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Discussion Starter · #1 ·
My 97 Duratec has been getting kind of lame mileage the past few years, and it's getting worse. At last fillup I calculated around 16 in-town driving, and a recent all-highway trip was 23.5. So it's getting serious. I did new upper & lower intake gaskets, cleaned carbon, replaced hoses, Autolite Pro plugs and wires are a year old. Also shot the MAF with electrical cleaner when I did the intake. The car runs like it did when new, silky smooth, silent, no misfire or stumble, no codes. But the fuel economy is getting to me. O2 sensors are original, they should probably be replaced but I don't like buying parts when I can't confirm I need them.

I used my Actron 9180 to read some live data, and recorded it and posted it below. Just fuel trims, O2 and MAF readings. I couldn't figure out how to do a slow-switch test on the O2 sensors, and don't have much experience reading sensor data and fuel trims. Any input is appreciated (and if anyone knows an easy way to convert scantool data to a jpeg I'd like to know that too :eek:. Cuz it was a PITA the way I did it). Thanks

 

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My 97 Duratec has been getting kind of lame mileage the past few years, and it's getting worse. At last fillup I calculated around 16 in-town driving, and a recent all-highway trip was 23.5. So it's getting serious. I did new upper & lower intake gaskets, cleaned carbon, replaced hoses, Autolite Pro plugs and wires are a year old. Also shot the MAF with electrical cleaner when I did the intake. The car runs like it did when new, silky smooth, silent, no misfire or stumble, no codes. But the fuel economy is getting to me. O2 sensors are original, they should probably be replaced but I don't like buying parts when I can't confirm I need them.

I used my Actron 9180 to read some live data, and recorded it and posted it below. Just fuel trims, O2 and MAF readings. I couldn't figure out how to do a slow-switch test on the O2 sensors, and don't have much experience reading sensor data and fuel trims. Any input is appreciated (and if anyone knows an easy way to convert scantool data to a jpeg I'd like to know that too :eek:. Cuz it was a PITA the way I did it). Thanks

Your first reading is at 664 RPM and shows 1 mph; the problem is it also shows 40.0% calculated load.

The second reading is at 1024 RPM and shows 1 mph; but again it shows a high calculated load of 56.0%.

The third reading is at 1396 RPM and 5 mph; calculated load is at 52.9%.

The last reading is at 2411 RPM and 16 mph; calculated load is at 50.9%.

The calculated load is way too high for the RPM readings and no speed.

The load value is computed based on data from the MAP sensor, TPS sensor, MAF sensor and engine speed. The value should be very low at idle, and high when the engine is under load. No change in the value, or a higher than normal reading at idle indicates a problem with the MAP sensor, TPS sensor or MAF sensor. These issues may not set a code.

The long and term fuel trims are not too bad; Short term fuel trims are typically +/-20% while long term trims are typically +/-5%.

I think the issue is with the load calculation causing more fuel to be burned.
 

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Discussion Starter · #6 ·
Turn your A/C off while running those tests
It was. A little Googling tells me I should have turned on TPS reporting too, so that I could compare that with calculated load and MAF sensor data. I still need to find some baseline data to have something to compare the numbers to...
 

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Load is based on the MAF output and rpm. You may have a bad MAF.
 

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Load is based on the MAF output and rpm. You may have a bad MAF.
What's interesting is the MAF FLOW GR/SEC readings. The idle reading appears to be ok - normal idle flows are around 5 gr/sec.

The higher MAF flows at the other points don't seem to change the load calculation much.

For the given RPM readings, were they taken at a steady rate or with an open throttle, like while accelerating?
 

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Is cleaning the MAF with Electric Parts cleaner safe? I was told this is a must clean with MAF part and theres no way around it as all other cleaners have the wrong chemicals in them?

Surly you didn't damage the MAF with lectric parts cleaner?
 

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Is cleaning the MAF with Electric Parts cleaner safe? I was told this is a must clean with MAF part and theres no way around it as all other cleaners have the wrong chemicals in them?

Surly you didn't damage the MAF with lectric parts cleaner?
You just need to make sure the cleaner does not leave a residue coating the sensor. Carb cleaner or brake parts cleaner will leave a residue. Most electronic cleaners state they are residue free.
 

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Discussion Starter · #11 · (Edited)
What's interesting is the MAF FLOW GR/SEC readings. The idle reading appears to be ok - normal idle flows are around 5 gr/sec.

The higher MAF flows at the other points don't seem to change the load calculation much.

For the given RPM readings, were they taken at a steady rate or with an open throttle, like while accelerating?
I think the first was at idle, and the last three were taken accelerating to no more than 30 MPH under different throttle conditions. Should I retry it while cruising at a steady throttle speed? I don't know how these tests are ususally done.
 

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I think the first was at idle, and the last three were taken accelerating to no more than 30 MPH under different throttle conditions. Should I retry it while cruising at a steady throttle speed? I don't know how these tests are ususally done.
I'm curious to see if the readings are significantly different while in a cruise state.

Found my '97 Service Manual. Here is some info:
LOAD VALUES:
Hot Idle: 15-20% at 700-730 RPM
30 MPH:20-35% at 1350-1650 RPM
55 MPH:15-35% at 1800-2060 RPM
 

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Discussion Starter · #14 · (Edited)
Bought a can of MAF cleaner, and knocked some slime off the rearmost MAF hot wire. Disconnected the battery, installed a new air filter...and we're still around 40% calculated load at idle. Grrr.

What's the baseline/average throttle opening % for idle? Mine is 18%.
 

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18% sounds about right.
 

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Discussion Starter · #16 ·
Wow, just ran across this...
"
6. Calculated load. All vehicles must report this parameter as a percentage. This is a very helpfill parameter with MAF-only systems. With a MAP-only system, you can estimate load based on vacuum; on a MAF system, this has to be calculated based on airflow and rpm. This is really the reverse of the speed density calculation. Now for the tricky part: The government required this parameter as a percentage, but it seems that's as far as they went. With most of the OEMs, the idle no-load reading is about 5% to 10%, which seems logical. A Ford, however, will report 25% to 30% under the same conditions. Hmmm.
This didn't make any sense to me until I drove down a big hill, under negative load (compression braking). The Ford load reading dropped to almost zero. So, Ford sets its baseline higher to include negative load conditions in the parameter range. The other OEMs don't read negative numbers, so there's no resolution in their negative load range. This is a central problem with OBD II; different OEMs implement specs in different ways. You can blame the vehicle manufacturer or the government; either way, the responsibility is on you to learn what to do. Remember, OBD II is a work in progress. 7. RPM. Nothing unusual about this parameter."

...located here: Driveability corner | Motor | Find Articles at BNET

This would seem to confirm what I just noticed in the Taurus. After taking it out for a few full-throttle jaunts, I noticed that releasing the throttle downhill dropped the calc. load down to almost 0%. Returning to a stoplight brought it back to 35% (40% with the fan kicking in). But I've read that GM products, and others, will display around 10 -15% calc load at idle. So I could only be off by 10% or so from the target range, it's just Ford has to be different and read higher? Man I'm in too deep. :(
 

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Discussion Starter · #17 ·
I'm close to going to the junkyard and trying another MAF sensor for $25 after testing all I can. But before that, one very specific question:

Can the IMRC ever partially fail, but not set the 1518 code? I'm wondering if the butterflies were stuck open at low RPM, maybe that could be why my grams/sec and calculated load readings are higher than they should be. I know I'm reaching.
 
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