TransAm2k4

Hey everyone i have a pretty rough tunning for my WOT (not that bad but still on the works) but i was wondering how to tune for cruising with tunercats

TransAm2k4

Any Ideas??

Houdini

I would like to know also..

Bump.

TransAm2k4

ttt

Doc99SS

What is it that you really want to accomplish?

For my OBDII 1999 SS, I tuned the MAF sensor flow curve to get the LTFTs in all fuel cells to a negative number, like 0% to -5%. It is also possible to alter the fuel injector constant, or the MAP table if it exists.

I specifically worked with the MAF table because i'm running a GMAF.

TransAm2k4

Basically lean out the cruising a bit more. right now its too rich and from time to time you can actually feel the car kind of choke.

Slow260z

How do you know the car is running rich? Did you do a data collection or wideband testing or just sop?

TransAm2k4

wideband, smell, guys with expirience tell me!!! beside you can fell it choke also got data log from freescan but its dyno not reaL crusing

Slow260z

Ok. What is AFR? Can you give data plot or a table for values? Dyno will be WOT which is different tables than cruise AFR.

Doc99SS

With the PCM in learn mode (which it should be in during cruising), you can NOT lean it out. The PCM, coupled with your O2s, will strive to be at 14.7:1 AFR all of the time. Now, having said that, O2s do go bad or can be slightly off. The result is then the PCM is trying to get to (for example) 14.2:1, not 14.7.

If in your tuner stuff, you can set stochic to 15.0, or you might consider new O2 sensors, just the front ones.

Slow260z

Thats why I asked what his values were. WOT has tables, open loop part throttle has tables, cruise does not.

Doc99SS

Yes, I understand why you ask that. The main point is that you really dont tune for cruising, except maybe timing advance. But, on my LS1 OBDII car, we do tune so that the LTFTs are negative, so as not to mess up the WOT tuning. You should tune the LTFTs to negative so that the correction factor at WOT is set to 0%. Then you can more precisely & consistently tune the WOT AFR. If the LTFTs are positive, then the fuel correction factor at WOT is positive and will effect the WOT AFR.

Slow260z

Ok

By negative do you mean to keep Long terms to <=128. I know if they go above 128 to say 132 then the ECM adjusts WOT by 132/128 times 'normal' WOT injector calculations.

If the long term is <=128 then no change to 'normal' injector time is made.

I think I agree if that is same as what I stated above.

Doc99SS

We have a mix of terminology here. I have been talking OBDII, as in my '99 car. Sorry about that.

Talking OBDI, yes, you are correct in that 128 is the baseline. A BLM value below 128 means that initially the engine was running rich, and the ECM responds by taking fuel away, therefore a number below 128. The reverse is true for a BLM value above 128. Nomally you want the 16 FTCs BLM values to be between 122 and 134.

I believe that on an OBDI system, when you go into fuel enrichment (WOT), the BLM value is always locked to 128, and no fuel correction is made. The fuel that is delivered is calculated by the ECM from several tables.

Everytime I data log an WOT event in my '87 car, the BLM value has been 128, no matter what it was in the various FTCs while cruising around.

Therefore, tuning for cruising on a OBDI ECM is basically adjusting the fuel injector constant a small amount to get the BLMs between 122 and 134. You could also alter the MAF tables (for a MAF car) or the MAP table (for a MAP car).

Slow260z

Agree when Long term is <=128 is an indication of rich mixture so ECM will try to correct by removing fuel.

When the ECM goes to WOT you want the fuel trims <=128 any number above in OBDI will add fuel in WOT. It ASSUMES there is a need it does NOT remove fuel when long term is less than 128. This is because GM made the fuel mixture safe for WOT

NO.

An LT1 WILL increase fuel if longterm is greater than 128 when entering WOT.

When 128 or less when WOT is entered no fuel correction is made. BUT above 128 there is an increase in fuel (long term/128 is multiplied by calculated fuel time). In an LT1 the ECM does NOT always lock the long terms to 128 at WOT.

Yes

I have no experience with old ECMs this is referring to LT1 OBDI.

For best mileage probably on lean side 128 - 134 is slightly better. But personally I get my car to be as close to 128 under all conditions. That way it will run well under all conditions. If you try to get a slightly leaner mixture I will bet you will also run HIGHER AFR under WOT because sometimes the engine will enter WOT >128.

Good luck