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Fuel Pump Relay Problems

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  #1  
Old 11-30-2010, 07:40 PM
haZZard haZZard is offline
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Default [SOLVED] Fuel Pump Relay Problems

I have a 1995 Ram 2500 8.0L V10, and just started having this problem when the weather started getting cold this year.

At first, when the temperature was getting down into the 40s, the fuel pump relay would click rapidly when I turned the ignition to ON and the check engine light would flash in sync with the relay clicking. The engine would crank just fine while this was happening, but it wouldn't start. I found that if I just move the ignition back and forth between ON and OFF a few times, the relay would stop clicking, I could hear the fuel pump run and the engine would start up and run like a champ.

Now that the weather has dipped into the teens, the fuel pump relay won't even click at all. I have tried swapping the relay with another, but it doesn't make a difference. When the temperature warms up into the 40s, the relay will start clicking rapidly again, and then I can move the ignition between ON and OFF until the fuel pump starts working and start the truck.

If the temperature gets above 50, the truck starts without a problem. In all of these cases, once the truck is started it runs great. No power loss, no sputtering.

Does anybody have any ideas what could be going on here? I'm at a loss. It doesn't seem like it's the fuel pump, since the truck runs fine after it finally starts. I've already swapped out the relay and that's not it. Could there be a wiring problem? Bad ground? How do I go about testing the wiring?

I appreciate any advice!

Thanks,
-haZZard
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Last edited by haZZard; 01-05-2011 at 10:33 AM.. Reason: Solved
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  #2  
Old 12-01-2010, 12:45 AM
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Check and clean your battery terminals. Follow the positive cable to the power distribution center, and clean that connection as well. Another cable runs from the PDC, to the starter, clean that one on both ends too. There are a couple grounds on the front of the engine, just above the power steering pump. Clean those too. There are also grounds on the back of the block, one to the head, one to the valve cover, I think...... Clean 'em.

Run thru that mess first, and see if that improves its attitude any.
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Old 12-01-2010, 05:20 AM
Sixtysixdeuce Sixtysixdeuce is offline
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The ASD relay controls the fuel pump circuit. That'd be the one I'd look at.
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Old 12-01-2010, 09:27 AM
haZZard haZZard is offline
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Thanks for the advice guys! I'll go through all of this tonight and report back.

-haZZard
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Old 12-09-2010, 01:58 PM
haZZard haZZard is offline
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Hey guys, I finally had some time today to go through all of the wiring. I checked every ground mentioned and every other one that I saw. I pulled them off, cleaned them and re-attached them all, even though none of them looked corroded.

I still have the same problem, but I did discover that it's the ASD relay clicking, not the fuel pump relay.

Here's what I've done:

Pulled the fuel pump relay and jumped ports 87 and 30: Fuel pump starts working immediately and I can start the truck.

Pulled the ASD relay and jumped ports 87 and 30: Fuel pump also starts working immediately and I can start the truck.

I've already swapped out all of the relays and it makes no difference.

If the truck is cold and the ASD relay is plugged in, I can turn the key to ON and if I pop the hood and listen closely I can hear and feel the ASD relay clicking rapidly. Eventually, depending on how cold it is outside, the relay begins to click louder and louder, until finally it just stays on and the fuel pump runs for a couple seconds and then the truck will start and run great until I turn it off and let it get cold again.

This morning when it was 40F it only took about 60 seconds for the ASD relay to stop clicking and stay on, but the other day when it was 10F, it took around 15 minutes.

Do you guys have any other ideas or advice on how to troubleshoot this?

Thanks!
-haZZard
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  #6  
Old 12-09-2010, 02:26 PM
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so, other relays put in the asd slot did the same thing? PCM controls ground to enable the relay. Might wanna trace that wire, and see if anything obvious presents itself.
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Old 12-13-2010, 11:49 AM
haZZard haZZard is offline
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HeyYou: Correct, swapping out the ASD relay doesn't change anything. I tried swapping with other relays in the PDC and, when that didn't work, I purchased two new relays and the behavior was the same with both of them.

