Bored out throttle body, REM, LTFT

[87MJTIM]

No, the topic is not a Johnny Carson "Carnac the Magnificent" sketch.

 

My 4.0 has a bored out TB and the long term fuel trims according to the REM has risen to 135-140 (normal S/B 128).  According to the RENIX Fuel Manual, an increased FT mean the engine is detecting a lean condition and is enriching the fuel mixture.

 

I just installed a new MTS fuel pump/sending unit (see my earlier thread about the OE FP with a broken ground wire).  I tested the fuel pressure and have 31 at idle and 39 with the vacuum removed.  When I turn off the engine, the FP hold steady for 15+ minutes.

 

The REM shows the O2 sensor working as it should - voltage rising and dropping from 1.00 to 4.98.

 

Other things I found:  When I remove the cap for the Schrader valve on the fuel rail, fuel leaks out.  It does not leak with the cap on.  Should it be leaking at all?

 

The engine will idle around 750 +/-.  It will periodically drop to 550+/- and stumble, but rises up again to 750.

 

I cannot find any 'obvious' vacuum leaks that allows un-metered air in.

 

Would the bored out TB, which is allowing more air, cause the rise in LTFT?

 

(PS - it was operating within the normal range prior to the restoration.  At that time, it had the old FP and the bored out TB.)

[Ωhm]

17 hours ago, 87MJTIM said:

According to the RENIX Fuel Manual, an increased FT mean the engine is detecting a lean condition and is enriching the fuel mixture.

 

17 hours ago, 87MJTIM said:

 

Would the bored out TB, which is allowing more air, cause the rise in LTFT?

Yes. The bored-out TB is the cause for your LEAN condition as seen by the ECU (O2S).

[pizzaman09]

The Schrader valve should not leak.  I assume it would be easy to change the core out just like a bicycle tube Schrader valve.

[87MJTIM]

1 hour ago, pizzaman09 said:

The Schrader valve should not leak.  I assume it would be easy to change the core out just like a bicycle tube Schrader valve.

 

Thanks.  So a regular bike inner tube will work?

[pizzaman09]

13 hours ago, 87MJTIM said:

 

Thanks.  So a regular bike inner tube will work?

You'll be wanting this or similar.  I suspect you'll want one specific for fuel as the seal material is likely different.  

https://www.summitracing.com/parts/ado-88894338?seid=srese1&ppckw=pmax-tools&gclid=Cj0KCQjw5JXFBhCrARIsAL1ckPt26ZhSFv0P4Td3rcMDDIRQLff2HUzwLvixWGubmfPMtRF00wWOUo0aAtpzEALw_wcB

 

You will need a schrader valve tool, they can be purchased as most auto stores or places that sell bike parts.