I blew up mine on the dyno in an extremely lean condition (14/1). I'm adding 30+% in the PE tables and was wondering if it will add this fuel when the engine is cold, i.e. before it goes into learn mode.

Thanks,
Mike

 

My car goes into PE mode when in open loop (engine cold). Granted it's a 1996, and OBDII, but I believe the '95's will too.

 

what program are you using? It's clearly defined in both versions of Lt1edit and tunercat that I have. You can adjust when and how much PE it uses:

In lt1edit under the fuel table, Power Enrichment - Temp button, then % PE vs Cool temp, couldn't be easier

In Tuner Cat, under tables, % Change to Fuel/Air Ratio Vs. Cool Temp @ WOT

Maybe you overlooked these?

 

Well, of course. That's the tables in which I programmed in the ~30% enrichment. However, the computer has to go into PE mode before it will use these values.

 

I'm assuming in tuner cat, WOT = PE the tables I listed above set the parameters to which the computer switches to PE or WOT, however you want to look at them. You set the amount of throttle you want vs coolant temp to tell the comp when you want it to switch into pe mode. so yes, it will go into pe mode before it goes into learn mode. your ecm is not in learn mode when in wot, it's in open loop running off of ve tables, not the o2s.

 

94-95 ODB1 does not use the PE tables until the PCM goes into closed loop. I spent an extra hour on the dyno one day pulling my hair out trying to figure out why my changes to the PE table were having no effect. A soon as I started doing pulls in closed loop, all was good.

Steve

 

WOT = Open Loop!!!

The ecm will NOT read the o2s when you are in wot throttle!! It uses the volumetric efficiency table, MAF, MAP, and power enrichment to set injector pulse width. Look at the BLM tables, where does the rpm limit stop? 2-3000 rpm? The Block Learn Means table is closed loop definitions, if it stops at lower rpms, then how would closed loop affect wot? Someone please step in and correct me if I'm wrong, but I'm pretty confident about my understanding of the ecm.

You may have the PE vs temp tables set high to where pe wouldn't come in while the engine was cold, other than that, closed loop doesn't affect it.

 

Closed Loop = All temperature conditions are met, Other systems are operating properly, CL timer has timed out, and the closed loop bit flag is set high.

If your in closed loop and not at WOT then your also in a condition called "Learn Enabled" If your in Closed Loop and go WOT, Your still technically in closed loop, it's just that your not "Learn Enabled" The PCM will use one of 2 cells (I think it was 15 and 18) for the WOT Block Learn, and the PE table for additional fuel adjustments. Check it out, Hook up datamaster and watch the closed loop bit, It stays high at WOT.


Open loop= Not up to temp, or the Closed Loop timer hasn't timed out, or there is another fault inhibiting Closed loop. System runs off of the Open loop tables, BLM's are not "learn Enabled" and it ignors the PE table at WOT.

Hope this helps,

Steve

 

SABLT194, my experience partially backs up your assertion that PE mode doesn't enable when the engine is in Open Loop. However, the following is from LJ's web site:

"Whether the engine is in closed loop or open loop, the PCM will jump to the PE fueling tables when you really lean into the throttle. "

http://para.noid.org/~lj/

It's under the "PCM Tutorial" tab at the left.

I don't really care who's right or wrong, I just want a definite answer.

 

PE <> Open loop <> closed loop

PE is open loop in the since that its not using the o2 sensors hense open loop fueling but the car isn't actually switching into open loop.

As far as I know there are no coolant temp enable triggers for PE in the 95 ECM. There is a hot pe which happens when then engine is over like 230 degrees. If you think about it also the PE modifier for coolant temp goes all the way down to -40 degrees.

In SABLT194's case I'll bet that there was a fuel trim pulling you one way or the other that you only recieved in open or closed loop.



One thing to realize about PE is that you can have BLM's other than 128 and that can give you a hard time on the dyno if your not paying attention. You can have BLM's greater than 128 but not less than 128. I'm getting this information from what i've seen in the 93 LT1 ECM hacks and if you think about it, it makes alot of since. Theres a line of code that throws a BLM's a reset unless the car is consistantly lean (and needs richening) GM didn't want a 02 sensor to pull the fuels lean (incase the sensor is screwed up) but it can afford to let the O2 sensors to add fuel at wide open. I would imagine it would be exactly the same for 94+ cars.

