DODGE RAM FORUM banner

1 - 3 of 3 Posts

·
Registered
Joined
·
86 Posts
Discussion Starter #1
2004 ram 1500 5.7L SLT 8' longbed. new O2's. I have poor MPG and low idle. I cleaned TB & IAC, little better, then after a few miles .....no. Suggestions?
 

·
Registered
Joined
·
86 Posts
Discussion Starter #2
I've ordered a new MAP

The ECM uses MAP sensor data to run crucial calculations, such as engine load, fuel injector pulse, and spark advance. When at rest, the MAP sensor reads atmospheric pressure at sea level (29.93 in. Hg). Because atmospheric pressure varies with weather and altitude, the ECM calculates this “zero” point just before the engine starts, fine-tuning spark and fuel injection mapping from that point.

When idling, intake pressure usually ranges from 16-22 in. Hg. Because this is lower than atmospheric pressure, air rushes into the intake. When the driver uses the engine to brake, pressure can go as low as 10 in. Hg. Upon accelerating, however, the open throttle body allows air to rush in faster, increasing pressure in the intake. At wide-open throttle, intake and atmospheric pressure are nearly zero.

MAP sensors fail by getting clogged, contaminated, or damaged. Sometimes, engine heat “overcooks” the MAP sensor's electronics or cracks vacuum lines. If the MAP sensor goes bad, the ECM can’t accurately calculate engine load, which means the air-fuel ratio will become either too rich (more fuel) or too lean (less fuel).

So, how will you know that your MAP sensor is going bad? Here are the key problems to look out for:

Poor Fuel Economy. If the ECM is reading low or no vacuum, it assumes the engine is at high load, so it dumps in more fuel and advances spark timing. This leads to excessive fuel consumption, poor fuel economy, and possibly detonation.
Lack of Power. If the ECM is reading high vacuum, it assumes the engine load is low, so it cuts fuel injection and retards spark timing. On the one hand, fuel consumption will go down, which seems like a good thing. However, if too little fuel is consumed, the engine may lack power for acceleration and passing.
Failed Emissions Inspection. Because fuel injection doesn’t correspond to engine load, a broken MAP sensor can lead to an increase in harmful emissions. Excessive fuel generates higher hydrocarbon (HC) and carbon monoxide (CO) emissions, while insufficient fuel may lead to higher nitrogen oxide (NOx) emissions.
Rough Idle. Insufficient fuel injection starves the engine for fuel, leading to rough idling and perhaps even random cylinder misfiring.
Hard Starting. Similarly, an excessively rich or lean mix makes the engine hard to start. If you can only start the engine when your foot is on the accelerator, you probably have a MAP sensor problem.
Hesitation or Stalling. When starting from a stop or trying a passing maneuver, stepping on the gas might not give you any joy, especially if the ECM is giving you a lean mixture based on faulty MAP sensor readings.
Check Engine Light. Depending on the age of your vehicle, MAP sensor diagnostic trouble codes (DTC) may range from simple circuit, or sensor faults, to correlation, or range faults. A dead MAP sensor won’t read anything, while a failing MAP sensor might give the ECM data that makes no sense, such as low engine vacuum when the throttle position sensor (TPS) and crankshaft position sensor (CKP) both show the engine at idle.

Bills86e
 

·
Registered
Joined
·
86 Posts
Discussion Starter #3
The PCM uses the O2 up/down exhaust sensors when the intake control system fails, and adjusts
the stoikymetric fuel/air combustion ratio to 14.7/1 mixture.

Just had to say this. Bills86e -
 
1 - 3 of 3 Posts
Top