1955 Chevy LS1

I have an LS-1 from a 1998 Camaro installed in a 1955 Chevy. The ECM was reprogrammed to disregard the uninstalled smog control devices.

The engine ran great for years then it started running rough and kicked out P0172 and P0174 codes (Fuel system too rich Bank 1 and 2).

First I replaced the MAF sensor and it did not fix the problem so I returned it.

Then in an attempt to be more scientific and stop the guessing game I bought Autoenginuity and found that the "Barometric Pressure Kpa and volts were beyond the 80 percent value causing the bar graph to turn red.

So naturally I thought that the MAP sensor was the sensor that sends out "Barometric Pressure" so therefore I replaced the MAP sensor but still the engine runs rough and rich however since I boogered up the old sensor when I removed it I am stuck having to keep (and pay for ) the new $65.00 MAP sensor.

Interestingly after I swapped out the old MAF to the new one and then swapped back the old one again the ECM has NOT kicked out any DTC's (even though MAF did did not fix the problem).

So I ran the engine and made a screen shot of the various parameters. Can someone please look at this screen shot and PLEASE give me a little hint as to what is going on?

Where does the engine get Barometric pressure? I thought the MAF.

If the screen shot comes in fuzzy I can email you a copy but here is essentially what all of the he red bar graphs in the picture are reading from top to bottom:

Barometric pressure 12.99 PSI Normal values are 1.45 to 15.54
Barometric volts 4.2 volts Normal values 0.00 to 4.98
Fuel Trim Learn just says Enable Normal values are 0 to 1 bit
Fuel Trim Learn just says Enable Normal values are 0 to 1 bit (same above)
Loop status closed just says enable and the normal values are 0 to 1 bit
Loop status closed just says enable and the normal values are 0 to 1 bit


I dont know why Fuel Trim Learn and Closed Loop repeat and why they are red but the only sensor that is showing red is the Barometric Pressure.


Any help would be appreciated!!!!

jimmyblue

iTrader: (11)

BARO is taken off the MAP sensor under certain
conditions. Like at key-on, or when throttle is well
open and RPMs are low, there is no difference between
manifold and atmospheric pressure.

BARO is a fixed value and ought to be near 100% of
1-bar MAP reading. You may be at higher elevation
since you're getting 13/14.7, but the number looks
sane enough.

Now if the MAP was not plugged into the intake, or
the intake somehow sees atmospheric pressure with
throttle closed, that would be a problem.

Fuel system rich, I have only seen when trying to
use a 85mm Delphi MAF with a 4th-gen F-body PCM.
The two don't match up unless you change the MAF
table. Other than the SLP MAF with its resistor hoax,
which makes it "close enough" for them to sell it to
you (but you get no cal info so it's all on you).

The picture is illegibly small. I can't get anything
out of it.

Figure you want running MAP between 40 (big cam)
and 80 (stock) kPa at idle, MAF Hz about 2000-2500
or so, and O2 sensor voltages bouncing fast and tight.
A rich code could result from a harness fault that has
the sensor outputs stuck high. But that's uncommon.
On the other hand you've probably had your fingers
in the wireball, so....

1955 Chevy LS1

Jimmyblue,

THANKS for the informative reply!!! Here are some answers to your reply:

>BARO is taken off the MAP sensor under certain
conditions. Like at key-on, or when throttle is well
open and RPMs are low, there is no difference between
manifold and atmospheric pressure.


So with this being said...the MAP is the sensor that is sending the Baro input and that is the tree that I need to be barking up.

>BARO is a fixed value and ought to be near 100% of
1-bar MAP reading. You may be at higher elevation
since you're getting 13/14.7, but the number looks
sane enough.

If I understand it correctly...when the engine is off and as a result the pressure on the inside of the intake manifold is going to be ambient. Then when the engine is started and at idle the barometric pressure should be much lower as a result of the vacuum that the engine is making. I should then be able to see the difference wouldnt I???

I live at 120 feet MSL so there should not be any appreciable difference between my reading and one at sea level.

>Now if the MAP was not plugged into the intake, or
the intake somehow sees atmospheric pressure with
throttle closed, that would be a problem.

The MAP was plugged into the intake and it looks like all hoses are intact. What is the purpose of the little hose that attaches to the MAP port at the back of the intake and then this little hose moves forward along the right side cylinder head to the front of the intake?


>Fuel system rich, I have only seen when trying to
use a 85mm Delphi MAF with a 4th-gen F-body PCM.
The two don't match up unless you change the MAF
table. Other than the SLP MAF with its resistor hoax,
which makes it "close enough" for them to sell it to
you (but you get no cal info so it's all on you).

It is all stock OEM equipment from a 1998 Camaro.

>The picture is illegibly small. I can't get anything
out of it.

Can I email you a copy?


>Figure you want running MAP between 40 (big cam)
and 80 (stock) kPa at idle, MAF Hz about 2000-2500
or so, and O2 sensor voltages bouncing fast and tight.

It is a stock cam. When you say O2 I assume you mean O2 #1 (the O2 sensor prior to the exhaust manifold? I am not running catalytic converters.


>A rich code could result from a harness fault that has
the sensor outputs stuck high. But that's uncommon.

As far as I can tell the harness is intact. I will look over it better when I get a chance. If there was a break in one of the wires then I was wondering if I record the MAP value then disconnect the battery (wait two minutes or so) then reconnect the battery. I believe the ECM will then loose its flash memory...then when I reconnect the battery I assume I will then read another value and that value being the default value???

THANKS AGAIN I greatly appreciate your input!!!

Bill

RADEoN

iTrader: (12)

jimmy that's a damn good explanation, thanks.