Modify Overkill tune?

[bevernden]

I'm still going through a bad experience with a tune from Will at Overkill. Long story short, I'm experiencing two issues with the tune: surging idle after cold startup for approximately 2 minutes and shifts that are firmer than what I prefer.

Overkill's website says that all of his tunes are editable with HP Tuners software. Although I don't have HP Tuners, if I find someone who does, can we open and edit the tune to make changes?

Any idea what could cause the surging idle? My stock PCM as well as the DHP PCM I sent him did not do that. I've put the stock back in to confirm that the issue is in the PCM. I'm at a loss...

My mods: 2002 GTP, 3.4", K&N cold-air, ZZP headers/downpipe/high-flow cat, port LIM & 180deg stat

Brent

[Reptile]

If it can be edited by HPT, it may also be edited by a Powertuner, Idle surging typically points to messed up timing at idle, but can also be other things too.
It all depends on if the file can be pulled off of the PCM though, if it's locked, nobody can look at it.

[SlowNA06]

I've had idle surge when I forgot to plug in my MAF... which you might have unplugged somewhere along the way. Good "I'm an idiot" mod.

[rah575554eg]

I am also having problems with my overkill pcm.

[matt5112]

Wait you have surging until it warms up?

I have the same ****ing ****.

Once it warms up its fine.

Until then it gets down as low as 500 RPM and feels like the car is going to shake itself apart.

sounds like that typical "overheated and stalled" noise everyone uses in the movies.

For the sake of the thread my car is calling for 20 * of timing at idle, when this happens the short term LFT goes to -25 IIRC. VAC goes to 15 or lower. primary O2's typically get stuck around 800-900 mV. IAC constantly opens up (in otherwords it opens up trying to solve the lowered idle)

[machinegunsquid]

I've got the same surge at idle on a cold start. I crank it, and it surges, but oddly it only does it in park, shift into reverse or drive, and it goes away.

This is on an Overkill PCM btw

[matt5112]

I know the surge can be from the PCM attempting to "learn" the car if thats what you guys are referring to.

Its mentioned in the printout that will sends with his PCM's.

[Overkill]

Matt, I can stop by your house to give your PCM an update and see if it helps with the cold idle surge. Did you get that misfire solved?

I've sent another PCM to Brent as well, hopefully it will fix his idle surge.

The issue has to do with the timing advance just above idle. I increase the timing advance in the 1200-1400 rpm range for vehicle cruising to increase the gas mileage. There are separate tables in the PCM (hidden in most tuning softwares but they're there) that have separate timing advance for idle, but they are not enabled until the vehicle warms up; when its cold, the PCM uses the main timing table, and if the high idle at first startup hits the increase timing advance mentioned above it will cause the idle to surge and then fall and repeat as the timing advance changes. Putting into gear lowers the rpms and creates some resistance against the motor, one of which or both is enough to stop the surging.

There's no harm being done but I realize this is 100% annoying.

The fix has been to increase timing advance at idle, decrease the cruise timing advance a little and so the timing stays more consistent. Whenever possible, I have enabled the idle spark tables at low engine temperatures so it uses that table (as it should) rather than the main table, thus being able to keep the higher cruise timing.

[matt5112]

Sure, if it'll help then why not?

Well I solved the misfire, but now its back. Only this time I dont have anyone I can bum an ICM off of haha.