newbie looking for how parameters interact

RF_Burns · Post by **RF_Burns** » Sun Sep 13, 2009 12:12 am

I have a Howell system on my GMC Motorhome, 455 olds FWD.

I am trying to understand how all the tables and parameters interact. I have been googling around and I have not found a good writeup that explains it all, just bits and pieces.

My main issue is my O2 will drop to near zero when I go off idle and stay there for up to several minutes. Meanwhile the BLM's go through the top, up to max. I can't fiquire out why the O2 goes low, its fine then I let off the gas and it drops to 0.01 and when I accelerate it stays there. O2 is reading low and the BLMs go lean!

So I am trying to fiquire this out. Howell has sent me several Bins but no luck.

Any suggestions would be appreciated.

Bruce

Post by **robertisaar** » Sun Sep 13, 2009 6:00 am

you might want to consider replacing the O2, because something is VERY wrong...

when you see the O2 go above ~.450 thats running rich. less is lean: see how the lettering works to your advantage

as far as how the tables interact: it depends on your codemask: i'm not sure what you're running but if you can give me more info, i can probably help

RF_Burns · Post by **RF_Burns** » Sun Sep 13, 2009 6:55 am

Sorry about that, Its a GM 747 ECM, with a 42 XDF.

I'd blame it on the O2 sensor as well but some others who have the same kit on the same Motorhome/engine combo have the same issue. They have changed O2 sensors and gone from single wire to heated and it doesn't fix it.

I would think with the O2 reading very low, (0.02 - 0.04 volts) the ECM should be making the it more rich, instead the BLM's go higher (which is more lean).

I could attach a log file, but not sure how to on this forum.

Thanks

dfddfd2 · Post by **dfddfd2** » Sun Sep 13, 2009 7:09 am

Exhaust leak maybe?

Post by **robertisaar** » Sun Sep 13, 2009 7:15 am

being a C3 ECM: you're only getting a 160 baud stream, so its probably not that accurate of a log.

if the ECM is removing fuel through the BLM going up, then it probably is running rich, its just that when the ECM polls the O2 sensor(at either 80 or 40 times a second, i don't remember which) and then outputs it to the datastream, its low.

why its constantly low: no idea, but trust the BLM and INT. those will be your key to getting the fuel tuned...

RF_Burns · Post by **RF_Burns** » Sun Sep 13, 2009 7:42 am

It does feel like it is leaned out, engine bogs badly when trying to accelerate.

If I'm just not getting data fast enough, wouldn't the rich/lean counter still be counting? It doesn't, it stops counting or counts change slowly.

I should mention this is a newly rebuilt engine, but it was doing the same thing before it was rebuilt. Careful attention was made to all gaskets to prevent any vacuum leaks. New Exhaust gaskets etc,

Also, is anyone using the DynamicEFI EBL Flash board? Any reports on it good or bad?

thanks

Post by **robertisaar** » Sun Sep 13, 2009 7:53 am

you didn't mention the rich/lean counter not changing...

that changes things a little.

so even the ECM thinks that its not running at stoich.

vacuum leaks wouldn't kill the AFR like it would in a MAF system, but since you've taken steps to eliminate it, i don't see the point in refering to it again...

does it pick up any knock? especially during these phases?

RF_Burns · Post by **RF_Burns** » Sun Sep 13, 2009 8:33 am

The Howell system in this application does not control the spark, its just a stock HEI ignition, so it doesn't have a knock sensor. They have a circuit in the wiring harness to fake some knock, I am not sure why.

When its doing this there maybe some light rattle knock, but certainly not the knock I got while setting the timing. Its a bit hard to tell, its a motorhome so there is always something rattling around in the back!

Where I especially see it is on the hyway, let off the gas to slow for traffic then step on the gas and the engine will bog. Or come to a stop from hyway speeds then drive off. At idle it shows OK running in open loop, a bit on the rich side, but then goes lean generally a couple seconds after I step on the gas, it has changed to closed loop at that point.

I was hoping to find a site that documented how all the parameters are used and how it comes up with a PWM ratio.

Post by **robertisaar** » Sun Sep 13, 2009 9:21 am

RF_Burns wrote:how it comes up with a PWM ratio.

you mean BPW?

simple to do since the 7747 is about the most documented C3 ECM there is...

and the fake knock simulation is because when in certain conditions, the ECU tests the knock sensor by adding extra timing when the MAP is above a certain point and RPM is below a certain point. it creates knock to tes the sensor. if it doesn't detect it, then it sets a code and tries to reduce spark.

does it bog for just a second or less? or is it quite a few seconds? if its just a second or less, richening the AE table will help there.

