Very lean cruise mixture, no open loop at high load, possibly bad ecu?

[HadesOmega]

I usually just drive my car around town or go from one city to another but I recently drove my car out to to someplace that was about 100 miles away. I have an autometer narrowband AF ratio gauge and I've noticed that when cruising at 70 around 3k RPM in open loop it will swing to the lower stoichiometric area and back down on fairly flat freeway. But I've noticed that after a lot of driving like 20-30 miles it won't be be showing anything at all as in very lean. My car has always been overheating (not very bad but will almost got 3/4) going up hills for some reason and when it was very cold it will run warmer (presumably from the denser O2) and even leaner in cruise. Is this normal? I think these two problems are related.

On hills I notice that it does not go into open loop mode and start dumping fuel in. I know my 95RS would do that, I had the same gauge installed in it. When I go WOT it gets enough fuel, it usually in the green or orange range, I know I narrowband isn't good for WOT tuning. However the car doesn't seem to be running poorly it runs fine.

Here's is some info on my car:
98 GST, 215k miles
running about 20lbs psi on s16G turbo
FMIC
190 pump rewired
EVO 9 560cc injectors
SAFC tuned with pocket logger- global is about -20%, I've tuned it for 1kRPM and 3KRPM to get the fuel trims as close as possible.

So my guesses it could be a couple things:
Bad ecu
vacuum leak
gauge could be going bad
SAFC tuning
Bad O2 sensor? It seems very responsive though...
etc...

Any ideas? Also the car did pass its last smog check couple weeks ago, if that makes any difference.

 

[viprez586]

A narrowband and the stock coolant temperature gauge are completely useless in tuning or supplying ANY accurate information.

Fix any vacuum leaks if you suspect them.
Ditch the narrowband. - FYI cruise and idle the gauge and reading on your datalogger will sweep rich/lean(or high/low voltage via datalogger) repeatedly and rapidly and should somewhat maintain "stoich" as per OEM design.
Fix your cooling problem.

Then worry about tuning and Air fuel ratio via a wideband.

 

[HadesOmega]

I'm aware of how the o2 sensor should work in closed loop, it does sweep and this is for cruising so the stock O2 sensor should be good enough. The maximum sweep is in the lean range. I'm not trying to tune it I'm trying to figure out when its running so lean.

Some more info: it doesn't throw any CEL and I pulled the plugs and they looked ok.

 

[pneumo]

I'm aware of how the o2 sensor should work in closed loop, it does sweep and this is for cruising so the stock O2 sensor should be good enough. The maximum sweep is in the lean range. I'm not trying to tune it I'm trying to figure out when its running so lean.

If it's lean at 3k rpm at half throttle, then use the SAFC to add fuel. I'd set the hi/lo tps points at 20% for lo and 50% for hi. This way you're in the Hi range earlier, so you can keep the Lo range tuned for cruising. Then just add approx 5% to 10% more fuel at 3k and 3500rpm on the Hi throttle map until it runs slightly rich when going up hills.

HTH.

 

[mathewdylang]

My 93 talon does this. It has a 91 6bolt, stock turbo with punishment racing hard pipe kit for the stock sidemount, gm maf/translator, cai on the turbo, boost controller set at 14-15psi, and as far as i know everything else is stock. I bought the car with everything but the maf/translator and hard pipe because the maf was bad and the pipe was leaking. I have a autometer A/F gauge (narrowband?) and autometer boost gauge. Yesterday when I was cruising down the interstate at 70mph at 3100rpm my A/F went way lean like flickering on the last light and every once and awhile itd flick back and forth. Its not tuned, no eprom, and no adjustments made. Lastly when at like 3/4 throttle in boost it cuts out like looses fuel around 35-5k rpm? Does anyone have an idea on this? Sorry to cut into the post but i had the same problem.