1996 Dodge Dakota Fuel Pump Power Issue

Hello there forum! This is my first post on here and I'm glad I stumbled across this site! The problem I am posting may be a little unique for this site but I feel that given the great electrical oriented minds on here i may be able to get some help :-D I have a 1996 Dodge Dakota Extended cab truck that I have been having problems getting to start. It has been narrowed down to a fuel delivery issue related to the fuel pump not powering on. The pump was replaced about 2 months before this current issue. I have tested power at the fuel pump connector while supplying a direct battery connection and it read at 10v. I did this with the connector removed from the pump. I originally thought the wiring harness had a break in it but that doesn't appear to be the case now. I am looking for some advice on what diagnostic tests to try. Also any tips/tricks etc. I need to get this truck running because its been sitting for a while and the city gets kranky about that kinda thing, lol. Thanks foruM!

If you connected a 12V battery across it, it should have 12V across it. Why is it only 10V? Bad GND? Or current so high it causes a voltage drop in the supply path? Reply ends. The rest is FYI in lieu of wiring diagrams and further info: Fuel pumps should be powered via a relay which is ECU controlled else some other "yes - the engine is running" mechanism - eg, alternator is charging; airflap is open; splugs or IgCoil are firing; crank or ring gear is rotating. (But NEVER oil pressure!) There should also be a priming function - eg - on for a few seconds when IGN is turned on (especially for EFI), or on when cranking. This can be done by the ECU else SPDT relays or dual-coil SPST relays or diode-OR connected signals; etc. But testing the fuel pump as you have with 12V directly accros it is a good first check. WARNING - that assumes it is a 12V pump (not 8V or 6V etc) and is disconnected as you indicated. Some pumps use a series resistor to drop voltage for various reasons. AFAIK however, all 12V vehicles use 12V pumps and only use a dropping resistor during low demand periods. (And I think that is rarely done.)

I appreciate all the information you supplied! I feel this will help me out. I have a few things to try today and I will post back with the results from there. Thanks!

so the pump is only getting about 7-10v at the connector. I checked the fuel pump relay, and the relay output (which feeds the pump circuit) is only giving me 7-10v when i pipe a direct battery connection to it. I have 12v at the relay power side, only about 7 on the output side that feeds the pump no matter how i attach power to it. This seems weird

I agree - it's weird.... If it's a normal relay, then Vin should be Vout except for insignificant contact voltage drop. (EG - if contact resistance is 10mR (milli-Ohm), then if 10A, from V=IR => V(drop) = 10A x 0.01R = 0.1V. But you have a 2V - 5V drop! (0.2R - 0.5R if a 10A pump; higher resistance if lower current.)    But if it's a special relay with inbuilt resistor or something, anything is possible. And there is a relay (for a 1997? Dakota) that looks long - a bit like some horn relays but with several pins in an attached plastic surround - I'm wondering if that includes a resistor? I reckon replace the relay. There are several reports of them going faulty. And since I can't find anything that suggests voltage dropping for the pump, I'm tempted to suggest try 12V direct to the pump (not via the relay). Maybe powering a 12V bulb via the relay (instead of the pump) might show flickering if contact resistance varies. (Could try both small 3W-10W bulbs and (non-HID!) headlamps.)     Else remove the relay and test its ON contact resistance.... Certainly if it is an ordinary relay (the mini Bosch/Hella types as shown here on the12volt), I'd swap relays, or maybe jumper the #30 and #87 wires/connectors together on the wiring harness or relay socket. (That's to connect power. Paper clips can work well - until they short to GND/chassis!) The above is a bit risky. I have no idea how your vehicles are wired (I'm in Australia mate!), though I feel fairly confident... (As I said - where do you find 6V or 8V fuel pumps??)    And FYI - Yes - I searched for Dakota stuff. Of note from Wiki.Answers was: How do you check the fuel pump on a Dodge Dakota?

