now comes the rocket science part: keep doing it until it's as good as you can get it.

What you're doing is, letting THE ENGINE tell YOU where THE ENGINE wants the timing to be, instead of YOU telling THE ENGINE where YOU think it should be. As I am fond of doing, I will paraphrase one of The Great Ones in a completely unrelated field: "If it RUNS good, it IS good".

See I told you it was really complicated, right??

Now, the REALLY complicated part, which only TRUE rocket scientists can understand fully: Take your timing light out of the drawer, see where the timing now is, and either that write down or make a mark so that the next time some moron thinks he can make it better by setting it somewhere else, you can put it back easily.

Next of course, some one of the sheeple is going to come on here and bleat something about "the book" and "specs" and "but... but.... {fill in excuses here about "the factory" this and "you can't just" that} and other such drivel. Feel free to nod politely, thank them sincerely and kindly for their concern and willingness to help, and go on about your business as if they had never existed.

 

I like it :-)

 

I agree!! I used to wrench for a dirt street stock, and that was the exact way we set timing. Can't argue with the car!

 

Soooooooo just set the initial time as I would set idle timing on any older carbed car? Easy enough. Used to time my old Merc with a cup of water... set it on the air cleaner and time for minimum rippling. Worked well.

I was under the apparently erroneous assumption that initial timing on a TPI was supposed to be 0, and that after plugging the EST back in, the PCM would take over and adjust idle timing etc. Trouble was I didn't know what degree the L31 notch was, 0 or 8 or what.

This, I can do. :-)

 

TPI with 122730 ecm timing is set at 6* with est unplugged to coincide with the base setting programmed in the ECM.

 

sofa, id love to hear you about 8 beers in .itd be fun!!!

 

If was funny, but not exactly correct in that the timing needs to match the base timing set in the programming or the spark mapping will be wrong. This is not a carb. engine so timing is crucial.

 

See what I mean about the sheeple?

THE ENGINE is a block of cast iron. It does not care about whether it has a carb or whatever else feeding it fuel. It has no eyes, and cannot tell how the fuel got mixed with the air. Neither does the fuel. All it does is burn. It instantly forgets how it got delivered THE INSTANT it mixes with the air, and it does not care how the determination of spark timing was made, either. All it cares, is that the spark occurs at the right time, as determined by when THE ENGINE ITSELF is happiest with it. By doing as described above, you will end up setting the spark timing so that THE ENGINE is happiest.

THe ECM does not "control" the timing, as such, if what is meant by "control", is a feedback loop (i.e. it has a "target" and it varies the timing looking for some sensor input somewhere to reach some correct value, like EFI does for fuel). It has not the vaguest clue when the pulse that it gets from the dist is occurring in relation to the engine's mechanical motion, and NO WAY WHATSOEVER of finding that out, or of finding out when the spark itself occurs. All it knows is, it gets an input pulse; based on how long it's been since the last such pulse (i.e. the RPM), throttle position, vacuum (MAP), air flow if so equipped (MAF), coolant temp, air temp, and so on, it waits a certain length of time, then outputs a pulse to the dist. The only "feedback" it has on timing, is the knock sensor; and all that does is, if it hears a knock, it BRUTALLY YANKS timing back out. Which will CERTAINLY be reflected in the "better" description given above, since all the sudden THE ENGINE will no longer be as happy because the timing will be WAY too late, so it will make FAR LESS power and lose its nice snappy response and all those other "good" things will go away; but at least it won't knock any more.

The factory's timing table as stored in the ECM is appropriate to a STOCK engine, and IS NOT appropriate to a MODIFIED one, any more than the timing curve in a STOCK mechanical dist is appropriate to a MODIFIED engine. If the entire timing curve needs to be modified, then it's time to re-write the lookup table... commonly referred to as "burning a chip", or in the case of aftermarket control systems, you may have control over it with a laptop or similar. In the case of an altered chip, you would set the timing to some convenient point which could be the same as the factory's choice but doesn't have to be, then program those values in the table for how long it waits before sending the spark pulse, and in writing your table, take into account the location you have the mechanical timing set, which is TOTALLY ARBITRARY except that it obviously has to occur BEFORE the output pulse. That's why in systems like FAST or the like, especially if you're using a crank trigger, one of the settings you have to give it before it will even run AT ALL, is how many degrees before TDC the crank sensor is mounted.

But, if you're NOT burning a chip or running one of those more flexible control systems, THE ONLY handle available to work on it with, is to twiddle the dist body. Like a factory mech dist, that's pretty crude, and will by no means "optimize" the timing curve for all conditions; but it's 100% certain, it will be AHELLUVALOT BETTER THAN just genuflecting before "the book" and setting it to the "stock" spec just because "the book says so".

