OBS 5.3 Tune help....very low speed idle surge

[danieltexpd]

Afternoon, folks.... I just bought a 1995 OBS truck with an DBC 5.3, 243 heads, Truck Norris cam, TBSS intake, 102mm TB, 4L60E

I'm not new to the forum, but I'm finally at the point where I'd like to learn/understand HPT for my own stuff...... Ordered a Prolink and wideband so I can get started....


So the truck drives good, idles fine but I am having a low speed surge coming to a stop that I would like to work out. Seems to happen in the 3-4 mph range... I've posted the tune that is in the truck and a log that I got today. There doesn't appear to be any huge timing jumps while it surges and as soon as it comes to a stop, it idles fine.... I also run into an issue where it likes to die when shifting from reverse to drive... From reading, that could maybe be idle advance timing?

I want to learn and am a newb, so don't burn me at the stake... Could just use a little guidance on where to start.


Appreciate the help.

[RDF1]

Look at ECM2130 and ECM 2131.

The reason the timing is staying static is because Throttle Cracker is in play.
As soon as you hit 2mph (ECM 2131) it goes from using ECM12610 table to letting the PCM start controlling idle again with IAC/Spark. At 10mph (ECM2130) Throttle cracker is active again.

Anytime Throttle Cracker or Throttle Follower is active then idle control is inactive.
ECM 12644 and ECM12645 are quite aggressive.

Looking at your datalog LTIT Gear and LTIT PN are pulling out a substantial amount of airflow.

Spark tables are crazy high unless your running 8.5 compression and 116 octane gas.
What injectors are in it? 12613412?

None of the injector data tables make any sense.

[RDF1]

Also its running in SD Mode and VE table numbers are crazy high so id check fuel pressure before going any further.

[danieltexpd]

Look at ECM2130 and ECM 2131.

The reason the timing is staying static is because Throttle Cracker is in play.
As soon as you hit 2mph (ECM 2131) it goes from using ECM12610 table to letting the PCM start controlling idle again with IAC/Spark. At 10mph (ECM2130) Throttle cracker is active again.

Anytime Throttle Cracker or Throttle Follower is active then idle control is inactive.
ECM 12644 and ECM12645 are quite aggressive.

Looking at your datalog LTIT Gear and LTIT PN are pulling out a substantial amount of airflow.

Spark tables are crazy high unless your running 8.5 compression and 116 octane gas.
What injectors are in it? 12613412?

None of the injector data tables make any sense.

Thanks for the reply.

Injectors are 32lb LS2 injectors from what I gathered from a cross reference. I'll do some research on how to adjust tables

Truck is speed density. Fuel pressure holds steady at 58lbs.

Would raising the TC disable speed help the surging issue, for now?

On the overspeed/underspeed timing, should I halve it as a good starting point?


Lots of tables, just trying to wrap my head around it before just jumping in. But eager to learn... I'm not trying to be a pro, but want to be good enough to mess with my own stuff...


Again, thanks for the reply.

[bk2life]

I want to learn and am a newb, so don't burn me at the stake... .

The following list really helps us, help you:

Vehicle make/model/year
Tune AND data log
Engine/size
Axle gear ratio / tire size
Computer and operating system used
Type of heads (317/243)
Transmission
Torque convertor stall
intake manifold
Intake tube / air filter
MAP part number
MAF part number
Injector part number
cam used (link to specs)
exhaust type (long tube headers, no cats, straight piped)
pictures of engine
pistons
compression
throttle body type, size and DBW/DBC
Fuel pressure at idle and while driving
fuel system type, FPR, pump size, returnless or no
ect ect

[RDF1]

Thanks for the reply.

Injectors are 32lb LS2 injectors from what I gathered from a cross reference. I'll do some research on how to adjust tables

Truck is speed density. Fuel pressure holds steady at 58lbs.

Would raising the TC disable speed help the surging issue, for now?

On the overspeed/underspeed timing, should I halve it as a good starting point?


Lots of tables, just trying to wrap my head around it before just jumping in. But eager to learn... I'm not trying to be a pro, but want to be good enough to mess with my own stuff...


Again, thanks for the reply.

So what is the injector part number?

If it is 12569113 Car LS2 injectors then the data is way off.

There is also a truck LS2 injector 19421333 and its not even close to the data you have.

Fuel pressure holds steady at 58psi even at 4000 rpms and wide open throttle?

Yea you can bandaid it by raising the TC Enable/Disable speeds by 20mph.

Copy factory spark idle Under/Over speed tables is a good place to start.

[danieltexpd]

So what is the injector part number?

If it is 12569113 Car LS2 injectors then the data is way off.

There is also a truck LS2 injector 19421333 and its not even close to the data you have.

Fuel pressure holds steady at 58psi even at 4000 rpms and wide open throttle?

Yea you can bandaid it by raising the TC Enable/Disable speeds by 20mph.

Copy factory spark idle Under/Over speed tables is a good place to start.

The guy used Amazon LS2 "car" injectors... These here...https://www.amazon.com/Injectors-028...d_i=B07T9J47Z3

As far as where he got the fuel injector tables, I have no idea....


I'll make the changes you suggested and see if it cleans it up.

Thanks!

[RDF1]

I would throw those away.
Better injectors can be had for cheap enough.
Look for some LMG's 12594512

[RDF1]

Here is the car data if you just wanted to try it.