FAQ: How to tune the PCM? (Series II SC)

Good question. The answer lies in the fact that the PCM optimizes spark timing for different conditions. For WOT operation, anywhere from 11-17º advanced timing is about right. Obviously, the more advance, the more torque you can make. Any amount of KR will decrease the advance (lower the number) by a specific amount. It is close to 1º spark advance for every 1º KR, but not exactly.

But there are other modes of operation: cruise and idle, in addition to WOT. Your friend's scan tool probably read the timing during a cruise (moderate or light throttle at speed, cruise control on or off). Some scan tools will show timing advance with a negative number, so your -22º was actually 22º timing advance, or 22º before 0º (TDC). This is very close to where a 3800 V-6 makes it's optimum torque, which I've heard is 26º advanced.

If you turn the cruise control on when driving the freeway and let the TCC engage in 4th gear, then lower speed to 46-50 mph, you may see timing go as high as 37º advance. That is one of the reasons for our car's ability to get such great economy in cruise. I don't fully understand why 37º is superior to the optimum 26º for optimum torque, but it seems to be the case. Perhaps volumetric efficiency is best with the more advanced timing. Whatever the case, our cars have different "ideal" timing advance depending on whether you are in WOT, cruise, or idle mode.

AA wrote:

Good question. The answer lies in the fact that the PCM optimizes spark timing for different conditions. For WOT operation, anywhere from 11-17º advanced timing is about right. Obviously, the more advance, the more torque you can make. Any amount of KR will decrease the advance (lower the number) by a specific amount. It is close to 1º spark advance for every 1º KR, but not exactly.

But there are other modes of operation: cruise and idle, in addition to WOT. Your friend's scan tool probably read the timing during a cruise (moderate or light throttle at speed, cruise control on or off). Some scan tools will show timing advance with a negative number, so your -22º was actually 22º timing advance, or 22º before 0º (TDC). This is very close to where a 3800 V-6 makes it's optimum torque, which I've heard is 26º advanced.

If you turn the cruise control on when driving the freeway and let the TCC engage in 4th gear, then lower speed to 46-50 mph, you may see timing go as high as 37º advance. That is one of the reasons for our car's ability to get such great economy in cruise. I don't fully understand why 37º is superior to the optimum 26º for optimum torque, but it seems to be the case. Perhaps volumetric efficiency is best with the more advanced timing. Whatever the case, our cars have different "ideal" timing advance depending on whether you are in WOT, cruise, or idle mode.

thanks for the quick reply! and again for the help! i think thats twice youve helped me out today lol. i totaly forgot to mention that was at idle while in park. i think i have done to much reading today and i just confused myself. that makes perfect sense

Yeah, I don't even think the car would run properly even at 0* advance. That's when I would be worried. The closer to 0* the advance gets, the worse the car will run.
You mention the slight backfire you get. That's a "characteristic" of this engine. Pull the resonator off and listen to how bad it backfires lol. It pops and spits all over the place. Put the car in 1st and drive it until about 5000rpms.....let off the gas and allow the car to slow down. You'll hear the resonator "ping" quite a few times. It happens. With my totally "not stock" exhaust, I can get it to sound like a shotgun LOL. It gurgles for a minute, then BAM! But, then again, I'm running a little more rich than you

Yep, mine does the backfire thing, too. Never noticed it till I removed the cat.

Abaddon wrote:

Yeah, I don't even think the car would run properly even at 0* advance. That's when I would be worried. The closer to 0* the advance gets, the worse the car will run.
You mention the slight backfire you get. That's a "characteristic" of this engine. Pull the resonator off and listen to how bad it backfires lol. It pops and spits all over the place. Put the car in 1st and drive it until about 5000rpms.....let off the gas and allow the car to slow down. You'll hear the resonator "ping" quite a few times. It happens. With my totally "not stock" exhaust, I can get it to sound like a shotgun LOL. It gurgles for a minute, then BAM! But, then again, I'm running a little more rich than you

That's what I was thinking with the spark advance thing. When I saw negative 22 degrees I was thinkin how in blue hell could my engine even be running? Like u said even at 0 degrees it would be noticable. Just figured I'd ask ya'll. And as for the backfire thing I'm glad it is a charactersistic of this engine in a way. It still botheres the piss outa me sometimes though lol

Yeah, it;s kinda annoying. I think it has something to do with the waste spark setup it has. At any given moment, 2 cylinders are firing at the exact same time, whether they need to or not (3 coils, 6 cylinders). I think that popping may be the excess fuel and/or exhaust gasses igniting on the cylinder that isn't supposed to be firing at that time.

Abaddon wrote:

Yeah, it;s kinda annoying. I think it has something to do with the waste spark setup it has. At any given moment, 2 cylinders are firing at the exact same time, whether they need to or not (3 coils, 6 cylinders). I think that popping may be the excess fuel and/or exhaust gasses igniting on the cylinder that isn't supposed to be firing at that time.

thats a verry good point. i guess i never thought of it that way.