RF_Burns · Post by **RF_Burns** » Sun Sep 13, 2009 9:27 am

PWM = Pulse Width Ratio for the injectors. I'm in electronics so since PWM is how the ECM controls the fuel, I was using my electronic's jargon.

It can last for a couple of minutes before the O2 starts swinging again and the lean/rich counts start cycling.

Post by **robertisaar** » Sun Sep 13, 2009 9:35 am

couple MINUTES? DAMN...

care to tell me what the current BIN you're using is and maybe a datalog? i'll see if anything else looks funny....

RF_Burns · Post by **RF_Burns** » Sun Sep 13, 2009 11:25 am

Shoot me an email to bruce a t perthcomm dot com and I'll email you my last couple bins and logs.

Six_Shooter · Post by **Six_Shooter** » Sun Sep 13, 2009 1:22 pm

BLM/INT above 128 = ECM adding fuel.

BLM/INT below 128 = ECM removing fuel.

So from what I read here, the ECM is indeed trying to add fuel.

What size injectors are you using? I would assume you are using a stock GM TBI, say in the 350 or better yet 454 bore sizes, I don't recall the actual bore sizes off hand but I want to say 454 is 2" throttle bores, and 350 is 1 7/8" (ish).

Is there a VSS connected to the ECM? Coolant temp sensor? TPS, etc?

RF_Burns · Post by **RF_Burns** » Sun Sep 13, 2009 1:27 pm

There is no Vehicle speed sensor, but there is TPS (set for .57V at idle) and engine temp sensor.

Ahh I maybe thinking at it the wrong way... >128 engine was running lean and ECM is adding fuel. Below 128 engine was running RICH so is sutracting fuel.

I was thinking >128 it is leaning the mixture and below 128 is making the mixure more rich..

Thanks for turning me around, makes more sense now!

RF_Burns · Post by **RF_Burns** » Sun Sep 13, 2009 1:40 pm

Robert, Files are now zipped

thanks

Post by **robertisaar** » Sun Sep 13, 2009 1:41 pm

i probably should have caught on to your misunderstanding quicker: my wife's GP always ran rich at idle (around 104 BLM)... took pulling quite a bit of fuel out.

BTW: from the BINs you sent me: i'm not so sure if i would trust a tune from these people. the VE is WAY off, they're trying to run around 130% through both tables. which if you know anything about GM ECMs, that doesn't work. they also disabled the checksum, which is kind of pointless unless you're emulating...

RF_Burns · Post by **RF_Burns** » Sun Sep 13, 2009 1:53 pm

So you are saying the the VE tables are about 130% higher than they should be?

I was comparing the Original to the AZFT9503 table which is as close as I could find and I didn't think it was wildly different. But hey I see that in some cells now

RF_Burns · Post by **RF_Burns** » Sun Sep 13, 2009 1:58 pm

Six Shooter,
Its a holley 502-6 670CFM TBI with 80# injectors I believe.

Six_Shooter · Post by **Six_Shooter** » Sun Sep 13, 2009 2:25 pm

Actually "130%" is possible with a GM ECM, just that the main VE table will only allow numbers up to 100% (I think it become 99.97% or something like that actually), and then the adder table can go above that.

A VSS would make a huge difference in drivability and functionality IMO.

Any reason you don't want to use full functionality of the ECM, by using spark control as well?

Post by **robertisaar** » Sun Sep 13, 2009 2:34 pm

Six_Shooter wrote:Actually "130%" is possible with a GM ECM, just that the main VE table will only allow numbers up to 100% (I think it become 99.97% or something like that actually), and then the adder table can go above that.

really? i always read that the ECM ignores values that adds up to over 100
%.... guess its time to go read some hacks to get the answer...

RF_Burns · Post by **RF_Burns** » Sun Sep 13, 2009 2:38 pm

I'd like to add the ESC to it, but the way the kit comes is just Fuel Control.

Once I get this working, then I'll try some more tricks!

http://howellefi.com/customer/product.p ... 272&page=1

RF_Burns · Post by **RF_Burns** » Mon Sep 14, 2009 3:27 pm

Robert,
I emailed a new log to you based on your Bin

Thanks

Biglar · Post by **Biglar** » Sun Jul 01, 2012 6:03 pm

I have a similiar question regarding where I can go on the internet to find out if the parameters I have recorded using TunerPro are within the operating range per original manufacturers specs for my engine. I have a 95 Chevy G30 454 (7.4) motorhome and I can see the various values for sensors, but how do I know if they are actually in (normal) range. I have no red warning, etc. on TunerPro but what still like to know if everything is within normal operating range. Do such sites exist?

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newbie looking for how parameters interact

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