Lean fuel ratio

Hock

Registered User
Ok I installed an A/F gauge today and I saw what I though my be a reason why my SC feels slow. The gauge reads really lean while idling and while driving. Under WOT it just gets in the stoich part of the gauge and around 5500rpm its around 1/3 of the stoich.

Now, I do have multiple things done to the engine. Here the list of what I have done:

CMRE Stage 1 Cam
Mildly ported heads and intake
Ported exhaust manifolds
Roller timing set
Custom CAI
Gutted cats
AFPR

I am running the stock 30lbs injectors and stock MAF. When I put the AFPR I set it at 39.5lbs static. The O2 sensors are brand new Bosch sensors. The engine has a slightly rough idle and no driveability issues besides that I feel its slow.

Now I was thinking about adjusting the fuel pressure 5 to 10 pounds higher.

Tell me what you all think.
 
Do you have a CEL? During steady cruise (45mph and up) the AFR gauge should be switching from rich to lean in a semi regular rhythm every few seconds. Does it do this?
 
Do you have a CEL? During steady cruise (45mph and up) the AFR gauge should be switching from rich to lean in a semi regular rhythm every few seconds. Does it do this?

No Light.

The gauge does not cycle, that surprised me as well. It stays pretty steady as cruise.
 
Autometer, narrow.

Toss it in the trash...serously. Don't waste your time with it because it is telling you absolutely nothing about what's going on for your fuel ratio.

Below is a graph of a narrow band sensor output. It is only designed to measure ratios from 14.0-15.0. The EEC is trying to target a voltage of .423, and it'll constantly change the fuel calculations to achieve that voltage. This is why the meter should "swing" back and forth during part throttle from rich to lean. When you're under WOT, your car should be commanding a ratio somewhere in the 11's. As you can see from the graph...you can be anywhere from 9.0 to 14.0 and it'll have the same output..which is why the gauge will read stoich. when you're at WOT.


NarrowbandOutputGraph.jpg


Put that on ebay and sell it to a ricer yuppie.
 
I'm not so concerned with him using a narrow band 02 sensor as I am with the fact that he is not observing switching during cruise. Regardless of sensor, you should see the 02 sensor switching rich/lean during cruise. That you don't see that means that the EEC is not able to go closed loop for some reason. Normally if the EEC cannot go closed loop within a minute or so of operating temperature operation then you'll get a CEL. No CEL and no closed loop concerns me.

Does the gauge use your stock sensor? If so, are you SURE you have it wired correctly?
 
I got a AEM wideband on my crown vic and i dont see it switching that much during cruise all i see is from 14.2-15.3 I dont see no full lean to full rich
 
I got a AEM wideband on my crown vic and i dont see it switching that much during cruise all i see is from 14.2-15.3 I dont see no full lean to full rich

If you look at the diagram posted above, 14.2 - 15.3 would constitute full lean/rich on a narrow band sensor.

On a wide band sensor it is not going to switch full lean / full rich because of the range capability of the sensor but it will generate a consistent switching pattern. Of course if you have your sensor too far down stream then it won't show very much switching. I also don't know how fast or responsive your AEM is, but my LM1 shows very clear switching on ALL vehicles during closed loop operation.
 
3.8L SC EEC-IV HEGO Pinpouts (example 1990)

Pin # ~ Color(s) ~ ~ Description
29 ~ ~ ~ T/O ~ ~ ~ ~ HEGO Right
43 ~ ~ ~ T/R ~ ~ ~ ~ HEGO Left
49 ~ ~ ~ O ~ ~ ~ ~ ~ HEGO Ground
 
Pin # ~ Color(s) ~ ~ Description
29 ~ ~ ~ T/O ~ ~ ~ ~ HEGO Right
43 ~ ~ ~ T/R ~ ~ ~ ~ HEGO Left
49 ~ ~ ~ O ~ ~ ~ ~ ~ HEGO Ground

I'm looking at the diagram in my chiltons and I don't see any pins labaled HEGO ground.
 
I'm looking at the diagram in my chiltons and I don't see any pins labaled HEGO ground.

See any diagram for EEC pinouts that looks like this?

60 xx xx xx xx xx xx xx xx 51 ~ 50 xx xx xx xx xx xx xx xx 41
40 xx xx xx xx xx xx xx xx 31 O 30 xx xx xx xx xx xx xx xx 21
20 xx xx xx xx xx xx xx xx 11 ~ 10 xx xx xx xx xx xx xx xx 01


The HEGO related pinouts I mentioned came directly out of a FOMOCO Engine/Emissions factory manual.
 
Yeah it has that but if I'm not mistaken the 90's have a 3 wire O2 sensor and my 92 has a 4 wire which will make some of the pin outs different. I do remember the ones u mentioned ealier from when I put one of these on the 90 that I had.
 
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Yeah it has that but if I'm not mistaken the 90's have a 3 wire O2 sensor and my 92 has a 4 wire which will make some of the pin outs different. I do remember the ones u mentioned ealier from when I put one of these on the 90 that I had.

Makes sense except that you're still not finding any dead-tree reference to a HEGO ground at all?
 
Makes sense except that you're still not finding any dead-tree reference to a HEGO ground at all?

No. Not seeing that at all just "sensor signal return" and those are pins 6, 46, and 29. And those wires are all colored gy/r.
 
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