...can't get a straight answer from same post in computer forum, not from searches either. Sounds like it's likely it does not (OBDI) use the PE tables in open loop, not sure though.

My dilemma is this. I have found that I can beat surge by running open loop. This is due to too much fuel trim for my cam overlap. However, I don't want to run open loop with a supercharger if the PE tables aren't going to be accessed.

I thought I had read about being able to limit the max fuel trim to like 120 in certain areas but now it looks like I misunderstood. I'd like to run closed loop just to be safe and make sure I access the PE tables, however, I don't know how to get around the excess fuel trim in the low load low rpm areas where I get the surge without going to open loop. Any suggestions? I thought a BLM locker would do the trick but apparently that's only to make WOT fueling more consistent (sounds weird, I know).

 

Subscribing.

According to LJ's website, it does use the PE tables in open loop. It would be easy enough to check though. Add 50% fuel in the PE table, start it cold, then hit the gas before it warms up (breifly of course).

That said, I think you can modify the VE tables at low load, low rpm to get your fuel trim right. Though I haven't had any luck doing this, most agree that it should work.

 

I have tried that among many other things with no luck. My VE tables don't appear to be used, as many suggest is the case with 94's (most say that they are only used in the event of MAF failure). Once I get around to driving it again I will just test it like you are suggesting, I had thought of adding a ton of fuel in the pe vs rpm just to see if it goes pig rich but didn't realize I could test that in neutral/cold. What about timers and what not? Doesn't it need to run x-amount of run time before it will use that table? (regardless of enablement of closed loop).

I may just leave it in closed loop and see if there's a way I can reduce the fuel trim enough to get rid of the surge ...we'll see. I've heard there is a way to set the min and max blm to 128 and that this will limit the integration to about 5% ...I don't recall seeing this feature in my version of LT1 Edit though (don't have it w/me right now).

 

I thought it only used PE vs RPM in WOT? I know my car is tuned open loop and we tuned WOT operation with PE vs RPM. The definition of "WOT" is in another table.

-Alex

 

From LJ's PCM tutorial:

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

"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."

"...the values in the VE tables are used as multiplication factors that are less than 1 (e.g. 0.93). Or you can think of them as percentages (e.g. 93%). For example, if the pulsewidth based on the current MAF value was 5.0 milliseconds, and the current MAP and RPM values point to a VE table value of 80, the final pulsewidth would be 0.80 * 5 = 4.0 milliseconds."

It would be easy enough to figure out though. Set the VE tables to all zero's and see if it runs in closed loop. Let us know the results. . .

Mike

 

This was debated extensively a number of years back on the email lists. I think it was found that in closed loop, they made basically no difference. I'm not certain about open. But as Mike mentioned, making a large change (I wouldn't try 0, as it may be ignored) should tell you.

When I was part of the tuning scene, people with big cams would just run open loop (for fuel) to stop surging and get a cleaner response. It wasn't as fuel efficient and did not compensate for climate shifts though. I ran closed loop for a while, then had some issues with it...tuned it all open loop (via wide bands) and it runs just fine.

BTW, the BLM locker was used to prevent additional changes to fueling in WOT operation over what the PE vs RPM table said (for BLs above 128 it would add fuel to WOT).

-Alex

 

PE vs RPM is used in Open Loop, when the MAF maxes out and when you reach a certain percentage of WOT (this is set by another table, based on RPM as well). If your long term BLMs are set to something other than 128, then it adds or subtracts fuel accordingly to get you back to 14.7 AFR.

TO get rid of surge, 1st check your IAC counts and make sure they are around 40. If they are really high, then you need to open your TB blades a bit. If they are really low, you need to close your TB blades. There was also a MOD listed somewhere about drilling the plug below the throttle body and running an extra air tube in there. THis helped send air to the right places using the IAC passages and eliminate cam surge and split BLMs.

 

Thanks for the tip, that isn't something I've tried. Perhaps that gets more fresh air in to help counter the exhaust contamination due to overlap. Car is still up on jacks and nothing but rain here anyway