VP44 Electrical question

[Cummins5.9]

So I finished the W-T ground mod and was finally able to rule out the injection pump as my no start problem. Sort of. I followed the diagnostic from Bluechip Diesel and others to do some basic electrical testing at the VP harness. I verified that pin 6 was grounding, and pin 7 had power at the RUN position on the ignition but NOT on the START position. I didn’t check the power situation on the wire to pin 5 after reconnecting the plug because I didn’t have power on 7 at the start position. I also ran test leads to pin 6 from battery ground and  pin 7 (fused) to battery positive. Truck fired right up. I couldn’t find anywhere on a forum so far where someone explains what might be the cause of pin 7 having power at RUN but not at START. Does anyone here have any ideas? I’m still looking at the PCM having failed as I posted in another thread. Although I thought the ECM was responsible for fueling and so maybe the pin 7 issue is an ECM problem?

 

Thanks for any thoughts..

[Haggar]

The ECM  (from pin 36) controls the coil on the relay that provides power for pin 7.  This is from a 2001 manual, but I suspect yours is similar.

 

HTH

 

Hag

[Mopar1973Man]

10 hours ago, Cummins5.9 said:

I couldn’t find anywhere on a forum so far where someone explains what might be the cause of pin 7 having power at RUN but not at START.

 

Here is the full wiring of the ECM and VP44 connection. Fuel pump relay in the upper right corner is controlled by the ECM to turn on the power from the ECM. 

 

As for the key switch... Follow the Start / Run part of the switch and it goes to the next photo.

 

Now here is the start / run circuit of the key switch.

[Cummins5.9]

Thanks for the diagrams.. as simple as it should probably be, I’m a little lost still. I don’t see where the power to the VP would be changed between the run and start positions. There should be power to the VP in both key positions as I understand it from the diagnostic from BlueChip, and I guess, from the bottom illustration here. Is the suggestion that there could be a problem within the ignition switch itself? Relays seem to not be the problem (only because switching them all around makes no difference). Haven’t found any fuse issues so far. There are no fuses or relays outside of the PDC or the drivers side dash right? The fact that I have power at the pump in the run position makes me think there aren’t fuse or relay issues, but I’m not seeing why it wouldn’t be there at the start position. 

[Mopar1973Man]

3 minutes ago, Cummins5.9 said:

I don’t see where the power to the VP would be changed between the run and start positions.

That's the point it doesn't. That why I posted the key switch part. The ECM is in control of the power relay directly. Ok wiring map take notice the Brown/White wire going back to pin 36 of the ECM. This is the only thing that controls the VP44 power. You can see the Fuel Pump relay in the upper right. 

 

 

Now as for the key switch. Look at the far right switch set up in the ignition switch. It drop off this map to the next image.

 

Now we move to the cab. The fuse panel in the left side of the cab. Fuse #9 is hot only when the key is in the RUN or START positions. The only time this power changes is when the key is in the ACC, OFF, and LOCK position which the power is OFF.

 

The only thing I could think to try at this point is change the fuses which I've seen many fuse crack and randomly work or not. Then I would replace the fuel pump relay. I've seen relay burn the contacts and randomly work and quit too. 

[Cummins5.9]

Thanks Mike.. I will check fuses again, but having it vary consistently only between key positions makes me think it’s unlikely to be a fuse or relay. Automotive electrical is an area I don’t have much experience obviously, but I have a logical mind and I learn well, albeit slowly sometimes. I was thinking to test the brn/wht wire from pin 36 out of the ecm and see if the power is consistent there between start and run positions on the ignition. If yes, then problem between ecm and vp, if not then problem within ECM or ignition or between the two. I’m not sure what else can be eliminated from the equation? I hate to start replacing parts randomly without pretty good confirmation they are defective. Replace ignition switch, send modules in, etc. I read somewhere that someone had a crank but no start issue (but hotwired vp44 worked fine) and it turned out to be his cam sensor.. My brother has been bald for years and at this rate I’ll be joining him soon..  

[Mopar1973Man]

2 minutes ago, Cummins5.9 said:

I was thinking to test the brn/wht wire from pin 36 out of the ecm and see if the power is consistent there between start and run positions on the ignition.

 

There might be software control of the ECM that might impact when and where that relay is active being the ASD relay should be capable of forcing the engine to shut down. Do you have security fob? Security system could prevent starting if available in your model. 

 

Got to ask is the WAIT TO START light coming on instantly? If not the ECM is brain dead till that light comes on which happens to be the first instruction in the ECM. If the wait to start does not come on it will not start at all. 

[Cummins5.9]

Yes the wait-to-start comes on and seems to act as it always has. The ASD might be an issue, but not the relay itself as I have switched that one around too. I did have a key fob that was an aftermarket add with a mopar system, but I couldn’t get it to disarm so I removed it completely. There was a harness on the steering column that was intersected by the security system harness (original harness disconnected, security harness plugged in and other side plugged into security harness). That seems like where any interruption would occur from the security system, but all of that was removed and returned to stock, unless there was/is something present in the ECM no longer seeing the security system and disabling the truck somehow. I don’t know how integrated those systems are in terms of programming within the modules. Seems plausible since someone who had time, could get into a truck and remove the whole system as I have and drive off.. perhaps the security systems have accounted for this possibility. ??

[Mopar1973Man]

Look over that security stuff again. I would double check everything is returned back to stock setup. 

 

Give me a call at 208-315-1470 I can tell you a neat one wire security trick for your truck. It will prevent starting completely. 

[Cummins5.9]

I think it’s all disconnected and returned to stock, I found the installation manual for the security system and reversed everything step by step, but whether the module(s) need to be reflashed, I’m not sure.. wish I could figure out how to bypass whatever is switching power on and off of pin 7 at the VP harness, I would just have it hot anytime the ignition isn’t in acc or off position. This seems like a security system type of interference; just cutting power to VP when trying to start.