Poor mileage and running rich

[fixkick]

as you can see driving and plotting any errant OBD2 car can be really revealing. above software is. Palmer scan software


https://www.palmerperformance.com/store/...ucts_id=36


even log CVS files and import them into Exel. and graph anything you what, even hours of data.

I don’t currently have a scan tool that can read o2 sensor data just a code reader but I had it at a shop that pretty much gave up on figuring it out. They told me that both o2 sensors were reading fine. The injectors passed the leak down test and and are all flowing the same according to my fuel pressure drop on my cheapo flow tester.  Since my last post I replaced the cracked exhaust manifold with a stainless header and seems to run just as rich as before. Looking at the spark plugs they don’t seem to be wet or look as wet as I would think they should for running rich. In the next couple days I’m going to borrow a friends fancy snapon scan tool to get better data.

the other poster here found alien china  $17 maf on his,  (after proving all else ok)  hot idle Injector PW at 3.2mS,, now passing sniffer smog, IM240 test.

but you  have good fuel pressure

• and if spark advance works and static timed right (free jumper used) the spark is ok for both,   (if static is good the scan tool will show computed advance)
  
• 170 PSI + is ok, compression
  
• ECT at 180f+ or 300ohms hot.
  
• O2  sensor must swing fast at idle. hot.
  
• the LTFT must show correct readings,  not railed. long term fuel trim .
  
• injectors not leaking (checked ok)
  

The leaves only the MAF, if ecu is not in limphome mode, (scan too shows closed loop status hot) at idle for sure.
OBD2 will show LTFT
On a good engine, we can see LTFT (long term fuel trim) about -5%  (minus) this is a good sign for fuel trim.
A good MAF run a tad tad rich then the 02 trim pulles this to perfect MIX.
We can add to inducted air some propane gas  to force the 0² sensor  to go leaner or richer.(as wanted to test , if closed loop can be hit)
Or cause and illegal air leaks to force lean. (a vacuum house pulled)
with a good scan tool you can see all sensor live. and trim, and all that.
no need for expensive tool just a real scan tool works.

the other posted (link above) added air, a vacuum leak and saw o2 wakeup and closed loop and injector PW go from crazy high to 3.2mS (my computer model predicts,2.8MS) close.
new maf fixed it, from rockauto (beck,cardone, Delphi  has good price.

my 96 I once drove around with the EGR defeated dead, (vacuum hose blocked) and ran great, full closed loop idle and 45mph easy cruise.
no limphome punishment,  did this for friend to prove this out (firmware magic and rules are never known fully unless tested)
I have not tried cat free, but that sure will not effect idle and fuel mix, there is no way for ECU  to know that, with no code DTC p0421 cat errors) dtc.
also the cat monitor is shut down if if The ecu does not like what it sees in O2 Front, sure does,  see that many a time, this prevent owners buying new cat,
with the test if run (421 cat performance test would lie to you if 02  front is bad) a good thing that.

a scan too can watch pending codes too.  and is very wise to look at that. for sure the tests that take 2 driving cycles to get DTC stored.
that is all i can think of  this afternoon
good luck to you and happy thanks giving to you and family.