miraclemann777

I have a stock MAF, on a 383, tpis mini ram, trick flow 195cc/2.02/1.60, zz9x, flat top 10:1, 30lbs inj. I'm new to tune and will not carb! When I get better at tuning, I'll modify the MAF. My questions are these...

Why do I change the MAF table values to tune when my MAF is the same as stock? Shouldn't I be changing other stuff instead?

I bought the MAF at advance when I put the motor together, I just told them to give me a stock one for an 89 GTA. It still has the screen.

Duts87ss

iTrader: (10)

To make more power, you need more fuel (along with more air). Adjusting the MAF tables/scalars will tell the ECM you need more fuel for a given voltage reading.

miraclemann777

um, (scratches head)... but I'm running pig rich on a stock chip...

Duts87ss

iTrader: (10)

If you're rich across the board then start by lowering the MAF scalars by the same percentage that your BLMs are off of 128. Then fine tune from there in the MAF tables.

Just doing this has gotten my tune really close at cruise. My idle still needs more fuel, and AE, along with PE, still need a lot of work.

RednGold86Z

iTrader: (1)

First, change the injector flowrate constants to 30lb/hr. Then check if rich again.

Duts87ss

iTrader: (10)

Absolutely. I guess I was assuming this had already been done. Maybe that's what I get for assuming.

pandin

Re: Initial Start-Up Analysis Ideas

One of the big challenges trying to tune the GM TPI is the relationship between the Maf vs true air flow, Injector flow vs injector constant, and the NB/WB output vs AFR.

None of the "variables" are "perfect".

They are only a "best guess" and you have to pick something to anchor your tune to.

The most accepted is, in Closed loop and at a steady cruise speed, use the BLM (128) as the anchor. Adjust the injector constant to match the injector flow. Then adjust the Maf/VE tables to bring the BLM to 128. This is not the only successful way to tune but is what quite a few TGO people have used.

The issue is you have 4 different items and not all of them, when set to a "proper amount", will give 4 acceptable numbers.

I have found, with my set up, is each is a compromise. If the afr/ BLM is at 128 then either the Maf or the injector constant is way off. And the NB/WB don't always read the same. AFR 14.7 and 128 BLM are not always together with each other.

This inconsistency really makes tuning a big challenge, because I never really know which "number" is "correct" and which is "fudged".

BWilcox

If your steady speed 1500 rpm BLM is at 108 then you are at the limit of what the ECM can adjust for and will need to adjust the injector constant and/or Maf table to level the difference from Idle to cruise.

I shoot for a 14.7 AFR/128 BLM at 55 mph, then move the Lower maf tables for a good idle rpm. The idle may or maynot be 14.7 AFR.



Also Maf sensors read different with different cams, at idle is the worst.

I hope this helps to answer your question.

miraclemann777

pandin, I believe it will, thank you

Orr89RocZ

iTrader: (20)

Like i've suggested, I like to tune MAF by setting injector constant and tweaking the MAF table values. I leave the scalars alone. It works well this way.

At closed loop, cruising... you play with MAF values alittle in the spots where the BLMs are off 128 by more than 5. Getting +- 1 from 128 is almost impossible sometimes. Leave injector values correct for your fuel pressure rating, ie 30lb injectors are 30lbs at 43.5 psi. If your more than that by a good bit, then it may make those 32lbs injectors or something, you have to calculate it. So get BLMs within 5 or so and your gravy train.


I even made my own MAF sensor for more flow and had to completely readjust the MAF values to get my fueling back in line. Tables can be adjusted, just make it smooth increase from step to step.

Also add timing until it doesnt want to take anymore then back it off 1-2 degrees. This will change BLM's / air fuel ratio alot at times, especially idle. I'd run 24-28 degrees timing at idle with that cam. The rest of the table you can play with. You have my bin already to play with. Surprised it didnt work out as well for that setup.

bl85c

iTrader: (2)

I'm sure I'll get flamed for this, but tuning via the MAF tables is the anti-engineering approach to tuning. Lying to the ecm and fudging things like this just creates more garbage. Like the adage goes- garbage in garbage out. You need to set things to what they really are as close as you can surmise. I don't tune for blm/int anymore either. Let the ecm do the adjusting- that's what the PID loop's there for. GM knew it would be off from the factory and continue to change throughout the vehicle's life.

If it's so rich the BLM's pegged you can widen the BLM's adjustment range or if you're using $32B you can tune by the pulsewidth vs airflow vs rpm table. $6E doesn't have this table, but you can change other things to get it in line without lying to it. If it's rich in open loop you really need a WB O2 to tune it properly, but you can creep up on the proper tune with the open loop tables.

Keep the screen in the maf. I wouldn't modify the maf without a flow meter. People have tried other methods to approximate what the maf is flowing after taking the screen out or making a larger housing, but is it very accurate? I think not. I've seen how much messing with the maf tables can throw things off when I switched to a t-bird maf. As little as 1 g/sec off can throw the ecm off a full afr point or more.

