Here is what I got intergrator125-129 blocklearn 108 idle thru 2600rpm wideband shows 14.5-15.2 in this area o2 430-844. Motor is a 406 cam HR 224/232 522/531 ls112 1.6rr. THANKS

for roughing in your calibration, disregard the int and o2. but your blm is 108 across the board, so you need to do something with that first (too much fuel across the board).

I saw your other post about 30# injectors. you need to tell the ecm that you have 30# injectors so that it compensates correctly.

I don't know much about the '85 870 ecm. but I think all 85's were 305, which means you have 30# injectors on a 305? just guessing, you didn't post your setup. you may need to come down on injector size depending on what you're doing.

do a quick search for "870 injector constant". some useful info to be had. from what I read, there is no injector constant for the '870, you have to manually edit lv8 vs pw type tables. I guess you could scale the whole thing by a factor of X/30 where X is the original injector size...just guessing though, I have no experience with 870.

have you considered moving to '730 or even '165? There is a lot more support for them and they have better aldl data streams.

Thats the point of blm, to get your afr to 14.7, your VE talbes (or injector constant) are to high, so the blm is low, trying to correct for the chip calibration being off.

'870 doesn't have injector constant or VE tables.

it is MAF, and has no injector constant.

Sorry I'm used to SD, but blm is still the same thing.

Ok I can get the blocklearns to 128 but when I do the wideband shows 15.7-16.2 Also with the ecm seeing 108 BLS I thought that the intergrator should start pulling fuel.What I am thinking is that the wideband is more suited for wot or is it something that I am missing. Also the engine is 406 with 30pd injectors. THANKS

some stock code commanded a leaner afr , like 15 and higher to 1.

WB works just fine at both WOT and non-WOT.

if your WB is showing 15.7-16.2 then either (A) you are running AFR of 15.7-16.2, or (B) your WB is not working/reading correctly. An easy way to tell is to use it on an unmodified car that is working/running/tuned correctly. As long as the O2 sensor is active (going hi/lo/hi/lo, or generating crosscounts) the WBo2 should display very near 14.7:1 +/- about 0.2 in my experience.

the integrator is not a major source of adding/subtracting fuel - BLM is. With a BLM of 108 the ecm is already pulling out as much fuel as it can, and likely still would pull out more.

is your NB O2 working properly? Do you have any exhaust leaks that would be letting oxygen into the system? Is the WB O2 in front of the cats?

make sure you read all of the sticky posts too at the top of the forum.

how are you getting your BLM to 128?

Yes my NBo2 is working fine and I have no exhaust leaks the wideband is in front of the cats and I have read the stickys.I get my blocklearns to 128 by reducing the injector pulse width vs load value scale.THANKS

Again , not sure on 870 code, but my 747 code has toggle values for the O2 sensor, there in mv. A higher value get the wcm to keep a richer condition. It sounds like your setup is calling for a lean condition.

I think that your cam and or timing could be causing this. I was working on a car with the conditions you decribed. It's idle blms are at 108 and wb read 16:1. So what I did was tuned the part throttle/idle by using the cross counts. The closer your tune is, the faster they go up. The car I was working on now idles smooth and right at 14.3 . I don't know what was going on, I guess you could say I tuned around it....

I think I will try that. Was the one you tuned an 85?

No, I got rid of my 85 electronics before I started tuning. I have a question, is your WB on the same cylinder bank as the NB? If not then switch the sensors and see if the condition/data changes. You might have a faulty injector or something that only one of the sensors are catching. Just a thought...

They are on the same bank.What are you using 165 or 730? Thanks for the responses.

The WB reads O2 content, and that is a function of AFR, and combustion effeciency.
Too far retarded will indicate a false richness, and too much advance can indicate a slightly leaner then actual AFR.

And the more self EGR'ing an engine is can also confuse matters.
The WB is always reading true O2 content. But, raw fuel from overlap, can cause skewing of the results also.

And all of this is similiarly true for the NBs, and they can even be more false indicating.

Again, we get back to what actually makes an engine happy and giving it what it wants. Which can vary from what's assumed. Each engine is an animal unto it's self.

I tune both systems. I would suggest to tune part throttle by using O2 xcounts. I can always tell how close my part throttle/idle is by looking at the xcounts. Once the xcounts are zinging, check the a/f ratio w/ the wb. Let me know what happens. It should help. Like grumpy said, some engine will just do that. So if all else fails then just ignore blms as long as you get the desired af ratio.

