85mm Mass Air help

[RandyWS6]

I log some wot with my efi live v7 and the mass air lbs/min at ( 52.88 ) and in my efi tuner v7.3 is showing (43.72) lbs/min. at 6200 rpm , none of the lbs/min matches at all ,there all way out ,this just a example at one point in the log. Does my mass air need recalibrated, its a 85mm SLP . If so how would i do this. Shouldn't they match ?

[Doc]

Da dum, dum...SLP's early idea to add a resistor to a 85mm truck MAF to "lean" out the factory rich situation bites yet another. No worries, do a search on making a MAF rescaling map in the scan tool. Essentially, you will have MAF frequencies on a col and wideband BEN values that you will log with the vehicle in Open loop with fuel trims and other modifiers off to correct/rescale the MAF. I would highly suggest removing the added resistor first. If you are not adept at soldering/desoldering then take it to someone who is. It is very easy to destroy it unintenionally by the well meaning unitiniated modder.

[SSpdDmon]

I answered this on LS1Tech.com...but what I don't understand about your post Doc is this. If the PCM is reading a raw frequency from the MAF, how would it know whether or not there was a resistor in the MAF itself? He's saying the MAF frequency logged out of the PCM is 'x', but the PCM is ignoring it and looking up frequency 'y' in the table. Doesn't add up to me...

[RandyWS6]

Yes the PCM is cal. for 43.72 lbs.min at that Hz. but in real life i am pulling 50.88lbs.min. at the same Hz. I wish i could post the graft from the logged file but i dont know how.

[redhardsupra]

if these two dont agree, then either your VE or MAF aren't calibrated. tune them both and you wont have this problem.

[Doc]

I answered this on LS1Tech.com...but what I don't understand about your post Doc is this. If the PCM is reading a raw frequency from the MAF, how would it know whether or not there was a resistor in the MAF itself? He's saying the MAF frequency logged out of the PCM is 'x', but the PCM is ignoring it and looking up frequency 'y' in the table. Doesn't add up to me...

The following is my caveman interpretation...
The way the pcm "reads a raw frequency" is this... the litttle resistors in the ckt have current running thru them. The ckt does it's best to maintain current flow as translated by the calibration(MAF table) which is presented to us humans as a Frequency. As air rushes over the resistors, cooling them down the ckt is forced to increase current to maintain the desired flow. This is how it "knows" what airflow is actually coming thru. This raw current is converted to a Freq and then to an actual airflow value. This explains why at idle the pcm is sampling btw the MAF and the VE table; at idle the engine is huffing in and out to a degree and MAF readings alone are not valid, however at above 4000 or whatever B0120 is set at, there is sufficient airflow rushing in to fully use the MAF Cal and readings. That said, in the dark ages of LSx tuning SLP found out that by soldering in a resistor they could change the total resistive value of the ckt significantly enough to lean out the already factory fat fueling.
Sorry gotta grab my towel, my movie is starting in 42 min...

[joecar]

Where exactly is the resistor soldered (I've never looked too closely at an SLP MAF)...?

If it's soldered in the bridge then it could well be shifting the frequency up (or down)...

[RandyWS6]

Mine has a resistor soldered in across the bridge, Should i remove it , when tuning or adjusting the mass air ,witch would lean out wot a little, raising or lowering lbs.min.

[Doc]

Ok, I am back now. I just saw Tenacious D-good movie. Wrong picture-my mistake. The arrow is pointing at the IAT sensor. Trying to find a pic of the huge resistor- you can't mistake it.

If you feel comfortable with either desoldering it-with a precision solder station that can provide instant substantial heat- with flux to get in and out and not put to much heat for too long-that can fry other components in the vicinity. You could just cut the legs with diagonal cutters...Bottom line if you don't feel dexterous about it find somebody who can.

