I have the mods in my sig and need advice. I am having a bad backfire through the intake when you get off the throttle. I am also running rich a idle and the idle is ruff. I have 30lb SVO's set in the chip as 32. I am using the ARAP.bin with mods as I go along. I need advice on where to start to get the idle right. I am using the Holley Stealth Ram and TrickFlow 195cc Aluminum heads.
Thanks

 

anyone?

 

Don't start looking to alter things to band aid over problems.

If your idle is rich then work on that first.

Set you injector constant to 30.

Then in Maf1 table start dropping the values a little.

Do you have a scan tool or some way or monitoring what your airflow is at idle?. If you take the table entry multiply it by the scaler, and divide that by 255 will tell you what that entry corresponds to.

 

Grumpy in a lot of the old MAF posts you STRESS not to mess with the scaler tables.Why the change of thought?

 

Assuming that you have the fuel pressure set at 43.5psi (stock),
the 30#/hr SVO injectors will flow 31.5#/hr.

So you are not bad with 32#/hr.

I would set the fuel injector flow constant to what it calculates out to be for your present fuel pressure, then do what Grumpy said about the MAF1 table.

What fuel pressure are your using?

30#/hr SVO injectors are very large for an NA 350.

 

Since I am using the Stealth Ram and Fuel rails my fuel pressure guage doesnt fit on the test port so I dont really know what the pressure is at. It is the non adjustable regulator and I believe that Holley uses the Buick Grand National regulator. I am not totally clear on how to adjust the MAF tables. I am using Craig Moats software and TunerCat.
Thanks!!

 

This logic shown below is what I learned on my '99 LS1 car and how I am going to tune my 350/395 this coming summer:

The BLM value is the Block Learn Memory, it is the long term fuel adjustment which is stored and kept even after shutdown.

The base line for BLM is 128 (+-6). If the BLM value is greater than 128, the ECM is adding additional fuel up and above the amount it calculated that it needed at that moment in time.

So lets look how the ECM calculates PW (fuel amount needed). The short story is (I dont know the long story) that the ECM knows the amount of air coming into the engine from the MAF sensor (counts), it knows the temperature and other parameters, such as, the fuel injector flow constant.

The ECM reads the counts of air coming into the engine thru the MAF sensor. The ECM goes to the MAF tables to associate the counts with "amount of air". The MAF tables are simply look-up tables for the ECM. There is nothing magic about it.

Now, if the BLMs are above 128, the engine is running lean over time because the ECM is adding extra fuel above the calculated amount. So if the engine is running lean, the ECM must have gotten an erronous value from the MAF tables (or the fuel injector constant is wrong). The ECM was told that less air was coming into it than was actually coming in, and the ECM calculated a too small Pulse Width for the fuel injectors. Too little fuel was added to the air and the ECM responded by increasing the BLM value.

What do we do about this????

We can increase the air flow rate in the MAF tables so that the ECM gets a more accurate value for the incoming air.

How much do we change it??? (I dont know for sure.)

But, what I would do is to increase the MAF table values by a percentage: (BLM -128)/128
and divide by 2 so that we dont go to far on the first change.

This needs to be done to each MAF table according to the BLM for each MAF table. Remember that there is fuel cells, I think there are 16. These fuel cells can be arranged into a grid where the sides of the grid are engine RPM and MAF flow rate (engine load).

So to carry out the changes to the MAF tables, you must have a good scanner and do alot of runs on the street, because the BLM will be different for each fuel cell. So you change each MAF table by a different amount, BUT you must be sure that you have a good flow values from table to table. Also, you can not go over 255.

Does this make any sense?????

 

Hey thanks for the info......I dont understand the fuel cell part tho......

 

Well, forget about the fuel cell part.

I was trying to explain that you need to match up a BLM value with a specific portion of the MAF tables.

I might be wrong about this, but I think that there are more than just one BLM value, in fact, I think that there are 16 of them.

BLM value #1 would be the lowest load state of the engine, possibly at idle, that would be fuel cell #1.

When you are at idle with the engine completely warmed up, take a scan, match the engine rpm, the MAF counts, and BLM value (for the idle case).

Also, at various engine load cases while driving around, take many scans and match up the same three variables. I think that you will find that there are different BLM values for the various engine load states. You are to modify the MAF tables (the specific portion of the MAF tables) according to the BLM value/engine rpm/engine load states.

See, at idle, you will have one BLM value, while at 3,000rpm in 3rd gear climbing a hill, you will have another. You are at different engine load states in these two cases. Thats what the various fuel cells are all about. (In my '99 LS1 car, I have 22 fuel cells.)

In other words, you might find out that you need to increase the flow rates in MAF table #1 by 10%, table #2 by 8%, table #3 by 5%, etc. Now remember the MAF tables most not overlap in there values, so you might have to increase the last value in table #1 by 9% (instead of 10%) and the first value in table #2 by 9% (instead of 8%) so that you have good continuity between the MAF tables.

A graph of the MAF tables (counts versus air flow) should be a smooth function (curve). In Excel, plot MAF counts (x value) versus MAF flow rate ( y value) for all 6 tables as one x-y graph. You should have a smooth curve, not a jagged line.

Is this any better???

 

Over the years as new info becomes available things change.

6-7 years ago, there was VERY LITTLE info around for doing any chip mods.

 

Define jagged?.
Pretty much so, but reversion and other items can disrupt your curve. THOU the values should at least be equal or assending in value.

And, no need to repeat the last entry on the first entry of a new table. A large jump may cause an erratic **stumble**, as you change table.

there is a page on the GNTtype list with some MAF hints.

 

jagged - any discontinuity in slope or offset that occurs in the plot of the curve: counts vs MAF air flow

Grumpy, your comment about ascending values is on the mark, of course, you know what I am talking about.

I'm a mechanical engineer with a flair for math, graphs, and geometry, but most of all common sense. I believe in conducting reasonable experimental tests and draw conclusions, put your best foot forward and go on from there.

 

the maf will definately have dips in air flow. im not sure that they are as quantifiable as wed like them them to be in terms of sensor readings. id bet more on the fact that the engines might be cross mixing cylinders with reversion instead of it directly affecting the maf readings. for a reversion effect to begin to stifle the maf readings it would take alot of flow. enough to drive vacum well past zero. but its gott to be taken into account. however the maf tables simple quantify vout of the maf into grams/sec so reversion shouldnt play to much havoc with it.

just more random thoughts.

 

Good info guys keep it comming......
One question tho......With the injector constant set at 31 the car smells real rich and backfires when the throttle is hit. However I lower the constant to 25 and it smells a lot better and no backfire???? I havent scanned it like this yet but whay would this occur....remember this is only at idle??? The car still shakes tho.....and is hunting for an rpm????

 

Look for a vacuum leak, sometimes you can locate it by listening for a sucking sound. When an engine hunts for idle, many times its a vacuum leak.

Check all of your spark wires, make sure none are burnt or shorting out against the exhaust headers or manifold.