How to read Ultra Gauge fuel trim data?

[California98Civic]

Ladogaboy and I have been discussing how to read the UG's fuel trim data, and I think it might deserve a thread of its own.

The UG offers longterm and short term fuel trim readings in percentages over or under 0.00%. Whether that can translate into "lambda" and if so how to do it is the question. Here is how I am thinking of it right now, with Ladogaboy's general, qualified agreement... what do you think? Quoting the Ultra Gauge's manual on the meaning of its fuel trim readouts: "positive values indicate a lean condition exists and the injector is left open longer to compensate, thus adding more fuel" (p.17). Now that means that a UG reading of +1.56% long term fuel trim is 1.0156 lambda, a lean condition, and my car will add more fuel to maintain stoich? That's not good for fuel economy. Better would be negative percentages, indicating rich condition, in response to which the car's ECU will seek stoich by reducing fuel.

Is that correct?

[nemo]

This is a good source of fuel trim info in pdf format. Other good info on the site also.

CounterPoint Archive 2001 - 2003 - Wells Vehicle Electronics

Volume 6 - 2002 Issue 4

Quote from above:

"Short term adjusts the air-fuel ratio in response to brief changes that normally occur during engine operation."



Long term is what you need to be looking at in terms of excess fuel usage and or a problem.

Looking forward to the responses in this thread.

[BHarvey]

My short term generally runs -6 to +3 and my long term runs pretty consistent around -4.
This is with E10 of course.

With E0, the long term will be consistent at -7 and go to -11 at times, mainly coasting.

From the wording in the online manual for the UG, minus is less injector time and plus is more.

[California98Civic]

Here is from vol.6, no.4, p.1 of the journal nemo linked above:

Fuel trim can also be expressed as
either a positive (+) or negative (-)
percentage. The percentage reading
represents the difference either above or
below the anticipated amount. So a short
term fuel trim reading of +20 percent
indicates 20 percent more fuel had to be
added to achieve the proper air-fuel mixture.
A -20 percent short term fuel trim indicates
that fuel had to be removed by shortening
the injector pulse width to achieve the proper
air-fuel mixture.

So if my long term fuel trim is +0.78 or +1.56, I am running rich. Darn. Need to figure that out. I'm leaving a margin of FE on the table.