LQ4 Extreme RPM Flare on Cold Starts

[dgold]

Hi,

I have a DBC LQ4 with a Texas Speed stage 1 cam, 8.1L oem injectors, headers, cold air intake, nv4500 trans. I couldn't find a 6.0 ecu, so I'm using a ecu out of an 01 5.3 Tahoe that I had laying around. I have no idea if you can flash in a complete tune from another vehicle, so I went through and manually changed every setting to match a stock 6.0 file from the repository. My problem is on cold starts it immediately revs to between 1,800 & 2,000 rpms, then it settles down to a normal idle after a few seconds. I'm concerned that reving to 2k before the oil reaches everything can't be good! After the engine warms up for a few minutes the flare is minimal and on warmer mornings the flare is more like 1,200 rpms. I don't know if the problem is caused from me missing something or if it's because the ecu still thinks it's a 5.3?

Please note the tune is still stock other than being deleted.


Thanks! Dave

Jeep 6.0 Base Tune.hptJeep 6.0 Startup log.hpl

[ns158sl]

I wouldnt change everything from a 6.0 to that file. I think the most I would do is swap the cyl volume and transient fuel tables (if available). Its going to have to be "tuned" being it is an aftermarket cam.

Honestly if you look at new cam break in from like ISKY, they say to rev the engine immediately to 2000 to get oil to the cam as soon as possible, so i wouldnt be worried about damage over the nuisance. Those tables would be in the Idle>airflow> friction and startup tables. But again If it starts and runs, i would leave those alone also, until you get the VE and MAF dialed in.

[Alvin]

I'd return to your idle tables back to the 5.3 stuff.


Log IAC counts and STIT and LTIT and let it idle for a good while in your log. This might be a vacuum leak.

[samuelkl]

go to spark tab the minimum spark- spark retard limits 0 to 2500 make -20 if its not a - number it will flare try that .

[dgold]

None of the suggestions here helped. I bought a LQ4 ecu and intended on swapping it in, but when I compared idle airflow and spark files with what I copied from a 6.0L file from the repository I found a lot of differences. So I copied those settings into the ecu that I have been using and surprise, problem solved! What the heck was with the (stock) file from the repository? Thanks to those of you that suggested fixes.