1989 Dodge Van fuel pump

Tiny
EUREKA 14
  • MEMBER
  • 1989 DODGE VAN
  • 5.2L
  • V8
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
Van starts nicely, runs briefly then shuts down. Does this several times until warm then stays running, but sluggishly. No codes given just 12 and 55. I have both rich white exhaust emissions and black, dry, sooty at the same time. 0xygen sensor is Ok. Could this be the problem. I turn key to run position and hear fuel pump running, it never stops. Does the same with key in accessory position and it still stays on. Never shuts itself off. I believe computer sees fuel pump staying energized and shuts down motor for safety. Is the computer suppose to de-energize fuel pump. What is suppose to happen when I turn key to run postion.
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Sunday, April 6th, 2014 AT 5:42 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
When you turn on the ignition switch, the fuel pump and automatic shutdown relays turn on for one second, then turn off until the engine is rotating, ... Cranking or running. If those relays are staying on when the engine isn't rotating, either someone hot-wired them which bypassed the safety circuit, or the crankshaft position sensor is sending a "noisy" signal that the Engine Computer is interpreting as a signal and is keeping those relays on.

The way the circuit is supposed to work is if the fuel line is ruptured in a crash, the engine can't run with no fuel pressure, so it stalls. Pulses stop coming from the crankshaft position sensor so the Engine Computer turns off the relays so fuel won't be pumped onto the ground and create a fire hazard.
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Sunday, April 6th, 2014 AT 7:55 PM
Tiny
EUREKA 14
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I am not sure about the crankshaft sensor, are you 100% sure that this year has one or is it going by the signal alone in the distributor. I cant seem to locate this sensor or its location on the vehicle for a 1989 b250 van.

Also I see only one relay under hood. Dkg/bl, b/yl, R, & b/wh wires coming from it which has to be the asd relay because I just turned key on the fuel pump stayed running, I unhooked relay under hood and the fuel pump stayed on. So where is the fuel pump relay suppose to be located normally. What would be the reason for hardwiring the fuel pump.
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Monday, April 7th, 2014 AT 8:36 AM
Tiny
CARADIODOC
  • EXPERT
The crankshaft position sensor is in the transmission bell housing, right behind the right cylinder head. It's just a few inches from the distributor.

I can never remember which vehicles this applies to, but some run the fuel pump on the automatic shutdown relay, and some have their own fuel pump relay. When there's two separate relays, the coils are wired in parallel so they both turn on at the same time and are controlled by the same terminal on the Engine Computer.

My guess is someone hot-wired the fuel pump relay because they thought the pump was supposed to run anytime the ignition switch is on. That's a common misconception. The Engine Computer turns those relays on when it sees pulses from the crankshaft position sensor and the camshaft position sensor.

The easiest way to see if the circuit is working is to measure the voltage on the positive terminal on the ignition coil, either smaller terminal on the back of the alternator, or the feed wire, (usually dark green / orange), on any injector. You should see 12 volts for one second after turning on the ignition switch, then again during engine rotation, (cranking or running). Many digital voltmeters don't respond fast enough to catch that one-second blip. A test light works better for that test.
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Monday, April 7th, 2014 AT 5:57 PM
Tiny
EUREKA 14
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Good news since the last time we spoke. Put in a new pcm and the fuel pump energizes and then shuts off like normal. But I still have just a couple two or three things to ask. A continuity test with pin #10 on 60 way connector which is asd input and terminal #2, 6 & 7 on the 14 way connector. These terminals are all grounds. The multi-meter beeps and shows 032. To me these wires have continuity and should not. Am I correct? I ask this because I have a few wires that have odd characteristics that don't seem correct. I would hate to burn another pcm which will happen shortly if they are not corrected.

There is no crankshaft sensor on this particular model. The signal to start fuel pump comes within the distributor and I currently have mine out of tune. Hopefully get things moving tomorrow.
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Thursday, April 10th, 2014 AT 7:26 PM
Tiny
CARADIODOC
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I checked a different source today and they indeed do not show a crank sensor, but they do list a carburetor for your engine, which is not correct.

I don't have a wiring diagram in front of me but I suspect the resistance readings you found are normal. The "ASD input" comes from the relay contact that gets energized when the relay turns on. The computer turns the relay on, and that terminal tells it it was successful. Also tied to that circuit is the ignition coil, injectors, alternator field, and oxygen sensor heaters. The fuel pump relay's coil, or the fuel pump, (when a separate fuel pump relay isn't used), will be on that circuit too. That coil, and all of the other things on that circuit could have a combined resistance of around 32 ohms, so your ohm meter would read 32 ohms between terminal 10 and any ground wires.

Another way of looking at it is there's 32 ohms of resistance to ground on that circuit. Using Ohm' Law to calculate current flow, (current = volts / resistance), 12 volts divided by 32 ohms equals.375 amps. That's not much. That circuit is usually protected with a 15 or 20 amp fuse on newer vehicles, or a rather substantial fuse link wire on older ones.

There is very little that can be wrong with the wiring that will damage the Engine Computer. The biggest threat is if the 5.0 volt supply wire to most of the sensors is grounded, but the computer will simply detect that and shut the supply down to protect it. Once the short is removed, you just turn the ignition switch off and back on to reset it.
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Friday, April 11th, 2014 AT 4:59 PM

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