I had a similar thought to that, just didn't want to bother trying to simulate an o2 sensor.

 

I don't know computers well enough to do such a thing but it sounds logical. I think it could be done.

 

I've been hashing it over with some of my EE major friends i'm ME so its not my bag, we're working on a plan.

I did have another thought though, theres a table in TC called fast 02 rich/lean threshold. I'm not sure what it does but it functions in closed loop, if you can manipulate that table and move the threshold for rich lean you can change the way the counts act at idle and target a leaner a/f ratio, the only problem being narrow band o2's are so far from linear that its scary. There is also a table that sets what TC is calling "closed loop mode" for the values in that table.

Vince, i'm curious if you got any farther with testing the pe idle stuff, and how its been working for you.

 

With my vehicle... I originally had the same rich idle. What I find is that you can find "band aids" to mask the problem... and sometimes it is required... however, it is often better to try to fix the problem first.

BTW... my car is a 383 with a custom grind cam similar to a cc306 with a 110LSA.

First thing... is increase the idle a little. I set mine to about 950rpm.

I then used the VE Master program (do a search for it) and logged the car and ran the program about 5 times. This not only helped my rich idle conditions, but also my split BLM's.

There is a lot of discussion of whether the 94-95 OBD1 cars actually use these tables... and I was skeptical at first... but logging after the car was tuned, you can see that the BLM's stick closer or a little lower than 128 (I set the target to 124 for WOT tuning). My theory is that the less the computer has to adjust (hence constant BLM's) the smoother the car will run.

I have done this with another 383 LT1 (OBD1) and while the BLM's did smooth out, we didn't have A LOT of time to log and his idle was still a little rich.

So what I did was similar to what is recommended here... set your PE mode at lower RPM's (where you idle) to 0 so that you enter PE mode and can tune those tables.

The only thing that was missing from previous advice is that the car will learn... and slowly, your BLMs at idle will approach 160 versus the 128 that it will start off with before it starts learning. This is because the LTFT will slowly increase to adjust for what the STFT are telling it to do.

So what to do about that?
There are 2 things you can do.... and you can do either one or the other... or both.

Firstly, limit the variances allowed to be recorded for the LTFT and STFT. The LTFT is set to be between 108 and 160. You can pull back some on each end and it'll add less fuel. The problem that may arrise is that you may require the car, in other cells, to adjust higher than the maximium/minimum you have set... and it will not compensate. Now if you've run VE master a number of times... this will not be an issue. I like to adjust both the Min and Max equally to make sure the programming is balanced. You can do this with the STFT as well.... but make sure they remain outside the LTFT parameters by the same amount as is set up stock (ie. if the LTFT is 160 and STFT is 198) then make sure if the LTFT is 145, that your STFT is ~170. This is just an example.

The other thing you can do is get BLM Locker... you'll need to do a search for this one. This will lock your BLM's in PE mode to 128. I prefer this method as it will also make you WOT runs more consistent as well (What it was really designed to be used for). By locking your BLM in PE mode, and having set your idle RPM's to be in PE mode at anything above 0 TPS, no adjustments can be made... and you can set your PE tables at idle RPM's to pull as much fuel as you want.

A little long winded... but I hope this helps. Try also searching for VE master, BLM locker, and other topics to round out your knowledge if you want to know more.

 

Yeah thats pretty much how i start with a tune. I just can never seem to get the idle as lean as i want it even when the blms are set and running 128 solidly at hot idle (and everywhere else) the car stinks of fuel. Maybe its just part of running a cam and i'm picking at something that isnt a problem. It just seems like with my cam there shouldnt be enough overlap to cause a rich idling condition, who knows.

Also when you're talking about running ve master on your maf car, are you doing it in speed density mode or are you letting it make adjustments with logs from maf mode.

 

I do it in MAF mode.

As for smelling rich....is it when you're warming the car up in Open loop, or is it in closed loop.

In open... it still gets a little smelly, until the motor warms up a bit. I don't think you'll be able to fix that. As for smelling during closed... are you pulling any fuel out in PE mode after setting idle to be in PE mode?

BTW, if you're not running a cat. converter... adding one may help.

 

Well when i first load a new tune into the thing or i pull the fuse to the pcm it smells fine but after some learning, it will apply that to the open loop fueling as well durring warmup, because the learning is stored in whatever blm cell its using at the time.

After that the rich smell is pretty much constant, I havent set my idle to pe mode as i havent yet given up on closed loop fueling at idle.

Also how effective does the ve master seem to be for you in maf mode, do your blms come around right away or does it take several iterations before you see any marked improvement.

As of right now i'm fighting a bit of a problem. Previously my blms were relatively close together. and now the thing has a 7% split all the time with the drivers side being the higher reading. Theres no vacuum leaks and the problem doesnt follow the o2 sensor so its not that, and they read the same hanging in open air heated up. The rich smell has to be related to the fuel being added on the drivers side. The wierd thing is even though theres a split they both stay together as far as adding or removing fuel. Anybody have any ideas of things to check for?

more specificly my problem cells are
16 143/128
18 141/127
2 127/122
6 128/121

The numbers do move around but the split stays pretty much the same under steady speed or decel. The wierd thing is that anytime in my logs when i'm accelerating midly or loading the engine going up a hill or what not the blms come together, not even necessarily at higher airflows or rpms just lugging the thing climbing a hill seems to be enough to bring em together.

