Hello All,

I'm looking to the expertise of anyone who can shed some light with my 94 Dakota. All of a sudden my truck acts like it's not receiving fuel through the TBI (from what I can gather). It will run if I pour gas down the throttle body but only last a few seconds. That tells me that at least I have spark. So after doing that a few times I've decided to test if there is fuel coming from the pressure test port on my 3.9L (with the ignition to ON) and there is absolutely nothing. No gush of fuel or anything. I'm thinking that there should be something coming out. Now would that indicate that I have a faulty electric fuel pump? Clogged fuel filter?

I'm new to the whole EFI thing; always messed with carbs. Is there some electrical troubleshooting logic that I'll need to go through?

Any guidance is much appreciated. ALOHA!!

 

Starting in 1992, fuel on the 3.9L was injected at the cylinder by a fuel injector, not mixed at the throttle body.

Try this:
Since you have spark, I know your Automatic Shutdown (ASD) Relay is good (that provides battery power to the distributor coil when the ignition switch is in the ON or START position) Go to the relay box. (Located right behind the battery.) On the bottom of the cover, it will tell you what everything is. Switch the Automatic Shutdown (ASD) Relay and the Fuel Pump Relay. Than, turn the ignition ON (not START); for a second or two, you should be able to hear the fuel pump pressurize the system (the fuel pump is in the fuel tank; there should now be fuel pressure at the fuel pressure port on the fuel rail).
If you have fuel pressure, but the motor will not start, the relay is bad. If the motor still has spark, both relays are good, but, there is a problem elsewhere.

If still no fuel pressure:
Remove the relay that is in the fuel pump relay location. Test for battery power at cavity 30 (the bottom of the relay will show what connector is which). If there is no battery power, you probably have a case of the "splice-gone-bad." Heck, even if there IS battery power, I'd rip into the wire bundle and find the splice (see picture provided, of course, disconnect the battery). There are a few splices in that general area, but the one I'm talking about was noturious for getting corrodied on these older Dakotas, and not allowing the motor to start (no fuel or spark!). Next week when I go home, I'm gonna do the same thing, just because I don't want to run into any problems.

After you are done with that, connect the battery and relay. (If there was battery power to the relay already, and you decided to not find the splice, skip this step). Put the key in the ignition, turn to ON, and do it all over again. If there is now fuel pressure, and the motor has spark, and will run on its own, Good Job! You can stop here. If not, continue on.

OK, you have battery voltage at cavity 30. You have spark at the spark plugs. Both relays are good. But no darn fuel pressure. Once last step.

Your going to have to drop the tank for this [:'(]. Yes, but you would have to drop the tank for a fuel pump replacement anyways... Disconnect the battery and drop the tank. I think you can manage to find out how to do it. After the tank is disconnected, bring out a multimeter. Reconnect the battery. Look at the picture (thats about how the fuel pump connector should look) Cavity 1 should have battery power present whenever the key is ON (or START for that matter). There should be continuity between cavities 4 and 6 (and, probably 5 as well) and a known good ground. If battery power is not present (but we know the relays are good and are getting power), there is a problem somewhere in the wiring. If there is no continuity between the ground wire and a KGG, again, there is a problem somewhere in the wiring. But, of course, if there is power at the connector, and the grounds are good, but the fuel pump never kicked on, the fuel pump is faulty, and needs to be replaced.

Post back with results, or if you need more info!

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Mr. dodgerules86,

Thanx for all the guidance....I'm gonna go through that sequence. Shouldn't the fuel pump make a fairly audible noise/humm?

At the fuel pump relay, should I ground my multimeter probe and use my hot lead to test cavity 30?

I'll keep you posted.

Tanx again.

 

Yes, for a second or two when the key is turned to the ON position.

Yes.

 

i had the exact same problem ur truck had,and it was a vacum line going to the egr valve...i replaced the pump and fiter..i didnt a bunch of crap and it was a vacum line.check ur lines out

 

Just a tip...

The starter relay is also the same as the ASD and Fuel pump relays so an easy test is to put the suspect relay into the starter relay spot. Then turn the engine over with key, if starter no work relay is bad.

 

Since my original post, I did some checking of the relay that you had suggested and those have checked out okay. I still have not dropped my tank due to not having time so my truck has sat for about a month.

Here's a note of Interest.....I started her up and on 2 different occasions she stayed running for roughly about 8 and a half minutes before dying out. On both occasions the fuel rail showed no signs of having pressure through the pressure test port. I'm at odds with that. Shouldn't the fuel rail be under pressure? By starting up those 2 different times, are these signs that my fuel pump is going through it's last 'hoorah' before finally calling it quits?

Have you or anyone else encountered this same sitauation or something close to it?

Also, the hanger bolts for the fuel tank straps, are those purchase items only through Dodge or can I get an equivalent replacement say like through Lowe's or Home Depot's nut and bolt section? Or through a parts store chain?

Thanks again for your knowledge base!

 

Your 94 should have 35-45lbs of pressure at the fuel rail. If it doesn't, I would be looking at either a blocked fuel line, clogged filter, or a bad fuel pump. I would check to see for sure that there is power to your fuel pump. Do you hear it "whir" for a couple seconds after you turn the key to the on position before you start it? If not I would suspect the pump.

There is also a filter in the bottom of the tank, fastened to the bottom of the fuel pump assembly. That may have become clogged with sediment and other foreign matter in the bottom of the fuel tank. If I were in your shoes I would be dropping the tank and checking voltage AT the pump. If you have voltage there and the pump still makes no sound, replace the pump.

If you have voltage there and/or the pump makes a sound. I would dissconnect the fuel line at the external filter, get a small bucket, soda bottle, jar, etc...., insert/aim the fuel line in/at it and have an assistant turn the key to on and see if fuel pumps out. If no fuel is presented upon that.....I would suspect the pump. If fuel comes out....then I would suspect the lines or the fuel filter were plugged and I would be trying to figure out a way to check the pressure right there. Fuel may come out of the pump, but it may be going bad and not pumping out enough pressure.

This I saw in a buddys Dakota. It pumped fuel, but not enough and only for a short while. He could drive it for about a half mile and it would die on him. Let it set for a couple mins, then it would start and run for a little bit. It was a long drive home for him he said.

 

What way should / could I use to "back flush" my fuel lines once I drop my tank and the external filter? Could I back flush from the pressure test port? Is that even possible? Aside from taking my tank to a radiator shop for some cleaning, what other safe alternative would I have to clean my tank with?

Thanks for all the experienced guidance thus far!

 

I used an air gun to blow out the fuel lines on my 88 dakota when it wasnt getting fuel. but then it broke a line off inside the tank. so I had to drop it anyways.[:@]
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