 

I 'twiddled' my dizzy, and it seems to like about 12* BTDC. Reconnecting the EST and restarting, and giving it some throttle... it seems to love it. Haven't driven it yet, I have a coolant drip that's driving me crazy... I think it's the WP, a brand new one at that.

Looks like it's off to the store to get another.

 

I cant agree anymore with sofa every car/truck is different i do all my timing by ear and feel.

 

What I 'm saying is, if you set initial timing at anything other than what the base setting says in the ECM then you add or take it away across the entire spark map. Say you set initial timing at 12 degrees instead of 6 that means you add 6* across the whole spark map at all rpms. OK at idle but will cause serious problems at higher rpms. The ECM does control the spark advance at all rpms and MAP.

 

Yes, it does do that, sort of; it replicates the functions formerly performed by the mech and vac adv in mech dists. And I would add, just about as crudely: it has not the vaguest clue what the "timing" (relationshiup of spark to crank position) actually IS; all it does, is wait some # of microseconds after it received the trigger pulse from the dist, and then outputs a spark pulse to the coil driver. The # of microseconds comes from a lookup table. Since it has no knowledge of crank position, it doesn't, and can't possibly, have the capability of working with "degrees"; only, microseconds.

It does NOT however, "control" the timing in the same sense as it "controls" the fuel, where it has means to sense whether there's too much or too little fuel in the mixture. It has no way whatsoever of telling that the spark is occurring too early or too late, except for the knock sensor; and when it sees that, its response is basically to yank SO MUCH timing out that by the "better/worse" method, it would become IMMEDIATELY obvious that the result would be "worse".

Therefore the simple fact that the ECM happens to have some degree of control over spark timing, DOES NOT in any manner way shape or form make the "better/worse" method any less valid. And yes you're exactly right, just like with a mech dist, if you twiddle the dist body, you add or subtract timing under ALL conditions. Again, doesn't make the method at hand any less valid with electronic control than with mech control. The purpose remains, GIVE THE ENGINE WHAT IT WANTS, instead of what some book somewhere says some OTHER engine is "supposed to be" given, in order to satisfy the requirements of emissions, altitudes, all climate conditions, and so on, which may or may not apply to THIS ENGINE.

 

Just for Sofa, I have some good rocket science for you... Took my Y pipe to have the O2 bung welded into it (I don't have welding setup yet). I get home, put up the Y pipe, and realize I had him put it on the wrong side (180* the other side of where I should have put it). So, my Y pipe has a useless O2 bung facing the oil pan, no way is the sensor going to fit... LOL. Lesson learned.

Doh!

 

I did that once on a Cheep with the mighty 4.0... I couldn't put the sensor in with the pipe in the car, but I could put it in the pipe then put the pipe on the car... but it turned out the front DS hit the pipe anyway as the suspension travelled, so I ended up having to re-make the pipe anyway.

Yeah, lesson learned, for sure: we keep on insisting on learning em "the hard way". We live and we learn, or we don't live long, eh?

 

One thing I have come to understand in my long life, is to beware of people that have a very high opinion of themselves and their knowledge and insist that you believe them, even when it is written in Latin.

 

Sounds good to me... be as ware as you like.

 

i agree with sofa, how we do it is get the car warmed up and then adjust to where you get a little bit of hold back when you start the car and then fine tune from there, has always worked for us, this is how we have done numerous wissota supers, hot rods, grain trucks, you name it

 

Gads, just get the car on the dyno in the hands of a competent tuner. He'll set the timing parameters right where they need to be.

 

I have literally googled the crap out of "Orlando ODB1 Tuner" etc and it is VERY slim pickings. It seems most around here are import specific. If you want to be helpful, refer someone you consider competent please?

 

My advice was technical, not tactical.

Ask on your regional forum for help finding a local tuner.

 

Maybe I'm overly sensitive, but your advice is similar to telling someone to not bother doing something themselves, go find a professional. The reason I, and I have to assume anyone else asking questions here, come here is to get a little assistance so as to do things themselves. It also assumes I had not already given the specs for my build to someone for an initial prom, which I do actually have. I may be new at this but I do read the forums extensively, and was as prepared as I figure I could be. I also fail to see how telling me to go find a tuner is even remotely technical, or in any way answers my initial question.

Now, as far as the timing issue... Sofa makes good points. BUT! In my case it won't work, let me explain why. A quick call to my prom tuner established that the spark tables are based on the 6* factory base timing. The motor is based on an L31-R Vortec, which likes about 16* idle time, 36* total. So, if I pull the EST and time by ear, I wind up with a base time of 16*. Great, right? Not when I plug the EST back in, and the prom runs the spark table... suddenly, my idle time is at 22*, with 42* total. As soon as the EST is back in, the spark table effectively advances the spark 6* from where I set it.

