hey guys,

I just put a sns stage 3 cam (his new version by cam motion) in, some messaged 243 heads, ported ls2 intake and tb and I have the tune dialed in pretty good but my idle feels like its fighting itself and the gas smell is pretty crazy. My wot and cruise is pretty on point as i can cruise around in 5th gear at under 1500 rpm without any real bucking which is pretty good for such a big cam I think. I have been reading a bit about EOIT and there are a whole bunch of different theories and spreadsheets out there and it seems like something I really need to get dialed in on my car. Can somebody help me with this or have a spreadsheet that they know works I can use? Our pcms use a boundary, normal and makeup tables and im not exactly sure what to do with them anymore lol. Thanks for your help.

I attached a copy of my tune.

 

Not familiar with the HP term EOIT --What is it ? I 'm sure EFILIVE has the same table but it's called something else--What are the issues you are having ?
A rich exhaust smell is usually caused by LT headers---As with LT's by design the front 02 bungs are moved aft almost 3 ft----This makes your front 02's not heat up correctly and give erroneous readings causing your engine to run RICH in closed loop or P/T
There is no 100% fix for this and is why LT's are illegal in most states---There are a few things you can do to help--- Many people install the rear 02's onto the front locations as the rear 02's are far more sensitive and heat up better--The other thing is to LOWER your front 02 switching points to trick your ECM into commanding a leaner closed loop AFR---Same goes for cold starts when the ECM is in open loop-- On my heavily modded 98 I had to command an open loop cold AFR of 16.10 in order to achieve the stoich stock AFR of 14.68----You must use a wideband to confirm the ACTUAL AFR's before making any changes to these tables either CL or OL--
PS If your cam is considered BIG--many will have to turn OFF the LTFT corrections as a large cam with lots of overlap will tend to make your LTFT's very unstable and a bitch to tune

 

its end of injector timing. i figured it out but it didnt really help much. i did trick my car into being in pe under 1200 rmp and set my pe under 1200 rpm to 16 afr and it did help the idle a little but i couldnt get it to come out of pe like i wanted so i was crusing at 16 sometimes and 14.7 sometimes. the car didnt like it so i set it back to the way i had it. Im pretty happy with how it is running now.

 

I was watching your other thread where I mentioned the PE idle, you never mentioned any issue so I assumed you had it figured out. You stated it idle'd better @ 16:1 hence my OL idle suggestion. Should not be any issue going back to CL above 1200 if you have set it up correctly, I can check how you set up the tables if you wish.

Myself when I had a big cam it was tough to get it idle correctly in CL, it was better in OL but very inconsistent especially hot restarts. I've down sized the cam as the ramp profile was hard on springs & I couldn't live with tuning/drive ability issue's.

 

I did get it to idle at 16:1 and it liked it but it would not come out of ol like i wanted so i went back to a normal idle. I can live with it, it just how big cam cars are going to be. I deleted the other tune but this is my latest tune and the car seems to be running good with it.

 

In closed loop or during P/T driving the ECM is always trying to achieve the stoich AFR of 14.68---However when you lift off the throttle say above 3500 RPM's another program kicks in. It's called DFCO Deceleration fuel cut-off---It is there to save fuel- and shuts the fuel off momentarily and the AFR will spike into the 16's-----
Most likely this is why you are recording some lean AFR's----Often times however with large cams tuners find they have to turn the DFCO OFF so the car won't die or try to die when lifting off the throttle--

 

i left my DFCO factory because i like the pop and changed my cracker and follower tables to come back to idle. it comes back to idle perfect evey time.

 

The stock injection timing will run into problems as we install cams with more and more overlap. The exhaust valve remaining open will result in "scavenging" a part of the cylinder charge (raw fuel) out the exhaust. This phenomenon will actually read as a lean condition on your wideband O2. As a result, your natural tendency is to add more fuel which just makes matters worse.

A simple procedure to resolve includes the delaying of the injection timing to wait for the exhaust valve to close. To determine how to do this, look at the injection timing table and see what the trend is as far as values (different parameters and direction of change for various years/os) that the oem shows. Injection time is always the earliest at cold and slowly is delayed as the temps increase. This is to allow more evaporation time in a cold engine. Also the LS methodology is to inject the fuel onto the back of a closed intake valve.

