I've got an '87 with a Mini Ram 383. It has been sitting for quite a while (battery disconnected), but I finally got a chance to fire it up today. I am using a mail order PROM tune (from Formato), and plan on going for a dyno session this spring to help fine tune it.

When I first started it up, it ran pretty rough (hesitation, rough idle, seemed to be loading up, running rich, etc) while in Open Loop mode. Once it switched to Closed Loop mode, it got better, but really didn't start driving / idling well until I made a few WOT romps (within the speed limits, of course!) to clear it out. Once in Closed Loop mode, the BLM and INT numbers were right on 128 (which actually surprised me - I figured I would see a slight deviation from 128 since this was the first time with the new chip and the computer was still "learning"). Is dead on 128 for BLM / INT normal for a new chip right out of the box?

When I got home, I pulled a few plugs. They definitely looked like they were carbon fouled at one point (carbon at the end of the threads / base of the ground strap, and a little at the porcelain base), but the ground strap, center electrode, and MOST of the porcelain looked fine.

I am thinking that it was running rich in Open Loop mode, but once I got to Closed Loop (and "cleaned it out" ), it was able to run where it should be.

My question is - does the computer "learn" in Open Loop mode as well? Meaning - as long as I don't disconnect the battery, will the ECM eventually come up with an ideal cell(s) for cold, open loop start up, so that it is not running so rich until it goes Closed Loop? Or not, because it doesn't know that it is rich? Is this something I need to address with my tuner and the PROM chip?

Sorry for the long post. I am also going to post in the Scan / Tune section, but I know a lot of you guys hang out here, too.

Thanks very much!
Dan

 

The tuner could have just changed the upper and lower values of BLMs to be both 128. This is pretty much making the car run constantly in a theoretical "open loop" and never deviates from a certain tune while in closed loop non-P/E. It is very easy to check for if you have someone nearby that can read chips, or you have the .BIN file for your program.

The $32b cars like yours and mine don't learn all that much, very little from what I understand.

 

Thanks Scorp. If that were the case, the ECM would still be using data from the oxygen sensor to control fuel delivery, once in closed loop, correct?

Does the PROM also have the parameters for open loop, or does that come from the ECM? If the PROM, it probably needs some fine tuning.

I am currently using just an Auto X-Ray scanner for this data. I now have a lap top (it's old - no USB port, just serial) - what else do I need to retrieve the .bin file?

Thanks!
Dan

 

What is there to be learned? By definition, the ECM receives little or no sensor feed back and ignores all of it. The engine runs off of preprogrammed tables. If it COULD learn, than it wouldn't be open loop.

RACE ON!!!

 

Thanks CFI! Where are the open loop pre-programmed tables stored?
(The wording in my HELMS was a bit confusing )

 

The learned values from closed loop are used in the next open loop cycle on some ECMs. So open loop isn't the same every single time.

To be honest, I'm not sure if yours is one of those that does this, but I'm sure the somebody will chime in soon and let us know.

 

In the prom. Most of your performance tuning is performed in the PE (Power Enhancement) tables, which is another preprogrammed (open loop) part of the prom. Normal, closed loop calibrations are only for drivability. For the dyno and the race track, open loop is where it's at.

RACE ON!!!

 

Thanks again, CFI!

One more question - is the open loop tune for cold start / idle different from the open loop "PE" tune?

:o

 

Bump here as well...

 

Yes, they are different.
Locking the BLM's to 128 doesn't put it in open loop, what it does is make the int do all of the corrections and you can see the changes you made to the chip happen faster. To lock into open loop you'd set the closed loop temp to max, so the ECM would never see it and would stay in open loop.
The 165 ECM with the $32, $32B or $6E codes learns plenty and plenty fast...It communicates at 8192 baud....fast enough?

 

Thanks Morley - more very helpful information!

Formato did the chip for me, and will tweak it as necessary to get it dialed in as best they can vial mail. I want to be able to properly communicate to them where I think changes are necessary. With the great information I receive here, plus a few pulls on a wide band dyno, I should be able to do that.

Thanks again, everyone - enjoy the holidays!!

Dan

 

Absolutely!
And they are BOTH different from the "limp home" mode.

RACE ON!!!

 

So, what are the parameters of all these "open loop modes," including limp home mode? How many open loop modes are there compared to closed loop modes?

 

I'm far from a computer expert, but the previously mentioned cold idle, limp home, and PE modes are all that occur to me for open loop modes. Closed loop modes? How many can there be??? Closed loop is closed loop. I cannot picture how there could be different modes. In closed loop, there are no look-up tables. The ECM controls the engine based on sensor input.

RACE ON!!!