1955 Chevy LS1

Hi Cyber Friends,

Can someone PLEASE give me some help?!?!?! THANKS in advance!!!

I have a 1955 Chevy with a 1999 Camaro LS-1.

The engine started running rough at idle and has poor acceleration.

I connected up my Auto-Enginuity scanner to it and it does NOT have any fault codes nor are there any misfires recorded.

After watching it for a long while and poking around at the various parameters I noticed that all of the usual suspects were in the green range on the Live Data Grid tab except the following:

Barometric Pressure Volts was steady at 4.78 volts and the min/max ranges are supposed to be between 0.00 to 4.98.

Barometric Pressure was also steady at 14.61 PSI and the min/max range is supposed to be 1.45 to 15.14 PSI.

Manifold Air Pressure 1 bar graph on the other hand was green and it was moving about as expected and indicating around 15 PSI at idle and the min/max should be between 0 to 37 PSI.

So my SWAG at this problem is the "Barometric Pressure" indicator is bad but I have never heard of a Barometric Pressure in a car except the MAP sensor however the Manifold Pressure is indicating as suspected.

I replaced the Mass Airflow Sensor and that did not fix the problem.

Does anyone PLEASE have any ideas???

THANKS for your consideration.

Bill

luigiandme

iTrader: (2)

The MAP sensor acts as a barometric pressure sensor on key on then as the vehicle is running, the ECM uses the MAP sensor strictly for MAP purposes. The reason behind this is so the ECM knows the Barometric Pressure that the vehicle is running in for fueling and timing purposes. That's why its always good to take a pitstop when on long trips that require a distant drive though higher elevations.

1955 Chevy LS1

Luigiandme,

Do you or anyone else have any predictions (SWAGs) as why my engine is running rough?

Specifically...no fault codes, no misfires but only that the "Barometric Pressure" is indicating in red on my Auto Enginuity but the MAP indications (volts and pressure) are indicating correctly (green bar)???

I just read from a GM tech manual online that the MAF (Mass Air Flow) sensor has a barometric sensor as well.

Where should I start...the MAF or MAP???

Any suggestions???

Old Geezer

iTrader: (3)

Maf does not have a baro in it. It has the air sensing wires and an air temp sensor.[In the later units]
Suggest you get a real scan tool. [1 that can do data logging.]

jimmyblue

iTrader: (11)

BARO is taken from MAP readings at key-on and/or low
RPM, high TPS (I found the writeup a bit vague in the
Helm manual, as to why it would re-update after key-on).

1955 Chevy LS1

>Suggest you get a real scan tool. [1 that can do data logging.]

My Auto Enginuity scanner does have a data logger.

Does anyone have any suggestions on what parameters I should look at?

I can log data and save it to a file so if someone would be nice enough to look at that file and give some recommendations?

Any help would be appreciated!!!

flame

iTrader: (13)

Start with the basics check spark plugs, wires, fuel pressure
What are your fuel trims at idle, cruising?

1955 Chevy LS1

Thanks Flame for the suggestions!!!

Regarding "Fuel Trims"...I understand what fuel trim is but when you say "what are your fuel trims" are you asking for a certain numerical value?

I found the O2 sensors at Rock Auto for $28.00 per so for $58.00 delivered I ordered 2 (half of the price of the local Autozone).

My car only has two O2 sensors (in the manifold) since I am not running cats. The ones removed were badly soot-ed and black as coal. The engine has 80K on it so I figured that even if they were not the problem they would be due soon. I will replace them and run the scanner again.

THANKS again!!!

2xLS1

iTrader: (25)

The first thing I check on transplants is the fuel pressure. Transplant fuel systems never seem to be as reliable as OEM fuel systems.