View Full Version : Proper air/fuel ratios

06-27-2013, 01:43 PM
On startup I can smell gas(car running stupidly rich) af ratios are like 16-17 when warm they sit about 13-13.5 at idle. While cruising they are 11.8-12.4 under boost they are well under 10(lowest my aem wideband will read)
Do these sound really rich?
90' st185

06-27-2013, 01:47 PM
At idle it should be bouncing around 14.7 when cruising it should be 14.7 under boost it will dip stupid rich that's from being a stock ecu it runs safe. Seems like you've got something going on, it's over fueling.

06-27-2013, 01:57 PM
The 3sgte runs lean on startup so 16-17 AFR is normal. Warm idle should be stoich(14.7) and between 14-15. When cruising the readings should be stoich and the wideband will bounce between 14 and 15 as the ECU tries to keep it stoich. 10 AFR on boost is perfect.

From your numbers it seems like you are running a little on the rich side. May need to check th O2 and coolant temp sensor. A small boost leak could also cause it. Especially if the leak is between the turbo and AFM.

06-27-2013, 06:48 PM
Alright thanks ill have to check my o2 and coolant sensors.
If my coolant temp sensor wire broke and I just soldered it on, would that cause a problem?

06-27-2013, 08:47 PM
If it's the coolant temp sensor the ECU uses to adjust fuel trim then yes

07-06-2013, 03:55 AM
So my coolant temp sensor wire was barely holding on by 3 little strands. Cut and stripped up a little higher and added a new female plug, and now my a/f ratios are exactly what you guys are saying. Bounces 14-15.2 while cruising, 14-15 warm idle, and 10.8 wot full spool. I'm still having a problem with my idle,1250 rpm warm idle and it almost sounds like a misfire but isn't constant, it kinda just pops when it wants to. Any ideas on that. I was gonna check my afm adjust screw to see if it had been messed with. Also check my o2 sensor.

07-06-2013, 04:11 AM
I am having similar problems, did you have a cel?

Sent from my Nexus 4

07-06-2013, 04:18 AM
Check ECU ground.

07-06-2013, 04:23 AM
In my case the ecu grounds are good as are the voltage the ecu is seeing. I'm starting to wonder if I have a problem with my coolant temp wire.

Sent from my Nexus 4

07-06-2013, 04:33 AM
I have been tracing wiring problems, I figured the temp wire was OK BC I have no cel. Now I'm wondering if is seeing some resistance just not the correct resistance.

Sent from my Nexus 4

07-07-2013, 01:56 PM
I did have a cel for awhile that was 25 and 26 I think. One is running rich, the other is running lean. But I also had a loose wire on my o2 sensor and that cleared itself before I fixed the coolant temp wire or the o2 wire so I really don't know. And should I check ground at the ecu or is there another point to test it at?