All,

Looking for suggestions to help me narrow down a problem with my 78 280Z. Here are the symptoms:

Runs good.....except has a lack of acceleration after about 3500 RPM, but I don't believe is is necessarily RMP related. It seems to not be getting enough fuel after about mid-throttle, ie. after the throttle position switch engages. My most recent diagnostic to support this is CO measurements during full enrichment (Pin 3-18 jumpered on TPS connector) was way below what Haynes suggests. I have it set at 1% during idle and when I jump 3-18 it actually drops to about 0.6%, way below the 5% suggested by Haynes for my altitude. FYI I have two 78 280z's and the same test on second (2+2) yeilds 1% at idle and 5.5% in full enrichment, needless to say this one runs great. Am I right in deducing the CO percent drops on the coup (the Z in question) because the airflow meter permits more air without increased fuel delivery? Another data point is driving the car with pins 3-18 (TPS) jumpered appears to yield the exact same performance as when it is connect to the TPS, indicating the state of the TPS is not effecting a change in engine operation, other than openning the Air Flow meter more. Driving it without the TPS connector connect and NO jumper on 3-18 give the lack of airflow symptoms (pop...sputter...etc.), supporting that the airflow meter appears to work as triggered by the TPS.

Should I be looking at the computer and/or temp sensors etc., or is this a fuel delivery problem. I have a put a new fuel filter on to eliminate this posibility, and have tested the fuel pressure (as per the factory manual) at the fuel rail and measure about 40 PSI. What about the fuel pressure regulator? The filter screen in the tank has been suggested to me as well, but I am skeptical. Could my fuel pump be week? The pressure reading doesn't seem indicate this. The previous owner installed a switch to kill power to the fuel pump for anti-theft, I am thinking of removing this just to eliminate the posibility it is limiting current to the Fuel pump.

FYI the car has the Big throat throttle body and cold air induction installed. I believe the problem existed before these were installed.

Any suggestions to help narrow trouble shooting time is welcome. Thanks.

Jay

 

Just wanted to trick some people into reading my original post and make suggestions. Didn't think I had a catchy enough title the first time. This trick works for "Bare Naked Ladies", (I am disapointed every time I see them, you would think I would learn, oh well at least I enjoy their music and I probably wouldn't of watched the first time if they were called "Fully Clothed Men"!) so I thoungt I would give it a try. Read my post and help me out if you can.

Jay

First Post: Too Lean at Full enrichment
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All,

Looking for suggestions to help me narrow down a problem with my 78 280Z. Here are the symptoms:

Runs good.....except has a lack of acceleration after about 3500 RPM, but I don't believe is is necessarily RMP related. It seems to not be getting enough fuel after about mid-throttle, ie. after the throttle position switch engages. My most recent diagnostic to support this is CO measurements during full enrichment (Pin 3-18 jumpered on TPS connector) was way below what Haynes suggests. I have it set at 1% during idle and when I jump 3-18 it actually drops to about 0.6%, way below the 5% suggested by Haynes for my altitude. FYI I have two 78 280z's and the same test on second (2+2) yeilds 1% at idle and 5.5% in full enrichment, needless to say this one runs great. Am I right in deducing the CO percent drops on the coup (the Z in question) because the airflow meter permits more air without increased fuel delivery? Another data point is driving the car with pins 3-18 (TPS) jumpered appears to yield the exact same performance as when it is connect to the TPS, indicating the state of the TPS is not effecting a change in engine operation, other than openning the Air Flow meter more. Driving it without the TPS connector connect and NO jumper on 3-18 give the lack of airflow symptoms (pop...sputter...etc.), supporting that the airflow meter appears to work as triggered by the TPS.

Should I be looking at the computer and/or temp sensors etc., or is this a fuel delivery problem. I have a put a new fuel filter on to eliminate this posibility, and have tested the fuel pressure (as per the factory manual) at the fuel rail and measure about 40 PSI. What about the fuel pressure regulator? The filter screen in the tank has been suggested to me as well, but I am skeptical. Could my fuel pump be week? The pressure reading doesn't seem indicate this. The previous owner installed a switch to kill power to the fuel pump for anti-theft, I am thinking of removing this just to eliminate the posibility it is limiting current to the Fuel pump.

FYI the car has the Big throat throttle body and cold air induction installed. I believe the problem existed before these were installed.

Any suggestions to help narrow trouble shooting time is welcome. Thanks.

Jay

 

Fuel Pressure Regulator first place I would Look. Also Clogged injectors.