So idle you car and record the lambda/afr reading. Go to the injection timing table and remove say 5%. Reflash the car, give it some time to adjust and record the lambda/afr. If you are going in the right direction and reducing the short circuiting, the readings shoud begin to show a richer mixture. Keep making small changes until you don't see an improvement. then go back to the previous setting. A rule of thumb would be to decrease eoit by the degree's of overlap. In some years it is specified in reference periods as well. Once complete, you can remove the extra fuel you may have added to correct and all should be right with the world again :-)

Hope this helps

Ed M

 

This thread got me thinking about trying to tweak the EOIT in my 2000 vette, running a Comp cam with 228/230 duration with XE lobes and 112 LSA plus 2 degrees of advance. After reading a very lengthy thread on the HPTuners forum I thought trying to get the EOIT around TDC was what would work best with this cam. I therefore changed the EOIT value to 6.22 which from what I read should have put it with a degree or so of TDC, vice the stock positioning of 301 degrees.

Car seemed to be running fine after the change. Couldn't really tell a difference in performance or fuel smell at idle. After having put several hundred miles on the car running with that I was out one day and proceeded to pass a couple of cars on a 2-lane highway. After clearing the last car as I was lifting off the throttle I got a very loud backfire. At the time I wondered if it was just bad timing that I lifted when hitting the rev limiter, set at 7050. Luckily I was data logging at the time so I could check that when I got home.

After I got home I checked the data log. Turns out when I lifted the rpm was only about 6400 so it wasn't a rev limiter issue. (Auto trans set up to shift at WOT at 6800 rpm.) Before doing the EOIT change I had dialed in the MAF calibration nicely - LTFTs were all slightly negative. Looking at this data log though I was surprised to see I was getting positive LTFTs - approaching 10 - in fuel cells 3 and 15. These fuel cells correspond to rpm conditions above 2200 and no load (3) and high load (15). Note that I don't often see rpms much above 3000 in cells 7 and 11, corresponding to high rpm in low and medium load conditions. I attribute not seeing the high fuel trims there to the engine not running that fast in those cells, whereas at WOT I'm obviously taking it close to 7000 and it drops to the corresponding no load cell whenever I'm at WOT high rpm and then lift my foot off of the throttle.

Looking at that data I had to conclude that the engine isn't burning the fuel efficiently at high rpms with the later EOIT. I don't believe through the stock PCM and HPTuners I have a way for an rpm-based variable EOIT, so I have decided to go back to the stock EOIT. After putting another hundred or so miles on the car after going back to this EOIT my cell 15 LTFT is back to slightly negative, cell 3 is decreasing but still positive. I suspect it is just taking longer for the computer to learn where that one needs to be. Car still has the fuel odor at idle. It may be a bit worse but hey, it's just part of having a big cam and no cats. (I don't know that it's worse - hard to really measure objectively.) Car seemed to have better part-throttle response after going back to the stock EOIT, but that may or may not be real.

Anyway, just thought I'd share my experience...

Edit - I'm running closed loop at idle and Power Enrichment of course...

 

Are you still using your MAF ??
Do you still have your LTFT's enabled ??
If so---On large cams I tend to always have to turn OFF the LTFT correction---
Added airflow for whatever reason will most always make your engine run leaner--
Then that will make your LTFT's go way positive --meaning that the ECM is always adding that % whether it needs it or not--Fueling demands happen in milliseconds but the LTFT's take a long time to settle down---This consequently means that you may get added fuel at times when it's not needed--Making it run RICH all the time---
Try disabling the LTFT's

 

I think you must have tuned my car before I bought it, LOL!

Yes - still using MAF

Yes - LTFTs enabled (should have been pretty obvious)

LTFTs were disabled when I bought the car. Car was running lean until the STFTs could catch up - they would go to positive 20s - meaning that every time engine switched to a different fuel trim cell where the STFTs would reset to around 0 the engine was running quite lean until the STFTs caught up.

Added airflow causing engine to run lean is a sign that you need to add a bit to the MAF calibration where it is going lean.

You and I have some pretty different tuning perspectives...

