Dodge RamCharger Central banner
1 - 6 of 6 Posts

·
Registered
Joined
·
639 Posts
Discussion Starter · #1 ·
this is a concurrent problem with the fuel preassure regulator. I get a code 13, no variation in MAP pneumatic signal. I've change the sensor and still get the code. It's doesn't come on when I turn the truck on or it's sitting ideling, but it seems to trip the code when i put the truck into gear, Any ideas? ???

James
 

·
Moderator
Joined
·
7,995 Posts
Well, I'm shooting a long shot...I wonder if your idle speed is too low? I assume you have replaced all the vacuum hoses related to the MAP circuit? Putting the truck in gear will affect idle speed and according to what I read the computer may be looking for a SET value for idle speed and if it doesnt see it it may throw a code? Other possibilities would be wiring, a loose electrical connector on the MAP or a bad computer.

Theory

The Manifold Absolute Pressure (MAP) sensor is used to monitor manifold vacuum (engine load). It sends voltage signals to the engine controller that represent the engine's varying load conditions. The MAP sensor is connected to a manifold vacuum source via a vacuum hose. Changes in manifold absolute pressure are determined by driver demand (amount of throttle). Changes in manifold absolute pressure are sensed by a silicon crystal, via the vacuum hose, in the MAP sensor. This crystal changes the resistance of the sensor depending upon the manifold absolute pressure acting upon it, and the change in resistance affects the amount of voltage that the sensor allows to flow back to the engine controller. The engine controller uses this information and other input signals to make decisions as to what output devices need to be adjusted to improve the driving conditions or emission levels.

The relationship between the resistance of the MAP sensor and the manifold absolute pressure is inversely proportional (as the manifold absolute pressure increases, low vacuum, the resistance of the sensor decreases and vice versa). The relationship between the manifold absolute pressure of the MAP sensor and the voltage returned to the SBEC is directly proportional (as manifold absolute pressure increases, low vacuum, the voltage returned to the engine controller increases and vice versa).

The voltage supplied to the MAP sensor from the engine controller is 5 volts, and its input voltage range is .5 to 5 volts. .5 to 1.5 volts indicates a high vacuum situation such as idle or deceleration. 1.5 to 3.0 volts indicates a medium level of vacuum such as a cruise or slight acceleration condition. 3.0 to 4.5 volts indicates a low vacuum situation such as hard acceleration or a mechanical failure. Any reading of 0 volts or over 5 volts indicates a problem.

The MAP sensor is also used by the engine controller during engine start-up. The engine controller looks at the MAP reading during key-ON-engine-OFF and compares it to a reading received once the vehicle is running and operating within +/- 64 rpm of its specified idle rpm. If there is not a significant difference between the two readings, then a MAP sensor code will be stored in the engine controllers memory.
 

·
Registered
Joined
·
639 Posts
Discussion Starter · #3 ·
All I can say is thanks for the input, Chump. Between this post and the other, you're probably gonna be sending me a bill for carpel tunnel surgery. I did adjust the idle and the timing following specifications. The computer will read a pretty low reading at idle, like 5-7 Hg", and that is probably insufficient, based on what you wrote, to make a difference for the computer. I'll try and look through the jungle of hoses for a leak. The explanation on the inverse relation (with examples) made a lot of sense, thanks again! I'll get back to you with my findings.
 

·
Registered
Joined
·
639 Posts
Discussion Starter · #4 ·
Ok, an update from today. I started up the RC and the map sensor read about 18"Hg and 1.6 to 1.8 volts. The problem is that as the engine warmed up, the vacuum dropped and got down to about 8"Hg while the voltage went up to about 2.8v to 3.2 volts. What do you think? Some vacuum line get's warm and starts leaking? Any other ideas as to why the vaccuum get so low? when the engine revs up to about 1200 rpm, i get the vaccuum up to about 20 - 21.8"Hg and the map is running at about 1.2 - 1.4v Opinions or theories?
 
G

·
This is related to the MAP sensor, but is actually a question for da Chumpmeister. When running a much hotter cam, and having a considerably lower vacuum, the MAP sensor will see this new reading, but things will be off kilter, thus, there will be some issues. I'm mainly thinking of the overdrive engagement on an '89 Dak setup. I was looking at those vacuum amplifiers used on the RC's, and was wondering if you could run one of these in-line between the vacuum source and the MAP sensor, and fool the sensor into "seeing" a higher vacuum reading which would change with engine rpm (if so, about how much higher would it read?), and thus, have the SMEC think things are hunky-dorey, and engage/disengage the OD as intended. I have no experience with the "vacuum amps" as they were called, and am not really sure how they work. If not possible, where would the problem(s) be?
 

·
Registered
Joined
·
639 Posts
Discussion Starter · #6 ·
Update part 2....Ok, I think what is going on is that one of the soleniods is opening up and there is a leak somewhere down the line of (the three EGR, Air Pump, and Vacuum Canister, i think?) Anyway, my question is if I disconnect these from the manifold vacuum will it have any adverse effects on the engine (I don't even have the smog pump, someone stole it). Thanks,

james
 
1 - 6 of 6 Posts
Top