Now, once the base time is set, Sofa's points DO come into play. Now, I can listen and feel at idle and under load, and adjust for 'feel' from there, tiny increments. The engine likes what the engine likes.... He's right. But, if you have a spark table for a motor that has a wide jump in timing from stock and a custom prom, IF the tuner based the table on the factory base, starting from the factory base time and adjusting from there will save a LOT of frustration.

Dang thing is running right nice, I tells you whats!

 

Right... it's no different from a mech distributor in that regard.

If you have one of those, and it's set up for, say, 30° of centrifugal advance and 14° of vac adv, then if you put the base timing at 6°, you'll end up with 36° of "total" timing, with some vac adv on top of that.

Talking about "as soon as you plug it in" is like complaining that you put electrical tape on the springs & weights and "set the timing"; but then"as soon as you take the tape off", it changes. Well duh... that's what it's supposed to do.

Identical in every detail to what happens with an electronically controlled one... only difference is, instead of springs & weights, the mechanism by which the dist adjusts itself to external conditions, is the lookup table in the PROM.

Which means, you tune it in the IDENTICAL manner to a mech one; just, instead of changing out springs & weights & vacuum cans, you adjust the values in the table.

And, in order to do THAT, you have to "know" WHAT THE ENGINE WANTS in the first place. In EXACTLY the same way that setting up a performance-oriented car with a mech dist is different from setting up a stock car with a mech dist. You can' tjust open "a book" that says, if the sheet metal wrinkles and stickers are "this", then set the timing to "that", and thinking that it's now somehow "perfect", no matter who published "the book". No difference between an electronic one and a mech one in that regard.

Problem is, in the Neanderthal relics from the Stone Age that these cars have for electronic controls, you don't just pull up that page in the config sheet in the heads-up display on your dash and tweeeeeeeeek away; you gotta write them by hand in assembly language, and "burn" them into a PROM, unplug the old PROM, and plug the new one in.

Meanwhile, in the IDENTICAL manner as using a stock mech dist in a performance application, if you can't do that, your ONLY handle on it is to twiddle the dist body until the compromises that it makes, are the way YOU want them.

Ultimately, given what you have in your hand RIGHT NOW, it's patently stupid and sheep-like to set it to whatever "the book" says, and think it's now NOT ONLY "as good as it can get", but even, "perfect" and "beyond any further question" like the sheeple seem to worship. ALL YOU CAN DO is adjust it til it runs the best. Then, if that's not "good enough" (which frankly, it probably won't be... there's often a HUGE difference between "as good as it gets" and "good enough") the only thing you can do is go to work on the electronics. Either get into PROM burning, or replace (or at least, augment) the electronics with something from the current century that gives you some communications and programming capability. You could go with anything from a pile of 27C256s (or whichever PROM it is for your particular ECM) and a burner, to an Ostrich and EBL, to Megasquirt and a mech dist, to FAST or DFI or Big Stuff. Until you get to that point though, the only tool you have in your entire toolbox, is to turn the dist body until it's "as good as it gets".

 

MadCelt, your are exactly correct. some people are never going to change their way of thinking about something which in many respects can be correct. They sometimes over think things. This whole p...ing match doesn't help the guy with the question as it only adds confusion. But, that is only my opinion and I have said enough on the subject.

 

Probably.

Do you know how to mark TDC on your damper with a piston stop? If you do, I won't insult your sensitivity by explaining it all here.

 

meh. I learned a long time ago to listen to all sides, take what I need, and throw the rest away. I have to thank just about everyone who responded. It allowed me to apply my old school methods to what to me is a fairly modern system. Take a little of this and a little of that.

 

Not to be a dick or anything, but could you explain it?

Cause i dont know how to do that, and would like to know.

 

Okay, I'm not trying to be, either.

This is an example of a piston stop:
http://www.summitracing.com/parts/PRO-66792/

With the #1 piston down in the hole a bit, you install the tool. Turn over the engine by hand until the piston contacts the stop. Mark the damper at the pointer.

Without disturbing the stop, turn the engine over the other direction by hand until the piston contacts the stop. Mark the damper at the pointer again. Exactly half way between the two marks is TDC.

This will be your reference point. You can either put on an aftermarket tab with degree marks on the timing cover (if you do, put the tab on before doing the TDC exercise), or put timing tape on the damper (http://www.summitracing.com/parts/SUM-162591/ - you need to use the right size for your damper). Now you can use a timing light so you know how much and which direction you are moving the timing when you adjust it.

 

Too funny. Just had to do this last night. Intake gasket on my RS gave up yesterday, and my HB and timing cover have (had) no marks, making it a wee tough to set time after reassembly. Painted a reference mark on the timing cover, and used my stop to find and mark TDC in relation to my reference mark. It's a very easy thing to do with a stop, and can really save your but on an unmarked motor.

 

For those who haven't done that before, you'd be amazed at how far off the "marks" often are... just another one of the reasons why some "factory" motors run so much different from others.