After watching this thread for a while now, if there's clicking with the FUEL PUMP relay, this may be an indicator that, under temperature cycling, you've got a BAD CONNECTION thus, when it's warm, it works and, conversely, when cold, IT DOES NOT FUNCTION.

Here's how it works. Both the ASD relay and FUEL PUMP relay are wired in parallel ckt to the PCM ground switching scheme to which, inside the PCM, there's a low-voltage, solid state relay that is responsible for switching the ground to BOTH relays IN / OUT of circuit.

I have one test you need to perform to rule / factor out a bad SSR at the PCM LEVEL and, that is: in the evening, TAKE THE PCM INTO THE HOUSE for five days to gain some statistical evidence that supports the theory and to prove one way or the other, it is at the PCM level and, under cold cycling.

Come morning time, install it and re-connect the negative battery lead. Do this for five mornings.

<IF> the truck starts fine 4 of five times AT THE SAME COLD TEMP, you've got either a bad / failing solder joint inside the PCM OR< a failing SSR at the PCM. Either way, the PCM needs to be opened up and repaired.

<IF> The problem PERSISTS and DOES NOT go away, you are going to have to look for a bad connection at the wiring harness level at the PCM interface all the way to the PDC and, quite possibly, all contacts in the PDC should be cleaned and de-oxidized and OHM'd out with a meter to ensure there's not carbon build up or, high contact resistance to which, temperature cycling is it's worst enemy.

The clicking sound is indicative of a LOW POWER condition in which, due to either CORROSION or, a POOR CONNECTION and OXIDE BUILD UP, it's not making full contact thus, there's most likely a large enough VOLTAGE DROP across the pin contact thus, not enough voltage to remain in a closed state at the coil to keep the relay contacted at the other side thus, providing power on the FUEL PUMP side.

When it's cold out, I want you to measure the B+ voltage right off the battery first before tearing into anything. Find out what the voltage is at source first. Second to that, measure the B+ at the FUSE SIDE and at the RELAY side. ALL SHOULD READ the same.

Example, if the voltage at source is 12.4, you should then see this same voltage present at not only the fuse but, also on the B+ at the coil of EACH RELAY (FUEL AND ASD) as they share the same feed.


Let me ask you this: ARE ANY OTHER SYSTEMS AFFECTED OR, IS THIS PURELY ISOLATED TO FUEL PUMP ONLY? Remember now, when it is colder out, the voltage at any battery based starting system is going to drop under cold temps and, you may find that the root cause is due to voltage falls below the minimum threshold at source thus, when the key is in the <ON> position for long periods of time, the current draw will induce a rise in temperature in a given ckt thus, when it reaches a certain temp, the relay starts to chatter. The more I think about this, the more and more this is starting to sound like a failing battery. Again, testing is everything and guessing is nothing. I'd test it out and report the results back when possible.

I've worked on this system a lot and, it's actually quite simple but, there's a few CKTs that share a common ground, bus bar, B+ etc etc. so, in order to root it out down to the root cause for failure, it can take some time even if you know what you're doing.

CM

 

cmckenna:
Sorry for the delay in responding, I didn't see your post until today. A couple days ago I started to suspect the battery as well, so I went out and bought a new one. It didn't fix the problem though :-(

I think you're exactly right in describing the problem, but let me consolidate a few things that I've discovered over the past couple days:

When the truck is cold and the temperature is <30, if I turn the ignition to ON and measure the voltage across ports 85 and 86 of the ASD and/or Fuel Pump relays I get 0V. When I leave the ignition at ON long enough for the relays to start clicking and then stop, I can turn the ignition OFF and then back to ON and see that voltage across ports 85 and 86 jumps to 12V for 2 or 3 seconds and then back to 0V. As I understand it, this is exactly what should happen when the ignition is ON but the engine is not running.

I will test the voltage measurements at the battery, fuse, and relay sides tonight and report back.
If the voltages are all the same, then I'll pull the PCM and do as you suggested, taking it into the house every night.

As far as any other systems effected: The only thing that comes to mind is that the radio doesn't work, and hasn't worked since I got the truck a year ago. But one time, as I was driving, the radio just started working all of the sudden. It worked for about 10 minutes and then shut off again and it's never worked again since then. I don't know if this could be at all related, but thought I would mention it.

Thanks for your advice!
-haZZard

 

Ok, I haven't had a chance to pull the PCM yet, but I did take measurements at the battery, fuse, and relay and they were all at the same voltage. Hopefully I'll have time to pull the PCM this weekend and see if leaving it inisde overnight makes a difference.

Another thing i noticed, is that while the relays are clicking, the check engine and maintenance lights flash in sync with the clicking of the relays. Does this indicate anything?

-haZZard

 

To be expected.

 

Ok so I think I've confirmed the PCM is the problem.

I pulled the PCM and left it inside overnight, then went out and hooked it back up. The truck fired right up.
I left the PCM in the truck all day (~20F outside) and then went back out to try and start it and it wasn't working anymore. Exactly the same symptoms as before.
So I took the PCM out again and took it inside for a few more hours, hooked it back and up and truck starts right up again.

So clearly, something in the PCM is failing when it gets too cold, but leaving the ignition on must be moving enough current to eventually warm it up. I called my local Dodge dealer and they found a remanufactured PCM for $656 + $120 to program the VIN back into it.

If that's my only option.. I suppose I'll just have to cough up the money, but I'm wondering if this is something I could fix myself? My thoughts are that it must just be a bad connection on some component in the PCM. Does anyone have any experience or advice for repairing one?

-haZZard

 

Or possibly a failed component. Trouble is, which one........ I don't know of any schematics for the internal pcm PCB, and such like.

Find a truck with a used pcm, close to the same year, and with same engine trans combo as yours. (doesn't matter if it is the same displacement...) take that one to the dealer, and have IT reflashed to your vin. MUCH cheaper.

 

My truck is a 8.0L V10. Will the V8 PCMs work as well?

-haZZard

 

I don't think so. If it were a v-8, then 318 vs. 360 wouldn't really matter.... the v-10 is an entirely different animal.

 

Ahhhh. There is the root cause right there. Failure at the PCM level and, environmental testing confirms this to be either a fault of either a bad solder joint or, worse, SSR, or, failure inside the controller / die, such as: wirebond at the substrate to gate or drain. That test works as you can see for yourself.

Now, for those questions: you will not be able to fix it yourself unless you know a bit about electronics. However, you can send those in to be rebuilt by a fair number of places. The place I used to buy PCMs from has closed due to the economy / low sales. So, that being said, you will need to either get another one or send the one you've got in for repair to a place that knows what they are doing and have a full warranty on repair work.

For the question regarding PCM: the answer is NO. you will not be able to use a V8 controller for a V10 for, the program is different due to additional injector driver CKTs and totally different A/F mapping and intake volume along with different sensor programming and different timing tables as well. So, no way that will work for you.

Happy Holidays,

CM

 

hey hazzard. i did the same test by removing the pcm overnight and bringing it inside..truck fired right up in the 20 degree weather. so its my pcm that is failing too. it is also a 94 v-10. im gonna try and find one cheaper then what the dealer want (roughly 700 bucks) if i find a place that sells them a bit cheaper ill let you know. if you find a place cheaper please let me know. thanks