- There is a relay that runs the fuel pump, but before you start probing around in there UNPLUG the PCM, (engine Computer), then loosen a fuel line and apply power to the relay and see if you get fuel. >>>> CAUTION <<<<<< I can't stress enough UNPLUG the MAIN ENGINE computer before you do this, If you don't It will most likely blow the computer. And from allexperts (Aug 2006): My 1996 Dakota was stalling when I come to a stop and we put everything in the way of tuneup and sensors on it then a guy at the car wash said his Dakota did the same thing and it was the fuel pump relay. I changed it and problem solved - cost $6.50.

Hey old spark, thanks for the reply again. This is actually happening with the relay removed and the multimeter sitting in between the pins. That is why it seems so strange. the factory service manual lists the pins on the relay as follows 5A: Iginition Switch Output 5B: Fused B(+) 5C: Fuel Pump Relay Control 5D: Fuel Pump Relay Output So my understanding of this is as follows: 5A and 5C power an electromagnet inside the relay itself. this magnet then pulls 5B and 5D together to close the fuel pump circuit causing power to run to the pump. It is the connection of 5B and 5D that I have the discrepancy. 5B is giving me full battery power of 12.3v output. As soon as that is connected to 5D via a multimeter (or paperclip, jumper wire, etc) is when i see the voltage drop. if i hook the battery direct to 5D, same exact scenario, with multimeter, jumper wire, etc. It seems like major resistance somewhere along the A141 circuit (what 5D feeds) perhaps? I really am kinda stumped at this point. I'm pretty new when it comes to electricity and such so I am still learning. I feel I have a fairly decent (yet basic) understanding of how this system is working though. Thanks for the extra info you gave me, I appreciate it! I feel like if i could run a direct 12v connection to the pump I would see an improvement in my situation; however I don't have the ability to do that right now. Thanks again for hangin' in there with me!

Okay - that's a bit vague. But before that, confirming the good stuff. (AFAIK....) Yes - that "control" is typical.... So 5A is IGN-switched +12V to the coil (aka #86). 5C "Fuel Pump Relay Control" is thus a grounded signal from an ECU etc to energise the coil (#85) to turn the pump on & off. (IE - apart from an initial prime, it should be off unless the engine is cranking or running. It's the equivalent of an air-flap or "ignition-sparking" or alternator-charging signal etc. ... and... 5B is fused +12V (aka #30). 5D is switched power (+12V?) for the pump (#87). What I don't get is that if a short (paper clip) connects 5B to 5D, then both MUST be at the same voltage - ie, 12.3V, or 7V etc.    If not, then (12.3-7=) ~5V must be dropping across the paper clip which means it might glow red hot for a while until it fuses... (LOL?? or Ouch!!) So can you re-check or clarify that? If "the clip" drops 5B & 5D to low volts, that means the resistance is "upstream" - ie, between battery-fuse-5B. That can be bad connections (break and reconnect them) or bad fuses (rotate or swap fuses), else maybe a burnout wire or bad relay mount joint. If the clip remains at (near) +12V, then the fuel pump should also be getting +12V. (Unless ditto - bad connections or wire). With the relay in, if 5B is 12V and 5D is significantly lower (say > 0.2V lower), then the relay has resistance whether that be bad contacts or inbuilt dropping resistor.    Note that connecting a voltmeter between 5B & 5D won't tell you much - it should read either ~12.3V else 0V. If it does read 3-5V or 7-9V then you do have a weird fuel pump (like it's floating but with a zenor diode etc...!?... No way! (??).) The above is fairly easy to understand with a pretty pic and understanding that a voltmeter passes/consumes negligible current (ie, 1uA versus >1A for fuel pumps; a voltmeter is a VERY high resistance).

Oldspark, I really appreciate you working through this with me. I picked up a spool of wire today at work and plan to run a direct feed back to the fuel pump and see what it does. Probably wont have time until tomorrow or so to do this but i will keep you in the know on what happens. would it help at all if i posted a copy of the wiring diagram n such that I have been using on this? I have a copy saved on the web that i can link in. thanks again!

Yes! That wiring diagram might (should?) show any resistor or dual-mode switching. That can change my ~90% confidence to 100%. (Well, 100% that no damage can be done, less whatever improbability factor applies LOL).

stand by I will get that for you right now.