blue86iroc

iTrader: (2)

Rectifying a surging idle, stumble upon rev, stall upon startup, and/or smelly idle with the oxygen sensor rich/lean threshold values.

I've decided to write this article because so many people seem to have idling issues with their TPI vehicles when installing a new camshaft or performing other modifications. This includes the following annoyances:

-- Surging or "searching" RPM at idle
-- Stumble upon revving engine as RPM falls back down
-- Immediate stall upon engine startup, often requiring feathering of the throttle to allow the engine to settle down
-- Smell of gasoline at idle

Now, I'm not taking credit for coming up with the following tuning ideas, because everything that I've learned has come from other more experienced forum members. It's just that trying to find these articles can be a hassle, which is why I've tried to consolidate it here (along with observations of my own). I hope that this helps some people out. I'm running a factory TPI system with a MAF and the $6E code, but I don't see any reason why this couldn't apply to SD setups.

I strongly recommend reading the following threads before attempting this on your own. In my opinion, it's important to understand why something works the way it does -- it gives a much better idea of the whole picture. EFI fueling is a pretty complicated subject.

o2 contants
R/L Threshold voltage
cam tuning question
ECM Proportional Control by Rob Rauscher

If you don't feel like reading everything, I'll briefly explain the gist of the situation.

In my tuning, I've experienced all of the above symptoms associated with idle since my motor rebuild. I'm running a ZZ4 cam with fifty degrees of overlap and ported 305 "601" heads which bumps the compression ratio to about 10.2:1 on my L98. Through experimentation and lots of datalogging, I determined that many of the unusual idling experiences were due to a heavily rich situation -- in other words, the injector pulse width was just too long for the operational condition of the engine at that point in time. Having a cam with more overlap than factory is a key contributor to this, and is probably one of the major reasons that tuning idle can be such a pain in the butt.

Cam overlap is the period of time, measured in crankshaft degrees, in which both the intake and exhaust valves are open. At low RPM, this allows some of the fresh intake charge (i.e. unburned fuel and air) to leave the combustion chamber via the exhaust. It can cause a car to smell like fuel when idling, depending on how much overlap there is.

Now, keep in mind that there is an oxygen sensor that measures the amount of oxygen present in the exhaust stream. When it detects the unburned intake charge from the high-overlap cam, it tells the ECM that there is a lean condition (assuming closed loop is enabled). The Integrator, INT, then changes to compensate for this "phantom lean condition." As the INT moves, it updates the BLM, essentially dumping extra, unneeded fuel into the engine because the ECM thinks it's needed. Run like this for a little while, let the learn feature kick in, and pretty soon your car will smell like a gas station AND it'll cause all sorts of unusual characteristics at idle. Observe the following datalogs:

RPM drops suddenly after falling from a rev at idle

In this example, the throttle is given a quick jab and released immediately. As the RPM begins to settle, note the BLM cell changes back to 0 (idle cell). Since it's already too rich (even though the ECM thinks it's lean), additional fuel is added and the engine literally begins to drown. The plot shows it very well -- RPMs decreasing and the injector PW increasing.

If the RPM gets low enough, the IAC opens to prevent the motor from stalling; this causes the extra fuel in the combustion chamber to react quickly with fresh oxygen, dramatically raising the RPM. You can see how this can lead to a surging condition, as well.




Immediate stall upon engine startup

This case is very similar to the previous one, in that the trouble starts once a "falsely rich" BLM cell is activated, though it occurs at engine startup. After the initial RPM spike, the engine tries to settle to the IAC-commanded idle speed... but that darn BLM cell 0 rears its ugly head again, sending the engine into a richness-induced stall. The injector pulse width reaches amusing values as RPM decreases. Part of this is because the load variable, LV8, is inversely proportional to RPM; changes in LV8 affect the open loop AFR ("Open Loop AFR % Change vs. LV8" in $6E), in this case reducing the AFR, further dumping fuel into the engine. Eisenhower's "Domino Theory" as applied to GM ECMs, haha.



