Intermittent start no start issue?

Tiny
DONKEY32693
  • MEMBER
  • 2001 DODGE DAKOTA
  • 3.9L
  • V6
  • 2WD
  • AUTOMATIC
  • 120,000 MILES
Truck stalled out and would start multiple times pulled and replaced fuel relay and checked all others still intermittent start no start. So, I was thinking sending the unit in fuel pump, replaced it and the harness because someone broke the clip that plugs into the pump. No power to pump fuel relay, never clicks and is new. Checked all fuses and relays, no issues. Checked fuel relay pins, have power on 3 pins but not on pin 85. Jumped relay to check pump still no power at pump. Getting frustrated with it thinking the TIPM or computer bad. Need help and also wondering if the CarQuest fuel pump could be wired differently than original pump.
Wednesday, October 4th, 2023 AT 7:03 PM

16 Replies

Tiny
DONKEY32693
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Also, in the process prior the dash security light came on and now off at times. The ignition when the key is turned on nothing would light up but has power. I also flashed the computer and tried to reset it, nothing. The obd2 will not connect to my reader and would before this issue.
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Wednesday, October 4th, 2023 AT 7:08 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Did you jump pins 30 and 87 at the fuel pump relay? Those are the ones to power the pump. Also, pin 85 is a ground part via the PCM. So, it shouldn't have power. However, it should provide a ground when the key is turned and in the run position. Have you checked for that?

Next, if you checked for power with the relay removed, you should only have power to pins 30 and 86. Is that the case? Note: Pin 30 should have battery voltage at all times. Pin 86 only has power when the key is in the run or start position.

Take a look at this link, you may find it helpful:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Let me know.

Joe

See pic below.
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Wednesday, October 4th, 2023 AT 7:41 PM
Tiny
DONKEY32693
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I will check and try relay is good. I know for sure, and the pump is brand new. Once I jump the pins for the fuel relay if the pump does not work, what is the next step? And if it does why won't the relay that's brand-new work? Asking so that I have a series of trials I read the link also. Thanks, I am in belief that there's a short in the fuel pump ground because I had a trailblazer give this issue and had to run a main ground directly off the pump but can't understand why the relay will not click when key is turned on. Chasing my tail I also think it could be in the TIPM or ignition due to when I shook the TIPM one time it primed and fired up I bought a CarQuest fuel pump and had to replace the connector on the harness with one off Amazon due to damage different color wires but I properly spliced them in order and also thinking that the new pump might be wired a different way but can't find a schematic for the pump to know exactly what's what.
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Wednesday, October 4th, 2023 AT 11:47 PM
Tiny
DONKEY32693
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Fuel pump good, relay good. No fuel pressure, no start and a no bus on dashes it the PCM or crank sensor.
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Thursday, October 5th, 2023 AT 12:17 PM
Tiny
DONKEY32693
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Tested crank cam and TPS voltage is good PCM pin 2 and 22 have voltage 31 and 32 are grounded pump doesn't kick on with relay in but when I jump it, it runs and brings fuel to the rail but no pressure the dash still says no bus abs check engine fuel light check gauges light is on, on the dash I'm down to PCM cluster or maybe a ground under the dash could use some more insight. Thanks
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Thursday, October 5th, 2023 AT 5:53 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

I doubt the PCM or Crankshaft position sensor is faulty. Also, I didn't realize there was a no-bus signal on the dash.

The PCI Bus failure modes are broken down into two categories, complete PCI Bus Communication Failure and individual module no response. Have you tried scanning the CAN to determine if there are specific codes that are stored for a specific module?

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

Also, I attached the wiring schematics for the entire powertrain management circuits. I highlighted all wires related to the fuel pump.

Confirm power is present to the two pins (30 and 86). Pin 30 should have constant power and 86 should have power with the key in the run position.

If that is present, check connector pin 85 for a ground signal when the key is in the start position. To do this, attach the alligator clip end of a test lamp to the battery positive. Probe the opposite end in pin 85. Have a helper turn the key to the on position. The test lamp will turn on if there is a ground path.

Let me know.

Joe

See pics below. Note: The schematic was four pages long. I had to cut each in half to make them readable.
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Thursday, October 5th, 2023 AT 6:18 PM
Tiny
DONKEY32693
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There is no communication when I scan, I have not been able to get any codes I've also tried 3 turns on the key to have the dash throw the codes nothing and tried to bypass PCM to get 5v to read codes still no bus no start fuel pump cycles on only with the jumper wire between 30 and 87.
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Friday, October 6th, 2023 AT 12:55 AM
Tiny
JACOBANDNICKOLAS
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Hi,

If you are unable to connect with a scanner, have you checked if pin 16 gets power at the DLC? It should have a constant B+ voltage and be powered by fuse 1 in the under-dash junction box. Also, pins 4 and 5 should be a ground on the DLC.