Sorry for the thread hijack.

 

No problem! I am haveing the same problem. Just curious, what are the specs on your cam?

 

You'll never get the dead on.... and I wouldn't worry about them too much if they are about 7-10 apart.

Using VE Master... it took about 5 times, in different driving conditions to get them where I wanted... my LBL is always a little higher than my right LBL... but the LBL remains nearer to 128, and RBL stays a little lower.

-------------------------------------------

I had the same problems with you regarding my idle... and had some other driveability issues as well... and I know it's a little frustrating at first... but one you fix it... you'll be happy again.

What I actually did was start with a stock tune. My car... had been "touched" by a number of tuners within the last 5 years before I decided to get a Wideband and do it myself.

Firstly, before even tuning the car, I checked to see if everything was mechanically OK. Usually, with our LT1, if we have a problem, it's an ignition thing... and with a lumpy cam, it's hard to feel if there is a miss. The way I test it, when I'm driving is that I rev the car from idle quickly. If it gurgles a bit before it revs... I know I have a miss. Then, in the dark... you can see if there is any arching. Having a miss will really screw with your tune.

Now onto the tuning. I only change what was necessary and tried to leave as much as stock as possible. GM Engineers took a lot of effort to create the tune... and my theory is that the less I touch.... the more steetable the car would be.

I changed all the values for my 383 volume , injector flow rate, gearing, thermostat, DFCO, cat overtemp, and some emmission stuff. I also increased idle speed to about 950rpm. Lastly, I altered shift points for my auto to the values I had before as it took a while to figure those out... and shift points have really no impact on the rest of the tune.

I then ran VE master... and tuned the car about 5 times... on different days, using it.

Next... I played around with the spark advance at idle. It is a few degrees higher than stock from 400rpm to 1200rpm.

Then... timing tables were adjusted. Now this is just a general feel, as it's tough without a dyno to determine exactly with what timing you got the most power. But I compared my old tune, with some other 383's and made some calculated decisions.

After that... I then worked on me PE tables for WOT. I always use that at the end.... and in reality, WOT stuff is the easiest stuff to tune... it's really all the other driveability stuff that takes the time.

So my suggestion... start from scratch if you can... and get the partial throttle cruising stuff done first... then worry about peak power later.

 

You've just described how i tune my setup just about to a t except for using ve master i havent made that step yet, I had intended to tune the car in SD mode with it. I've set my idle to 850 and there according to the map and bar press its making approx 15.5" of vac in gear. There are no ignition gremlins no arcing and if i blip the throttle all i get is a quick trip to 5k rpms, or if i'm in gear a smoke show, all parts under the hood have 7k on them. I've worked with the idle timing changing it two degrees at a time up to about 30 degrees 26 seems to be what its happiest with.

My main problem is with the blms being split... which one do i tune to? by the smell of the exhaust i'm prety sure the high one is adding fuel i dont need. I've been looking at the individual cylinder fueling tables and i know that would adjust things and may end up doing what the computer is doing anyways, but i find it really hard to believe while the lt1 manifold is no gem, that there is a 13% variation in airflow from cylinders 2-4. I also do not believe that the airflow on a cam/heads engine even remotely resembles what the stock is even at high rpms. I may copy it over to a new folder and try to adjust the tune down a new path.

The car runs and drives extremely well, its very smooth. but heres the thing when i come to a stoplight with my window down the stink of gas flows inside my car and i know the thing can be better, and i cant leave it alone thats just how i work. Also of interest, if i rest the computer frequently by pulling the fuse for the pcm, i can get close to 25mpg, otherwise if i let it learn it stabilizes about 20-21.

Also curious what did you adjust in DFCO and what exactly does that do? And how about some tips for setting up a baseline PE idle, and what do you do about the intergrators that still accumulate during pe idle. because once you give it any throttle input dont the things apply and you run richer than crap since the car cant change its fueling at idle.

Perhaps my best course of action if my individual cyl fuel trim plan doesnt work out is to tune the pass o2 to the best it can be, and then lock the max blms to a low number say 132. Is it at all possible to lock only certain cells or is that a global parameter.

rtracy: my cam specs are, 222/230 112lsa, lift is .543/.564 with 1.6 rockers.

 

I would think that cams with a lot of valve overlap will always smell of gas, because you are getting unignited air/fuel going straight through both valves and out the exhaust. This is why you get false lean readings from the O2 sensors and why PE idle can be helpful.

The tables for Individual Cylinder Fuel Trim fixed my split BLMs. They are within a couple points now. Definitely use them in your tuning, especially for cammed cars. If you have the money, consider buying an IR thermometer, and check each cylinder's exhaust at idle (with headers it's even easier, otherwise just point it at the manifold closest to each exhaust port. Tune until they are close in temperature.