So, how can you improve the situation? Well, there obviously has to be a reduction of fuel in BLM cell 0... but if the cam overlap confuses the oxygen sensor, how do you decide upon the right amount of fuel without melting the engine? From what I've read and done, the four main ways of doing this are by exhaust smell, header/manifold temperature, plug reading, and "engine happiness." A WB O2 wouldn't do much good in this situation, because it would read the extra oxygen from the overlap just like the factory NB O2.

Tuning via smell is fairly straightforward, but I'd imagine that with larger cams, there will be a certain amount of odor that you won't be able to get rid of. Just don't go so lean that the headers start glowing... Now, from my understanding, headers can get super-hot by either being lean OR rich. A very lean mixture will simply cause higher combustion temperatures, raising the temperature of the headers. Being overly rich can actually cause the unburned intake charge (from cam overlap, etc.) to ignite within the header tubes. I haven't personally experienced either of those situations, but I could see how it would make for a contradictory tune -- but take into account how much overlap you're actually running, I suppose, to figure out if excessive header temperatures are lean- or rich-based.

Member 87_TA comments on header temperature from the "cam tuning question" thread above:

Plug reading is simple, too. Let it idle for a bit, shut it down, and pull a few plugs. If they're really black, you know you're too rich. White is lean; tan is good. See this page if you need some visual references. Lastly, "engine happiness". Grumpy and numerous others have used this term, and it's quite true -- tune for what the engine likes best based upon its response. For example, before I really understood that I had a fueling issue, I reset the ECM (BLMs to 128), disabled closed loop, and pulled out a bit of fuel at idle. The engine could be revved without stalling or stumbling, so I acknowledged that as an improvement and one more step towards making the engine happy. When you can't reliably depend on an oxygen sensor it helps to think this way. I ended up with about 1.90-2.15 ms pulse widths at 700 RPM on a warm engine, but YMMV.

Alright, so you've gotten the fuel the way you want it by changing the MAF tables, VE entries, etc. We now come to the most important thing for maintaining a stable idle in closed loop: preventing the O2 sensor from thinking the engine is lean when it's really not. If you ignore this, you might see your BLMs doing something like the following:



We can do this by manipulating the "ideal" AFR that the oxygen sensor expects, in millivolts, to compensate for cam overlap. Again, I'm going to provide a basic explanation of how this works, but for the big story, read the aforementioned threads.

The typical narrow-band oxygen sensor is set to read a certain AFR at a certain median voltage (usually 0.450 V). The ECM maintains this stoichiometric AFR by constantly "switching" between rich and lean states, equalizing the amount of time spent in each state. Each transition from one state to another is called a "cross count."

At idle, with lots of cam overlap, a value less than the median voltage will be reported by the oxygen sensor. The ECM will then increase the fuel until the median voltage is reached, and it will switch states to maintain this voltage. By lowering the median voltage one can account for the extra oxygen and reduce the amount of correction that the ECM employs. This is the same way the ECM operates the AIR pump and diverters; when air is being injected into the exhaust stream, the oxygen sensor threshold is reduced by 0.100 V. Note: If you have removed your AIR pump and diverter solenoids, ensure that you disable its operation the EPROM. Read Removing Smog pump, AIR: $8D 730 modifications for more information.

The nice thing about the oxygen sensor threshold in $6E is that there are different settings for different MAF flow rates... in other words, you can tweak the idle and let part throttle alone. I'm not sure of the tables on a '730, but I know they're there.

I determined the values for the table by looking at what the oxygen sensor was reading as soon as the engine entered closed loop, before the INT/BLM entries had a chance to change. I was seeing about 0.230-0.250 V at 8.xx g/sec, so I set the two lowest table entries to 0.260 V. Only do this if you're SURE you're not running too lean with the fuel settings you've specified earlier.



I'm now in the mid-130s in terms of BLM, and the car idles much better than it ever did. The surging is gone, it doesn't stumble when revved, it starts on the first try, and it the smell of fuel is greatly minimized. The plugs look fairly good, too.

