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2nd Gen Ram Tech 1994-2001 Rams: This section is for TECHNICAL discussions only, that involve the 1994 through 2001 Rams. For any non-tech discussions, please direct your attention to the "General discussion/NON-tech" sub sections.

Fuel Pump Relay Problems

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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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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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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
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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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