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.

[j12piprius]

James, what have you found with your fuel trim experiment?

Long term fuel trim on mine stayed at -0.78 on a short trip today, and I'm not sure what the short trim does yet.

[Cobb]

Yall getting fuel trim on a honda with an ug? I didnt think hondas let you monitor that?

[jcp123]

I was under the impression that fuel trims were a straight reading of how much fuel was being added/taken away? Ie, my LTFT stays kinda high, around +8% meaning that it is adding 8% more fuel vs it's base parameters?

Fuel trims are hella handy for diagnostics.

[California98Civic]

Originally Posted by johnlvs2run

James, what have you found with your fuel trim experiment?

Long term fuel trim on mine stayed at -0.78 on a short trip today, and I'm not sure what the short trim does yet.

It seems that the fuel map calls for enrichment when you accelerate harder, such as when I am always hitting 80% engine load to accelerate to an EOC injector cutoff speed. By only running the engine for this somewhat high load accelerations, I get slightly enriched long term trim readings. Usually it is just +0.78 but sometimes it is a little higher. But in recent months, since sometime in the spring or summer, I have done a lot more steady cruising at very low RPMs in high gears, like 1300 rpms or lower in fifth at maybe 35 or 40 mph. Adding that kind of driving to my overall mix has been associated leaner longterm fuel trim, such as -0.78. Also using DFCO a lot seems to reduce or eliminate postitive longterm fuel trim readings. I still think the car burns rich at high load, but the average is leaner when combined with cruising events in which short term trims reach -10 or even -24.

Originally Posted by Cobb

Yall getting fuel trim on a honda with an ug? I didnt think hondas let you monitor that?

Seems so. I guess the O2 and MAP sensors provide the needed data?

Originally Posted by jcp123

I was under the impression that fuel trims were a straight reading of how much fuel was being added/taken away? Ie, my LTFT stays kinda high, around +8% meaning that it is adding 8% more fuel vs it's base parameters?...

I think that is correct.

[sokdo]

keep up the good work... it's amazing what modifications can do

[sokdo]

I'm also looking forward to receiving my ultragauge this week.