I'm greatly thankful for all of the helpful people on these forums and the wealth of knowledge we've amassed as a group. I hope that this helps some people tune the idle on their cammed engines... it's a world of difference. If I've goofed in my explanation or turned anything upside-down, I'd appreciate any criticism.

Even with all of the fueling "logic" explained, I've still experienced a few anomalies that I don't understand -- maybe someone has something to offer. Before I got my BLMs to settle down by adjusting the O2 threshold, I let the engine idle as the BLMs ascended to 160 (closed loop, of course). Unusually, the injector pulse width did not change to reflect the added fueling... only when I placed the transmission in Drive did the PW increase by about 0.30 ms. Shifting back into Park or Neutral brought the PW back down, but the BLM stayed the same. I thought that the fuel correction was accounted for at all times in closed loop. Can anyone shed some light on this?

87_TA

Very Nice!!!!
Thats soo cool you quoted me in the artical

Good work, Have not read in entirly yet but looks very good so far!

This is a much needed artical as there were some members totally misleading people on this subject who did not totally understand overlap.

It should be added that some cams just will not allow you to get away with 02 L/R threshold, and that only helps idle.
sometimes it is best to go openloop, and tuning with a EGT guage can help that lots. as well as a hand held pyrometer that you can pick up at your local sears on craftsman day pretty cheap.


The PW raised in drive because it raised the load on the engine therefor requiring more fuel so (It thought) It was merely following the VE with the xx% added for the 160 BLM learned.

Sonar_un

Wow! Great article!

This sounds kinda like what is going on with my engine (I at least hope). I am gonna re-read this article tomorrow when I am a little more awake.

Thanks!

RednGold86Z

iTrader: (1)

A ZZ4 cam is extremely mild. I've been to your other threads (a long time ago) and am not convinced yet that you aren't fighting another problem. "Giving it what it wants" can cover the true problems sometimes. "Calibrating" is the right way. Calibration requires tools to determine whether you've met the requirements (like not fouling plugs, not burning up headers, not stinking like fuel, not misfiring - all requirements), and whether you're fighting a problem. Calibration requires an understanding of the system as well. LV8 will increase as an engine stalls, just as MAP would increase in the same stall situation. The increased MAP or LV8 calculates a higher PW. Keeping all the plugs firing (and correctly timed firings) and the AFR correct will prevent the richness that causes the stall in the first place. Keeping the AFR correct requires the control strategy to have accurate input (i.e. no vacuum leaks, no exhaust leaks, no spark problems, no fuel delivery problems, and fully functional sensors) and accurate lookup tables (calibration).

My advice: give it what it wants, and then figure out why (if at all) what it wants isn't what you thought it should want, BUT, make sure all the parts work first. Then calibrate it all to optimize it.

blue86iroc

iTrader: (2)

Thanks for the input so far, guys. I forgot to mention two additional tables are needed in changing the O2 threshold... in $6E, there are tables at $0459 ("Upper Zero Error Ref for Slow O2 R/L") and $0462 ("Lower Zero Error Ref for Slow O2 R/L"). These are the boundaries of error, with relation to the median voltage, that the ECM tries to stay within.

For example, at 8 g/sec, the lower limit might be 531 mv, the threshold 575 mv, and the upper limit 620 mv. You need to set all three of these if you want the oxygen sensor to respond properly... only change the threshold point and you'll experience some interesting things, as I did the first time I tried this .

Note that the upper/lower tables are not included in TunerPro, but I'm not sure about Tunercat or any of the other editors out there.

RednGold86Z, it's true that many of my previous problems were related to non-ECM/EPROM issues. The most sinister of them all was a faulty MAF connector, which made trying to tune completely impossible. I posted fairly recently about an issue with the car idling better with the MAF unplugged. After trying numerous sensors and doing the usual vacuum leak check, I decided to look hard into a datalog and see what the engine was really doing. It turned out that when the MAF sensor was unplugged, the g/sec reading was lower because the ECM was relying on fixed/calculated airflow rates -- in other words, it reduced the amount of fuel present at idle, which reduced the richness-induced stalling/surging as noted when the MAF sensor was attached. Lowering the fuel was merely the first part of correcting the problem; you also need to prevent the ECM from reading the cam overlap and reversing your changes (as you know).

