Will reflash help?
 

Is there anything that reflashing the chip will do for a stock setup?
or is that only for when you change something?

With out headers, cam etc, or some performance mods I would think you`ll gain very little

Well I know that it's necessary if you change something such as cam or headers, but I'm trying to figure out if there is anything more you can squeeze out of the stock setup with no mods. My research on here is inconclusive.

To answer the original question.

The issues with the Blazer's and tuning are the following:

AFAIK ! and have researched for my build.

- I have yet to see conclusive evidence and especially "FIGURES" on tunes made on engines without any other modification. One thing that shows up in many experience reports is lower mpg thou.
- Many reports are about better response and acceleration but very often if not always do not state any problems with that, i.e. surges.
- The 4.3 V6 has been built for low rpm torque over the decades and has seen use in such vehicles as trucks or Chev Malibu and Monte Carlo. It should go low on gas with good mpg which can be achieved by restricting inlet and exhaust ports for high speed of air and fuel mixture for good low end performance. The factory tune reflects this and there may be some little gains with a tune but at the expense on some other factor, i.e. max torque moves to higher rpm.

Despite what aftermarket makes us believe the factory ECU's are really good! These ECU's can do a lot more than just meter the correct amount of fuel. They do cold starting as well as a reasonable job of cutting fuel upon throttle release at higher rpm to bring it back smoothly. Since the beginnings they have some very interesting logic inside related to the vehicle. Again we have to look at the package and at the goals of modifications. Have a look at this thread and my writeup about mods for MPG.

https://blazerforum.com/forum/perfor...s-69167/page4/

There is a little bit about the goals of a modification. State the goals first, then act on the goals.

A word of CAUTION:
Every year Blazer is a little different to the previous. Some years are very particular and in some years there is a transition from one product, to another sometimes with some oddballs using a mix of parts. It will depend on your particular vehicle and what has already been altered on it what can be done or what the base of a tune is. Another aspect of a tune and the ECU is that some behaviour and how the ECU works can cancel a tune's intent.

i.e. 1994 4.3 V6 4x4 S10 Blazer with LB4 engine (TBI injection). Today I know that any modification between headers and after the catalytic converter is money thrown out the window. Why? Simply because the collector pipes, Y pipe and cat are from the V8.

i.e. The lambda sensor (O2 sensor) can be master in closed loop operation of the ECU. Maybe the tune would like to inject more fuel in acceleration to up the hp/torque but on some ECU's even in acceleration it keeps the O2 master which will simply pull the fuel back to achieve a predetermined lambda in acceleration and your tune is simply worthless.

You need to understand the in's and out's of your particular fuel injection in order to make correct decisions.

My build is meant to:
- Retain the OEM torque curve or up it by some 5 - 8 % (I am prepared to loose 1 - 5 % up to 2'000 rpm as the camshaft may not be able to keep the mixture speed high enough at low rpm <2'000 rpm at a stall speed of around 1'200 rpm the fuel flow should not be too terrible in acceleration from standstill.)
- Expand the torque curve further upwards by some 500 - 750 rpm (Camshaft)
- Retain the OEM 1994 TBI with an engine dyno tune set and re-calibration on a chassis dyno and the road.
- Rise the rpm limiter to 6'000 rpm (but we may be limited to 5'000 rpm because of number of cells in the ECU - we'll see once we have the readout of the EPROM and the engine on the dyno in maybe 2018)

I stand corrected, and if somebody had figures of before and after a tune that would be a treat.

Well then, since mine ain't broke, I ain't gonna fix it. 😁

Mine is a '96 (1st year of OBD II / Can). The factory muffler was clogged up with bits & pieces of the cat internals so I cut it all out and put in a Dynaflo muffler. The muffler guy put in a spacer for my O2 sensor he calls a "bong" to fool the computer into thinking the cat is still there and working perfect. To insure that, I put in a brand new O2 sensor.

I have to admit the muffler keeps it quiet at idle but holds nothing back when I put my foot into it. It doesn't sound as awesome as my 89 Mustang GT but, for a V-6; it sounds real nice. Acceleration seems faster and smoother but often I smell fuel when I turn off the key. The cap & rotor are old now and sometimes it has a rough idle.

I am wondering if a "Re-Flash" would correct the computers interpretation of the free flow exhaust and missing cat. A buddy of mine suggested I get another emissions box (EGR?) from a junkyard. I'm not sure I know what it even looks like

Something isnt right, thats why you smell gas and thats why the cat went bad

So what does a "reflash" accomplish? Reinitialize the on board computer (ECU) for the motor? When done, does the ECU then reset its operating parmeters?

Would this be appropriate for me to have this done having recently replaced the distributor cap, rotor, spark-plug wires, spark plugs, installed a Dynomax exhaust, and upgraded to the MPI fuel injectors?

