Richard, do you have the offsets for the 02? Is it the same as the 01 that you listed?
I also added a pair of 5.7 heads(milled and cleaned up)so that also may have my ltrims in the +.

 

Well Gonz, I really believe some would call BS. I thought it would be good to have a timeslip and a video to back it up. Give me a minute, and I'll get you your info.

twobit - The more you change your truck (especially the internal components), the less likely the ltrims will be dead on 0. As long as they are close, call it a day. If they are off 10 or more, you need to get them cleaned up.

 

I ran out at Redline the other night and my ltrims locked in a +8 and the o2s were .965

 

During a WOT run, the LTRIMS are not used. Basically useless. LTRIMS are only used to compensate for air/fuel mix under normal driving conditions. The PCM reads the O2 sensors, and the ltrims are the calculated adjustments that are used to add or remove fuel. The ltrims should adjust enough to make your A/F ratio 14.8:1.

When going WOT, the PCM just looks at your Power Enrichment table and adds the specified fuel as prescribed by MAF flow and RPM. The ltrims are not used.

Only log your ltrims during normal driving. .965 is pretty heavy on the rich side. But without a wideband, there is no way to accurately tell. My O2 readings at WOT N/A are in the .88-.87 range until I run out of injector then they can get ot the lower .80s.

 

Ltrims at WOT ARE used just not adjusted since the computer is in open loop. If his Ltrims are +8 the computer is adding fuel at WOT. I bet that's why his o2's are so high. The best thing to do is get the Ltrims very close to zero or just slightly negative at idle. Most of the time this will get them at 0 during WOT but, they still may need tweaking.

If your trims are positive at WOT the computer will add fuel but, if they're negative the computer will not pull fuel at WOT. If your Ltrims are usually very close to 0 during normal driving they'll lock in at 0 during WOT.

 

John, you are saying the +8 from the LTRIMS are added on top of the fuel the PE dishes out? Explain this in more detail. Since the Ltrims are different values in different rpm ranges, how can the PCM just pick one value? I've had my ltrims + at idle, near 0 under light loads, and - at higher rpm loads: How does the PCM pick one value?

 

Yes, on the adding part. So say you have +8 Ltrims at WOT and your o2's are at .965. You adjust the PE ratio to compensate and do another mod to the truck that lowers the trims. Now, all the sudden you don't have fuel being added at WOT by the Ltrims and the PE table is lowered so you're running way lean. That's why it's best to get the Ltrims to 0 at WOT before adjusting on the PE table.

It's my understanding that the PCM looks at the cells just before WOT to decide on what the trims should be at WOT. When I was doing alot of logging and fooling around with the MAF tables it was easy to see this in the EFILive logs. I'll try to get some logs and do some LS1edit tweaking soon to show all this stuff in a graphical way.

 

I need the graphical view. That doesn't sound right.

If you go WOT at low rpms where you have a different LTRIM reading, you may be really screwed up in the upper rpms.

I always understood it as the LTRIMS just go inactive and don't change. Like if its +5 when you go WOT, they just stop responding, but still read 5 because it was the last logged value.

 

I don't think I explained it good enough anyway. It's not really based on the Ltrims before you go WOT everytime but, more of a certain area in the fuel map and what the Ltrims are at that point. It's like a learned value. Say your Ltrims are 0 at idle but, for some reason are +10 at the point the computer looks at for WOT trims. You go WOT from idle but, the computer doesn't use the 0 Ltrims for WOT but, the +10 value of that certain point that it has learned. I've never had such an extreme case like that except for when my fuel regulator was missing the little o-ring.

I'll try to get some graphs of it this weekend sometime with explanations of what they are.

 

Come on John, explain yourself.