MAF Tuning?

**EagleMark** · 12-17-2011

Toatally new to me and I don't even know where to start?

In my 1994 LT1 PCM $EE there is a Flag that can be set to run Speed/Density I have tried it and ran just as good, BLMs were all close to 128. But it is not enabled stock so it's running MAF and BLMs are all close to 128.

So what do you do to tune a MAF system?

**dyeager535** · 01-14-2012

I *believe* the LT1 stuff was pretty unique isn't it?

I only work on my '165 MAF stuff, and even as ancient as that is, I still don't "get" all of it!

I suspect with having both MAP and MAF, it's going to be substantially different in tune than the old junk I tinker with.

**EagleMark** · 01-14-2012

I think the MAP on the LT1 gets a barometric reading when started, actully all MAPs do. But then it runs off MAF. But there is a flag to run speed density, I guess that turns off MAF but have read it is also a backup of MAF failure.

LT1 bin still has full VE tables. Also MAF tables. I've just never read up on MAF to understand the grams per second? readings...

Does the 165 have a MAP sensor?

**dyeager535** · 01-14-2012

No MAP on the 165. Strictly MAF tables/scalars.

As I understand it the early MAF stuff like the '165 is fairly limited and "imprecise" but if that's the case, MAP would take me a whole lot longer to even begin to grasp. GPS is how much air the MAF is flowing.

Everyone says how forgiving MAF is, but with "just" Vortec heads, SDPC Vortec base, 24lb/hr SVO injectors, very mild retrofit hydraulic roller cam (chosen for low end torque/economy), roller rockers, and headers, a stock bin gets into knock retard very quickly. Absolutely unforgiving in a truck with any sort of incline or load.

Have spent a BUNCH of time playing with the bin, thought I was getting the hang of it, until a non-obvious bad plug wire coupled with some apparently too-old gas threw me for a tuning loop. :) Back on track now, but busy trying to learn $42 for my Dad's project.

**EagleMark** · 01-14-2012

Vortec heads make a big change! We have some vortec TBI bins around here, but that won't help your VE tables since you have none...

I won't even start a tune with old gas anymore! Ethanol enhanced has made it worse! 6 month old ethanol enhanced is worthless. I hate to admit how many hours I wasted on old gas! Twice!

MAP is easy, so is $42. Start a thread for your dads truck, I'll help and everyone around here's friendly! We have no rules but so far no one has been insulted, flamed, belittled or insulted, no warnings have even been sent and we have only banned spammers! just fun and help!

**RobertISaar** · 01-19-2012

the later (OBD2) PCMs actually use both MAF and speed-density at the same time in almost all situations. good chance that the 94-95 LT1 does the same thing. i haven't disassembled/commented enough to know for certain, but other than selectively modifying either the MAP or MAF signal, there would be no other way to determine which .

**EagleMark** · 01-19-2012

When weather gets warmer and I can drive it again (no snow tires) I may try that, but my tune is perfect right now. One thing I did was run a WOT BLM Locker program on the bin, I don't know what it does? But WOT does lock to 128 and adjustments to WOT PE AFR are very responsive! Wide Band O2 sensor stays steady at 12.8 to 1 AFR. O2 sensor readings are steady in .900 range with not cross counts.

Coolant temp was off by 10 degrees do to wrong conversion.

**Mean LT1** · 02-02-2012

I actually prefer tuning maf tables to get my optimal air/fuel. When dyno tuning I turn off the maf and tune the ve tables first and then turn the maf back on and do the same. I only do this if the customer wants it bc if the maf fails it will just go into limp mode wich is still driveble. Only thing to really watch out for is not to inverse the numbers in the tables or you'll certainly notice it. I add/subrtract fuel by scaling the number in the table. Adding fuel when scaling would be 1.05 for 5% and taking away fuel would .95.

**EagleMark** · 02-02-2012

Thanks for the info!

So on the LT1 it can run SD if changed in bin, but it is also limp home for MAF failure. I'm assuming the MAP sensor still does a barometric reading at start up? But then the system is run totally on MAF? Or is there a combination of MAF and MAp going on at any other time? Actually from what you said it runs MAF...

**Mean LT1** · 02-02-2012

Originally Posted by EagleMark

Thanks for the info!

So on the LT1 it can run SD if changed in bin, but it is also limp home for MAF failure. I'm assuming the MAP sensor still does a barometric reading at start up? But then the system is run totally on MAF? Or is there a combination of MAF and MAp going on at any other time? Actually from what you said it runs MAF...

Good questions. The pcm is actually using both the map and maf sensors for precise fueling. I use Tunercat for my tuning and in the switch table you can switch to SD mode and run strictly SD fueling therefore eliminating the maf out of the equation. If left alone the pcm will be looking for a maf reading and of course if not hooked up will throw a code and go into limp mode.Yes, the map still does a baro reading upon every key cycle.

**EagleMark** · 02-03-2012

I've seen the bitmask switch for SD in TunerPro XDF as well. Never tried it though. Car runs to good to mess with really.

That WOT BLM Locker program was quick simple fast huge improvement. My wideband confirms 12.8 to 1 AFR which is close to what bin is set to.

Just need some 4:56 gears and posi, 100HP shot of Nitrous, black out the windows, gut interior, electric exhaust cutouts, have a set of Buick aluminum mag wheels getting 2 inches put in for bigger rear tires and I have my 12 second White Woodgrain Station Wagon sleeper bracket racer!

**Mean LT1** · 02-03-2012

I would love to get my hands on the blm locker def file.

**93V8S10** · 02-03-2012

Looking good!

You mentioned your coolant temp being wrong, what conversion are you using?

**EagleMark** · 02-03-2012

Originally Posted by Mean LT1

I would love to get my hands on the blm locker def file.

It's in the LT1 ECM thread? It's a program that does it for you. You could do a bin then compare to find the changes. But no need, it works!
http://www.gearhead-efi.com/Fuel-Inj...rmation-EE-EEB

Originally Posted by 93V8S10

Looking good!

You mentioned your coolant temp being wrong, what conversion are you using?

X * 1.350000 + -40.000000 and X * 0.750000 + -40.000000 From the ALDL file:

23 COOLDEGR RAW LINEARIZED COOLANT TEMPERATURE
DEG C = .75N - 40
DEG F = 1.35N - 40

But I think that is corrected now, there was somthing off before...