Ok,

So I just spent the last 30 minutes reading the newbie sticky and my head is spinning. As suggested in the sticky I won't be asking what to tweek before researching and trying things myself.

But I do want to ask a more general question... I have a '91 Z28 with a 305 TPI and automatic. Everything is stock except for the things I've added which are:

- Hooker Headers
- 3" Exhaust
- Delete Smog Pump (aka A.I.R.)
- Rebuilt rear with 7.625" 3.73 running on torsen diffy

Is it time for me to start adjusting my PROM?

The whole reason I ask is that when I put in the rear this year, the shift points and the power band seems all goofed up. Basically, 1st gear is great but all other gears seem kinda wimpy when I'm at WOT.

I guess what I'm wondering is would tuning my PROM make this better? If not, then I'll turn to upgrading intake since I think that might help. If you guys think tuning is a wash, then I'll wait until more major updates are made. (like T56 tranny and 350 engine swap)

Thanks,
Jeff

 

By deleting the smog pump and not changing the prom, the ECM will always be adding a little too much fuel because it still thinks the extra air is in the exhaust and it's not. Well, not "always", but at least during warm ups and a few other short time periods.

Other than that, the mods you have don't require ECM programming. But you will need to have the Dakota Digital speedo buffer box to change the VSS signal to accommodate for the 3.73 rear swap. Without it your speedo is off by quite a bit and that can cause several driveability issues. You'll have to have it when you go to a T56 anyway (unless you like seeing your speedo buried when you're doing less than 10 mph LOL)

 

IMO, the stock proms leave alot on the table as far as drivibility goes. But, I've been tuning for a while.

A *chip* for what you done, isn't going to set the world on fire, HOWEVER, it's much easier to learn, and experiment on a somewhat stock engine, rather then when you have a real hot rod to figure out. As the level of Hp goes up, the less forgiving the tune is, so a stocker is where to get your feet wet.

 

one thing, the chip isn't going to change how your transmission shifts.

im still pretty new to chip tuning & i say get into burning your own now.
my motor is dead stock, & with just a few minor changes in the bin it runs better now than it did with the stock chip.

a few examples of what i have done. i didn't like it running at 220+ sitting in traffic with a 180 T-stat, a small change to the chip got it down to below 200. i raised my TCC lockup speed. it has a better idle now.
i turned on hiway mode & picked up a few more miles from each tank of gas.
it will pass the emissions test here without cats.

my next tuning purchase will be a wide band O2 & then i'll get into really playing with the VE & other things.
when i do start making some changes to the motor, i'll feel much more confident when i start tuning for the mods with what i have learned so far.
there is so much about chip burning that doesn't make sense when you don't it, but it starts to fall into place after you get into it.

 

I read and reread the stickies about 8 times before it started making sense. For me it was kind of like the light bulb thing, all of a sudden it was there. Seriously, it really isn't as hard as it first appears. I got an Autoprom and adapters from Moates.net (it came with Tuner Pro software!) and started playing with the tables.

I'm with Grumpy on the start tuning now point. You won't regret it. The great thing is you can always reload the previous bin if you don't like your changes!

 

The stock bin (tune) is too rich to begin with. Your mods would make it more inline with the stock tune. Low RPM may be off a bit but probably not much.

Listen to AtomicTruck's advice is. It is probably the best advice you will hear from someone just starting out. In general, it is great advice.

 

I agree with all of the above.

Do you NEED an eprom? Not really. And, an "off-the-shelf" eprom like Hypertech will do little (if anything), and most likely even hurt you. "Mail Order" custom proms are a little better, but still a waste of money (for a basically stock engine).

But, as mentioned by the others, you are at the perfect place to start learning. You could experience an increase in performance, fuel economy and driveability as you become more proficient in tweaking your prom (which could easily pay for the equipment you purchase to burn your own eproms).

As mentioned by Vern, probably the most serious issue at this time is the removal of the AIR System without making the necessary change to the eprom.

 

And the charcoal canister if you removed that as well....

 

Thanks guys, this is very helpful. I was kinda thinking that with the minor mods that I've made that a chip tune wouldn't change the HP or drivability by much.

But you all bring up a good point. If I dump the EPROM binary at this point I don't have to change a whole lot. Fixing the AIR thing sounds like a must plus maybe some slight tweeks to the fuel mappings. The EPROM isn't the part that scares me the most. I'm a software engineer by trade so writing embedded code doesn't worry me. I also do electronic hardware design when I get a chance

What I lack in is the understanding what are all the aspects of a fuel injected combustion reaction. I know spark + fuel + proper CAM and Crank timing = Horsepower. (duh) But when I look at all the different 2D and 3D table, I'm left scratching my head wondering why so many things are needed.

So I basically have the reverse problem than most newbie tuners. I think most guys grew up on building carbed engines and look at software in bewilderment. I on the other hand have been doing software for 10 years but have yet to take apart an engine by myself.

I'm definitely in store for a lot of fun and frustration as I work through this project. After reading your replies I think I'll work on tuning my EPROM next spring before I get into any engine mods. Thanks for your suggestions.

BTW: VernW, regariding the speedo. For 89-92 f-body's the used a "hybrid" speedo gear so all I had to do is replace the drive and driven nylon gears and my speedometer has never been more accurate. So at least I don't have to worry about this problem!

Jeff

 

there isn't any more needed for a fuel injected motor than there is for a carbed motor, its just that with FI you have more control over every thing, you can adjust everything better, quicker & easier.

to kind of simplify what im talking about, & if i can word this right, with a carb, the amount of air flowing through it controls how much fuel the motor gets with a certain size set of jets. the float level also has an effect on the amount of fuel flow. there are other parts you can change in a carb to alter fuel along with the choke for cold starts, but even the best carb can't be turned as good as fuel injection can be. with a carb once the choke is fully opened the amount of fuel is the same at part throttle at 3500 RPM no matter what the temp of the motor is, with FI you can make it leaner at hotter temps if you need to.
its the same with ignition timing, with a plain vacuum/centrifugal advance distributor, once its fully advanced you can't pull timing back out at full throttle and high RPM. plus there is nothing to pull timing if you get a bad tank of gas.

yes, i love electronic fuel injection

 

It just varies by driver..... Some guys think the stock chip is great, and then once they get into it, see just how bad it is. Then if you're one of the fussy guys, you'll really perfect it, and then REALLY get how bad a stocker is.....

It's all a matter of what degree of perfection your looking for. Drive a car with an ACCEL Gen VI, and you'll immediately appreciate just how good a GM ecm is.

There's no *most newbies*, you'd be surprised by just how big of gathering of past experiences, and no experience there is, here.

While it might no always seem to make immediate sense, what folks might recommend you, there's a heap of experinece here.....