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Dan, ASE Certified Technician
Category: Chevy
Satisfied Customers: 2270
Experience:  20 Year Factory Trained Current GM Technician
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engine has high calculated load 29% at idle. map is good. long

Customer Question

engine has high calculated load 29% at idle. map is good. long term fuel 23% at and short fuel trim at -83% on bank 3. Any ideas? TB '02
Submitted: 4 years ago.
Category: Chevy
Expert:  Dan replied 4 years ago.
Hello <a href="../profile.aspx?PF=18725306&FID=26"Customer

Those trim #'s are high. We see a lot of issues with those oxygen sensor in the exhaust manifold. That would be the place to start along with a new fuel filter and then drive it and recheck those trim #'s.
Customer: replied 4 years ago.

OK< says i have oxygen sensor voltage bank 1, sensors 1 and 2 along with 2 heated ones. Since it is a straight six, what does the 2 banks mean on the two regular ones?

Expert:  Dan replied 4 years ago.
There are 2 oxygen sensors on this. sensor 1 is in the exhaust manifold and sensor 2 is the one behind the converter to monitor the exhaust converter. Both of them are heated. They use bank 1 and bank 2 to determine which one on the V6 and v8 engines
Customer: replied 4 years ago.
This also can cause the calc load to be off then too?
Expert:  Dan replied 4 years ago.
Dont read much into that. I have seen it higher at idle before. cant tell anything by that reading.
Customer: replied 4 years ago.
ok, this is a last ditch effort to get fuel mileage up for a 720 mile trip. Will break loose tonight and change on the way tomorrow. Will let you know then. But would the fuel filter cause these problems also?
Expert:  Dan replied 4 years ago.
By the trim # XXXXX gave me, Not sure of the -83. Don't think they go that high. The computer thinks its running lean so its trying to add more fuel. Faulty oxygen sensors can cause this to happen.
The front oxygen sensor is not as easy as it looks. They get very tight in the manifold and can cause problem coming out. Don't attempt unless your prepared for a fight.
Customer: replied 4 years ago.

the short term fuel trim on bank 3 does swing quite a bit -83% to 82%, but bank1 stays

-1.6 to -5.5. Again two different banks. Which cylinders are they referring to? using elm327 interface

Expert:  Dan replied 4 years ago.
There is not a bank 3 on this vehicle.
Watch the short term and long term fuel trim #'s. they should stay between -10% and +10%
Customer: replied 4 years ago.
ok, bank 3 IS a phantom reading, that explains the odd readings. long term is -5.5 to -1.6 and short term is -10.6 to 3.1. So to interpret, vehicle thinks it is lean, so it is dumping in extra fuel. Is that correct?
Expert:  Dan replied 4 years ago.
Those readings aren't that bad. Earlier you said long term at 23%
Customer: replied 4 years ago.
sorry, phantom readings from bank 3. bank 1 always staying negative. Are there any readings I could give you to help understand excessive fuel comsumption, or stay with the o2 sensor. Sorry if my info was misleading. I want to give you the dta you need to help me without wasting your time. I appreciate your help.
Expert:  Dan replied 4 years ago.
Those are the main things that help with the gas mileage( the trim #'s)
Make sure the coolant fan isn't staying engaged. That will cause it to use more gas. (Easier to hear it than to watch the readings)
make sure the engine temp get up around 190
watch for it going and staying into closed loop
Those are the main things to watch. Of course there is a bunch of other things that contribute to gas mileage.
Customer: replied 4 years ago.
closed loop and temp are correct, tire pressure good. so still start with oxygen sensor?
Expert:  Dan replied 4 years ago.
Great starting point. They don't last much over 100K.
Customer: replied 4 years ago.
changed sensor, same results. Is there a way to send you pid data to decypher?
Expert:  Dan replied 4 years ago.
You can insert an image with the tree button above.

Did it change the fuel mileage?
Expert:  Dan replied 4 years ago.
What is the MAP readings?
Customer: replied 4 years ago.

12.4 in hg at 824rpm


Expert:  Dan replied 4 years ago.
Check the volt reading of the MAP sensor at idle and at wide open throttle.
Customer: replied 4 years ago.
1.2v idle 4.6v wide open
Expert:  Dan replied 4 years ago.
I would not pay much attention to the load #. The MAP sensor looks like its reading ok. That is just a callicated # XXXXX the MAP readings and the rpm's.
Customer: replied 4 years ago.

gas mileage still same. injectors firing for 3.2ms at idle and still negtive in trim. Is there way to test fpr operation on this one, or is that a common problem?


Expert:  Dan replied 4 years ago.
You can do a injector balance test to make sure all the injectors are dropping the same. This is done with a scan tool or an injector tester.
You can try a different MAP sensor but your readings are normal
You can clean the throttle body and then disconnect the battery.
Customer: replied 4 years ago.
have scan tool and all injectors are the same. cleaned tb already
Expert:  Dan replied 4 years ago.
They have updated calibrations for the engine computer. May be worth getting it reprograming and see what it does.
Customer: replied 4 years ago.
ok, but problem happened at once, so there has to be a fault somewhere. what about fuel regulator. are you stumped also?
Expert:  Dan replied 4 years ago.
Would you like me to opt out so someone else can chime in with their thoughts?

Edited by Dan on 1/17/2010 at 4:15 AM EST
Customer: replied 4 years ago.



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