doc

I seem to be going OK at this point, having just started on learning about custom burning my own chips.

I've read my hypertech (HT) EPROM and my CarPro EPROM. Also, I downloaed a stock '87 350 GTA bin file. I've been spending alot of time comparing these three bin files with tunercat.

Questions (I have about 100 Qs, but lets start simple):

I noticed that in the constant table, the HT and GTA files show 23.0#/hr injector flow rate, while the CarPro shows 20.8#/hr. I have stock 22#/hr injectors. How is the constant value for inj flow rate used by the ECM? Would using 20.8 make the engine run richer or leaner as compared to 23.0?

AND
For the CarPro file, the "WOT %Change to Fuel/Air Ratio Vs. RPM" table is set to 0.0 for all values. If I determine that I need about 5 to 10% more fuel at the dragstrip, should I up these zeros to 5.0 as a starter for the RPMs above 1600? (I have a 2200rpm TC).

Man!!! I need a little more speed out of my car. My step son with a '88 Mustang has run a lower ET than me late last fall. This has got to change!!!!!!

TIA
doc




------------------
'87 L98 TPI IROCZ, AFR190 heads, 3.70 gears, ZZ9 cam, 2400 Art Carr TC, SLP 1 3/4" headers, SLP cat-back, no cat, no AC, no MAF screens, Accel manifold base & SuperRam, Edelbrock double roller timing chain, MSD ext coil & distributor, trans cooler, 52mm TB with airfoil, TB coolant bypass, AFPR(58psi), K&N filters, Hotchkis lowering springs, Car-Pro custom chip, Lay Ind. ram air kit, 265/45R16 Kumho V700 tires.
ET 13.39sec @ 107.21mph
'90 Eagle Talon AWD, no rust thru 9 winters
'99 Camaro SS, red, 6-spd, T-tops, Mcleod clutch, Pro 5.0 shifter, MAF processor, Direct Flow airlid, K&N filter.
313.7Hp & 320.6ft-lbf, ET 13.55sec @ 105.1mph
next mod: 4.10 rear gears

Yelofvr

The injector constant is used directly to determine fueling along with the cyl volume and VE tables. If you increase the inj. constant or cyl volume up, you get a proportionate amount more fuel. Why do you want more fuel at the dragstrip than what the ecm would already command? Best power occurs at an Air-Fuel ratio of about 12.7:1. Check what the base PE mode A/F is set right now before you go too far with the % change entries.

------------------
Dave Zelinka

Grim Reaper

If you increase the injector flow constant, it will shorten the injector pulse width (leaning it). Conversely, decreasing the injector flow constand lengthens the injector pulse width thus (richening it).

Its quite logical when you think about it. If you had 22# and installed 26#, you will get more fuel in a given period of time. Thus the ecm will shorten the injector pulse width to ensure you are still getting the same amount of fuel.

However, if you leave the stock injectors in, you are causing a "wholesale" decrease in the injector pulse widths thus leaning the engine at all rpm/load values.

I would only adjust the injector flow constant if you need a global change to your engine. For example, if you are running a scan tool (with your BLM locked at 128) and notice that all values for the INT are noticeably below 128 (say in the 110 range), then you would want to consider increasing the injector flow constant to make it lean the engine out throughout the powerband at all loads. But if you notice that the scan tool gives "mixed" readings (some higher than 128, while others lower than 128), then you should not use the injector flow constant to fix it. Only for globabl changes.

doc

Those are good responses, thankyou, BUT

I have a MAF car. There is a table called "BPW Fuel Vs. Load". Its a table of rpm vs air flow (in gm/sec) vs injector pulse width.

I was wondering if my ECM even uses a formula, because the injector PW is listed directly in the look up table. Does my '87 MAF ECM employs a fuel formula?

What do you guys think? I'm lost here!

NickG

From reading through the hacks, I think that by default, this table is not used. There is one control bit that controls how the ECM determines the injector pulsewidth. By default, the ECM uses the airflow reading from the mass air meter and calculates the injector pulsewidth required.

The table you mentioned is the alternate method. It provides a lookup table for the ECM to determine how much fuel to spray, rather than let it calculate the pulsewidth. Making changes to the table, without enabling it, will have no effect.

Nick

Guest

Ok... I dont know what Carpro did, but maybe they set the constant wrong, forgot to change it, or intentionally did it. That I do not know.

Now... fueling... The 87 system uses the base pulse width when you first fire up the car after the battery has been disconnected and the memory of the 'learning' capability of the ECM is gone. Once it 'learns' the engine and how it runs from readings off the TPS, MAF, and o2, it adjusts the fuel flow from the base pulse width table and remembers what it did to it. This can make tuning somewhat difficult. The o2 has a major bearing on part throttle though, I can tell you that. It takes the readings and uses the information from the o2 to supply fuel and adjust the tables as necessary.