 

I run BLM locker and they hold firm at 128 /128 when PE mode is enabled. My WOT fueling is not affected by Long or short terms. WOT fueling after the closed loop flag is set is based on MAF and PE table. I'm not totaly sure what controls WOT fueling before closed loop bit is set. "But I know it doesn't use PE table as an adjustment"

Steve

 

tuner cat tables, pe tables highlighted
http://216.77.188.54/coDataImages/p/...0847Image3.jpg

tuner cat PE table
http://216.77.188.54/coDataImages/p/...0845Image1.jpg

LT1 Edit fuel table window
http://216.77.188.54/coDataImages/p/...0846Image2.jpg

low coolant wot tps threshold (stock 95 caprice ecm)
http://216.77.188.54/coDataImages/p/...0848Image5.jpg

just posting what I see, sorry if I seem thickheaded, everyone seems set in their ways since we're all pretty much self taught. trust me, if my project was anywhere near road worthy I'd be out testing the theories, but it's got more parts on the floor right now than bolted to it.

 

I have done all the testing to varify this too and what Ive found out is that Open Loop doesnt use the PE table at WOT. My guess is it uses the Open Loop AFR table. I can remember back when I was setting up the whole idle PE(essentially WOT sitting still) I found changes as large as 10% in the PE table werent affecting the the AFR at all which had me scratching my head. Soon after I gave up and went to work but on the way I noticed it was idling a lot leaner than it had been. Only variable I could contribute this to was the fact I never let the motor reach closed loop.. Id fire it up and watch the O2s for at most a minute and shut it off. Thats my first bit of evidence.

Then...
My Datamaster does show PE enabled, Learn disabled, Open Loop when I first start my car but based on O2 sensor voltages and my sense of smell the motor still ran well on the rich side. Once the Closed Loop flag says enabled then the O2 voltage drops down just like I intended. So what I have done is leaned out the open loop AFR in that Open Loop AFR vs Coolant Temp vs MAP table and that seemed to compensate for those few minutes before PE kicks in. Hell, just recently its been bitterly cold around here and the AFR table in that coolant temp range hadnt been modified yet so it was a little too rich. So going to that Open Loop AFR vs Coolant temp vs MAP table, I attempted to lean it out but went a little too far. My motor would fire up like normal but b/c it was so lean it blew right out. All I did was return about half of what I took out and now its all good. So in that instance I was running Open Loop, PE mode and obviously had affected the AFR with the Open Loop AFR table.

So you can believe what you read or do like I do and believe what you see with your own eyes... do your own testing and let us know if it corrisponds to everyone elses experiences.

 

I think you answered your own questions but just incase you didn't there are open loop adders and enrichers that add even more fuel that PE.

This is the reason why I do open loop tuning in ways other than just moving the closed loop qualifiers. If you just set a car to run in open loop the entire time it will be targeting AFR's that are richer than needed.

I haven't seen anything in any hacks indicating that PE isn't used in open loop. If anyone has seen anything I would like to see it. I'm at least 99% sure that it will hit PE in open loop with the 1993's which I'm much more familiar with than the 94+. Hacks are avaiable all over, you should be able to find one and find out for sure.

Another bit of fuel for the fire... Sometimes I'll use PE extensively to work out bumps in the AFR line. For instance if theres a little hump at 4500rpm I'll sometimes work it out in the PE. Now, sometimes after getting the car tuned in it will be heat soaked so i'll let it sit for a few minutes so the customer has a good power run to compare his first and last with. That 1st run after a cool down is almost guarenteed to be a good 1.5 points richer than the warmed tuned runs and the line is still dead smooth indicating the PE adjustments are still in effect.

 

I haven't seen any raw evidence such as the formulas used to calculate fuel at WOT in open loop vs closed loop. However based on the countless hours Ive spent dailing in my car Im 99% sure 94-95 OBD1 computers do NOT use PE enrichments at WOT unless its in closed loop. I know you have a wealth of knowledge far greater than mine in this field but I cant deny what Ive witnessed... maybe its just another difference between 92/93 and 94/95 LT1 computers.