Search through some of Grumpy's old posts, he had a pretty good grasp on how things should work.

pandin

bl85c

No flame here but how do you determine what is "fudged" and what to use as "correct".

I have seen inconsistency in every variable that a tune can be anchored to.

It is like trying to run something by a committee.

bl85c

iTrader: (2)

If it's misrepresented (like changing the inj. constant) then it's been fudged. I understand why people (and even GM in some instances) do it. For example turbo buick guys will use maf's 4 times larger than stock with injectors 4 times larger than they need and change the inj constant to 4 times the injector size to bring fuel back where it needs to be without having to rewrite the code. Gets the job done but also creates more inconsistancies in the way it's being run. I suppose it's imperfect perfection setting things to what they actually are because there's always inconsistencies even in a properly programmed system, but I also don't want to introduce more potential problems.

Orr89RocZ

iTrader: (20)

I'm not sure i'm following what your saying. The factory computer was tuned for the specific motor combo. The injectors/MAF sensor work together to calculate fueling.

You change heads/cam/intake then your 'tune' will be off and the only things controlling that fuel are the MAF values and/or PE mode % enrichment.

a 22 lb injector will only support so much hp. If your over that limit you have to get larger injectors and make adjustment in the chip so that the fuel calculations are correct or else your 'fudging' the numbers aka lies to the computer.

Set your injector constant, then play with your MAF tables/PE mode enrichment to get the fueling correct. This is the only way to do it with 6E IMO. I've done this with my 383 very easily and that motor ran very well.

Tune MAF table 1 and maybe 2 for idle and light part throttle since idle air flow for cammed heads motors will definately be different than stock.

Leave 3-6 alone and use PE mode to get your heavy throttle to WOT tuning ok. Your PE vs rpm enrichment will follow your torque curve. Peak torque requires the most fueling. My motor peaked at 4000-4500 so i have alot more PE vs rpm enrichment there. PE will fall off abit after that as torque dies down then will pick up again if your revving over 6K rpm and need fuel up there for peak hp

Its very simple to do. Matter of 6 quick pulls on the street I had my air fuel close. Timing table will take more time to perfect but i used someone elses base table for a 383/cc306 cam and it turned out ok. Set WOT table to what you want first before you do any WOT fueling.

Went to the dyno and 10 pulls of fine tuning to bring midrange air fuel down since its hard to get airfuel vs rpm data in the 2500-4500 rpm range on the street with a near 500hp motor

That was it. It all can be done in a matter of hours and you can be racing

bl85c

iTrader: (2)

The turbo buick refrence was just an example of how it can be advantageous to fudge certain things sometimes. Really doesn't have a bearing here unless you plan on using a larger maf. But here's how it works.>

Say you wanted to use an LS1 maf that flowed 510 g/sec. You could hook it up and program in the LS1 maf's curve up to 255 g/sec, but anything above that would be unuseable because the stock algorithim's limited to 255 g/sec. You'd have to rewrite the algorithim to double value (each bit equals 2 g/sec) to use the whole flow curve in this manner.

Instead you can cut the LS1 maf's flow curve in half, put that in the maf tables and use injectors twice as large as you need with an injector constant twice as large as the acutal flow to deliver the proper amount of fuel. Although the ecm will only be reading 1/2 the actual airflow twice the fuel will be output.

-An injector twice the size needs approximately half the time to flow the same amount of fuel.-

Now of course there's still problems with nonlinearity of injector flow, but this can be compensated for using a maf translater with an adjustable output, or editing the maf curve in the bin.

All this is contrary to engineering practice, but it gets the job done without having to rewrite the algorithim, albeit at a higher cost.

Orr89RocZ

iTrader: (20)

I understand that, but the topic here is using stock maf system which is more than capable of handling the 383 at hand here. I'd still stick to the basics, you dont need to complicate this tune for this particular motor

bl85c

iTrader: (2)

You asked and I explained. I've gotten off topic so back to why I originally interjected- you don't need to fudge the maf tables to get things inline.

Orr89RocZ

iTrader: (20)

What else can you change if you dont change the MAF tables? For WOT you can use PE mode which i recommend but idle and part throttle, i dont see any other way to adjust fuel without doing the MAF tables.

miraclemann777

that is exactly my question. so far I've been tuning only at idle. I look at my MAF readings and change only that table to adjust AFR (which is at idle, no load). the next time I tune I will definitely drive the car and see what's going on while cruising.