 

Yeah i thought of that i have a couple of IR thermometers around. Kinda wish i had an egt for every tube like i do on my engine test stand.

 

I wouldn't suggest touching the cylinder fueling tables... as you'll have the same problem regardless... and as you increase RPM's, I would think the stock values would be better than any possible changes you could make. What I'm assuming you were thinking of doing is pulling fuel from one bank of cylinders, so the BLM's become closer. Regardless of the changes... your O2 sensors will still pick up a false "lean" condition as O2 passes through your motor unburnt and tells the O2 sensors that more fuel needs to be added. Regardless of how much fuel you pull out of one bank... it will still max out. Playing around with the banks, you may actually lean them out too much at WOT or higher RPM... which is worse than being rich.

Try VE Master to keep the BLM's closer to 128 (preferably even under 128). Then use BLM Locker to lock the BLM's at idle to 128 and pull fuel from your PE tables at idle... to prevent any compensation above and beyond 128 if it still smells rich narrow the short term and long term to decrease the possible amount of fuel being added. If in normal driving (not driving) you see the BLM's after VE master staying lower than, lets say, 135... then set the max Long Term to 137... and set your Short term to 147. I also adjust the minimum as well so they are equal above and below the 128 mark. The car may always smell a little rich... but nowhere near as much as what your are describing. You may also get a lean code if you idle too long, that goes away after you start driving. You can tune out the code if you want as it gets alittle annoying.

When you're driving... lets say on the highway... and you let go of the throttle, fuel is normally cut off... as there is no reason to burn fuel on decel. Amongst other variables, vacuum is one that is used to calculate when to shut off fuel with our cars. With larger cams however.... the vacuum characteristics of the motor change... usually enough that the DFCO is never activated, and you're burning a lot of fuel on decel that is not needed. What I did was log the car when driving normally. I'd let go of the throttle (O% TPS) at different speeds, and looked at the MAP values. I slowly increased the DFCO Engage and Disengage vacuum values until it started engaging. The problem if you increase them too much, is you will find that when you go down certain hills, or other conditions, that the fuel will turn on and off... so you need to make sure you don't go overboard. I also changed RPMS of when it was activated as well as the "hysterisis" (sp?!) as with a lumpier cam, you want a greater vacuum and rpm value. These can be found in the constant tables... and there is a DFCO specific table as well in Tunercat.

You'll need to really drive to determine what you like... and with an M6 versus an A4, you may want more or less. But you will save some fuel for sure.

Don't go crazy pulling a ton of fuel... but you will see that the car starts bucking a little if you pull too much fuel. Use your nose for to smell for gas. In reality since O2 values from an O2 sensor can't be used to determine adequate burn... if any of your contacts had a machine to measure CO2... you could in theory tune your car for idle. We have these for our "Drive Clean" programs in Ontario... but I've never used one. In theory, the more "burn", the higher the CO2 levels.... so you want to get the most CO2 levels, with the least amount of fuel possible.


Each "cell" has it's own values.... you idle in Cell 16. You drive in a number of other cells. Someone may correct me on this one... as cell 16 is a funny one... but for every other cell (determined by MAP and RPM boundaries)... the computer really only uses the memory from that cell in particular. So you should be fine driving after locking the idle trim.

As above... stay away from indiv. fuel trim plan as you may cause more problems. If you don't have individual IGT's for each header.. how would you know if one cylinder was running too lean? Not a good way to ruin a perfectly good motor.


BTW... my cam is a 23x/24x with a 110 LSA. While each vehicle is different... I suggest using VE Master first... and see how it goes... then apply each "band aid" (BLM Locker & tighter BLM boundaries) to see if it fixes the problem. The fewer "band aids" the better.

 

Forgot to mention on the previous post.

The only "problems" I see here are with cell 16 and 18... being apart 7 points is not much for the other cells. You should try logging a stock LT1... they are never "perfect"... hence why BLM boundaries are set from 108-160

As for 16 and 18.... 16 is at idle at 0 MPH... 18... is at 0 TPS, and moving a little.... so really it's the idle issue that is the problem. Not bad though... a really lumpy cam, will shoot values up to the max of 160.

 

I only call those problem cells because everywhere else my blm's are either 128/128 or 128/126. but i agree the idle cells are the problem most certainly its just that 2 and 6 seem to have a similar split. I have never logged a stock car to see what the values look like, anybody wanna provide a datamaster log of a bone stock lt1?

Only reason i thought about the individual fueling is that the stock values seem to be so drasticly wild from one cylinder to another. Some cylinders are getting 8% enrichment while the ones next to or acrossed from them are seeing 5% trimming which is if you think of it in terms of air and fuel a 13% flow difference from locations less than an inch apart.

Thanksgiving week i should have all kinds of free time to try and get this squared away, i'll try your suggestion first and get everything as close as i can and hopefully the things will just natrually come together. What i hope is that as the numbers near 128 the numbers come closer together, i have my doubts in the stock pcm being very good at adjusting much more than a couple percent.

The thing i cant quite wrap myself around is which blm do i tune for? the high one or the low one?