Pretty much says it all. Just really got started on tuning and we're starting with the VE tables. We've logged and updated the VE tables twice so far After updating with the latest new data we went on a short drive (10 minutes). With the MAF still turned off the LTFT/STFT look pretty darn good (+2/-4). I know I need more data to really check these but didn't have the time this afternoon. Anyway, turned the MAF back on and drove another 10 minutes and LTFT are adding a lot, (+9/+23) with the higher percentages at higher RPMs. I know the MAF will need to be tuned but can it be this far out of whack? Could the MAF be bad or does it just need some major tweaks to the table?

The MAF is descreened (I know but I bought it that way before I knew) and it's got a custom made CAI (3rd Gen conversion car). Stock 2001 manifolds w/ custom exhaust, no CATs.

 

Hi.

I SD tuned my car to 0's and -2's and then I plugged in the MAF. It went to +7 when under part pedal and plus 17 under near WOT.

Earlier today it was rainy and it changed to about 5 and 15. So I am guessing if the MAF was correct it would be helping.

I get bad gas milage when the MAF is plugged in now and the car seems to be slightly eneregic as if it was under PE all the time.

From my intution, I would say the MAF is making both of our cars over rich. We should probably both tune the MAF or accept the fact that we aren't going to be getting the 14.6 AFR with the MAF plugged in.

 

The MAF is next on the list for sure! Just want to make sure we've got the VE dead on before we move on to the MAF. I knew the MAF was probably off but didn't realize it could throw things off this far. I can't imagine someone doing a swap like we did and then not doing/getting a tune. It's amazing to see how much needs to be tweaked when you start looking at scans. Some of the tweaks almost need a BFH adjustment they're so far off.

After we get through this VE and MAF tuning we're going to be doing some WB tuning to get PE dialed in. Would use it now for VE but haven't got a bung in yet. After that I told my son we'll do a track day to see where we're at. The old L98 TPI should have been a bracket car, slow but consistant from 9.45 to 9.55 (1/8) depending on the weather. Hoping to see an 8.4/8.5 w/ the LS1.

Rambling now.....

 

Mine was off considerably after tuning the VE table. We are talking >10% difference. I use the HPT MAF Histogram and monitor the STFT's only. I have the STFT's within -4% and 0%.

 

The only problem is if you don't have HP Tuners (me) all you can do is tune SD and then hook up the MAF then adjust until the trims are the same again.

 

My ported MAF was off by almost 40%. Descreening, and even something as unassuming as an air lid, can have a pretty dramatic effect on the MAF.

 

Back to the top w/ more info. Any help or suggestions appreciated! This is a 98 LS1 conversion 88 TransAm GTA.

Did 3 VE logging runs with MAF fail set to zero but MAF still connected. DTC codes showed up and you can tell by the shifting MAF is off. At idle shifting to D it goes into gear hard. Anyway, each time I logged and updated the VE tables the next log got better. The last log I captured was a little over an hours worth of data. I didn't get as many cells in the 3.6 and 4.0 ranges as I would have liked but still a pretty good log. LTFTs with the exception of .04 and .08 row of cells were all within +1/-3. I adjusted my primary and secondary VE tables with these new numbers and thought I should be pretty close to dead on. Now on to MAF tuning.

I originally started this thread because after I would finish VE logging/tuning I would turn the MAF back on, reset the LTFTs and go test drive and see LTFTs. Each time they were still adding a ton of fuel. Finally decided the MAF was just way off and I needed to finish the VE table and then calibrate the MAF.

Well it sounded like a plan but not working great so far. Did some logging tonight (MAF hz & Dynamic AF) and used the spread sheet RHS put together. I know I could use the histogram but wanted to see how the spread sheet worked out. After logging about 30 minutes of data, 9K plus hits I ran the data. The results showed some very minor increases and even a few decreases for the MAF table. Decided it probably needed more data, did another 30 minutes, added that data, exact same numbers.

