you'l have to learn to read these at some point...
do you see anything weird in the log?
are iac counts staying above zero now?
how's the left vs right bank BLM split once it warms up?
you'l have to learn to read these at some point...
do you see anything weird in the log?
are iac counts staying above zero now?
how's the left vs right bank BLM split once it warms up?
OK, first let me say I appreciate you taking the time to do this. Trust me, I obsessed with learning this and getting this engine running like a top. NOBODY in my club, that has lots of hot rodders, engine builders and racers, believe that this LT1 is worth the effort. I'm DETERMINED to prove them wrong.Originally Posted by steveo
Now, I have been going over this XDL file with TP. What "view" do you use when reviewing a log? I've used "Data List Views", "Data Dash" and "Data History". As a NUBE I can tell you that one of the toughest things to figure out is WHAT to focus on. There are a LOT of items with running values: MAP, Map kPa, TPS, TPS%, LEFT & RIGHT 02’S, LEFT & RIGHT BLM AND INT. You know you should be looking at IAC POSITION, but then you see IAC MINIMUM POSITION. Does that mean the switch is already at 32?
It's difficult knowing just which ones are relevant to what you are trying to accomplish and are the values your looking at NORMAL or not. I may be watching one value, when it is, totally, useless to what I'm trying to do. That will become clear the more I work with it, but I mention it because as you develop that sticky your working on, it may be useful knowing what NUBE's see when they look at a running log for example.
I'm reviewing the log using Data List Views. My IAC counts never come off of 0. There was a left/right BLM split that seemed to remain constant throughout the run. I also noticed that Left/Right INT and left/right BPW followed that same trend. The BLM split seemed to even out, as did INT and BPW, when I rev’ed the engine to about 2000 RPM toward the end of the log.
so your IAC is still bottomed out. that means more air is flowing than it requires, and the iac can't control idle. it also means air is coming from somewhere other than the idle passages, which isn't good. i'd be looking for a vacuum leak.
any value in the log you need explained, just ask.
you can ignore iac minimum position. you can also ignore INT, there's very little useful information from the integrator at this stage.
the important values you need to watch (and you can make a view with them to simplify stuff) are:
- MAP KPA, manifold absolute pressure in kilopascals. 100kpa (or whatever atmospheric pressure is where you live) is full engine load, lower is less load (more vacuum). there's a line between accel and decel that depends completely on what cam you have in there. logging a gentle cruise will show you that.
- rpm, if you dont know that you're fired. moar is faster
- iac position, idle air control valve. 0-255. somewhere between 30-60 steps at idle is ideal on an lt1. less than 20 will be a rougle idle. 0 means that it's closed all the way and still can't achieve its target speed.
- spark advance. that's a complex subject.
- left and right blm, that's the 'learned trims' of the left and right bank, less than 128 is removing fuel, more than 128 is adding fuel.
- left and right o2 voltage, you mostly watch these to make sure closed loop is working properly. if it is, the o2 will be switching rapidly between over 800+mv and under200mv kinda thing.
any other value in the log can be ignored for what we'll call 'basic initial tuning and diagnosis'.
OK--I replaced the IAC switch, with one of the several I scrounged from the salvage yard, and ran a log. The idle tried to set right at 700 RPM (too low for this cam) I opened the throttle plates (probably not the proper thing to do) just to get the idle up around 900. I haven't viewed the log yet, but while it was running I can see there is a WORSE BLM split LOL. So, I think I moving in the right direction. Here is the log.
BTW-Thanks for the explanation above that will help me greatly.
Last edited by terpngator; 10-11-2014 at 07:48 PM.
QUESTION
Would an exhaust leak, upstream of 02, cause split BLM? Would it cause BLM to max out?
Last edited by terpngator; 10-11-2014 at 09:15 PM.
Luckily, you're absolutely right about how ignorantly wrong your club is about the Gen2 LT1's potential.ANY leak[s] between the either the MAF sensor [if your engine also uses that], or the inlet manifold [since your engine DEFINITELY uses the MAP sensor] and the pre-cat O2 sensors will cause fueling inaccuracies.
If the leak[s] favor[s] one side, split BLMs.
If the leak is / leaks are big enough, BLMs can max out.
[BLMs that consistently remain between 122 & 128 can be considered accurate.]
