Emergency - Can a mechanical fuel pump fail intermittently?

23438 Views 119 Replies 5 Participants Last post by av8r115, Mar 24, 2013

av8r115

Discussion Starter · Jan 28, 2013

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?

1 - 20 of 120 Posts

Bob Lincoln

· #2 · Jan 28, 2013

You really would have to have a fuel pressure gauge spliced in to measure the pump pressure to diagnose it. Or disconnect the fuel line and crank the engine (with primary coil disabled) with the fuel line inside a glass jar, and observe whether it delivers constant fuel supply.

Very possible that it's flooding, and that pumping the gas gave it more air to compensate by opening the throttle plate. And that's why it would take 45 minutes for it all to evaporate before it would start.

Flooding vs fuel starvation should be easy to tell, by removing the air cleaner lid and smelling for gas. If none, starvation. If heavy odor, flooding.

av8r115

Discussion Starter · #3 · Jan 28, 2013

Bob Lincoln said:
You really would have to have a fuel pressure gauge spliced in to measure the pump pressure to diagnose it. Or disconnect the fuel line and crank the engine (with primary coil disabled) with the fuel line inside a glass jar, and observe whether it delivers constant fuel supply.

Very possible that it's flooding, and that pumping the gas gave it more air to compensate by opening the throttle plate. And that's why it would take 45 minutes for it all to evaporate before it would start.

Flooding vs fuel starvation should be easy to tell, by removing the air cleaner lid and smelling for gas. If none, starvation. If heavy odor, flooding.

Ok, flooding would explain why it runs again after a while. What would cause it to suddenly start flooding out? What should I check/adjust? I know the carb is getting fuel now because it will run fine after it sits.

av8r115

Discussion Starter · #4 · Jan 28, 2013

So is it pretty unlikely that the fuel pump would be failing intermittently?

av8r115

Discussion Starter · #5 · Jan 28, 2013

The more I think about the flooding, the less sure I am about that. If it flooded enough to kill the engine, I should have been able to smell through the vents. Plus it didn't sputter or surge or anything at all - it just died.

Haynes doesn't say anything in the troubleshooting about flooding, so no help there. I guess I'll put a new pump and filter on it and see where that gets me. I've just never seen a fuel pump or clogged filter act this way.

av8r115

Discussion Starter · #6 · Jan 28, 2013

Guys, could it be an ignition coil going bad? That would explain why it just up and died w/out warning, and then starts again after it sits a while.

It just doesn't act like a fuel pump or filter problem. It's starts fine and revs up fine. And while it was running I shook the truck good and hard to see if there was any junk in the fuel tank. Engine didn't miss a beat.

I know I'm rambling fellas, but I'm barely able to rub two nickles together right now, so I'm sweating putting the $$ in the right place.

Bob Lincoln

· #7 · Jan 28, 2013

Check fault codes first:

http://www.allpar.com/fix/codes/index.html

av8r115

Discussion Starter · #8 · Jan 28, 2013

Bob Lincoln said:
Check fault codes first:

http://www.allpar.com/fix/codes/index.html

I'll take a look. I think the ENGINE light doesn't work.

I noticed that the tail pipe is coated with soot, inside as well as about a 1/4 around the outisde.. That means the mixture is too rich, right? Also, this time when I was checking the revs, when I idled back down there was a puff of black exhaust and the engine died. There's a lot of moisture and black on the ground by the exhaust where I've been revving the engine.

Bob Lincoln

· #9 · Jan 28, 2013

That's running way too rich. I suspect a carb rebuild is necessary.

Autozone and other parts stores can read your fault codes for free, with a code scanner; so the Check Engine light doesn't have to be working.

av8r115

Discussion Starter · #10 · Jan 29, 2013

Bob Lincoln said:
That's running way too rich. I suspect a carb rebuild is necessary.

Autozone and other parts stores can read your fault codes for free, with a code scanner; so the Check Engine light doesn't have to be working.

Where do they plug in the scanner? I haven't seen anything that looked like an OSBII plug. (Oops - OBDII)

All right. I'm just going to have to try driving it. I'll go to AutoZone first and see if they can pull the engine codes.

valiant67

· #11 · Jan 29, 2013

1987 Dakota won't give you any codes with the check engine light, that started in 1988 for them.
You could have a fuel devlivery problem like sediment clogging the pick up tube or a pinhole in a fuel line that sucks air instead of gas sometime or (my favorite that drove me crazy one time) a kink in the rubber house by the fuel filter.
It's a feedback carb so if it is indeed running rich the O2 sensor could be a problem. As could many other things.

av8r115

Discussion Starter · #12 · Jan 29, 2013

I just drove 20 miles of city streets and interstate - no hiccups at all. I guess I blew out all the crud while I was revving the engine earlier.

The O2 sensor on the left manifold looks like the original. I need to replace the manifold (cracked) and I just figured I would replace the O2 sensor at the same time. Found a manifold in a local pull-a-part, but can't get it to come loose from the cylinder head.

How hard is it to rebuild the carbureter? And any ideas on how to break a manifold loose?

valiant67

· #13 · Jan 29, 2013

Sometime you've got to tap the manifold with a hammer to break it loose after all the bolts are out. They can stick stubbornly to the engine.

av8r115

Discussion Starter · #14 · Jan 29, 2013

valiant67 said:
Sometime you've got to tap the manifold with a hammer to break it loose after all the bolts are out. They can stick stubbornly to the engine.

You can say that again! I even tried prying gently on it at the three places it connects to the cylinder head. When I have the $$ I'm going to head back with a foot long piece of 2x4 and my small sledge to see if I can knock it loose. My engine has a small coolant leak in the head gasket on the right front end, so I had planned to just do all of it at the same time. I'm going to have to rethink that since it looks like rebuilding the carb and replacing the O2 sensor are now a bigger priority.

Any tips on rebuilding the carb? I've rebuilt an old motorcycle carb, but nothing as complex as this.

7T3440CHARGER

· #15 · Jan 29, 2013

C

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..

av8r115

Discussion Starter · #16 · Jan 29, 2013

Yeah, I never top off the tank for that reason. I've only had the truck for 4 years, so I don't know about the person who had the truck before me.

The issue you described w/ the pickup plate is exactly what's happening w/ my truck, and it would explain why the engine simply quits w/out sputtering or running rough before.

How do you check for spark at the coil wire? Do you mean hold it close to the distributor and have someone crank the engine?

7T3440CHARGER

· #17 · Jan 29, 2013

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.

av8r115

Discussion Starter · #18 · Jan 29, 2013

7T3440CHARGER said:
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.

If I understand, you mean a weak coil could cause a new pickup plate to fail?

7T3440CHARGER

· #19 · Jan 29, 2013

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.

av8r115

Discussion Starter · #20 · Jan 29, 2013

The distributor cap, rotor, plugs, and wires are about 3 years old. What are the symptoms of a failed coil driver in the SBEC?

1 - 20 of 120 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.