I'm trying to get my VE tables in line and am having an issue with these values. My motor is a 383 with a fairly large cam, I'm using tunercat, Datamaster, and VEmaster to help with my VE tables. I am getting a code thrown #33, MAP voltage high. After datalogging I notice that the highest value when driving was 103.3 kpa and during idle around 70kpa. When using VEmaster I receive an error that an overflow occurred when applying the new adjustment factor to literally every cell, the proposed adjustment factors range from 1.0-1.38, and when applied to the existing VE value over shoots the 100 maximum (example below*). I initially expected that one of the constants in the tune was off, such as the cylinder volume but it checks out fine. There are no vacuum leaks nor exhaust leaks.

So the question is how to correct for this, could I simply rescale the VE cells down by 38%, as the largest adjustment factor was 1.38. Somehow I don't think that this would resolve the issue as the PCM would always be trying to relearn and in effect compensate for these adjustments. Any thoughts?

ll Old VE Adj. Factor New VE

VE table modifications:
cell[400][20] 48.4 1 48.4
cell[400][25] 52.7 1 52.7
cell[400][30] 98 1.17 (*)
cell[400][35] 97.3 1.35 (*)
cell[400][40] 99.6 1.35 (*)
cell[400][45] 98.8 1.35 (*)
cell[400][50] 99.6 1.35 (*)
cell[400][55] 99.6 1.37 (*)
cell[400][60] 96.5 1.39 (*)
cell[400][65] 93.7 1.39 (*)
cell[400][70] 95.3 1.39 (*)
cell[400][75] 96.5 1.39 (*)
cell[400][80] 93.4 1.39 (*)
cell[400][85] 97.6 1.38 (*)
cell[400][90] 98.4 1.38 (*)
cell[400][95] 96.1 1.38 (*)
cell[400][100] 98 1.38 (*)
cell[600][20] 50.8 1 50.8
cell[600][25] 54.7 1 54.7
cell[600][30] 99.6 1.17 (*)
cell[600][35] 98 1.35 (*)
cell[600][40] 99.6 1.35 (*)
cell[600][45] 97.3 1.35 (*)
cell[600][50] 97.3 1.35 (*)
cell[600][55] 95.3 1.37 (*)
cell[600][60] 96.9 1.39 (*)
cell[600][65] 97.3 1.39 (*)
cell[600][70] 98.4 1.39 (*)
cell[600][75] 93 1.39 (*)
cell[600][80] 96.9 1.39 (*)
cell[600][85] 96.1 1.38 (*)
cell[600][90] 97.3 1.38 (*)
cell[600][95] 98.4 1.38 (*)
cell[600][100] 99.6 1.38 (*)

(*) - An overflow occurred when applying the adj factor to the
original VE table entry. The old value is being used, but it is
recommended you look for exhaust or intake vacuum leaks, since VE should
never be in excess of 100 (or less than 0)

 

I'm assuming you have put this thing in Speed Density mode?
You didn't say what is in the engine, but a correctly modified engine will surpass 100% V.E., and the way GM wrote the OS 100% is the largest value you can enter. LT1 PCMs with modified engines in SD mode have to be band-aided & lied to when fueling them. Stock engines are no problem.
What do you have that can't use a MAF?

 

Nah, I'm still running a MAF, the car is NA. The car just runs stronger when my BLM's are around 124-128, plus it is good to have in place just in case.

 

Then, your going to be a while seeing much change working on the V. E. tables, since they aren't used once the car starts when the MAF is used. Use V.E. tables that will idle and drive to get the vehicle home if the MAF fails, as that is the only time they are used while running.
Had to finally convince myself many years ago when first told this. Your just running off the MAF, and Open Loop fuel table.

 

Ok. So the consensus is to simply tune the MAF tables and leave the VE tables alone. I guess I've been working on the other side of this.

 

If you have time, put it in SD mode and get the V.E. tables as good as you can get them. If the MAF does fail you can still drive it to get a new one. Your WOT fueling will be way off (lean) that way, but you can drive it. Then put it back in MAF mode to do your final tuning.
Hope this helps.

 

I am split on some of that. And what I have done is..... I locked it into SD mode and tuned it in. So like he said when and if it fails it won't hickup. Weither it be going down the track or not. BUT what I did is......I setup so once it hits 80 Kpa it goes into SD mode. When it see's WOT it is SD mode. And when in closed loop I also have it fine tuned. Sorry not buying into closed loop it runs perfect! Mine didn't and took some time to get it dialed in for closed loop also. I've spent over 1000 bucks to get it tuned and no one could get it leaner than 13.5:1 in closed loop. Kept getting told that closed loop the MAF and O2's adjust..........NOT. The MAF table was not correct for my motor and modified a couple of other tables also. And then found out that the VE would.........Just be prepared to possibly rework the tables a little bit after you tweek the VE table. And tuning open loop does take some time. If your doing it yourself you will know whats going on with that motor no questions asked by time you get finished.