 

Not really just after tuning 1500 + cars I kind of know where to look for issues and what happens with mods--
You basically say the same thing as I did only in different words
YES Mods will create more airflow
So at P/T with mods if you have a +20 fuel trim that 20% is being added ALL the time ---until as you say " the STFT's catch up " this means that it will in fact run RICH--not LEAN

 

Why do you believe that +20 fuel trims mean it will run RICH?

 

if your STFTs are off by 20% then you need to spend some more time tuning your ve and maf.

 

It didn't take much time at all to address those.

Still would like to know why tblu92 thinks +20 STFTs means the engine is running rich.

 

If LTFT is adding 20% at part throttle (closed loop) it will also add the 20% when you go WOT.

Tuned a C5 that the customer had added headers and a CAI to.
Brought it to us complaining that it blew black smoke at WOT.

Scanner showed LTFT +10 to +15%.
On the dyno checking it as delivered, WOT AFR was 10:1.

Reset trims with the scanner and tested again, WOT AFR was 11.5:1. Right in line with what the factory tune calls for......yes the factory calibration is that rich for a 97 six speed car.

I believe this is what he was trying to explain.

Ron

 

hmmm. i thought ltft's and stft's were not used during wot. just maf and ve

 

Thanks Ron. That makes sense, although I wouldn't go so far as to generalize that fairly large positive fuel trims mean the car is running rich as a rule. Clearly they can as your illustration shows.

I'm not a fan of disabling LTFTs - I think getting the MAF and/or VE calibration dialed in much closer is a much better solution. I suppose many of the "professional" tuners due it as a tuning shortcut as opposed to tuning in a good calibration. I've done probably about 100 tunes for my vette - well over 1000 probably for my truck. They are tuned in the sense of a musician tuning their instrument(s) - playing a note, tweaking in the direction to bring the note closer to true, and repeating until happy with the result.

In my car, when I bought it, with LTFTs disabled every time the engine would move into a different fuel trim cell it would run 20% lean until the STFTs adjusted. At WOT with LTFTs disabled and no STFTs, it would stay lean. Obviously not what I want. If LTFTs had been enabled when shifting between fuel trim cells the fueling wouldn't jump back to lean every time until the STFTs caught up - the LTFTs are essentially the fueling memory for each fuel trim cell and without them the system isn't remembering what it is learning. Yes I want to tune the MAF and VE calibrations to minimize the LTFTs, but turning them off prevents the learning which will help the engine run with a healthy AF ratio if something gets off such as MAF or MAP sensor issues, vacuum leaks, etc.

 

You are very close. STFTs are not used during WOT. LTFTs are only used if positive. Basically if LTFTs are adding fuel the computer adds it as a safety to make sure the engine is running rich at WOT. If they are taking fuel away (negative trims) they are not applied - again as a safety measure to make sure the engine is rich at WOT. With narrow band O2 sensors the engine has no way of knowing how rich it is running so it is in a sense running blind and erring on the side of running too rich versus too lean. This shows the value of doing WOT tuning with wideband O2 sensor(s).

 

I agree. We want the MAFand VE dialed so as to minimize trims. You will then have a happier engine!
Because I did heads, cam, headers, intake, injectors all at once, I started out in open loop and tuned with my wideband. It's very time consuming.
Then went to the track and dialed in WOT with the wideband as well.
Then I put it in CL with LTFT disabled and used the STFT for the fine tuning.
I just never turned the LTFT back on. I should do that sometime and could then dial in the last little bit.
I still like them off though so I know I'm not getting any unexpected adders at the track.

I have a 2000 C5 with the stupid dual VE tables. I'll admit that I struggled so badly with tuning that mess that I have just left my car MAF only. I'll put an 01 tune in it someday as I'd like to try a nice SD tune.

My nova is a turbo 5.3 with a 3bar OS. Tunes very easily! On E85 even. And I run it closed loop with LTFT turned off.

I work as s tuner dyno operator at a Dodge perf shop. Essentially they run a SD system. And you can't disable the trims, so we use LTFT religiously. Thier system updates LTFT a lot more often than the GM system. WOT of course we use the WB.

BTW, I like seeing folks tune thier own cars. It's pretty fascinating stuff. 😄
Ron