2007 Trailblazer 5.3L Surging

[Ikyo]

Stock File: Attachment 15257
Modified: Attachment 15258
Log: Attachment 15256

Everything seems to be running okay except for what feels like a surging at around 2k RPM. When I am driving on the highway around 2 to 2.5k it seems to surge every couple of seconds or so. I don't see a change or anything in the tach, but I am sure it is something I am not noticing.

Does it have anything to do with the TCC?

[WarWagon]

That surge is very clear. Looks like the ETC throttle is being snapped open 5%. Now to find out why.

Use your status bit display to log the AC clutch. Perhaps this is loading the engine. It really mucks things up on the TBSS.

Also look at DOD. Look at going in and out of DOD mode, may be the root problem. So log that status mode if you can.

[Russ K]

Also zero the A/C spark retard table as shown.

Russ Kemp

[Ikyo]

Programming it now and will drive it some to see if that helps. I will upload the log.

[Ikyo]

Log: Attachment 15273
Tune: Attachment 15274

It is still doing it. I am going to run a stock log just to see if that will help.

[WarWagon]

There is your answer. You see where is goes into DOD - high MAP reading and right back out of DOD mode.

[Ikyo]

Stock Log File: Attachment 15277

What can I do to correct this? I am open to suggestions.

[WarWagon]

I am seeing a higher load on the engine via higher MAP readings with the changed tune. (Higher MAP = higher engine load. Otherwise the engine would simply speed up and bring the MAP reading back down.) Perhaps there is a higher load via wind etc. Otherwise you may be entering DOD with too much load for 4 cyl mode. Take smaller steps as the current step size allows it to enter DOD mode and quickly hit the settings to exit. This happens at the higher load speed rpm range. So reduce the DoD Enable vacuum over 2000 down until the oscillation stops.

There is a limit to what you can get out of a 4 cyl engine. This is why a bigger engine can get better fuel economy because it doesn't work as hard. Esp true at higher speeds due to higher wind loads.

[Ikyo]

Okay, I took those values from Russ' post in another thread. I will take a look at them and see what I can come up with.