I traced the wires you mentioned and actually did find a Dark Blue/Yellow wire that was badly marred. According to the service manual, this is the wire from the PCM to the ASD relay. The truck was already warm, and thus the fuel pump was functioning correctly with the key in the ON position. I cut the wire and the fuel pump no longer ran with the key in the ON position. I then re-spliced the wire and everything worked great. I thought this fixed the problem until the next morning when the truck was cold again, no fuel pump.

Does the fact that this problem is very consistent with the temperature indicate anything else?
- If the truck is above 50F, the truck starts and runs perfectly
- 35-50F, the relay will click rapidly for a 10-60 seconds. Once it stops clicking, the fuel pump will run and the truck will start
- < 35F, the relay does not click when I turn the ignition to the ON position, but if I leave the ignition ON for several minutes (the colder it is the longer it takes), the relay will eventually start clicking, and when it finally stops, the truck will start.

I read in the service manual that the PCM monitors the MAP, Coolant Temperature Sensor, Intake Manifold Air Temperature Sensor, TPS, etc... Could any of these sensors be affected by the temperature and cause the PCM not to energize the ASD and Fuel Pump relays?

Thanks again for your help!
-haZZard
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Old 12-13-2010, 12:18 PM
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The PCM will energize the ASD relay, (and, by default, the fuel pump relay) at key on. If it doesn't get a signal from crank sensor, it will turn fuel off, until it DOES get a signal from the crank sensor. Since yours isn't doing anything at all, even with the engine cranking, when it is pretty cold, I would begin to suspect that driver in the PCM itself is where the problem lies.
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Old 12-13-2010, 02:41 PM
haZZard haZZard is offline
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Quote:
Originally Posted by HeyYou View Post
... I would begin to suspect that driver in the PCM itself is where the problem lies.
HeyYou: Thank you for your help thus far.

Do you know if there is a way to test the PCM, or will I just have to replace it and see if that fixes it?

-haZZard
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Old 12-13-2010, 02:54 PM
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I think without hideously expensive equipment, there is no way to test. You can grab a used PCM from the yard, from a truck of the same year, and same engine trans combo as your, slam that in there, and see if the problem goes away.
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  #11  
Old 12-14-2010, 12:24 AM
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Originally Posted by haZZard View Post
HeyYou: Correct, swapping out the ASD relay doesn't change anything. I tried swapping with other relays in the PDC and, when that didn't work, I purchased two new relays and the behavior was the same with both of them.

I traced the wires you mentioned and actually did find a Dark Blue/Yellow wire that was badly marred. According to the service manual, this is the wire from the PCM to the ASD relay. The truck was already warm, and thus the fuel pump was functioning correctly with the key in the ON position. I cut the wire and the fuel pump no longer ran with the key in the ON position. I then re-spliced the wire and everything worked great. I thought this fixed the problem until the next morning when the truck was cold again, no fuel pump.

Does the fact that this problem is very consistent with the temperature indicate anything else?
- If the truck is above 50F, the truck starts and runs perfectly
- 35-50F, the relay will click rapidly for a 10-60 seconds. Once it stops clicking, the fuel pump will run and the truck will start
- < 35F, the relay does not click when I turn the ignition to the ON position, but if I leave the ignition ON for several minutes (the colder it is the longer it takes), the relay will eventually start clicking, and when it finally stops, the truck will start.

I read in the service manual that the PCM monitors the MAP, Coolant Temperature Sensor, Intake Manifold Air Temperature Sensor, TPS, etc... Could any of these sensors be affected by the temperature and cause the PCM not to energize the ASD and Fuel Pump relays?

Thanks again for your help!
-haZZard
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
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Last edited by cmckenna; 12-14-2010 at 12:44 AM..
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  #12  
Old 12-16-2010, 04:52 PM
haZZard haZZard is offline
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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
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Old 12-18-2010, 01:57 PM
haZZard haZZard is offline
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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
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Old 12-18-2010, 02:53 PM
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To be expected.
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Old 12-23-2010, 04:03 PM
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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
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Old 12-23-2010, 04:24 PM
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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.
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Old 12-23-2010, 04:28 PM
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My truck is a 8.0L V10. Will the V8 PCMs work as well?

-haZZard
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Old 12-23-2010, 04:36 PM
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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.
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Old 12-23-2010, 09:45 PM
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Quote:
Originally Posted by haZZard View Post
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
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
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Old 12-27-2010, 09:08 AM
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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
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