nevrenuf

I spoke with Steve Cole recently. The subject of LTrims came up. I was inquiring about whether there was any difference between a -2% trim and a +2% trim. Steve told me that if your trims already indicate a rich condition to the PCM, then fuel enrichment will NOT be enabled at WOT....

Can anyone confirm that this is actually the case? It seems to me that if fuel enrichment is set to 10-12% normally, and if you are 2% rich FE will not be used, you run the risk of being fairly lean.....

Comments"

Camaroholic

iTrader: (1)

I'm still learning the LS1, but on the LT1, that is true.

In the LT1, block learns are centered at 128. If you are running at, say, 120 (rich) when you're staging, and then when you launch, your LTrims will jump up to 128 at WOT "automagically".

If you're running at, say, 150 (lean) when you're staging, your LTrims will stay at 150 at WOT. This is especially a problem if you're running split block learns; 135 on the left bank, 150 on the right, will cause uneven fueling at WOT.

Again, I'm not sure if this same thing applies to LS1's, but it probably does. You'd just have to change 128 to 0%, and then look at the other values accordingly. Unfortunately, I can't test, because my car is down right now. <img src="gr_images/icons/wink.gif" border="0">

-Andrew

Kilroy's 99 TA

so does this indicate you want ltrims to be + all the time, so you can get this enrichment at WOT?

Camaroholic

iTrader: (1)

For tuning and consistency, I'd prefer that I run rich, and have my LTrims go to 128 (in the case of the LT1) or 0 (if the LS1 indeed does that; I don't know if it actually does or not).

Do a WOT run and log the LTrims. If you're rich when you start, they should go to 0 and stay there through the run (note with an M6 car they could change when you lift off the throttle, though, if the car pops in to a lean cell). With the LTrims at 0, you can tune using the PE vs. RPM table for rich/lean. If the LTrims are (+) [lean], then your fueling is going to be based on whatever cell you land on. Like I mentioned before, this can cause split LTrims and inconsistent fueling between left and right sides of the motor.

Me, I tune my LT1 car for 'slightly rich', and I'll do the same for my LS1 car (whenever I put it back together).

-Andrew

66ImpalaLT1

This is quite possibly true, it has been a source of aggravation for many. They are disabling this 'feature' in Buick GN's and 92-93 LT1 proms, but last I recall they havent found the code to disable on anything newer.

Eric

Doc99SShome

This is what I was told by a LS1 PCM tuner:

The PCM will add the amount of fuel as a percentage if the Ltrims are positive (that is adding more fuel) when you go to WOT. If the Ltrims are negative, the PCM will not take out fuel when you go into WOT (fuel or power enrichment).

So, if the engine is running lean while just driving around, the Ltrims will be positive, the PCM is adding more fuel. When you step on it, the PCM will not only add the fuel from the enrichment table, it will add in the Ltrim value.

However, if the Ltrims are negative, the PCM will not take fuel out at WOT because this may result in a lean condition which could be bad for the engine.

In tuning my car, if the cruising around Ltrims are positive, much more fuel is added in during WOT. My scans at WOT show a positive Ltrim value. However, by switching my MAFT base to +20%, my cruising around Ltrims are about -5% to -10%. If I kick it down and take a scan at WOT, the scan shows 0% for Ltrims.

I hope this helps,
Doc

kewlbrz

Right on the money Doc99.

Mike Morgan

Correct.

Part of the key to tuning a car, is too make sure that the car will run the same from Zero learning to months later.

The MAFT is an OK device to help fine tune, but when you need to make some serious adjustments programming is the only way.

Another word of caution, a ported MAF will cause an extreme lean condition when installed before the computer adjusts. Once it has had time to learn you usually end up with LTrims over +20%. This then usually results in too rich at WOT.

The MAF calibration is not linear it looks more like a sqare curve. Most of the resolution in the PCM is for cruise conditions. I'd estimate 1/2 the mapping is for less than 10 lb/min of airflow.

Like I've said in other posts there are several ways to achieve good tune. You just need to know which way is right for a particular application.

[ February 08, 2002: Message edited by: Mike Morgan ]</p>

Doc99SS

iTrader: (2)

See Mike, I have not forgotten what you told me. I confirmed exactly what you said about tuning and the Ltrims by running several tests with ATAP.

After working with my MAFT, I definitely have more power even though I have not gotten back on the dyno to prove it. If you recall, I was at 389Hp at the drive wheels with no tuning whats so ever, not even tuning with the MAFT.

I have been tuning my '87 IROCZ with the aid of TunerCat and burning my own Eproms. The OBDII PCM system on my '99 is similar in some aspects, but alot more complicated in most issues. With the aid of LS1Edit, I hope to tune my PCM so that I have small negative numbers for Ltrims, and run about 13.1 for air/fuel ratio at WOT. I'm hoping for over 400Hp at the drive wheels.

Do you think that I can do it????

BTW, with the MAFT set at +20% base and -10%WOT, my O2 sensors went from 960mV(no tuning) down to 890 to 900mV.

