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91 Dodge W150 timing/cam

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91 Dodge W150 timing/cam

forrestmagee0125 forrestmagee0125
New User | Posts: 1 | Joined: 02/14
Posted: 02/13/14
07:52 PM

Hello, I have a 91 dodge w150 with a 318. It has the throttle body fuel injection. I am having problems getting it in time. It won't idle or when I can get it to idle I has no power. The truck has a bigger comp cam in it and my mechanic tells me that this is causing problems with the stock fuel injection system which in turn makes it run poorly. He says also that since the map sensor is for the stock cam that this is a problem. My options are to 1. Put in a stock cam. or 2. see if there is any way to find a map sensor to work properly with this cam. Thank you for any information!  

wayne712222 wayne712222
User | Posts: 88 | Joined: 10/13
Posted: 02/14/14
04:43 AM

please cycle the ignition key on 3 times within 4 seconds.. without starting the engine .. this will cause the check engine light to flash..

count the flashes.. they are all 2 digit..

code 12 is one..

_______O_______O___O_______________________O___________O___O__________ you get the any codes..

there are  a bunch of things to check...

and. there may be a way to freak out the voltage to the computer to fool it into thinking that there is actually more vacuum.. but its going to be a challenge..

post what codes you get.. i will be watching..

you may be the second person to have this issue.. big cam.. factory fuel injection.

are your oxygen sensors hooked up????

is the engine coolant temp sensor hooked up??

do you have the proper thermostat??? 192F installed..

do you own a digital volt meter so you can check some voltages for me..
does your meter have a millisecond or a duty cycle setting..

lastly.. do you have a radio shack nearby??

more tomorrow.. i have research and i need to know info on what you have properly or impropperly hooked up...

grounds between the engine block and the firewall..

computer wiring harness properly grounded..

all the computer sensors properly hooked up????

pick up one of these from radio shack...

1K-Ohm 15-Turn PC-Mount Cermet Potentiometer/Trimmer
Model:  271-342
Prs1c 2160216W345
its in the parts drawers.. there is an second model that is a 10K ohm .. i don't think that one will work for what you might be doing..
you will ONLY use the first and second terminal or the second and third.. not the first and third.... i use the 10K version of this to bypass broken vats ignition switches on gm cars..

there are 3 versions of this usually.. pick up the version with the smallest openings..

12-Position European-Style Mini Terminal Strip
Model: 274-680
Prs1c 2266713W345

do you have access to a mopar repair manual for your truck or a free account over at autozone so you can look at theirs online..

before going thru all this.. hook up a hand vacuum pump the map sensor. and apply 14 inches of vacuum. see if the truck runs better..

Image 20429

an even better idea is to put a TEE in the vacuum hose between the manifold connection and the map sensor.. put the vacuum pump in the line off the TEE..

get the truck running.. how much vacuum is getting to the MAP sensor.. should be manifold vacuum....

now for a test..  use some pliers and squeeze the vacuum hose between the TEE and the manifold..  so you are blocking the vacuum from the manifold..   then slowly increase the vacuum by pumping the vacuum pump slowly.. see if the engine smooths out at idle.. ???

this is just a test to see if changing the voltage output of the map sensor will correct your problem slightly...

i still need to examine the map sensor circuit to see if the voltage drops with an increase in vacuum.. if it goes the other way.. you may need to install the trimmer in the ground circuit to the map sensor instead of the signal output..

you can hope see where i am going with this line of thought..

i cannot guarantee this will work.. so you might be out 10 bucks at radio shack and 30 bucks at harbor freight..  but the brake bleeder kit will come in handy later..  

wayne712222 wayne712222
User | Posts: 88 | Joined: 10/13
Posted: 02/14/14
04:48 AM

MAP sensors, or Manifold Absolute Pressure sensors, have two specific responsibilities in the engine management system: measure barometric pressure at key on, and report engine load to the powertrain control module. The powertrain control module uses the information for proper air/fuel mixture control under all operating loads and altitude conditions.

A common addition to boost horsepower on today's engines is a turbocharger. Turbochargers contain two turbines; one is driven by the engines exhaust flow, the other moves ambient air from an external source into the engines air intake system. The task of the turbocharger is to compact more air into the combustion chamber than the engine would be capable of ingesting on its own. When you compact additional air into the combustion chamber, the engine will also require more fuel. When you have the combination of more air and fuel in the combustion chamber, the end result is more power. A system such as this allows a vehicle to have a fuel-efficient engine, yet create an abundance of torque when the engine is pressed into a higher RPM range.

Fuel control on engines today is performed by the engine's computer system. The computer analyzes the sensor inputs and then calculates the amount of fuel that is needed for the engine to maintain an air/fuel ratio of 14.7:1, which is the stoichiometric value, or the most efficient mixture of air and fuel. Because the turbocharger is changing the engine's calculated air intake value by pumping air into the engine, the engine load value must be measured differently. A sensor that is capable of adapting to both a positive and negative pressure within an engine is required when utilizing a turbocharger. Manufacturers will use sensors that can read these pressures at a barometric pressure multiplied times 1, 2 or 3.

A 1 BAR MAP sensor reports barometric pressure times one, which is approximately 14.7 psi or 30in/Hg (inches of mercury). As an example, a typical three wire MAP sensor has 5 volts and ground to power the circuit. The signal circuit, or return voltage to the computer, is about 4.5 volts at barometric pressure of 14.7 psi; this measurement is taken at key on engine off. The sensor can withstand about 1.5 BAR of pressure, but the return voltage will peak out at about 4.8 volts. This type of sensor is designed for a normally aspirated engine to read a negative pressure, or vacuum, at a typical barometric pressure.

2 BAR or 3 BAR simply mean two or three times above barometric pressure. The sensor will measure each direction, vacuum or pressure.

For reference:

   1 BAR is for a normally aspirated engine
   2 BAR will handle a forced induction up to 14.5 psi of boost
   3 BAR will handle a forced induction up to 29.0 psi of boost

Return voltage on a 2 or 3 BAR sensor at key on engine off will be approximately 2.5 volts @ 30in/Hg pressure depending on the sensor calibration. The engine vacuum, or pressure if it's in boost, will send the voltage below or above the 2.5 volt level.

A vehicle's computer is calibrated to function at a specific level as programmed by the design engineer. A 2 or 3 BAR MAP sensor placed in a system designed for a 1 BAR sensor will not function correctly; in fact the system will run very rich because of the low return voltage signal. A computer that is programmable is a must for any tuner attempting to boost their engine's output with the addition of a turbocharger and a 2 or 3 BAR MAP sensor.

the version on your truck is a 2 bar map sensor..

wayne712222 wayne712222
User | Posts: 88 | Joined: 10/13
Posted: 02/14/14
04:54 AM

because your trucks application uses a 2 bar map sensor..

this may..... work... you may need a relay to bypass the resistor in KEY on engine off.. so it can read the PROPER BAROmetric pressure..  

again.. i have to look farther tomorrow.. its almost 4 am.. need some sleep..