Need help with exhaust gas analysis Please

[efoden]

I have a 1999 Nissan 2800 4X4 PU assembled in Mexico with KA24E that is a fuel hog (8mpg at best). Had the exhaust gases measured:

RPM 2820 PRM 780 CO 0.96% CO 1.56% CO2 12.9% CO2 12.7% HC 99PPM HC 123PPM O2 0.5% O2 0.4%

Can anyone comment on these numbers in light of poor fuel economy?Thanks

[NISTECH]

is it carburated or injected?

[efoden]

Injected

[NISTECH]

Hook up a fuel gauge and do a leak down test to determine if your injector is leaking. If you dont find a leak there you may want to take a look at you maf readings and see if its registering to much air. Easiest way to test is to swap out a known good maf and see if there is an improvement.

[Q45tech]

Examine block learn [adaptive compenstation] to make sure the average delivered fuel is near the preprogrammed value [100%].Is this MPG empty or hauling significant weight in 4WD or RWD

[efoden]

No the 8mpg is empty and in 2WD and not going over 60 mph. If I go to town and back which is about 18 miles each way I will consume 1/4 tank of gas from the full mark which is worse than 8mpg. 8mpg is highway driving.

[efoden]

How do I examine the block learn? Can this be done without equipment?Thanks.

[NISTECH]

No that is the expensive equipment test. Block learn is a typical GM term. You need to look at your alpha if your going to do this with a consult, or look at long term and short term fuel trim with an aftermarket scan tool like the snap on scanners.

[Q45tech]

18 miles each way I will consume 1/4 tank of gas from the full mark which is worse than 8mpg. 8mpg is highway driving.

One can never rely on the fuel gauge for accuracy...[measure real consumption vs real miles [KM].......exactly how many miles per gallon is fuel consumption measured by a dozen refills [amount vs accurate number of miles driven. Important to AVERAGE at least 500 miles.

Crank up and warm up [first 5-6 miles] consume 3-4 times normal highway consumption.

This may be normal [assuming your REAL consumption is like 12 mpg [fuel gauge error]. Are you adhering to the methods in which MPG is calculated:No AC not to exceed 61 mph average 55 mph, no brisk accelerations driving like a 80 year old grandmother?

[efoden]

My hope in doing the post is that someone would look at the gas analysis numbers and comment as to a rich or lean mixture and perhaps where to look. As far as my calculation of 8 mpg I can say that it is over several thousand miles of driving and mostly highway and normally 120 miles each way. So the number is valid and it is poor without question. My comment about using a 1/4 tank of fuel to go each way to town was just an observation, not hard data, but something to be included in the analysis of the problem. Thanks for all the help it is appreciated.

[NISTECH]

To answer your question yes it is grossly rich. You need to determine if the injectors are leaking fuel, if your fuel pressure regulator is functioning properly and that the load sensors are reading properly. This would be mas air flow sensor, coolant temp sensor,oxygen sensor. Those are the most dominant inputs for fuel control and would be the ones most likely to give you that high of a co%. But you must first determine its not a mechanical fuel problem with injectors or regulator.