L29 Build update - gremlins persist

[Philip Parker]

Hey all - some updates on my L29 build:

I dove into HP Tuners and through the help form folks on the HP Tuner forums figured out that my timing table was no where near what it needed to be. I've been flashing updated timing on the ECM and things are improving with every new table.

One thing that is persisting is this: the engine feels like it is misfiring at 1200 rpm with a 70kpa load. This basically equates to 10% throttle input like you would use accelerating from a stop sign or holding to go up a slight hill around town.

It immediately goes away when the table move to the 1600 rpm map and starts running a slightly more advanced timing. The heads flow most of their air down in that region and I'm told that too much timing at that kpa and RPM can get dangerous, but it is very much in the normal driving zone of where this engine ended up landing. Any advice?

 

[PlayingWithTBI]

One thing that is persisting is this: the engine feels like it is misfiring at 1200 rpm with a 70kpa load. This basically equates to 10% throttle input like you would use accelerating from a stop sign or holding to go up a slight hill around town.

It immediately goes away when the table move to the 1600 rpm map and starts running a slightly more advanced timing.

Are you running a Knock Sensor(s)? Either that or look at your plugs for detonation. Then maybe try using the same SA and VE from 1600 RPM and 70 Kpa. See what happens while data logging to see what you get. Watch out for SA Launch Mode (if you have it) which will add SA to your timing tables.

Here's a link to what you may see on your plugs.
www.dynamicefi.com/SparkPlug.php

 

[Philip Parker]

Are you running a Knock Sensor(s)? Either that or look at your plugs for detonation. Then maybe try using the same SA and VE from 1600 RPM and 70 Kpa. See what happens while data logging to see what you get. Watch out for SA Launch Mode (if you have it) which will add SA to your timing tables.

Here's a link to what you may see on your plugs.
www.dynamicefi.com/SparkPlug.php

The truck has stock knock sensors that are currently unplugged because my first guess was that I was getting significant knock retard. Once I was able to see the spark table and the airflow measurements, O2 values etc it was clear that the timing was just laid out this way. I am starting to think that the combo of the heads and the vortec intake just flow tons of air at 1200 rpm, which is great - that was the goal. I just don't want to break anything. If the vacuum of the engine is that strong to create basically 70 kpa right off idle, I assume the mixture is going to need the extra time to ignite and burn, and perhaps needs a richer mixture to prevent detonation.

I pulled the last set of plugs and they were white, so I am thinking that more fuel is probably needed.

 

[PlayingWithTBI]

If the vacuum of the engine is that strong to create basically 70 kpa right off idle

MAP values in Kpas is the inverse of vacuum, the higher the Kpa, the less vacuum you have. Yes, you are running gobs of air through it. Are you tuning with a WBO2?

I would hook the Knock Sensors back up. You can help reduce KCs with more fuel up to a certain point. It's a combination of both VE and SA. Are you running 91 or 93 octane?

 

[Philip Parker]

MAP values in Kpas is the inverse of vacuum, the higher the Kpa, the less vacuum you have. Yes, you are running gobs of air through it. Are you tuning with a WBO2?

I would hook the Knock Sensors back up. You can help reduce KCs with more fuel up to a certain point. It's a combination of both VE and SA. Are you running 91 or 93 octane?

After I wrote that I looked up what a pascal was and my 8th grace chem class came roaring back into memory. I do not have a wide band only because I have no idea how they're typically done. New bungs for both sides? Or are there models or harnesses that interface with the black box? Lack of research is my only excuse.

I'll get the Knock sensors hooked back up. I will run either but I try to run 93 from the shell station in town. With the heads and stock bottom end I think I'm around 9:1. After doing the math the stock ones are most definitely 9.4:1.

I am currently seeing 25 degrees at 60 kpa and 1200 rpm. That's where the trouble starts and goes all the way to 75kpa. Next column is at 29-27ish for the same kpa but obviously fuel is changing too.

 

[Philip Parker]

MAP values in Kpas is the inverse of vacuum, the higher the Kpa, the less vacuum you have. Yes, you are running gobs of air through it. Are you tuning with a WBO2?

I would hook the Knock Sensors back up. You can help reduce KCs with more fuel up to a certain point. It's a combination of both VE and SA. Are you running 91 or 93 octane?

Actually I am getting conflicting information on this from a couple tuners. There will never be positive intake manifold pressure unless the engine has forced induction, the highest it will ever achieve is the same as the static barometric pressure of the elevation you're at. So an increase in kpa reading on the map is simply the reduction of vacuum, which means that I either have a vacuum leak somewhere or the calibration of the timing map to kpa needs to be significantly altered.