Truck currently does not start I can disconnect one data link wire from vp and it will fire up and run. Currently it has dtc P0523 oil pressure sensor voltage high code. 

If there is no tach signal it will not start. The ECM requires tach signal to turn on fuel to the VP44. If it early 2nd Gen it will be a crank sensor, late it will be cam sensor.

When I unhook one data link wire and make it start and hook it back up while running there is no tach movement in the dash but scanner shows rpm’s. 

Does the truck have a key fob? If the security system is up it will not start.

 

Second, without any tach signal to the dash means no tach signal to the PCM. Being the ASD (auto shut down) relay is controlled by the PCM may be going to allow it to run till the tach signal is seen.

 

In another example 97 12V I had lost the crank signal since the engine is mechanical but the alternator will not turn on till the tach is seen by the PCM. The same is true on the 2nd Gen 24V. Since the entire fuel system on the 24V is electrical there is a safety system that relies on the tach signal to start both VP44 and lift pump also if you are in an accident then when the engine does the ECM can shut down both the lift pump and VP44 so it does not just pump fuel into a possible fire.

Bought the truck used I’ve never had a key fob. Is there anyway of telling if security system is shutting it down. Would it tell me when I put the scanner on it? Thanks 

Three times in the last year the key fob has temporarily stranded me. Once in my driveway, twice at stores including just today when the engine would spin and start for a few seconds then die. As I was scratching my head trying to figure out what was wrong I remembered the key fob and clicked the locks closed/open and it started right up. I don't understand the relationship between fob/running but if my only 2nd gen worry in life is the fob, I'm good with that! 

I also cannot get any body codes with a scanner. Could this be a pcm issue?

First off check the OBDII socket and make sure your pins haven't push out back. There is two bus line of SCI and CCD buses. Make sure your making connection. 

 

If the PCM was having issue communicating it of toss a error code and No Bus message in the odometer. 

2 hours ago, bshoemaker83 said:

also cannot get any body codes with a scanner. Could this be a pcm issue?

the PCM in these trucks only will display the  Power Train "P" codes.  They are not advanced enough or have the capability for body "B" codes.  

 

Does your truck have the high-line or premium Central Timer Module (CTM)?  The premium CMT controls the Vehicle Theft Security System (VTSS). You can identify this type of CTM by it having two wire plug connectors.  The standard CTM has only one connector.   

 

 

The ctm is the little black box inside the cab under the dash and it’s like 2” x 3” right? If so it only has one plug on it. 

Below is a High Line CTM.  You can see the two connection points on it.  If yours only has one connection point then it doesn't have the Vehicle Theft Security System (VTSS).

Are you getting a wait to start light?

 

Yes wait to start light is working 

 

Standard CTM since it's only a single plug. If you want to shut up the chime just put a piece of duct tape over the chime holes. 

Wish the chime was the only thing I was worried about lol but now that you mentioned it the chime only works for a little bit and quits could this be any of my issue as far as the no start is the box bad ?

 

Could something have went wrong in my instrument panel and this would be the reason tach quit?

31 minutes ago, bshoemaker83 said:

Could something have went wrong in my instrument panel and this would be the reason tach quit?

How to test...

 

Press the trip button down and turn the key on but don't start. Now when the word "Chec" shows up in the odometer display release the trip button it will test all the functions of the cluster. After the test, it will display 9xx codes in the display if anything is wrong. As for the tach make sure your crank sensor is good. Then the really weird one you might have to pull the crank sensor and check to see if the tone wheel is still on the crank. I've seen where the screw of the tone wheel fall out and the tone wheel got mashed up on the crank and landed in the oil pan. The truck will not start if there is no crank signal.

 

34 minutes ago, bshoemaker83 said:

Wish the chime was the only thing I was worried about lol but now that you mentioned it the chime only works for a little bit and quits could this be any of my issue as far as the no start is the box bad ?

PCM and CTM have little impact on starting the truck. If you have a key fob which you don't being you have a standard CTM there is no security feature to disable the truck. So the PCM and CTM could be removed and the truck will still start. Being the ECM can be used as a standalone module and the engine would start and run. So this brings it back to why is there no tach signal which could be...

• Bad crank sensor
• Bad crank sensor wiring back to the ECM
• Tonewheel fell off the crank

 

So the truck starts when you remove one data link wire tho. So will the truck run with the tone wheel broken in this situation?

12 minutes ago, bshoemaker83 said:

So the truck starts when you remove one data link wire tho.

 

You are just running off the VP44. Without the data link, there is no way to pass throttle information, timing information, etc. If you look up hot wiring the VP44 if you supply power to the VP44 and no other wires it will start and idle but you'll have zero control over the engine without the datalink wires. 

 

No the truck will not run without the crank signal being the VP44 will be forced off, the ECM assumes the engine stalled so power to the VP44 is cut off. 

 

This is a safety system to prevent the fuel system from pumping fuel when the vehicle has been in an accident. It shuts down both the lift pump and the VP44 if the crank signal is lost or absent. 

Edited March 17, 20232 yr by Mopar1973Man

Ok so this tells me the tone wheel is there and the oil pressure sensor must be good. 

Crank sensor not oil pressure 

2 minutes ago, bshoemaker83 said:

Ok so this tells me the tone wheel is there

 

Not necessary, you would have to visually look into the crank sensor hole and see if it is present. A bad crank sensor will not produce a crank signal either so it's a possibility. Then if the wiring between the crank sensor and the ECM is damaged it could prevent the signal to get to the ECM. This is not a voltage but a type of sinewave that the ECM counts the pulses and can calculate the RPM by count and time. 

 

6 minutes ago, bshoemaker83 said:

oil pressure sensor must be good.

Most likely the sensor is bad if there is a code for the pressure sensor. There is a voltage issue there is out of range so the oil pressure sensor code. 

I’m getting an rpm reading with the scanner when I make it run taking away the data link wire to start it and then hook it up while running. Is this signal coming from somewhere else ?