I've skimmed over the prom burning tech article, and I intend to study it more closely when I've got the time, it was a bit over my head. But I've got a couple simple questions.
I've got a 350 TBI pickup which I have been experiencing some "drivability problems" with. It's been taken in for a diagnostic, and I was told, it's running "better than most". The problem is fuel curve related, I think, there is a lack of power at part throttle, full throttle is fine.
There are some engine mods I've got planned for the near future and it seems like doing something with the prom is inevitable.
But it would help to get the ball rolling if someone could tell me:
What the parameters are that determine;
a)fuel delivery curve?
b)spark curve?

And is there a governor, rev limiter, or speed limiting device on my vehicle?

It's an '88 silverado 1/2 ton 4x4, TH700 from Cal. (if that matters)

...I just can't help but wonder

thanks

 

If it stock and now has problems, you must fix the cause of the problems, however hard they may be to find. ie, the truck probably ran fine at some point in its life until old age and/or modifications crept in...

Fuel and spark curve changes can help an engine dramatically but increase/decrease emmissions as well. For an OEM motor with a better exhaust/no cat/intake, the OEM PROM is pretty good and some Fuel Pressure changes along with a timing advance a bit usuallly helps quite a bit.

 

Hi, thanks,
I'm beginning to believe that the "problems" I'm experiencing are just something that's inherent to the design. I'm sort of used to carbs, so it feels wierd.

 

I am working on my '91 3/4 ton 2wd pickup and have found a few interesting things. Some of the perameters I have to work with are similar to the ones you would find for your truck. For example, there is something called WOT (wide open throttle) delay (also called Power Enrichment delay) that prevents the engine from really opening up for a certain period of time. Apparently, this was designed so that towing vehicles didn't spin their tires all the time when towing heavy loads.

Download a trial version of TunerCat (www.tunercat.com). It comes with the ECM definition file for your truck (assuming it uses the 1227747 ECM). You should be able to look over this to see what perameters you can modify.

Although I haven't burned a prom yet, I've learned a lot about how the computer controls the engine. I really don't see how people are able to get the true performance out of their modified vehicles without programming their own proms.

Also, make sure your engine is in good shape. My truck has over 160K miles, but burns no oil and is in very good working condition. Check your compression and make sure your in good tune. Set the timing to what the book says (or what is on the air cleaner). The timing curves the computer uses is based off of the initial mechanical timing and that can really mess things up if it is not set correctly.

good luck

 

thanks for that tip on tunercat.
wish i had the time to get into it right now, i'll be taking a closer look at that soon tho'.
i had my truck in the hills (3000ft.) for the first time since i bought it last july, it needs help, badly.
i'm looking at the possibility that the AIR pump diverter valve is not getting a signal from the ECM, thus causing the O2 sensor to signal the ECM that the mixture is richer than it actually is.
any opinions on that?
i have to give it a lot of pedal and it's always looking for a lower gear.
...MUST FIX!
thanks for help

[This message has been edited by 88tbi4x4 (edited October 30, 2001).]

 

Other things will also make the engine run rich. Vacuum leaks, hotter cam, modified intake, etc. Basically, the computer thinks the engine is working harder (higher MAP value) than it really is so it feeds it more fuel than it needs.

I've now burned about 20 chips and have learned a lot about the programming for my truck. I started with the Volumetric Efficiency table (which the 7747 has too) and made an vast improvment. I was running too rich because of my mods.

The other thing I learned that has paid off greatly is just how my ECM's Power Enrichment mode works. I now have much better acelleration and can get onto the freeway in a reasonable, if not quick, time.

Check out some of the engine monitoring software, it will help you understand what's going on in your truck.

------------------
1991 Chevy C2500HD 5.7L HD. 16147060 ECM
Mods: Crane PowerMax 2030 cam 204I 214E @ .050 and 423I 446E lift, Jacobs Pro Street Ignition System. Using DataMaster and TunerCat with $85 ECM files.

 

Thanks,
Glad to hear you're still out there, I haven't checked this thread in a while.

Apparently if I'm ever going to get this engine running right, I'm going to have to get into burning chips and I don't have my own computer right now.
Is there a way I can begin getting my feet wet in the chip burning world using the equipment in public computer labs?

[This message has been edited by 88tbi4x4 (edited October 30, 2001).]