I have a mail order tune- PCMforless and I finally got around to installing a wideband. Being up here at 5200ft, I figure my tune needs tweaking. I have a 180 t-stat in now with fans coming on at 180. When the car is at the 1/4 mark on the temp gauge, car runs pretty good. When fully warmed up, 1 needle click above that mark, it seems off. This is the data I've noticed when car is warmed up.

Idle- 15.3-16.0 AF ratio- seems a little lean to me. Also, I notice the RPM gauge stumble. When the car is warming up it stays around 14.4 and idles smoothly at 1k rpm.

Deceleration- Pegged lean 16.0+, slight poping from exhaust (cold or hot).

Throttle under 1/8- Hangs around the 15.2-15.5 mark. If I increase throttle, it has a slight lag and when I see the AF coming down to around 13.8 you can feel the car accelerate much better.

Half throttle- 13.1-13.3. Power seems good, no complaints

Full throttle- Haven't done it yet as I'm waiting for my new rear end before this 10bolt croaks.

To me, these AF ratios seem lean and under the hood is definatly hot. Even though the temp gauge stay at 1 click above 1/4, the fan is always running. The only plus side is I get 18-19MPG city (never on the highway so I don't know) with premium fuel. I tried mid and low grade with poor results. Will the 160tstat help me? Keep in mind, I need a working heater for the winter months as the baby rides in the back.

Based on these zones- what should I try to target the AF at? I haven't bought tunercats, but I will. I'm sure I will have many more questions when I start playing around with fueling and timing.

Thanks,
James

 

A 180* t'stat only starts to open at 180*, and isn't fully open until about 200*. Setting the fan "on" temps at 180* means the fans are fighting the thermostat. The fans are probably running way more than they need to, and the t'stat is limiting coolant flow when it shouldn't.

Lean at decel is normal. The PCM shuts down the injectors until the engine reaches lower RPM.

Mid 15's at idle isn't lean. The factory tunes closed loop to stoichiometric 14.7:1, because that's the A/F ratio required for the cats to work efficiently. Running 15.5:1 or even a bit leaner at part throttle/closed loop will probably net you better fuel mileage, and won't hurt the engine. I'm surprised the tuner would have even attempted to alter the closed loop A/F ratio on a bascially stock engine.

Where is your wide-band sensor located? Is it reading one bank, or combined exhaust of both banks?

 

Doesn't sound like the closed loop target has been altered. The factory tune will go for around 15.2 in closed loop (mine did anyway).

The fueling sounds fine and typical to me and I wouldnt touch it unless you Need to for some reason.

 

Ok, I'll leave it then for now. What about the 160* tstat? I have the o2 on the right header facing out towards the door.

I'll do some data logging to see more closely. When I drove home tonight, I opened up the cutouts and the car seems to run sooo much stronger. Idles way smoother too.

 

the 94 PCM is set up to run a bit leaner than stoich., 14.7. Additionally remember that the car will intentionally hunt around the crossover voltage of 425 mV YES this is different from true stoich of 450 mV, hence why I say our cars will run leaner than stoich. I have adjusted mine to 450 mV and you could also but no reason to. You would have to adjust your MAF to compensate...and got worse gas mileage too.