Sunday, January 27, 2013

Dodge Ram 1500 Sport Has No Fuel Pressure and No Power To Coil



1998 Dodge Ram has no fuel pressure and ignition coil shows no voltage, Tested MAP sensor it shows 5 volts.

Experts Answer to these problem:

There are few possibilities that can cause these problem or such types of relative problems:----

The most possible is faulty PCM ( Powertrain control module).
But without confirming other possibilities directly replacing PCM is not a good idea.

WHY i think it can be PCM because ...............

The PCM is not alert, and that is one reason for fuel pump not running, 

Another possibility there is no power to the coil from the ASD relay, and definitely your fuel gauge and voltmeter don't work with the key on. The 5v you observed at the MAP sensor conveys to us that the PCM may be trying to power up, but it's far from the accurate 5v you must see with the key on.

But on some cases at our garage we recognize that it all appears like faulty PCM but at last something diffrent gets diagnosed as cause of the problem.It can be a loss of power or ground to the PCM. So without forget get the wiring checked to and from PCM.Also check all fuses so your next step would be to check right at the PCM. 
For inspecting the wiring one easiest thing on your vehicle is unplug the black connector and you'll see the terminals are labeled underneath. 

Your focus should be on pins 2 and 22, these two must have battery voltage with the key on. Pins 31 and 32 are the grounds. Its recommended to check these pins using a headlamp or fog lamp bulb if feasible, anything that will allow for some amperage flow.

Once you check and confirm that voltage and ground is OK, then the next step is to ensure that there is no short to ground on the 5v reference point circuit. The 5v reference circuit travels to the TPS, MAP, cam and crank sensors. 

A ground wire getting short on this circuit will take the PCM down. And not let PCM to function/operate and control its parts.
So it can be either wiring problem or internal shorted sensor. 
As per our auto repair experience and knowledge of what we have observed through years the crank sensor is the most common sensor to cause this. 

As per your vehicle mentioned the 5v reference circuit will be a violet/white wire.

If in your case that also checks out ok then further you have to check for a short to voltage on the sensor ground wire, which goes to all sensors and is black/light blue. If this wire is shorted to voltage because of a wiring issue or internally shorted sensor then it will prevent the PCM from functioning.

If almost everything checks out ok then the problem is interior in the PCM.
And you will need to replace the PCM.

These details will help.

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