Performabuilt

Ok first the lockup clutch in a converter is simply that a clutch. Just like any clutch in the trans it is applied by a piston with seals. Fluid is directed thru the input shaft that applies the piston which in turn applies the clutch.

1-Possible reasons for failure within the converter
There are only two. One is the rubber seals are not sealing however if the converter is relativley new and the clutch has appled since it was installed this is the least likley possibility and very unlikley.
The other is the Lockup clutch friction material either was burned off or just separated from the surface. If this occured there would be several tell tail signs. Rubbing or grinding noise at lockup,metal and or what appears to be friction material in pan and or a distinct burned smell to accompany this. Neither of these will result in occasional lockup and should result in a code PO1870 if the PCM comands lockup and it does not ocur this code will always set So you can be sure that if you dont have lockup and are not seting this code or any other TCC related code your issue is tuning or sensor related.

2- Possible reasons within the trans in order of likley hood
A- PWM solenoid. filter becoming clogged or converter regulator valve bore worn out. This should not be and issue if PWM is eleiminated which it should be with any performance trans and all with a small diameter converter 9.5 or other smaller converters. These cannot handle the slip of the PWM regulated properly. There is just not enough friction area .
B-Damaged or worn seal on the input shaft this will result in No LOCKUP.SLIPPING LOCKUP not to be confused with the PWM which is intentional slipping lockup. Will set code PO1870 if no lockup and may set this if slipping lockup.
C- Excessive bushing clearance or wear in the input shaft or pump stator ,
This will result in partial lockup. no lockup , slipping lockup eventual converter clutch burn up but again will not be intermitant.Will set code PO1870 if no lockup and may for slipping lockup.
D- STUCK TCC VALVE this will result in no lockup ussually hot or cold or not at all is generally predictable. Will set code PO1870

3-Engine running issues, These are the most irratic.
A-ENGINE MISSFIRE Will result in intermitant lockup or none is the most comon cause of lockup issues particulary with a cam. This may or may not set a code. Cure is repair cause of missfire and or raise missfire tables threshold.
B-TPS also very comon but will ussually result in poor trans and engine performance.Improper shift times and poor engine idle. This may or may not set a code cdes only set if TPS is outside its operation range, These can give incorrect readings yet still be within that range.
C-VSS No lockup will occur without a speedo signal. Again this will result in poor shift quality or timing.
D-MAF a dirty or failing MAF will cause the PCM to missinterperate engine load and disable lockup this same condition can also result in trans failure.This again may or may not set a code since though it may be sending the wrong readings it may still be in range.
E-Coolant temp sensor , The PCM will not comand lockup if it does not know the engine is warm Aprox 130 degrees. This may or may not set a code.

4-Trans electrical -
Bad TCC enable solenoid , This will cause no lockup period.
Bad PWM solenoid again this will not be a factor if PWM eliminated mechanically. Will result in slipping lockup ,No lockup and intermitant lockup ussually temperature sensitive. This will allmost allways set a TCC related code.

All the lockup issues I have seen over the years that did not set a code have been tuning or other sensor related.

Hope this helps someone I see so many no lockup post though this would be good info.

FASTFATBOY

You forgot one, this is what mine is doing. Trans fluid temp reads -40*..will not allow lockup and the trans will not shift under WOT as commanded, will shift early.

I have changed the temp sensor "manifold" and it did not fix it. I can manually lock it with a tech2. Any ideas?

This car was converted from a six speed to a 4L60E, the lockup worked before it was dyno tuned...the original program was loaded and it still did not work.

David

Performabuilt

The -40 may be the answer , Lock wont occur bellow a certain temp and it sound like you may have a maf calibration issue on the shifts this has come up before post this on tech in tuning section

grasshopper645

what would be possible cause if you force the apply valve into the apply position but still have no lockup?