Hi Folks,

First post, not a mechanic and not good at this stuff. I'll do the best I can and hopefully get this solved.

I have a 1991 Pickup V6 4x4 original owner, 305k. I rarely drive it anymore, just start it and drive it around the neighborhood once a month. I keep it for sentimental reasons, and also the hope that someday I can relocate and it can be my farm truck!

Anyway, I went out yesterday to start it and drive it and it will not start. By the way. I always disconnect the battery when it is just sitting. I reconnect for my monthly drive. Battery is strong. I put the key in and turn it and all the normal lights, etc come on and engine cranks like normal, it just will not start. I have been doing a lot of reading and it seems like it may be a fuel issue? or fuse issue? I am not sure what people mean when they say do I hear the fuel pump when I turn the key. I have seen a lot of people saying to make a jumper and test FP to B+ but I don't know what that means. I had an old Haynes guide from many years ago when I was much younger but cant seem to find it now.

Any suggestions would be much appreciated. As I said previously, I'm not good at this stuff, which is why I always take my family cars to my mechanic when there are issues, but for this I just cant justify spending a lot of money on a vehicle I don't drive any longer, and when money is super tight like it is right now. Unfortunately, if this gets too costly I will just have to abandon the repair and let it sit.

Thanks in advance!

 

The larger unit shown in the picture above is the fuse block inside the engine compartment. Attached to it, as you can see, is a small device, usually with a black cover on it. Open the cover and find the two female spade terminals shown in the picture. Either make a jumper wire, as shown, or, as many do, use an unbent paperclip, and put it into the two indicated pins.
With the jumper in place, you turn the key on. Not to start, just to the position it is in when you're driving around. That is the ON position. You hear a fairly quiet sound when the key is turned to ON. That is the fuel pump. Sounds like a small motor running, coming from behind you. It's hard to describe. Maybe a quiet whining noise, low frequency. It will start out at a certain tone, and then, once the fuel system is fully pressurized, the tone drops in frequency. Gets lower, not in loudness, but in tone. Not a lot, but noticeable.

That's what the people are talking about. By the way, Fp means Fuel pump, B+ is the battery positive source. When you jumper them, and then turn the key to ON, you turn the fuel pump on by applying the battery voltage directly to the fuel pump, skipping past all the safety features your truck has. If so desired, if you hear the fuel pump running, you can then try to start the engine briefly. If it starts, you have isolated the problem to the safety devices that your truck has. The are there to shut off the fuel pump if you have an accident, that might break open the fuel system. That way, the truck isn't pumping fuel all over itself, the ground, you, and so forth. DO NOT drive the truck with the jumper in place. If it starts, it has given you valuable information as to where your problems lie. Shut it off immediately.

IF it starts, your truck has told you one, or more, of the safety devices has gone bad. It could be the Circuit Opening Relay, the Mass Air Flow sensor, or the system's fuse, which there are several of. Here is a picture of the systems complete schematic, if it does you any good. If not, maybe get a friend that CAN read it to help you.


This demonstrates all the safety devices and fuses involved. Some of the fuses shown, the little S shaped things on their side, are in the engine compartment's fuse block, as shown in the above picture, some are in the inside fuse block, unde the kick panel on the driver's side.

If you want, I will try to explain the schematic for you. Just let me know.
I hope all this is a little bit of help...
Pat☺

 

Hi Pat, thank you so much for the detailed instructions.

So I put the jumper in the 2 ports as instructed, turned the key to the on position while my son had his head down by the gas tank, and nothing. We reversed roles, and I did not hear anything either.

So is this a pretty clear cut case of a bad fuel pump? I'm thinking since you said the jumper bypasses all of the safety mechanisms, the issue will not be any fuses or such?

 

IMHO, yes, that indicates the fuel pump has gone south on you, UNLESS: You need to verify one thing. That you have battery voltage at the test connector's B+ contact, and that it can be felt back at the top of the fuel tank, where the wiring goes down into the fuel tank. There's two connectors on the device on top of fuel tank, called the fuel pump hanger, that the fuel pump is hung from, and dangles down into the tank. Removing this by taking the screws out from around the outside will permit removal of both the fuel pump, AND the fuel level sensor, the sensor that sends the amount of fuel in the tank information to your gauge on the dash board..
They are both under a gel looking protector. You can easily lift it up with the meter lead's tip, and slide you multimeter's probe tip under the gel to the metal of the contact to check the voltage. It should read something close to what you read directly on the battery terminals. One of the wires is the battery's positive voltage, the other goes to the frame for ground.
IF you have battery voltage on the B+ terminal of your test connector, you should have it on one of the wires on top of the fuel pump hanger. If not, you have a broken wire someplace, and you need to start following the wire to find just where it might be broken. Easiest way to do this is to split the system in 1/2, and test the two halves. For example, let's say the wire goes to a plug in the cab, and from there, to the test connector. Unplug the plug, and read the voltage on the wire going back to the fuel pump. If you have voltage there, but not at the fuel pump hanger, you have determined that the back half of the wire is broken somewhere.
And, to be honest, that can be a problem. Where the bundle of wires going into the cab, from the rear of the truck, enter through a hole in the floor, they can rub, and rub themselves apart. There's supposed to be a rubber grommet in the hole to prevent this, but it can get old, brittle, and fall apart. This leaves the wires free to rub on the metal edge of the hole.
Having said al that, I would really tend to think your fuel pump is bad. I can put up the how-to on removing and replacing it, if you need.

If you want/need I can post pictures and so on from the FSM. Bear in mind, a decent multimeter is an incredibly helpful tool for troubleshooting most problems. If you don't have one, I strongly suggest getting one. Harbor Freight carries several, or they are easily found on-line. Just look for Multimeter.

I wish you good luck on your trouble!
​​​​​​​Pat☺

 

I thought I read that either the tank has to be dropped or the bed removed in order to access the fuel pump. Is this not the case?

I will definitely check for any worn or broken wires once I find where they are routed.

Instructions / pictures would be great as I think I will have to try to tackle this myself.

Thank you again!

Rob

 

With the pickups, yes, you either have to remove the bed, and/or drop the tank to try and check the connections on top of the fuel pump hanger. Or to replace the fuel pump. It make's life a bit tougher on the pickup owners. One reason I haven't bothered to replace the fuel level sensor. My P/U's fuel gauge reads normally, down to 3/4, then drops to the bottom, and stays there. Pretty sure it's the sensor in the tank.

I don't have the time right now to post up the instructions (I'd have to find them first, is what would take me some time), but I will get them posted for you ASAP. May be tonight or tomorrow. Hope that's acceptable. I'm doing my best for ya

Good fortune to ya!
​​​​​​​Pat☺

 

Thank you Pat!

Instructions would be great.....at your leisure, no rush at all.

Thanks again. I appreciate all of the help.


Rob

 

Great info Pat, thanks! I've got the exact same issue and have top replace my fuel pump as well.

S/F! Mike