FWIW I had random popping at idle and on decel until I replaced my fuel injectors with bench cleaned/flowed injectors. No can of injector cleaner ever took care of that issue for me.

I am looking at buying a scan/tuner. Do they make one that does both?

The two tuners available (DHP & HPT) both include a scanning package, which is a separate application. You scan using one program, tune and flash using another. In my experience, DHP's scanner isn't the best, so I use AutoTap instead. Maybe someone else can speak for HPTuners.

More info/discussion here: https://rivperformance.editboard.com/t2100-good-scanner-tuner-software-to-use

ok so i know whats next for me after my Hogan down pipe will be a PCM tuning (HP Tuners)

i guess i just want a heads up on whats to come when i do tune it.

is it a pain in the a**?

thanks for the help guys this forum has really helped me out alot

Lots of reading in this thread, should help you figure out what you need to do. Probably won't need to tune after the downpipe - it's when you add boost that you'll need to adjust for more fuel.

well i know its not alot but im currently running a 3.5" pulley
and i have a FWI and a catback exhaust and a 180* stat
you think it would be worth it?

You can improve even a stock car immensely just with tuning. But you usually don't absolutely need to until you want to step down to a 3.4" pulley. It's a steep learning curve if you haven't done it before. Read through and then we can answer any specific questions.

would i have KR if i do drop to a 3.4" with a tune and the other mods i already have.

thanks a lot AA.

You might have KR right now. You can't really know the answer until you scan. But if you do find some KR, you'll probably be able to tune most of it out, considering the mods you have.

Read this: https://rivperformance.editboard.com/t23-faq-modding-101-how-to-increase-acceleration-performance

ive read this whole subject and am completely lost lol. no but here is my question. i want to run a 3.4 pulley, headers, and down pipe, and either an FWI or CAI, as im reading you're basically telling me that a shop (with a dyno etc) can tune my STOCK pcm, so i dont have to get an aftermarket one with a generic tune?

That's correct. The only difference between stock PCM and an aftermarket one is the aftermarket has been reprogrammed using a tuner. This can be done with the PCM still in the car, so if you can get the car hooked up to a tuner, there is no reason the physically remove the PCM.

It sounds like you want to know more about modding, too. Read through our FAQ threads (Modding 101 is a good one):

https://rivperformance.editboard.com/t1585-series-ii-supercharged-faq-listing

awesome thank you

highwaywarrior wrote:

ive read this whole subject and am completely lost lol. no but here is my question. i want to run a 3.4 pulley, headers, and down pipe, and either an FWI or CAI, as im reading you're basically telling me that a shop (with a dyno etc) can tune my STOCK pcm, so i dont have to get an aftermarket one with a generic tune?

Read the modding 101 link AA posted, and here are a few more tips -
Headers is the downpipe too.
Running a 3.4 pulley with stock valve lift (even with headers) will generate too much KR, unless you tune it into a slug. Based on experience I advise to get an MPS and a 3.5 pulley to start, and as tempting as it may be, do the pulley last out of your list.
A FWI will not help much. A true CAI will make a good difference, and is NOT an open cone in the engine compartment. Read up on it.
Be sure the shop has GM PCM tuning equipment, not all do. Our cars tend to require HP Tuners (anyone know if EFILive does 3800s?) but '96 and '95 need something different still.

ok so, headers and down pipe, CAI, pulley last, i did contact the shop that i want to tune my car, they do in fact have hptuner . so you are saying if i want to do a 3.4 ulley then i should get the 1.9 rockers as well?

i literally read alot of it last night, lol was reaaaaly tired going into work today ( US Navy Special BOat team)

I have a lot of days like that.

highwaywarrior wrote:

ok so, headers and down pipe, CAI, pulley last, i did contact the shop that i want to tune my car, they do in fact have hptuner . so you are saying if i want to do a 3.4 ulley then i should get the 1.9 rockers as well?

Yes, even with headers I had KR I couldn't lick on my 3.4 without removing so much timing from WOT to hurt performance. Exhaust is limited, but is not really the restriction until you are pushing more power than that. The airflow through the intake side on the stock cam doesn't give enough lift to get the air out of the supercharger without building up too much heat. The more you compress the air the hotter it gets. If you can get it into the cylinders without compressing it as much you won't have the heat/KR problems. Before you do 1.9 rockers, though, think about how much you have the speed bug. If you want to go further (cam), you can't use the 1.9s, so might want to consider that. That's why I recommend starting with a 3.5 pulley and an MPS, you can tune a stock valvetrain for that and still be impressed, and have a lot of fun.

wow, you guys are very informative. i thought i learned(learning) alot here in the US NAvy about machining and engines, but here i am learning about boost etc. ive owned one boosted car an 84 t bird turbo coupe.. i think i know why that car died all the time lol. alright. i will get the 3.5 with mps, downpipe, plog and cai. colder plugs