But you're right, I've basically been to hell and back with this car. The ZZ4 cam isn't radical by any means, but I still think it's enough to throw off a factory tune. Your strategy of giving the motor what it wants, and then ensuring that "what it wants" makes sense in terms of "what you think it wants," along with observations, is basically what I've done. In the beginning (after the non-ECM/EPROM things were fixed), it wouldn't idle right, the plugs were nearly fouled, and it smelled like gas. The datalogs confirmed that too much fuel was being added, and removing fuel made the situation better. Computer logging seems to often provide the "link" between what you see the parts doing and what's really going on.

Also, I don't think that LV8 has much do to with the base PW calculation (in closed loop) -- but someone please correct me if I'm wrong. My notes show that BPW is calculated via MAF airflow, AFR, injector flow rate, and inverse RPM. Final PW is then modified by BLM/INT. Now, the reason why LV8 seems to matter in the "stall upon starting" situation is because in open loop, AFR does depend on an LV8 reading.

87_TA, I thought about LV8 having something to do with higher PWs, but for the reason above, it doesn't seem to hold water.

87_TA

My fault, thought you were map..
But still when you were in drive it, may have been taking you out of your idle cell. Would have to see some scan data to figure that one out. Maybe battery voltage vs pw? Maybe getting some AE in there but would not think so.

TRAXION

I'm surprised that Bruce hasn't jumped in and told you that you were wrong. He says that it's all Self-EGR'ing and that you don't get fresh intake contamination of the exhaust. Although this does happen ... it also happens in this manner too. I've always been a supporter of the "phantom leanness" as you call it and was one of the first to discuss it here ... while using a 230+ duration cam on a 350 with <110 LSA I adjusted the O2 settings a couple years ago with great results. I'm glad that others are seeing the light and doing the same thing. Awesome.

Tim

vernw

iTrader: (2)

Great info!!! I'm $8D (speed density), but the same logic would apply I would think. So I'm wanting to try and make the same kind of adjustments and tests on my 383 SuperRam.

Can I jump in here with one quick question? Don't want to hijack the thread.....

In over a year of reading all the DIY stuff I can while tuning my setup, one question I've always had and never been able to get answered clearly to me is the difference between these constants:

Fast O2 Rich/Lean Threshhold at Idle
Fast O2 R/L Hysteresis Threshhold at Idle
Upper Zero Error Ref Slow O2 R/L at Idle
Lower Zero Error Ref Slow O2 R/L at Idle

and which ones to adjust based on the discussions in this thread. My WB O2 shows the rich idle end condition, as do my plugs.

Hope no one minds my butting in here with the question....

blue86iroc

iTrader: (2)

vernw, you're completely on-topic with your question. In the $6E mask, three of those items are tables based upon MAF airflow. On an SD car, I've gathered that they are constants (one for idle, one for everything else)... but again, I don't have an SD setup, so I can't guarantee that. Maybe someone else knows?

"Fast O2 Rich/Lean Threshhold at Idle" is the median voltage that the ECM will try to obtain via the oxygen sensor.

"Upper Zero Error Ref Slow O2 R/L at Idle" is the upper boundary of the median voltage, and "Lower Zero Error Ref Slow O2 R/L at Idle" is the lower boundary. Think of these as "error margins" for the ECM. As long as the oxygen sensor stays within the upper/lower boundaries, everything's cool -- but it's trying to aim for the rich/lean threshold.

As for "Fast O2 R/L Hysteresis Threshhold at Idle," I can't comment on that one -- it's nowhere in the $6E hack. "Hysteresis" refers to the lag between making a change and the result of that change. If I had to wager a guess, I'd say it has something to do with the amount of time the ECM stays at a certain O2 voltage before adjusting the fuel to produce a change.