Logging now with latest updates to VE and MAF tables LTFTs are still adding a lot of fuel +9 to +21. I did reset the the LTFTs right after loading the new tune.

Am I just missing something here? Do I need to just drive it for a few days and see where these settle out? Hoping someone can steer me in the right direction.

 

With trims of +20 you are running lean. Without the MAF connected/enabled, you mentioned the trims are fine. This points towards more air coming into the engine that the PCM thinks there is (more are than accounted for=lean).

Two general sources of the additional air are:
1) MAF mis-calibrated (saying there's less air than there actually is)
2) Air leak after the MAF (air coming in that the MAF isn't reporting)

Don't recall what year the PCM is, but the earlier ones (before 01) had 2 VE tables. Disabling the MAF forces the secondary one to read, and re-enabling it reverts to the primary one......Hope you weren't tuning the secondary one with your MAF disabled

 

Muncie, thanks for your reply. I agree it appears to be running lean based on 02s and they're adding fuel to correct. I thought the MAF calibration would be my fix but as I said, logging the MAF data showed that it wasn't very far off. I'll go back and start checking for other air sources too, that may be where the problem is. I've tried using a hose to listen around all the suspect areas but guess I need to try the propane check.

As to tuning the VE tables, the 98 does have two tables. As I understand it, you must change both to properly dial in the VE tables. If you don't change the secondary VE table then your next logging run with the MAF turned off will give you the exact same results. Plus you want the secondary VE table to be correct if the MAF actually fails at some point. Now the High/Low Octane tables are a different story. You have to copy High to Low to do the tune but then you should set low tables back to stock when you're done.

 

Sounds like you are on track. Good luck.

 

Well why didn't someone else think of this, it was so obvious..... Only if you think about a conversion car where you bought piece parts at a time.

LS1 I purchased came with fuel rails and injectors, didn't bother to check them and I should have. Injectors are from 99/00 year model, 26.4 instead of 28.4 that I was tuned for. Just updated the tune with cells from a 99 TA and did a quick drive. LTFTs are still up a little 6/7 but way better than they were. I only put a few miles on it but evident they're going to be much better.

Question is do I need to go back and do the VE tables again in SD mode? How does the injector flow rate come into play in SD? If I adjusted my VE to get almost 0 LTFTs will they still be accurate with the new IFR?

Thanks!

 

The trims would be so far off from the injector flow rate. But at least now you can truly fix the VE!

 

One other question, any other tables that need to be adjusted when you change the injectors? I did a compare on the same file I used to get the IFR table and noticed a couple other fuel related tables are different. Initial Adder vs. ECT, Offset vs Volts vs. KPA, Short Pulse Adder and FA Mult Stage 1 vs. Time are the four with differences that show up under the General Fuel tab.

Thanks again to those that have responded. If nothing else chasing these problems helps me learn more about the different tables.

 

Bump, any input on the "other tables to change" question. Did any of you guys that installed new injectors tweak anything besides the IFR?

I am going to start over from scratch on the VE table tuning just to make sure it's right.

 

If you get your IFR right, you shouldn't need to tweak anything else to compensate for it... at least not as far as I have experienced. For your basic tuning it will be fine.

 

well i am wondering how far also a MAF can be off by??? mine is descreened, lid and filter....so i have been getting my fuel trims in order and she is running quite well in SD, but when i plug my maf in WOT goes WAY Lean. i have a A/F gauge on my stock O2. i know this is not very accurate but it gives some idea of whats going you know. in SD it lights up the first Green LEd which is slightly rich when she was stock it was close here. now when i have the maf plugged up it goes off the gauge lean. so i think i need to tune my maf, but i didnt think that they could really be off by that much.

 

bump...I've been having some issues with this myself

 

Same thing happened to me, I am good SD then I plugged the MAF in and it got all out of whack.

 

If the VEs are good, log dynamic airflow vs. Maf hz to see how far off the maf is. This should get you in the ballpark, but only if the VE table is on target.

 

Exactly, although i've never seen one up to 40% off, I have adjusted maf's that were close to 30% off.