I know that a leak between an exhaust manifold and the pre-cat O2 sensor causes a false-lean condition, which the pcm gets tricked into 'correcting' by running rich.
I want to guess that a leak between an MAF sensor and an inlet manifold (which I've never had, luckily) might cause a false-rich condition, which would be more dangerous?
Yeah, with the help of guys here, like Steveo, victory will be OH SO SWEET! I get the LSx rubbed in my face every week, but revenge is a dish best served cold.
I may have a leak on my right bank, I can't seem to locate it, but these headers, I purchased from Summit, have been a big disappointment and could be leaking between the pipes where I can't see it, but I hear it. The idle issues have been resolved by the new IAC valve, but still running way too rich, fouling the plugs again.
you need fix that before you rinse your rings or something.
yes a leak upstream of the o2 will cause mis-measurements, but that was a pretty gigantic split you had before.
also if it's just a blm split, probably one bank will foul the plugs way quicker than the other.
how much of a split do you have now?
do keep in mind a big cam can cause decent sized blm splits just because it's hard to measure afr and airflow when you're running 1000rpm and your cam operating range starts at like 2000rpm, and since it's so inefficient at that range, sometimes, you just have to pull some fuel. really big cams can't even achieve stable closed loop operation, and sometimes you just have to go open loop for that part, which you can hack using power enrichment (there's a writeup on that on my fbodytech.com site i think)
My BLM split when I first started it up was running L-113/R-147. When I reved the engine to about 2000 RPM the BLM's were dead even at 123. I'm going to pull another log tomorrow. For now, here is my last log, after I replaced the IAC and the idle finally came down to normal.
this is good news so far, your IAC counts are good and its definitely affected your trims.
however i noticed although your TPS hit 0% near the beginning of the log, it landed at 1.3% later? your throttle plates may be binding (maybe you closed them too far) or you have a dead spot in the TPS. were you touching the throttle at all during this log?
your blm split is still really bad; 110/160 at some points. since you're fouling plugs, those trims are obviously wrong. the right just seems to climb and climb which means its dumping a ton of fuel on that bank and pulling a bunch from the other. if it's not the cam doing it, i would suspect a leaky intake gasket or reversed o2 sensors, something like that. that's quite the split.
it shows a 700rpm desired idle speed too, somehow that seems too low for this particular engine? i'd try a bit more timing at idle and a bit higher idle speed..
definitely needs more work but at least the IAC is responding now.
just for fun, go into the "O2 Int Delay - Airflow" table and double everything there. then go to 'CORRCL Airflow%" table and cut everything in half. raise your idle RPM to about 900 and throw 30 degrees 'closed tps spark advance' at 400, 800, and 1200rpm. lets see if it calms the split down.
one more thought, is your exhaust connected or are you running open headers?
I'll try all of this tomorrow when I go over to the shop.
I have open headers, but I have 12' long flex pipe attached to the down pipes just after the 02's. Mostly just to get some of the fumes away from me and pointed out the door. No mufflers etc.
??? Are you saying that my throttle plates should not be completely closed?? (risk of sticking??)
When I started the engine, my throttle plates were completely closed and the idle was really low, to the point of almost stalling. I reved it up to about 2000 RPM for a few seconds, TPS goes to 10%. When I let it settle back to idle, TPS returned to 0. When you see the RPM climb, it was me trying to "clear" the engine (running rich) a bit. A minute or so later you see the TPS rise just above 1%. That was the result of me using the throttle adjustment screw to bump the idle up to around 900. About half way through the log, I backed the throttle plate screw out to bring the idle back down around 750-800. TPS drops to .8-1%. Sorry, I should be more informative about the logs. I forget that you can't hear the engine running lol.
your blm split is still really bad; 110/160 at some points. since you're fouling plugs, those trims are obviously wrong. the right just seems to climb and climb which means its dumping a ton of fuel on that bank and pulling a bunch from the other. if it's not the cam doing it, i would suspect a leaky intake gasket or reversed o2 sensors, something like that. that's quite the split. it shows a 700rpm desired idle speed too, somehow that seems too low for this particular engine? i'd try a bit more timing at idle and a bit higher idle speed.. definitely needs more work but at least the IAC is responding now.[/QUOTE]
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