CASE & Misfires

[Cougar281]

My friend with the 99 LQ4 just put a new motor in the truck (three injectors blew out their nozzles and apparently two torque converter bolts backed out and hit the block). So it's got brand new motor, injectors, coils, plugs... pretty much everything on the motor. Aparently on the way home, it threw a blinking CEL (usually means misfire). I'm also told it idles a little rough ( haven't heard it run since it came back). From research I've done, the CASE is for misfire detection. Could an incorrect CASE cause it to think it's misfiring when it actually isn't or cause it to misfire? Any thoughts on what could cause a brand new motor to idle rough and/or misfire?

Only thing I've done witht he PCM it is I loaded up a 2002 LQ4 OS and fixed the altenator issue (turned off code for the unused terminal) and fixed the speedometer since it's got 285's instead of the stock 245's.

[Chevy366]

I would read the DTC and see what else is there besides a P030x code .
Could be any number of things.
A CASE relearn is something you should do after a swap anyways unless you are running the same PCM for that motor.
And yes CASE trips misfire codes or can.



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[ScarabEpic22]

Try a CASE, if its the original PCM and new motor, the PCM will be using the CASE settings from the old motor. Pretty simple procedure, warm the engine up, set parking brake, initiate relearn in Scan Tools DVTs, rev to 4k, wait for stumble, let it fall back to idle. Shut off and wait 15sec. Should be set.

[Cougar281]

Ok, I think I figured it out.... Could someone tell me if I'm right, on the right track or totally derailed...

I did the CASE relearn and reset the fuel trims. The codes that where on the PCM prior to me clearing everything where P0300 and P0174. The fuel trims for bank 2 shot way up to the high teens. The truck has a nasty exahust leak.... I'm thinking that the exahust leak is causing the PCM to think bank 2 is running lean, cranking up the fuel trims (probably to max), causing bank 2 to run stupid rich but the PCM thinks it's actually lean and is pretty much unable to try and compensate any further. I'm guessing running stupid rich is probably causing it to misfire..... Am I close?

[joecar]

Could be... pull a plug or two on bank 2 see if they carbon and/or fuel fouled.

[Chevy366]

Before I got the headers welded up would throw the exact same thing so you could be correct (PCM thinks it is lean because of to much air) , plugs can cause it as well. A cam will cause a P030x code if it lopes at to low a RPM also.


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