TRAXION, I actually had a paragraph written on just what you've said... but the little argument in that thread became tense, and I didn't want to induce off-topic conversation in this thread. I think most agree that self-EGR happens, as well as the opposite. The fact here is that adjusting O2 voltages works, and intake charge transfer seems to explain why. I haven't read of any other theories as to what would cause "phantom leanness" at idle in a properly-functioning engine.

blue86iroc

iTrader: (2)

I've added the upper/lower O2 tables to TunerPro's $6E XDF file, if anyone wants to use it. They're labeled as I've referred to them above.

http://home.alltel.net/usaaf/etc/6E_O2.xdf

vernw

iTrader: (2)

So changing these values only affects IDLE? I know that's the title, but I ASSumed that it affected more than idle..... probably wrongly so....

Grumpy

[QUOTE][.

Grumpy

*seems*

Grumpy

Is it?.
Have you put a WB and scope (with no filtering or averageing with the WB's output), in a tail pipe, and watched the what's going on?.

Slow89Iroc-Z

Traxion with the 230 duration cam which way did you have to go at idle? Richer or leaner??
Thanks
Great thread!!

gta324

On my engine, 415cui and 9.0:1, and a 230/245 cam I have 32 deg at idle, headers will easily glow if I go lower and my MAP will increase (se previous post by me) I also get the best idle with 13.0 AFR but after 50sec I get a code 45 havent decided if I will go open loop or disable it or do something else with the O2 limits....

/N.

blue86iroc

iTrader: (2)

Assuming that there is unburned intake charge flowing into the exhaust, either a NB or WB sensor would pick up the extra traces of oxygen. I haven't invested in a WB yet, so I can't vouch for its comparison to the factory NB. Are you talking about sticking one right in the tailpipe or on the header?

Before adjusting the oxygen sensor thresholds, it registered lean and the car idled like crap. Adding fuel, to counter the "leanness," made it run even worse. Pulling fuel out reduced the smell of gas, prevented plug fouling, and the engine ran better. Even without a WB, I think it's safe to say that the motor was rich due to the presence of an assumed lean condition.

Dominic Sorresso

blue86,


Excellent article. I haven't been following this lately since I have been struggling with an elusive oil leak and fuel pump circuit gremlins. In the 7747, the ability to manage O2 thresholds is a bit less flexible. Primarily, the idle has an O2 bias voltage which is added to the o2 voltage threshold tables similar to the ones you've shown. In the 7747, there's a Rich O2, Lean O2, and a Mean R/L O2 table.
You and I have communicated because we've both done similar cam upgrades to our motors. They're both mild but probably pushing the ability of the stock ECM code to handle. Mine utilizes a 108d LCA. To your point, my idle has gotten a bit better by lowering the Idle O2 bias value. Now my idle problems began when we found that WOT AFR was way too high using 10.5 psi for Fuel Pressure. But at 10.5, the idle was smooth as glass. At 20psi, I experience a lean surge, and a stumbling on decel.
I'm going to try dropping the O2 v values at the 0 an 16gm/s levels. I'll let you know what happens. But thanks for your efforts.

Magman

iTrader: (6)

blue86,
Thanks for the write-up, much appreciated. I put it to the test on my 7730 and it worked well. I can now go through a drive-thru without being told to turn my car off! My tests and results are in this thread: https://www.thirdgen.org/techbb2/sho...hreadid=311190

Thanks again!

blue86iroc

iTrader: (2)

I'm really glad to hear that the oxygen sensor tweaking is actually helping some peoples' idle!

Dominic, how small are the PWs at 20psi at idle? Have you had any luck with fixing those issues?

IROC Magman, I see that you take detailed logs like me . I have yet to buy an infrared thermometer... I'd be curious to see what my header temps are.

It makes sense that your swinging BLMs tightened up once you reduced the oxygen sensor error margin -- less possibility to be inaccurate for a smaller period of time. Interestingly, I didn't seem to notice any drastic changes in plug color throughout my testing. At BLM=160, they were definitely rich, but the change at BLM=128/9 wasn't much different... although, that could have been due to old or previously-fouled plugs. I've since installed new ones and the color seems to be pretty close to what (I think) it should be.