I attached the wiring schematic below for the can circuit. The next to the last circuit on the left is the PCM signal. If there is a communication error (bus) that is the area I would start checking. I highlighted in the last pic below a joint connection between the DLC and the PCM. If you disconnect the PCM, check to see if there is continuity in the pink wire between the two.

Let me know.

Joe

See pics below.
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Friday, October 6th, 2023 AT 8:00 PM
Tiny
DONKEY32693
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Replaced PCM with used one no bus is gone turned off and ran for a few rough had a guy tried to program it with VIN wouldn't allow him to reprogram had one code flash the dash p1282 with the new user PCM.
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Friday, October 6th, 2023 AT 8:20 PM
Tiny
DONKEY32693
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Relay clicks and checks out no fuel pressure on rail and pump does run and the original PCM was fried could possibly be the used one is bad also or grounding out and fried first PCM and is now throwing code about to fry the second still confused why he couldn't reprogram it.
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Friday, October 6th, 2023 AT 8:24 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

The code is related to the fuel pump relay circuit. I attached the diagnostics below specific to your vehicle and the code.

I have a question. If you feel the relay click, that tells me the primary side is working. If you are not getting power to the pump, there is likely an open between the two. If there is power, the pump may be faulty. However, the pump shouldn't cause this code.

Let me know.

Joe

See pics below.
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Friday, October 6th, 2023 AT 9:00 PM
Tiny
DONKEY32693
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The pump is brand new and runs for two seconds or so when key is turned on there is power at relay and works properly but can't seem to get pressure to the rail.
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Friday, October 6th, 2023 AT 9:31 PM
Tiny
DONKEY32693
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I will check for resistance tomorrow and let you know I'm thinking like before either it's a ground on the pump. When I replaced the harness connector I either flipped them opposite but don't think is possible unless pumps 4 pins were reversed from original wiring and why would pump run I'd it's backwards or we got a faulty PCM it was a used one but why wouldn't it allow it to be programmed to my VIN.
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Friday, October 6th, 2023 AT 9:38 PM
Tiny
DONKEY32693
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And why would it not throw any other codes and still power everything up properly but basically put it in limp mode figured it run like that and threw the one code p1282 because it needed programming, but the Mechanic couldn't get it to work.
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Friday, October 6th, 2023 AT 9:40 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,124 POSTS
As far as the pump, are you sure by accident you didn't switch the supply and return lines? I've seen it happen before.

As far as the PCM, I'm not sure what to tell you. If you were able to get the VIN programmed, it should work. The fuel pump, on the other hand, will automatically shut down after the prime. For it to turn back on and run constantly, you need to have ignition. Are you certain there is spark to the plugs?

Let me know.

Joe
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Friday, October 6th, 2023 AT 10:37 PM
Tiny
CARADIODOC
  • MECHANIC
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Hi guys. I stumbled across this and have been waiting to learn the solution. I'd like to add a comment of value in case it helps.

I had the gas tank out of my '88 Grand Caravan twice to replace a plugged strainer, and both times, being the expert I think I am, I switched the fuel supply and return hoses. They're different sizes, yet I was able to mix them up.

More importantly, since your tank was out, I suspect you pumped the gas out. Inside the tank, the fuel pump housing and strainer sit inside a bowl that prevents the gas from running away from the pickup when you go around a corner or uphill when the fuel level is low. That bowl is kept full by the fuel coming back on the return line. When you start out with an empty tank and add gas, it dumps right into that bowl. All I needed to get my engine started was a pint of gas.

On my '94 Grand Voyager, they use a similar setup, except when you put gas in, it misses that bowl. I found when parked on level ground, I needed to put in close to five gallons before it would get high enough to spill over into the bowl. Once that happened, the pump could draw fuel, the engine would run normally, and the returning gas kept the bowl full, as usual. At that point you could use up the entire five gallons. The point of my sad story is you might have to put more gas in the tank to get fuel pressure up for the first time.

As Joe mentioned, the fuel pump only runs for one or two seconds when the ignition switch is turned on. That's supposed to be enough to get pressure up for starting in case it bled down a little over days or weeks. After that, the pump doesn't run until the Engine Computer sees engine rotation, (and develops spark). When you start out with 0 psi, one ignition switch cycle usually isn't enough to get fuel pressure up high enough. Try turning the ignition switch back off, then on a second or even a third time. Each time the pressure will jump up a little more. If you simply try to start the engine, battery voltage is drawn down a lot by the starter motor. That lower voltage means the fuel pump runs a lot slower than normal, so it's less likely to build pressure any faster than the injectors are bleeding it off.

Hope you guys get this solved soon.
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Saturday, October 7th, 2023 AT 6:58 PM

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