If all you want to do is tune for an AFR and ignore the BLM's, I'd think you'd be time and stress ahead to just kill the o2 sensor and run full time open loop. If you just want to run some given AFR, then why leave the ECM in the picture with it's BLM's to throw ya off?

I've been a bit puzzled by your tuning by the O2 cross counts. Assuming everything is working as designed (stock), It seems like you should get just as many crosscounts at BLM 110 as you will at BLM 148. The ECM intentionally adds fuel till the O2 sensor goes rich, then removes fuel till it goes lean, and repeats forever. The BLM is just a measure of how big of a discrepancy there was between the VE table and what is happening in real life. So if the VE table is 20% off and you are running BLM 110, the crosscounts should still be happening rapidly no different than if the BLM was any other value (just means the ECM is subtracting 20% fuel from a VE that is 20% too high, and the net effect is an identical injector pulsewidth and thus same afr). The only time you'd see a reduction or cease of crosscounts, is if the tune was so far out (BLM pegged at 108 or 160 and the tune is actually further out) because then the ECM can't add or subtract enough fuel to generate a crosscount. This would also (should also) generate a check engine light.

at least, that's how i understand it...

If you have a catalytic converter your kind of stuck at tuning for 14.7,in general. SO, I know one thing about xcounts. It the ecm counting every time the O2 go past .450 mv. And .450mv means 14.7:1 to the ecm. So I believe that when the cross counts increase at a higher rate than before, the tune is closer. I don't know about what you said but the cross counts will change with different calibrations. It's just one method I use to check my tune.

Alot of the senior members of this board runs in open loop all the time. But if you don't have a catalytic converter and do have a fat cam/high comp or boost, you will need to run richer that 14.7:1 at part throttle,in general. I have tuned those types and can tell you that alot of engines like to be richer than 14.7:1 at part throttle and/or idle. And closed loop doesn't work so well at that point. Cause the ecm keep changing what you have programmed to be correct(making fuel corrections,etc).

Here is a bad analogy. Let's say that you have a solid roller motor with noisy rockers and open headers,etc. No matter what you do,the knock sensor will try to retard the timing.Because the drive train is too noisy and creating false knocks. OR let's just say you have a hot little 406 sbc. That engine is externally balanced(unlike a 305/350). So the harmonic frequencies are different. In turn causing false knocks.

There can be reasons to ignore/bypass certain ecm functions. So if I was Mr Kidd, I would just ignore the blms and tune for the desired a/f ratio. If the blms get in the way, then I would then suggest to disable closed loop. But I'm not going to suggest skipping to open loop to start with....

One thing you will notice is that if VE tables are out, blms in any certian cell can be richer than they should be, then some cells imediatly around the rich cell will be leaner than they should be (or vice versa). This will kill most of the X-counts in that area, but drivability will be good.


So how do you correct this? Well, I like to set the tourque converter to lock up at very low speeds, then slack the TV cable off, and find some hills. Let the motor stay at the same rpm and load (easy to do if you drive a stick). This will get the VE cells alot closer (using the blms for tuning of course). Theres some other stuff that helps tuning via the blm , like integrator delays, and prop gains.

Mr kidd, have you though about spreading the blm cell boundaries out? I think there is people here that has done it...

I think I know where your going with this but explain why you suggest this.Thanks for all the replys guys.

I have never spread the blm cells out. You should talk to others that has done it. They could explain it better. BUT, if your car is real effcient at part throttle, you might not hit many cells, from what I hear is more cells are better. I'm not so quick to do things like that. My old cam/engine hit the cells like it should so I didn't have a reason to modify the boundaries...

Ok what would happen if I changed the blocklearn parameters from 108 to 88 would the ecm pull fuel to that point.

It could go as low as 88, the only reason gm set limits on how high or low blms can go, was incase there was a physical fault (ie: exhaust leak before the O2 sensor). That way the motor wouldn't stray to far from stock VE trims, and melt the motor.

So lets say I set it to 88 but when the BLS got to 98 the ecm had pulled enought fuel to get the ratio to 14.7 if it works this way what would happen with the BLS would they stay at 98 or return to 128. I hope I worded this ok

The blms would stay the same for a Ve cell, as long as the cell value , or your injector size constant wasn't changed.

Why dont you repin to 1227165 and run $6E? Those ecm's are very much available. Hell I've got about 5 of them, and I even have one with a modified memcal for sale.

I just don't see why you would keep the '870 setup.. ?

-- Joe

I agree that you need to upgrade the ecm. It should take less than 1 day to repin the harness. That means keeping the existing harness and just switching the wires that goes into the ecm connectors. It's too easy

Thanks guys for all your help I am going to stick with my 870 for now.