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Emergency - Can a mechanical fuel pump fail intermittently?

23397 Views 119 Replies 5 Participants Last post by  av8r115
Hey guys,

My '87 3.9L Dakota just quit on me and I've got to get it fixed TODAY. I think it's the fuel pump, but let me know if you think it's something else.

Going down the road the engine just died - no sputtering or anything. BUT when I pumped the gas it ran briefly, less than a second. That was while I was still coasting in Drive. It did that the first 2 or 3 times I pumped the gas, but not again.

After sitting about 45 minutes, it started after cranking for a couple of seconds.

I think the carb is being starved of fuel, the brief seconds it ran were when the accelerator pump shot fuel from the bowl (assuming this carb has a bowl), but then ran the bowl dry. I think that's also why, when it did start again, it took a few seconds of cranking.

But I don't understand why it would start again after sitting a few minutes. That's what makes me unsure if its the fuel pump or not.

The fuel filter was replaced in August.

If I was flush with cash I'd just slap a new pump and filter on it. Right now I've got be careful what I spend the $$ on.

I thought about water in the gas, but wouldn't that make it sputter for a while before it just quit completely?
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Check for spark at the coil wire when the truck stops. Dakota and Ram pickups had a problem with the distributor pick up plate. I installed these on a constant basis as a technician in; Symptom is shut down when the engine is at full operating temperature, no spark, runs rich due to lack of proper spark.. The carb usually will cause black smoke from the tailpipe if too rich. When fueling this truck, stop when the pump clicks off... continuing to fill will cause the vapor lines to fill the charcoal canister with fuel, hence rupturing the canister and filling the carb bowl with charcoal..
Hold the coil wire about 3/4" away from a ground, the intake will work if a clean unpainted spot is found.(Keep away from fuel source) Have someone crank the engine and look for a clean blue spark. If a red spark is present there is not ample spark, further diagnosis is required to see if the coil is the culprit as well. If there is a ton of miles on the vehicle a coil is advised with the pickup plate, cheap insurance to avoid back to back failure of a new pickup plate.
Correct, too much resistance can and will cause failure...

Faulty plug wires or cracked distributor caps can spike the pickup as well. There is a computer on the truck in the left fender behind the battery. This is a SBEC, single board engine controller. If a faulty pick up plate is left in the system, resistance can take out the coil driver in the SBEC.
The SBEC is probably ok at this time.. When and if it fails, the truck will not start, no voltage would be at the coil for spark, or the charging system will be inop as the voltage regulator is built in to the SBEC. When the truck stops again, a simple test can be performed, unplug coil wire and have someone crank the engine.. Check for spark, if no spark is present, unhook the 2 wire connector at the base of the distributor. If you place a piece of wire in the female terminal on the harness end of the 2 wire connector, intermittently touch the wire to ground, spark should emit from the coil wire. This tests the SBEC to the pickup connections and internal SBEC for proper operation. More than likely you have the beginning of a pick up failure. These symptoms will continue until it goes completely, and, can continue for months.... In the early 90's this was a common failure in Dodge trucks, Dakota's and B vans.......
Pickup plate is usually less than $75.00 for OEM.. Use a quality part, not a big box auto parts special.... If the coil is original, look for oil leaks at the coil wire terminal, sealing edge at the housing and at the wire lug terminals. If oil seepage is present replace the coil. Set ignition timing on your V6 at 12 degrees before TDC for better performance and fuel economy.. I've worked on these engines since they came out in 1987 in the dealership and have owned a few as well. The last one I installed had to be obtained aftermarket as the manufacturer no longer serviced the plate. You will have to remove the distributor to properly install the pickup, you can check the drive gear once the distributor is removed for excessive "Feathering" of the gear. This will indicate dist. drive gear wear. This was a common issue in the later fuel injected Magnum motors, not carb equipped 3.9's.
Agreed, yet the bulletin Chrysler published is for the Magnum engines. This is a pre Magnum truck, drive gear wear is not inherent in the early engines, timing chain wear will not create a stall, heat soak, no start issue... TSB 18-08-93 dates to 1993 and up.

I could be wrong on this one, but have done this professionally in the Dealership since 1978.. quite a common problem..
Early 1987 requires removal of the reluctor on the distributor shaft to get to the plate. Later 87 models had a plastic plate that did not require reluctor removal..
Due to current mileage, some slop is normal. As long as the timing mark does not jump 10 to 12 degrees when checking the timing you should be ok. Mine has 300k, the timing jumps about 5 degrees when checked with a timing light.. It runs almost as good as it did in 88 when I bought it.. almost......
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