But by all means remove it one way or another if you have any mods other than just a lid as you will go too lean. The worst possible combo I have personally seen was on a guys camaro that had a SLP Maf and the Hypercrap caned tune in it. You could litterally hear the "can of marbles" pinging at WOT. I'll remove your resistor if you could come over and help me pull my tranny tommorrow.:)

[Doc]

Where exactly is the resistor soldered (I've never looked too closely at an SLP MAF)...?

If it's soldered in the bridge then it could well be shifting the frequency up (or down)...

Yes, that's exactly where it is at. And other "aftermarket" MAFs I have seen are doing the same thing. Granatelli-sp?

[RandyWS6]

So with my mods. i should remove it (resistor)? 2000 WS6 TransAm -M6 LS2 418cid ,4.030 bore & 4.100 stroke & 6.125 rods, cam .650/.650-250/266-112+2 ,Fast 90/90 ,85mm mass air with (resistor) Dart stage III cnc ported 255cc intake runners ,2.100 int. & 1.60ext.valves 59cc chambers, Right now im a little rich at wot .930mv to .940mv

[TAQuickness]

Actually, with your mods, you should consider purchasing a Wide Band O2 sensor. You've got quite an investment in your motor, I'd hate to see you loose it to NB inaccuracies.

[SSpdDmon]

I still don't get it. The MAF produces a signal regardless of what the PCM has in the tables. You hook the MAF up to a flow bench and it'll still spit out a signal. My point is...the PCM simply should read the signal from the MAF, use that as a lookup value to the table that we populate in our software, and then calculate fueling accordingly. IMO, all the resistor does is "shift" the operating frequency range in the MAF table. Yes, it affects fueling. But, not because it's changing numbers on a whim. The variation I believe you're seeing is the PCM's calculated airflow based on the VE table's settings & SD calculations AND the frequency lookup airflow value from the MAF table. Even when both are tuned, they're not going to equal each other....even at higher airflows. That's why cars switched to MAF sensors. They're more accurate. Just ask the engineers...

[Doc]

Frequency of a signal is only one aspect. Votage and current are also important. It's Ohms Law. A resistor in series/parallel does not have a direct effect on a "freq" o/p per se. The added resistor does directly change the current flow which in this case is proprotional/converted/compared to a Freq o/p of the MAF ckt. The reality of the ckt, how it works is the resistors are heated (by delivering current thru them) and airflow running accross them cools them down, forcing the control/comparason ckt to compenstate, adjust, by increasing current flow to maintain a predeterimined set point that is in the calibration. Now when we modify our cars the predetermined set points of the MAF calibration are no longer valid and the only way to accurately rescale the values is with EFI Live and a wideband O2. Does that make sense ? I believe it is essetially a bridge ckt where one leg is the standard and the other is compared to it.

[Scoota]

Mmmm, It's all a very strange way of doing things, I would have to say I'm with SSpdDmon on this one. Keep the soldering Iron in the draw that it came out of and use the tools that are provided for us by EFILive.

Do you guys not have a Maf Error Map to dial the Maf in after a SD tune. On a Dyno the Maf can be calibrated in literally 5-10min with BEN.


Cheers Scotty.

[TAQuickness]

I still don't get it. The MAF produces a signal regardless of what the PCM has in the tables. You hook the MAF up to a flow bench and it'll still spit out a signal. My point is...the PCM simply should read the signal from the MAF, use that as a lookup value to the table that we populate in our software, and then calculate fueling accordingly. IMO, all the resistor does is "shift" the operating frequency range in the MAF table. Yes, it affects fueling. But, not because it's changing numbers on a whim. The variation I believe you're seeing is the PCM's calculated airflow based on the VE table's settings & SD calculations AND the frequency lookup airflow value from the MAF table. Even when both are tuned, they're not going to equal each other....even at higher airflows. That's why cars switched to MAF sensors. They're more accurate. Just ask the engineers...

For the sake of splitting hairs, in our applications, MAF's are only as accurate as the mass-flow look up table. They do offer a higher resolution of determining air-mass, which offers tighter control off fueling, which results a happier EPA. In the case of the automotive MAF, consitancy is more importnant then accuracy.