Dominic Sorresso

blue86,

Its been a while since I logged the info, but I seem to recall the PW was in the 1.2msec range with a .540msec Injector Bias. So that means the actual time the injector was open was in the .66 range. Pretty short. Recently, the idle has gotten more steady. I did drop timing in the lowkPa/lowRPM cells and that seemed to help soemwhat. It still won't hold a raised idle. Cruise is great with AFR in the high 14's to low 15. Right now I run O/L idle from 10mph down. I am going to try dropping the O2 swing points for idle. In the 7747, its a bit different but the same principle.
I'm also going to try increasing the Injector Bias which should richen up the idle, then drop the FP a bit. Maybe I can pickup additional PW at idle while still being able to supply WOT fuel requirements.

anesthes

iTrader: (12)

Would that "phantom leanness" cause a skip condition experienced at all RPMS, that seems like an electrical problem?

I'bve replaced EVERY single electrical component, and I'm having a light skip at any rpm.

-- Joe

DAVECS1

iTrader: (2)

Well if yo all do not mind I would like to jump into this thread. I realize I am late to the game, but here it goes.

I am getting the fumes at idle and have not had any luck tunning it out. The motor is the following

360 SBC
COMP CAM 112LSA 218/224 @.50 .495/.503 @.50
ProTop Line Heads
TPI with ported SLP runners and plenum
730 ECM

I have adjusted my target idle speed and that seems to help, but then I suffer tip in problems. At 700 RPM idle the car smells OK, but the idle takes a while to recover and tip in is poor. At 900RPM tip in is good, but the torque converter seems to be loaded and the fumes are bad.

I have adjusted the VE table were the engine is idling according to the ECM852 DOS program I am using as a scanner on my laptop. The values are from 700RPM- 1000RPM and 40KPA to 55KPA range. I can hit the the so called 128 INT target, but that smells extremely horrible. Right now I am running at 136 INT and that is better, but not ideal. I can go leaner, but I run into tip in problems again.

This brings me to my last comment. anesthes stated he had a skip condition. I was getting that for a while and it started turning into a car stall condition. I have rplaced the following to no avail.

Distributor twice
Ignition coil
harness from ignition coil to ignition module
plugs( which read tan because when it is not idling it runs pretty good except for the "skip"
I have ohmed out the 4 pin from the module to the ECM. It reads zero on all 4 wires.
New fuel pump
new AFPR
new injectors for 24lb (set to 26 in the EEPROM)
I have never had an SES light (yes it does turn on with the key on diagnostic check)

I usually do not admit this, but I am stumped. Nice car, but all it does is sit in my garage because of these problems. PLEASE Help!

anesthes

iTrader: (12)

Mine is either tune or a bent valve. I had some exhaust issues that were causing the narrowband, and wideband to read wrong.

EGT and , cutting the exhaust off before the cat showed me that the car was running crazy fat when everything else said lean. Could be a cause for the skip. Plugs agreed.

Once I get the new headers in place, and a decent tune I'll know if it's that or a valve.. I also replaced dizzy again, and bought an ignition box. (mallory hy-fire)

My car has been on my lift since 9/14 btw. I got pissed off and bought a Jetboat. I've only started looking at the car again this week. I needed a break.

-- Joe

Dominic Sorresso

Joe,

I have TFS23d heads as well. Great heads. Just ran a 13.3 using my Xfire manifold. What head gasket did you put them on with?
If its a FelPro 1010, do a leak down test.

anesthes

iTrader: (12)

Yeah I used a Felpro 1010. Why??

-- Joe

DAVECS1

iTrader: (2)

Yeah, I also bought an ignition box. Pertronix Second strike. It did not help. I had marked improvement when I replaced the plugs, but I think I just shifted around whatever is causing my problems. I also have turned to other hobbies out of frustration. I have been working on my bike and truck. I have thought about having valvetrain issue, but I am not convinced just yet. The car runs to well when it is not having the problem.

