[Diy_efi] Post 4-Wire O2 Sensor Swap Observations...

[Mike Frels]

The O2 sensor swap was in *preparation* for the headers. They are still up in the attic waiting for a couple of days opening in my schedule to justify the vehicle downtime for the install.

As far as the lean condition I am convinced I still have an leak somewhere allowing oxygen into the exhaust before the sensor. The sensor says lean but the hard starts with the smell of raw gasoline afterwards, the missing while idling, and the slight popping on deceleration tell me I am much fatter. Fuel that is...

Mike

-----Original Message-----
From: David Cooley <n5xmt at bellsouth.net>
Sent: Apr 21, 2005 4:22 PM
To: 'Mike Frels' <mfrels at ix.netcom.com>, diy_efi at diy-efi.org
Subject: RE: [Diy_efi] Post 4-Wire O2 Sensor Swap Observations...

Don't see anything contradictory or wrong... You increased the efficiency of
the engine with headers, so now are slightly leaner than before, being lean
increases MPG...  If you bump up base Fuel pressure 2-3 PSI, it will bring
the BLM's down, but mileage will probably stay up.


> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org 
> [mailto:diy_efi-bounces at diy-efi.org] On Behalf Of Mike Frels
> Sent: Thursday, April 21, 2005 8:54 AM
> To: diy_efi at diy-efi.org; gmecm at diy-efi.org; third-gen at lists.f-body.org
> Subject: [Diy_efi] Post 4-Wire O2 Sensor Swap Observations...
> 
> About a month ago as part of preparation for my header 
> install I swapped out my single wire O2 sensor for a four 
> wire AFS97 from a fourth gen F-body. I wired the heater in 
> via a relay to hot at all times in the back of the fuse block 
> and grounded via the A.I.R. Port Solenoid ground line. The 
> sensor I gounded to the back of the diver's side head. Since 
> the the swap I noticed two what I consider contradictory 
> results. My BLMs went up between 5 and 10 to what were 
> already lean ranges. My idle was around 145 before and now 
> it's up to 150. Same approximate changes in all my easy 
> driving ranges. The second nice but puzzling change has been 
> my gas mileage. Previously with my not yet properly tuned 
> Vortec headed 350 I was getting 15-17 mpg for all driving 
> types. Now I get 17-18 mpg stop and go short distance driving 
> and low 20s highway. Why does this not make sense to me?
> 
> FWI one of the main reasons for wanting to get the headers on 
> before getting the tuning right is tuning ability. In the 
> passenger side collector I have added a bung which will allow 
> me to use a wide band O2 sensor so I can see whats really going on.
> 
> Mike
> '86 MAP TPI Z28