[ February 08, 2002: Message edited by: Doc99SS ]</p>

kewlbrz

[quote]Originally posted by Mike Morgan:
<strong>
The MAFT is an OK device to help fine tune, but when you need to make some serious adjustments programming is the only way.</strong><hr></blockquote>

I beleive programming is the best, but dont discredit the MAFT so fast.

Remember the MAFT still utilizes all that fancy GM programming. It just skews the perceived load in one direction or the other.

Also FWIW:

min F-out := 1.3 kHz
max F-out := 14.6 kHz w/ limiter
input frequency sampling time := ~10ms
WOT transition frequency := 8 kHz


For F-in < 8 kHz
- F-out = F-in * (0.03440 * BASE + 1)
For Fin >= 8 kHz
- F-out = F-in * (0.03440 * BASE + 1) * (0.00407 * WOT + 1)

ToplessTexan

[quote]Originally posted by kewlbrz:
<strong>

I beleive programming is the best, but dont discredit the MAFT so fast.

Remember the MAFT still utilizes all that fancy GM programming. It just skews the perceived load in one direction or the other.

Also FWIW:

min F-out := 1.3 kHz
max F-out := 14.6 kHz w/ limiter
input frequency sampling time := ~10ms
WOT transition frequency := 8 kHz


For F-in < 8 kHz
- F-out = F-in * (0.03440 * BASE + 1)
For Fin >= 8 kHz
- F-out = F-in * (0.03440 * BASE + 1) * (0.00407 * WOT + 1)</strong><hr></blockquote>


Shawn, remember that those equations were empirically derived by zzz. Mike has never confirmed that that is a correct analytical model nor did I ever find out why zzz chose the model he did. Never did get around to scoping myself...

kewlbrz

[quote]Originally posted by ToplessTexan:
<strong>


Shawn, remember that those equations were empirically derived by zzz. Mike has never confirmed that that is a correct analytical model nor did I ever find out why zzz chose the model he did. Never did get around to scoping myself...</strong><hr></blockquote>

Topless, I have a TEK 475A, well have to get together, with some brew and "scope" it out for sure. <img src="gr_stretch.gif" border="0">

I made a table also, just to see the numbers based on those figures. It may be wrong if the equations are wrong.

http://www.dragracepro.com/cgi-bin/maf.fcgi?func=show

ToplessTexan

Some time back there was talk of making a MAFT with a dynamic transition frequency utilizing the TPS signal. I don't think it ever went anywhere. The reason for developing the math models in the first place was to examine the discontinuity in the translation function at that frequency.

Shawn, you're on for that brew.

[ February 08, 2002: Message edited by: ToplessTexan ]</p>

Mike Morgan

[quote]Originally posted by kewlbrz:
<strong>
min F-out := 1.3 kHz
max F-out := 14.6 kHz w/ limiter
input frequency sampling time := ~10ms
WOT transition frequency := 8 kHz


For F-in < 8 kHz
- F-out = F-in * (0.03440 * BASE + 1)
For Fin >= 8 kHz
- F-out = F-in * (0.03440 * BASE + 1) * (0.00407 * WOT + 1)</strong><hr></blockquote>


Pretty interesting, I've never really done any serious testing of the MAFT to see what the frequency response was.
My testing has been on the dyno, and by looking at your WOT trans freq, it seems about right.
This is part of the limitation of the MAFT.

Here is an example:
Your goal... To achieve optimum A/F ratio with a 0% LTRIM at WOT. To do this C/L LTRIMS must be less than 0. The result will be proper A/F without the computer having to relearn if there is a computer reset.

Situation.
W/out a MAFT the car is running extremely lean when the computer is reset (14.5:1) at WOT. After learning for some time the LTrims go up to 22%. Dynoing after learning results in a A/F ratio that is 11.7:1, way too rich.

Solution:
The common though would be to do one of two things.
1. Lean out the WOT setting 10%. This will probably get the A/F back in shape. But also has two problems. First if the computer is reset, then you will need ample time for the computer to reset, or the car will be dangerously lean (15.5:1 or leaner). The 2nd problem is that the WOT adjustment isn't really effective until about 3500+rpm. SO you really haven't improved the low end resulting in a loss of low end torque.

2. Set the base to +25% and WOT to -12%. This is probably closer. Now the LTrims are staying 0 or slightly negative. Unfortunately, you still have the problem of the low rpm range not being adjusted. The other problem is that the MAFT has reached its limit of adjustment. Also, with a high negative WOT, if you watch the a/f meter, it will gradually get leaner as rpm increases. So you may have 13.0:1 at 6000rpm, but at 4500rpm it may be 12.5:1. This is opposite of what you want when you tune. An engine has a better BSFC at the torque peak than at the HP peak. Engines tend to make best torque with slightly leaner mixtures than what they like at the HP peak.

IMHO, the MAFT is an excellent fine tuning device. I advocate it to all our customers running our custom tuning also. This allows them to adjust the A/F in small ranges at the track to adjust for conditions that the computer may not optimize for.