Edit: Or would a "reset" of the ECU be all I need to do?

Dont think it would be needed in your case. better after higher performance upgrades

Most of the GM ECU's use and used EPROMS to retain the internal code (Operating System) and the tables containing the "tune" and some memory which can be erased.

Hence:

RESET
Is usually done on older models let's say before 1996 by taking away the power from the "whole" system for a time period long enough to erase all volatile memory (RAM). Just disconnect the battery. Some ECU's or other components in the electrical system may have some means of keeping data for a short while even whith the battery disconnected.

Newer vehicles may need an intervention with correct testing equipment or need special procedures such as pulling specific circuit brakers before or after disconnecting the battery and resetting them in a specific order after applying power.

I'll use my 1994 CHEV S10 Blazer 4x4 as a reference because I know that vehicles in's and out's. The ECU in the 1994 needs the battery disconnected for at least 10 - 15 seconds to erase the volatile memory. (It has some fuel trim tables it needs to adjust i.e. "SHORT TERM FUEL TRIM")

What are the volatile parts of the memory? They are some tables with values that the vehicle "learns" when driving. Some are engine related, others transmission related. Most even old ECU's have some "self-learn" capability on metering the fuel which can take account for an ageing fuel system or other parameters which change only over long time. Some tables retain values for sensors values i.e. TPS.

This can sometimes help eliminate errors which cause small deviations i.e. after fixing some fuel issue to have it re-learn faster.

REFLASH
Strictly speaking a "reflash" will act on the whole memory chip of the ECU or "chip's" in some cases. An EPROM (electrically programmable read only memory). The EPROM can be erased when a specific and specialized connector is used or the EPROM depending on it's socket removed and inserted into an external reader/programmer. EPROMS are standardized electronic components.
After erasing the content a new content is written to the EPROM and from now on the ECU has a new "personality" hence a new set of instructions and tables.
These can be the factory datasets or a "tuned" set of instructions and data.
I wonder what we would see when comparing the stock vs. a "reflash" EPROM from some third party.

If only a small part of an ECU's instructions or tables are corrupted it will most probably stop working altogether or throw a code or do very, very weird stuff to the engine. Actually I never heard of one fail without very sick outcomes, like flooding an engine on start or not activating the injectors all together. Most troubles with ECU's come out of the wiring to and from the ECU.

If you buy a "tuned" chip all you get is an EPROM to be put into your ECU with a new set of instructions and tables.

ABOUT THE ECU's WORKINGS:
The ECU is a little computer with very limited skills - but these skills are super-fast. So fast, that it can control the engine over it's regime.

It has a set of instructions that enable it to take inputs and generate outputs, to know where his memory is and on what ECU it is sitting, this is the "operating system". The OS can access a set of instructions to know and decide upon inputs what to output. Throttle is opened, add fuel for acceleration.

The information on how much fuel or for other decisions it has to make is available in tables that the ECU can now access. As it has to take more than one parameter into account we have a two dimensional table i.e. "rpm" vs. "throttle position". The table can now be entered with these two values in the same way as we would look up a table, rows/columns and you drop onto a field in this table. The value found there is i.e. the amount of fuel to be injected.
Imagine a chessboard and now we just place 64 figures on it ranging from little values "pawn" up to high values "kings". When placed, we throw a blanket over them and all on a sudden we realize that we have created a landscape with a particular form. We now have a 3D model. That's what the ECU does. Take two values and create a third as output.

Tuning will alter the values in these cells to create a new landscape, giving a little more fuel here and a little less there.

It's more complicated than that then even a 1994 ECU can do interpolation to smooth the values between cells, add some more logic such as cold start enrichment, act on the ignition advance, cut out fuel upon accelerator release, take corrective action based on "lambda" from the O2 sensor(s) and later versions tell if something is wrong in the emissions system (OBD II - MIL).
Plus the ECU fit's nicely into your car's electronics and drives such things as the dashboard, tach, temperature indications and others. This is one of the reasons it is not so easy to switch to an aftermarket injection ECU.

ABOUT THE TABLES and VE
The "tune" or tables in an ECU are based on a particular build of engine with a particular set of sensors, injectors, fuel system, fuel pressure etc.
The tables also reflect VE (volumetric efficiency) of that particular engine which is in a large part determined by the camshaft and the valvetrain including the cylinder heads and exhaust system.

This is one of the reasons why "mail tuned chips" will most probably never work properly and always be fuel guzzlers. In order to compensate for unknowns most "mail tuned chips" will inject more fuel than required to avoid some severe problems with spark ignited engines.

I hope that I'm not too boring with my lectures in the blazerforum.