I have an electric cutout before the CAT, does anyone think that opening and shutting that on regular basis could be hard on the O2. My car actually idles pretty well in open loop, but without a code I am hesitant to start second guessing which sensor is the culprit. Non of them look far off on the scanner.

Dominic Sorresso

Read this thread:
http://forums.corvetteforum.com/show...10&forum_id=48

RBob can also enlighten you on the 1010. It appears Felpro manufactured a defective gasket. Its a possibility that you should be aware of. It took me 12 months of playing around and then an oil leak to find it was the cause of my idle problems.

Z69

Well isn't that nice.
I just put a set of 1010's on that I'd had laying around for about a year.

Dave-https://www.thirdgen.org/techbb2/sho...hreadid=311190
and-https://www.thirdgen.org/techbb2/sho...hreadid=195745

DAVECS1

iTrader: (2)

I think I will try making a mean O2 adjustment a see what happens. I do not think that will solve my intermitten cutout problem.

I let the car idle for approximately 15min last night. I yanked and pulled on the harnesses to the distributor, ignition coil, and the TPS and temp sensors. I could not get it to stumble in the garage.

It seems to only happen under an acceleration situation, and usually if I back out of it and re apply the gas it will go away. During this whole process the only indications seen on the scanner are a possible knock count, but I attribute that to the miss, and a BLM surge rich, But I do not really trust the narrow band O2.

Engine only has about 2000 miles on it. THe first 1500 were very smooth, after some tunning. It has gone down hill from there. I have Pete Jackson quite timing gears (they were free). I am not registering more than 10 knock counts during a thirty minute drive, and I think 1 or 2 of those are from starting the car. I attribute the others to my tansmissions inability to down shift quick enough.

anesthes

iTrader: (12)

Wonderful.. just wonderful..

-- Joe

Dirtbik3r

Was reading up on some other threads and thought this would be a good add in for newcomers.

ScottyDTA quoted this:

shuanm

How do you find what your overlap is? How do you tell if it's too much for stock tuning. At .050 my duration is 212 on both intake and exhaust. Datalog says it's way lean, but the rest of the cells are pretty close.

DSmith

Shaunm, you need to know what your lobe seperation is to figure out overlap.

pandin

212 Dur @ .050 or .006 is not likely to have a lot of overlap. on a 305 maybe 350 383 no.

large overlap makes your Vacuum low. So check that. 15" and higher is good at idle.

If you know who ground the cam. Contact them for a spec sheet.

shuanm

Part Number12-314-4 Engine1955-1998 Chevrolet
262ci-400ci
8cyl. Grind Number CS 260H-12 (350/T.P.I.) DescriptionIntakeExhaustValve Adjustment0 0 Gross Valve Lift0.444 0.444 Duration At 0.006 Tappet Lift260 260 Valve Timing At 0.006 OpenCloseIntake22 58 Exhaust66 14 These Specs Are For The Cam Installed At 108 Intake CLIntakeExhaustDuration At 0.05 212 212 Lobe Lift0.296 0.296 Lobe Separation112
----------
That didn't work quite right
----------
It's a 260 Duration at .006 and 112 lobe separation.

Chris89GTA

iTrader: (2)

Very good thread. Subscribed!

pandin

overlap is 36 degrees.

Mine is 40 degrees

shuanm

I assume that my overlap is insignificant in this discussion. What else would cause a lean idle and light throttle? I have 24# accel injectors running at 44 psi with no vacuum, with an injector constant of 23.88 and I have an idle blm of 142 with about 295 hp. I should be able to get it real rich with that setup.

pandin

(Blm of 142 is car rich, computer pulling fuel trying to lean back to 14.7 afr.)

No I am confused this wrong Rbob corrected me.



I have 24# fms injectors and a 23# injector constant, it also runs rich at idle.
160 blm

This is true from data log, my car is confusing me. should be rich, but running lean.

shuanm

obviously I'm confused about blms. I was under the impression that high blms were were adding fuel to compensate for a lean mixture since they go higher when I lower fuel pressure.

