I've been thinking about jumping in and getting involved with the whole prom burning thing, weighing the pros and cons… and one thing came to mind:

I've got a lot of experience programming aftermarket setups, which are notably different then doing the OEM thing, but one thing that I've had on a few cars (we use it all the time dialing in/finding problems with my brother's haltech controlled car) is a fuel trim ****. Basically a potentiometer that is wired into the ecm that allows you to adjust the fuel delivery across the board a few percent richer or leaner just by turning a dash mounted ****. It makes it really easy to figure out if the soft spot/rough spot is rich or lean, just grab the **** and tweak it a little till it goes away, then you can even read it's position using a laptop to tell how much fuel you added or took away at that point to get it right.

Has anyone done something similar with a GM ECM? I've been thinking of how to do it, and the best idea that I've got so far is to connect into the IAT or CTS output and modify the signal slightly. It's not perfect, a simple potentiometer could work for making it run richer, but I'm not sure what the best way to make it go leaner would be and it would have some effect on timing but I suspect that it would have a bigger effect on fuel delivery.

Anyone have any [better] ideas?

 

http://www.customefis.com/afrtool.html

http://www.customefis.com/maptrick.html

 

Mark, I don't think that this is your style but you could always try to locate an Accel Variable Injector Controller.

http://www.bescaredracing.com/ecm/vic/

I originally ran one a long time ago and it worked great. I only removed it (and sold it) because I wanted to keep my setup as simple as possible.

Tim

 

For the same amount or less effort, you could be editing .bin files, and getting somewhere.

Once you get into doing it for a while you'll get the feel for how to change what how much.

 

If you follow his instructions of using a 5K, that'd mean your so far out of the ball park, as to be laughable, IMO.

7-8 years ago, using a variable resistor was an option, since the DIY community just didn't have the info to work with.

 

Get Tunercat RT, AutoProm, or the Prominator, and get in there, and get used to what the changes do, and take notes.

Better yet, get a WideBand, and datalogger, and then go thur the tables, dialing the fuel and timing in.

Long Term it's just so much easier to do it right once.

 

True - but what happens when you run into a cylinder that runs lean? or rich? You can't change that with .bin editing. Granted - I don't like the complexity of adding extra stuff for tuning. But, when you have the need to do such a thing then you need to add something that can accomplish it.

Tim

 

What's this got to do with the original posting?.
His MAT temp correction dealy is for universally changing the fueling.

And depending on ecm/pcm used you can do individual cylinder trims, since some allow for that.

A seriously lean or rich running cylinder is more often a mechanical problem, and usually a mechanical problem is best fixed with a mechanical answer.

Not to mention depending on what code he's running a MAT/IAT temp fooler might not do anything.

 

This has everything to do with the original subject since you can trim the fuel by *****.

This is a thirdgen forum. Mark has a thirdgen. The ECM is either going to be a thirdgen ECM or the 749. It doesn't have individual fuel trim control.

The MiniRam is a perfect example of the desire to trim fuel on a cylinder by cylinder basis. If you want to call this a 'mechanical problem' then ok.

I never said anything about a MAT or IAT temp fooler.

Tim

 

Interestingly enough, Craig and I are working to get a 3 channel "remote control" that works with the AutoProm and TunerPro (making use of the AutoProm's 3 channels of A/D).

With this you'll be able to assign a channel to any constant/table/AddrRange/etc, and twist a **** or flip a switch to alter that parameter (during emulation) in real-time.

This would make it much easier to tweak in values while driving without the use of a helper in the passenger seat or a need to pull over (very similar to adjusting the volume on your good ol' original stereo head unit).

Cool, eh!

Thanks to Ken73 for lighting the fire on this idea!

 

Whatever.
He mentioned the IAT, and you first mentioned the individual cylinder trim.

Yes, the poor design of the minram is what leans out the rear two cylinders, I guess you missed the posts about it.

 

Ummmmm - I WAS THE ONE MAKING THE POSTS ABOUT IT. I guess you missed the posts about it. Yes, he did mention the IAT/CTS. My bad.

Tim

 

Huh, amazing… Somehow I have this effect on ECM discussions (which is also a large part of the reason that I've entirely stayed away from ECM tweaking in the past). Somehow all I have to do is say something about it and Bruce and someone is arguing… Bruce, one of these days I'll have to meet you in person. I bet we'd get along even though it seems like online we usually argue.

Not my style… um, costs money and is overly complicated… probably not. I'd probably figure out a mechanical way of doing it. In your example I'd be cutting and grinding on that miniram long before I resorted to something like that, but I'm hard headed that way…

so how did you do it? I'm not thinking in the place of actually tuning it, I'm thinking "I'm rolling down the road and I have an unhappy spot, I'd like a way that I can figure out which way and how much it's unhappy. With the Haltech setup in my brother's car you can just grab the **** and dial in some more or less fuel to see if it makes a difference. Once you do that you can move the maps around any way you think will help, but you have a much better idea of what's wrong and it saves tuning time.

OK, lets assume that I don't have about $1K laying around for all the goodies that you listed. Forget assuming, the reason that I haven't dived in with both feet long ago was the initial price of entry (funny how many mechanical hacks I've worked out for all this stuff trying to avoid what I really know is the best solution).

Yea, I can see myself getting a burning setup soon, but I doubt that I'll get into the emulation thing as quickly.

To be more specific, '87 Formula 350 with a 165. I'm seriously weighing the advantages of going with a MAP conversion and some 808 bins over converting to a 749… seems like the people that have messed with the 808 stuff really like it, of course, the 749 and 730 stuff seems lightyears ahead as far as what is available

OK, since you guys are avoiding this like the plague, I can assume that there is something really wrong with it? What is it?

On a similar note, will anything along these lines (even a fuel pressure change) be compensated for by the ecm after a little driving around? I know for sure that on the LT1 stuff the PCM eventually figures out that "these values and these values are a little off of what I expect them to be, so I'm going to adjust everything, even the WOT, AE and PE a little to get things to make a little more sense." Do the older ECM's do the same?