Starting to Learn on 95 G30 5.7 for Towing

**Fast355** · 01-27-2019

Originally Posted by donf

I might have found a little clue for why the numbers in the data logging do not match up with the data log. The od TP5 v251XDF supposedly compensates for initial advance changes. The adx does not, reasonable since there is probably no communication between the two files. "Change last number(offset) to initial advance of engine, for correct display." Still adding a flat 9.8 to the log files do not exactly correlate see the pdf info posted on post #91 so "correct" may be wishful thinking. So far my OTC scanner has come the closest to recording the most believable timing numbers, especially when the main timing value goes to retard when there is a low total value on the main table and a high initial advance. If you see a crazy number in $od logs it's probably just the retarded areas, but the fact that it does that makes me think other areas may not be quite up to par either. One thing I am wondering about is the log file for the xdf. If the main timing table auto compensates for any initial advance on the chip, try changing it and only that from 0 to whatever you choose. Now look at the log file. You will see the change log made a note for the initial advance change but no timing table changes were noted. If I am understanding how this particular xdf works it should have knocked the value of the initial advance off and rewrote the value to the bin and logged the change too?

With emulation, it's not possible to make changes while running, correct? I had chip emulation set up on the dyno, but the one time I tried to push the change to the chip with the van running nothing changed then something happened and the file was corrupted the next time I tried to start up and would not start at all. It would be handy if that would work for changes on the dyno especially for part throttle timing.

I put off pulling the valve covers to re-check lifter preload hot and running instead of the static set. The one side is a huge pain in the van, but most everything else so far checks out or is fairly close to a reasonable value. So I guess that is today's project.

With a hot engine I would not go more than 1/4 turn preload.

**Kitch** · 01-27-2019

I've set the lifters pre-load both static and running at different times. You're right it's a pain in a van, one side has the AC pump in the way and the other has the engine harness running over the top.
I do 1/2 a turn preload cold.
If I'm doing all the lifters then I just use the when X is rocking set Y method. When I'm just checking one bank (and I can't see the rockers under the other cover) I use an old dizzy cap that I hole-sawed the centre out of so I could see the rotor. So for example when the rotor lined up with where the lead for cylinder number one was, I'd set both the lifters for number one. I'd only use this method on an engine that's been running because I know the dizzy is installed correctly.

**Fast355** · 01-27-2019

Originally Posted by Kitch

I've set the lifters pre-load both static and running at different times. You're right it's a pain in a van, one side has the AC pump in the way and the other has the engine harness running over the top.
I do 1/2 a turn preload cold.
If I'm doing all the lifters then I just use the when X is rocking set Y method. When I'm just checking one bank (and I can't see the rockers under the other cover) I use an old dizzy cap that I hole-sawed the centre out of so I could see the rotor. So for example when the rotor lined up with where the lead for cylinder number one was, I'd set both the lifters for number one. I'd only use this method on an engine that's been running because I know the dizzy is installed correctly.

Anything over 1/4 warm and running is giving away torque as well as RPM. Any non running adjustment is also not accurate.

FWIW, this time around my L31 is getting Comp reduced travel roller lifters and 1/4 turn preload. They are designed in a way not to collapse more than about 0.020" total. So 1/4 turn puts them right in the middle of their travel. The lifter can neither collapse or pump up enough to cause any issues. Running 150# at the seat and 375# open spring pressure.

The problem is usually weak valve springs that allow the valves to bounce on closing, introducing slack in the system causing the lifters to pump up and hold the valve open. With 1/4 turn preload your lifters can never pump up.

**donf** · 01-28-2019

Originally Posted by Fast355

The problem is usually weak valve springs that allow the valves to bounce on closing

https://www.summitracing.com/parts/s...1/applications are the springs I am running. The cruddy import vortec heads Jegs sent had pathetic valve train. So I upgraded to be safe, not as strong as what you have but stiffer than the stock specs for vortec springs and I have the fuel cut off set at 4600. I think stock was 4200. Installed spring height was measured and set, a few springs did require small shims, more poor machine work. I got side tracked and ran out of time so the valve covers stayed on today.

**donf** · 01-28-2019

I am editing this so not to confuse anyone. Mostly I was just confusing myself by editing things with little explanation of how it works. It was a good lesson though and I didnt hurt anything.
The OD adx file in tuner pro and others shows crazy numbers in retard. It's not a huge deal but if you see it that's just what it is. The reason 0 in the altitude bias on the bin helps the crazy numbers is the bias is a subtraction so zeroing that one part out while leaving the matching table actually raises the timing. The ADX also doesn't show the initial spark advance if it's anything above 0 with out editing. So if you have some missing timing in the logs look there first. The ecm does look at the initial advance and is supposed to subtract that from the main spark table. I found a few older photo copied papers that explained the biases vs the tables a bit better. Still there is no where near the explanations that you find on the later GM stuff but it helps.
This pdf I found online was too big to post here. www.gmcmi.com/wp-content/uploads/2014/05/How-to-Tune-a-GM-EFI-System.pdf The other one attached also explains the timing bias a little too.