Dominic Sorresso

BLM of 142 says motor is running lean. The INT should be running the opposite way to try and richen it up. See if your bin has a Injector Bias for idle or low airflow. You could increase that allowing the injector getting effectively a longer PW.

RednGold86Z

iTrader: (1)

[QUOTE=Dominic Sorresso;3660278]BLM of 142 says motor is running lean. The INT should be running the opposite way to try and richen it up.QUOTE]


??? Confused about the "running the opposite way" comment.

INT and BLM both work the same way. 128 means not changing from the open loop. 140s means it's adding fuel to try to get to 14.7 (i.e. open loop cal is lean).
140s BLM and ~128 INT means open loop is lean, but it's actually running near 14.7 (or Lambda=1, don't obsess about the actual AFR please) because BLMs have adjusted properly.

If BLMs are in the 140s and INT is 110s, it's still trying to correct itself, so wait until BLMs are stable to get the final answer as to what the open loop error is.

If INT is stabilized, it's running 14.7. If INT is on the move, it's running lean or rich.

Dominic Sorresso

Red,

What I meant to say is the INT will move in the opposite direction of the BLM.
If the BLM is indicating lean, ie > 128, the INT will move to < 128 and add fuel in order to richen the mixture and get back to whatever "stoich" is defined as in the bin.
This is in Closed Loop. In Open Loop, the ECM is using the base VE tables with none of the correction from O2 sensor input taking place.

pandin

My confusion is with fms 24# injectors and 50# fuel rail pressure (27# ?)
Cell 0 and 1 are at 150 - 160 lt blm.

The car has stock 350 bua chip installed. 23# IC

It was my understanding that this would richen BLM, open loop, AE, PE, and wot. At change from open loop to closed loop motor steady throttle, motor speeds up. MPG goes up. o2 mv go down from 900. to 600/700

15 mpg city 20 mpg highway @ 70 mph 2000 rpm cell 6 or 10 128 blm.

Does any body have any words of wisdom.

Dominic Sorresso

Is the injector size and/or FP different from stock bin? If so, have you
re-calc'd the IC? 600-700mv on the O2 sensor still sounds rich.

RednGold86Z

iTrader: (1)

Nope, INT works the same as BLM, where >128 is adding fuel, and <128 is removing fuel. Stoich is found by the O2 sensor, and the actual AFR is determined by the fuel, whether or not it matches the bin.

pandin

Thats just it, its a stock bin/memcal. I have bua(3.07), buc (2.56), and abtk (3.40).

All run the same.

Used a wells maf (had higher gr/sec, richer?), it would stall when going into drive, cold or hot.

Used a weak, 187 max gr/sec (lean?) bosch. and it runs the best of all the combinations that I have tried.

Ordered a prominator from bill. was going to raise 23# injector size. That will lean the cell 0 and 1 even more.

I guess low maf tables will then have to be raised to richen idle.

also no stumble, lean pop, or hessitation off idle. even at 1200 rpm 4th.

RednGold86Z

iTrader: (1)

What happens if you disconnect and reconnect your ECU? Then, warm it up and let it idle, and watch the BLM and INT.

In closed loop, if all is well, the O2 voltage should be swinging down and up and down from 200-700 roughly, depending on the heat in the sensor. Staying higher than 450 means it's still rich.

Maybe you had (but now fixed or it went away) some problem or leak that got the BLM up, and now the INT can't get low enough to get the O2 to swing, which might prevent BLM from changing (not sure if O2 crosscounts are needed for BLM update).

pandin

I have tried 4 diff ecm boxes. Had batteries off more than I can remember.
after startup a little rough idle then settles to smooth. comp 12-408-8 cam
206-212 @ .05 480 lift 1.5 rr

o2 counts have always been high with the 24's. tried 3 differant o2.

stock exhaust mufflers no cat, o2 goes cold at idle. Thinking heated or WB.

been playing and reading for 6 months waiting for extra cash for prom equip.

broke crank/case in 02 indian, oops ($6000) bumped rev limiter (6000 rpm)once too often 1-2 gear.