And for side note....for a full SD tune.......... spring and fall temps help dial it in, because of the cooler temps. I have mine tuned down to 15 below. My buddy's thought I was nuts tuning my car this winter. Reason why I did it.......didn't have much if any snow when we had those temps this year in Minnesota. And a perfect time to get those blocks tweeked. Probably not gonna need it.......but it is done none the less.

 

and also the numbers that you put in the tables are just a number that the computer uses as a reference. Like in the Open loop vs load vs temp table.......that isn't the actual A/F ratio the computer is using. There are other tables that add and subtract from that reference block. The computer is dumb actually it can't tell what the A/F actually is TILL......... you can use a wideband.

 

Thanks for the info! I'll have to play around with it and see what happens.

 

Interesting views on things. I have to wonder where you got some of your information, to make some of those calls.

 

I would be very much interested in knowing this as well, it is very much in line with my own experience(s).

On a similar note, is there any provisions within working with the MAF tables to account for large splits in BLM's? I don't see anyway I can do so.

 

What in the world did he say that is in line with your own experiences??

Split BLMs have nothing to do with the MAF or VE tables.

 

When using VEmaster it has in the past helped in correcting split BLMs, although I'm not entirely sure why. After running these corrections to the VE tables it performs much better even though I'm not in SD mode and am running a MAF.

 

To prove to yourself that you are right, log your fuel trims at idle. Then fill the V.E. tables with zeros and do it again. Get back to us with the huge change in your fuel trims.

 

You may have seen an "effect", but you mis-identified the "cause".
Possibly what you saw was the absence of learning just after flashing the PCM.

 

To be honest I can't make sense of it either but it has consistently done so over multiple iterations, and not just transiently as if it were due to relearning etc.

At the moment I'm out of town on business but can test out logging the fuel trims as suggested in a few days.

 

If I were you I'd take Ed's advice like the gospel. He is one of the best lt1 tuners in the country.

 

Thanks! But, it is easy to prove for yourself.

 

I have did a lot of learning on my own. Read and reread write ups. And then went out and tried something and made note of what did what. Its kind of frustrating cause it takes so long to go through the changes. I'm not going to name names but if they raise an eye at my way of doing things and think it is wrong. Look Patrick Dirckx up on there customer list and they will know what I think cause I have saved tunes that I would love to send to them and tell me what the hell they were thinking at the time!

And I got lucky and found a mail order tuner that answered some of the questions I had. And things started to fall into place.

Had a local tuner that was suppose to be so good, do a suppose to be a full dyno and a road tune. Got it back and 13.0:1 for cruise, come on even I got closer than that at the time. And then the dyno tune for WOT was somewhat decent. 12.7-13 A/F ratio but only tuned to 5000 rpm and told me the opti, plugs or wires were bad. I'm in a wheel chair so I didn't load it to see but when I got it home filled up with gas and problem solved. He got it and ran the tank dry. Plus he got another 100 bucks out of me on top of 500.

Im not saying I know everything or what to do it for someone else. But I know quite a bit and not closed minded to learn some new info from someone else. I've been at this since I started upgrading my engine. Started with a hyper tech unit, and then I down loaded that file once I got LT1 Edit. And figured out what they did. But there is no one way of doing something. Many I have seen try changing the MAF tables only.

I went a different route. and also I had an issue with the injector constant. There weren't any tables out there so I tried varies other ones that I came across and got inconsistent data. I finally found something by going with Bosch values and poof everything feel into place. So they are VERY important also. in the normal Batt volts there was a difference of .20 volts that really made a difference. So when I upgrade injectors again. I am getting injector offsets with them or I am not buying them. When I did my build there wasn't this big aftermarket like there is now.

 

and with the computer that just uses narrowband O2's it cant tell what the A/R is. It just knows that 450 is 14.7, 850 (or so is 13:1 or so have to veryify with wideband) And 200 is lean. That is why it bounces back and forth. In closed loop it doesn't stay a consistant A/R. If it did it would stay at the A/R it is told to run at....at that load (kpa) vs rpm vs temp. When tuning you have to take in account for the air temp also. When air is colder you need more fuel. As to when it is warm. But on flip side of the coin. When you get an over temp you can shoot more fuel into it to help cool it off or a lean condition.

But I am talking about stock OBD2's there are some aftermarket systems that are doing a pretty good job. However I was talking to Doug Rippie in Mpls, MN and he is a big name in LaMans racing. He told me the best computer system out there now is the LSx OBD2. They said aftermarket is getting better, but just that the OBD2's have tables in there that we dont have access to that really set it apart from aftermarket. For a street they recommend LSx OBD2 and strictly race...... aftermarket is probably better cause they do their own special tuning for where they are at anyways.