RedWS6 00

A while back i changed my fuel injectors for the racetronix 42lb/hr @ 40PSI, I corrected the Injector Flow Rate vs KPA VAC, table entiries range from 48.86 to 53.51, as the fuel rail pressure is near on 60PSI these i beleive are the correct values to enter. This may not be the root of my problem but thought I'd better mention one of my last modifications.

Anyway I have turned off the MAF, doing a SD tune, logged many cells at operating temprature, some of my cells 30map and below are -15. Now I look at my VE table for example one of my cells has 12 in it, now if I take away 15 i will have negative numbers in there. Should I go negative? Am I doing something wrong, have been reading some examples of SD tuning and you just take your logged figures away from your VE table, smooth out the peaks etc....

Questions is, should they entries in the VE table go negative or have I gone wrong with the injector numbers?

Black02SS

iTrader: (36)

Are you sure the car is in SD? And you shouldn't be subracting -15, you should be taking away a percentage. I am going to assume your table is 15% out for that cell. What are your Wideband readings l ike? If not a wideband, are you using LTFT/STFT? Several will tell you it is a PITA to tune with LTFT/STFT.

EDIT - Just saw your sig. Disregard the wideband question.

RedWS6 00

I set the MAF faile frequency to zero, and the SES light comes on, so pretty sure I'm in SD mode.

Have read a couple of places you just take your LTFT reading away from the VE table, I thought it looked a bit harsh doing it that way. So for my example of -15 in the LTFT, 12 in VE table. We would work out -15% of 12. Gives us -1.8, so our new VE value would be 10.2 rounded to 10. What do you mean by the term 'PITA'?

Hopeing to get the wide band fitted in the next week or so. Got the pod on the dash, just need to get someone to drill a hole and fit the threaded part in the exhaust just before the cat.

Black02SS

iTrader: (36)

Pain in the ***. Take the MAF table and zero it out just to make sure. That is how I would do it.

RedWS6 00

Okay I will zero out the MAF Airflow vs Output Frequency table. I'll give that a go.

The other thing I was going to mention, if I was doing it the wrong way, say my LTFT was -15, and my VE cell was 30, and I make my VE cell now 15, which we know is way too low as it was the incorrect calculation, how come next time round it wants me to take more off, if I over shot the mark, surley it would make the LTFT possitive next time, but I still see approx -15 next time too, even though I zeroed fuel trims and driven for a couple of hundred miles. Also do we tune all cell or ignore ones below 30kpa?. I have noticed I only get up to 97kpa at WOT is this normal?

I will zero the MAF table and see if I can get meaningful LTFT's, it just seems strange that I take way to much off the VE cell and it wants me to take more off.


Thanks for your help Black02SS

speedracer5532

iTrader: (8)

I see that you have a 2000 car so make sure you are making the changes to the secondary ve table. On 98 - 00 cars when it speed density they run off the secondary ve table. 01 - 02 cars only have a primarly ve table so might want to think about upgrading to an 01/02 OS.

Black02SS

iTrader: (36)

This is a VERY VERY good point as I sometimes just assume people know this already. Make sure you are making the changes to the backup ve table or flash a 01-02 OS onto it. This would make your tuning experience a little easier especially when you get the wideband. Thats speedracer for pointing that out to him.

If you need any help going to a new os, just let me know and I can walk you through it.

Black02SS

iTrader: (36)

One more thing, make sure your Injector Flow Rate table is scaled properly for the 42lb Racetronix. Depending on the conditions and your location, you could see anywhere from 90-100kpa at WOT. I see about 99kPa where I am located but people that live in higher elevations may only see 94.

RedWS6 00

I have no secondary VE table, I have the HP Tuners 1bar Speed density OS in the PCM.

Thanks for the help, just going to change the pump and wll do some logging later on today.

RedWS6 00

Well the Walbro 255 fuel pump install went rather well.

Off to go and do some data logging.

If I was doing it the wrong way, say my LTFT was -15, and my VE cell was 30, and I make my VE cell now 15, which we know is way too low as it was the incorrect calculation, how come next time round it wants me to take more off, if I over shot the mark, surley it would make the LTFT possitive next time, but I still see approx -15 next time too, even though I zeroed fuel trims and driven for a couple of hundred miles. Perhaps zeroing the MAF may sort this out, thats what I'm going to try now.....

LoWeLL216

iTrader: (1)

Sounds like you're doing things correctly, but are you sure you don't have a secondary VE table? The formula for tuning with your LTFT's and STFT's is pretty easy.

LTFT + STFT = Correction to VE Table

Are you STFT's around zero when you're making your corrections? If not, you may want to try driving around a little more until they are.

Ragtop 99

iTrader: (7)

According to your sig, you have very minor performance mods. Why are you putting in huge injectors?

You're stock VE table should not be very far off. If you are cutting the VE a lot it is because the injectors are not set up properly in your PCM.

RedWS6 00

Good point. I got the larger injectors for future mods, will CAM it, drempt of supercharging it, so I wont choose a cam jut yet until I know what my future mods will relisticly be. So the larger injectors are for the future.

The stock VE table isn't far off. Wanted to get a feel for tuning while the car still works. I thought I had the injectors set up right, but then some posts say the may be liner or log, so that will dramatically throw them off. Over all when I do a LTFT log, its only below 30kps which reads -15 or more, 40kps and above seems to sit around -4, which is nothing to worry about. At WOT I could get 950mV but then 5 mins later, WOT would be 890mV. Olny have narrow band at the moment, Wideband is on my desk.

Ragtop99, what values do you think I should have in the injector flow rate table?

Thanks for you input.

VORTECFCAR

iTrader: (2)

nobody ever answered the question of: when doing a VE table adjustment and the LTFT cell says 10, do you add 10 to the corresponding VE cell or do you add 10% of that VE cell to itself? This could make a huge difference!

LoWeLL216

iTrader: (1)

The VE table is already in percentages. So are the corrections given via the fuel trims. What ever the correction is add it directly into the table.

ie LTFT = 10, add 10 to the corresponding VE cell

There are a couple good spreadsheets out there that makes this really easy in the stickies.

VORTECFCAR

iTrader: (2)

I understand the VE table is in percentages, the question is still valid.

I ask this because I had a similar issue when I tried to add my ltft numbers to my VE table and smooth it (graphically). My 'after' LTFT's were off by even more than before. I was curious if this was because I had added too much (by a factor of 10) to my VE table. It appears that it was not. Back to the drawing board.

joecar

Do you add 10 to what's there or 10% of what's there to what's there...?

Black02SS

iTrader: (36)

Here is someting I don't know if you have thought of. If you see a -4% for LTFT then the car is rich so you need to subtract that percentage. That is how I do it at least and it works for me. I think of it this way, if you see the car is trying to remove 4% to compensate for the richness, then why wouldn't you take 4% off of the ve table. I have maps setup in EFILive that take this back to a BEN factor and it appears to work. I have only done it a few times as I only rely on a wideband to tune.

joecar

That's what I would do, -4% of what's in that cell in the VE table (not -4, but -4%).

So, you'll never end up with a negative number in the VE table.

joecar

The VE Table may be being displayed as a percentage of cylinder volume...
But the LTFT is the percentage that that percentage is out by.

i.e. they are percentages of two different things, so you can't just add/subtract the percentages.

Think of it like this...
If LTFT is -4%, then multiply VE table cell by 0.96.
If LTFT is +4%, then multiply VE table cell by 1.04.