I need more advice on what to do when something happens. for example, when I change my MAF tables, my afr gets better, but my rpms go up. (scratches head)
so I'm gonna pay more attention to cruise tuning than idle tuning, what do you think?

oh yeah, I always set the inj constant at 30, what do you guys think I am? a wildman? and I got a WB too

bl85c

iTrader: (2)

Well let me ask what mask are you using and where are the blm's pegged? If you're using $32B you can tune the specified pulsewidth table, if it's $6E you can widen the blm range (just because it's not 128 doesn't mean it's not stoich, it just means the calibrations off), you can tweak the o2 window to get it to cycle leaner, if it's rich at certain temperatures you can use the 02 offset vs temp table as well. You can tweak the way the blm cells function as well to give it more resolution and better cover where your engine operates. If your engines so far off that the blm's are still pegged after you widen the blm range there must be some other issue. Maybe your injectors aren't flowing what you think they are? How do you have your O2 sensor hooked up?

dimented24x7

iTrader: (2)

Just jumping in at the end here, but one thing to keep in mind is that the MAF is an air flow measuring device. The MAF tables are not there to 'tune' with, but to calibrate the sensors voltage output to correspond to the airflow rate into the motor. This is the beauty of mass airflow. Once the tables for the sensor are calibrated, and reporting an accurate measure of the airflow, there is no further tuning needed for the steady state fueling as the MAF is independant of the engine behind it. On a good MAF system, the MAF calibration table is a 'set it and forget it' affair. The only time its really adventageous to mess with the tables/injector constant is when your using a different sensor, tricking the computer to get past the 255 g/sec airflow limit on bigger motors with larger MAF sensors, or otherwise trying to squeeze more fuel out when the MAF pegs.

Also keep in mind that the stock 3rd gen MAF systems are very primitive, and the fuel calcs are limited to the required duty cycle for the injectors. Not very accurate, nor very able to keep up with rapidly changing engine conditions. Because of this, the MAF systems will never run perfectly. IMO, having the AFR within +/-5% of whats desired would be what I would call a 'good' tune with the stock system. Its hard, if not impossible to get it much closer than that.

pandin

So someone explain why a new Maf holds a 128 blm @ 24# injector constant and a rebuild Maf needs a 30# IC. The difference in air flow was only 10 Grm/sec.

It seemed to me that a relative small change in the Maf tables and/or Air flow made a big difference in the amount of fuel (AFR/BLM).

I suspect that is why more people adjust "fudge" the air side then the fuel, because changing "fudging" the injector constant really changes the AE, PE, and cold start.

bl85c

iTrader: (2)

And why do reman maf's last half as long as new? Because soldering in new components f's it up and changes the resistance of the wire. Quick and easy gets the job done.

doc

I am going to jump in here late also. I have been tuning for about 12 years on my '87 IROCZ. I am a big believer in setting the injector constant to the advertised flow rate, and then tune the MAF tables in order to achieve as close to 128 in the FTCs that I "see" driving around. Right now I have 126 to 129 in the 4 FTCs I drive around in with my new HSR setup.

Previously, I had been running my MegaMAF (a factory MAF guts stuffed into a 3.5" aluminum tube). The only way to get this to run right was to make a massive change to the MAF scalars. It should be obvious that I seriously changed the calibration of the MegaMAF vs the factory MAF table. I had increased the flow area about 38%. And therefore, the factory MAF table was way off! I ran a 12.12 with the MegaMAF & Accel SR combo.

miraclemann777

I'm using 6E. I widened the blm range but i'm not sure that helped. I've changed the plugs six or eight times already. The car does okay with new plugs but after about twenty minutes of being so rich they foul. Nothing I've tried so far seems to hold water. I can get it to lean out but as soon as I put it in drive and go it gets real rich. I've messed with the scalars and tables but once my plugs foul it's over til I get a new set. My afpr reads 40 psi so I tried lowering my IC.

Something that confuses me is that there are so many similar tables. There may be one item versus two things like PE vs rpm and PE vs temp. Do I change both tables equally or will changing one do the trick?

I'm gonna get a new nbo2 and try closed loop. The o2 offset vs temp will have to be used in closed loop, right?

pandin

Lowering the IC (in the prom) will richen the mix, try raising it. Upping the Maf table numbers (bigger number same volts) gives more fuel (richer) , lowering the maf numbers less fuel.

First you need to get it lean enough to quit fouling the plugs. Watch your blm's if they are not between 108 (too rich) or 160 (too lean) then keep adjusting until the BLM's are between those two extremes, idle may be different than a steady cruise.

Just try to get something out in the middle so you can see where you are at.

If it gets too complicated, go back and start over. As a temporary start just use a stock bin and change the IC to get away from plug fouling. Then change the Maf tables and bring the IC back to the "correct" size.

On mine, I had to raise the lower (Table 1) Maf numbers and that evened the BLM's.

tequilaboy

If we can assume that the MAF and injectors are working properly and the injector constant has been corrected, then it suggests that the injector offsets are resulting in too much fuel.

Most likely the battery voltage compensation table needs to be reduced for the new injectors. I'd start by setting this table to zero and then work upward if the blms run too lean at zero.