Fuel pump works...then doesn't.. then does...then...

[mudpie]

I know, lots of fuel pump threads. I read through them, including a few of my old ones. I just want to verify a couple things before I pull the bed, again.

I put a Delphi pump in maybe 4 years ago. Had an issue 2 years ago that turned out to be the relay, and no issues since. Left the house yesterday, realized I was very low on gas and headed to the station. Made a stop along the way, shut the truck off, and it wouldn't restart. Pulled the relay, jumped terminals 87 and 30, and no fuel pump. I borrowed a car, went and bought another Delphi pump, got back and the truck started. Drove it home and put 5 gallons of gas in it that I had for the mower, and decided to replace the pump today. The truck seems to run fine today though.

At this point I'm assuming the fuel pump overheated because it was low on fuel, and started once it cooled down. Is that a fair assumption, or am I missing something? I've never run it out of fuel, but I've run it very low, and done it several times in the past 6 months or so with fuel prices the way they are. I tend to put 30 bucks at a time in it when it's low rather than keeping $150 worth of gas in it. i would think though that the cooling effects of fuel would work from the inside out as the fuel passes through the pump and all the parts that move, even if the body of the pump is not entirely submerged, but obviously I could be entirely wrong.

Should I assume that this pump is now living on borrowed time?

 

[strikk]

My pump had a poor ground wire to frame rail. It wasn’t allowing full amperage to flow through the circuit. It would run and not run seemingly at random.

The ground for the fuel pump is located on the driver frame rail near the full tube location. Make sure it’s clean. And make sure the wires are in good shape under there

 

[454cid]

I think the whole low fuel, over heats the pump is a myth. Maybe it was true at one time? Our pumps, and I believe most are made this way, put the actuall pump motor in a plastic bucket that stay full of fuel unless you really run out of gas. There could be an inch of gas in the tank, but that bucket stays full.

Next time your pump wont run, grab a rubber hammer and hit the tank on the bottom, right where the pump is, and see if it gets it going.

 

[mudpie]

Five years I've had this truck, and replaced a few regular maintenance items like brakes, starter, alternator, no big deal. But the one thing that makes me want to light it on fire is whenever it decides it's going to have some fuel issues, because the truck is always like, hey, maybe I'll run, maybe I won't, and just when you think you got it figured out I'll magically heal. It's like a truck from a Stephen King novel.

So it started today and ran fine, so I went out to run some errands. Parked, came back, and it won't start. Pull the relay, put in the jumper wire (that I now carry with me all the time), and it starts fine. Put the relay back and it won't start. OK, so I've narrowed it down to the relay, which has a lifetime warranty from O'Reilly's. Put the jumper back in, drive to O'Reilly's, shut it off and just for kicks put the relay back in and it starts right up. It then ran fine the rest of the day.

There doesn't seem to be any rhyme or reason to how or when it's going to die, and what's going to get it going. I was convinced it was the pump, then I was convinced it was the relay, and both times the condition that made me think that was temporary.

Only thing I can think of, and it's probably a long shot, is the relay connections. One of my errands today took me to Pick-n-Pull and I checked a few other Chevy's for relays. When I pulled them out they seemed much tighter in the socket than the one in my truck. Maybe it's just not making a tight connection? I don't see any corrosion or signs of arcing on the relay contacts that might indicate a loose connection, but I'm kinda at my wits end and grasping for straws.

I'll check the ground, but last time I put a fuel pump in I made sure that connection was solid. Been 4 years though, but I'm in the PNW, so we don't have issues like rust or road salt that cause electrical issues.

I appreciate the suggestions.

 

[1998_K1500_Sub]

Only thing I can think of, and it's probably a long shot, is the relay connections. One of my errands today took me to Pick-n-Pull and I checked a few other Chevy's for relays. When I pulled them out they seemed much tighter in the socket than the one in my truck. Maybe it's just not making a tight connection? I don't see any corrosion or signs of arcing on the relay contacts that might indicate a loose connection, but I'm kinda at my wits end and grasping for straws.

You can always check any connection by measuring the voltage drop across it, e.g., using a DVM. Ditto with the relay's connections and internal contacts.

Just offhand, IMHO more than .1V drop across the entire relay assembly would be suspect, considering the fuel pump's not drawing much current (~5A).

Get a DVM and start making measurements, you may be surprised by what you find.

Also check the voltage drop on the wires to and from the pump. Water can find it's way into the wires and cause oxidation, which in turn increases the resistance of the wire and, thus, the voltage drop.

 

[Erik the Awful]

You may have more than one issue, but you know the relay is bad. Chuck it. Relays can absolutely act intermittently. They're electro-mechanical devices, and when the contacts get old they can get sticky. The poor fitment may or may not be related.

I just ordered a new contactor (aka relay) for my home A/C because I had to use a screwdriver to push it on, and now it hasn't shut off in over a week. Ugh. Still, better than the $5000 the heat and air guy quoted me to replace the entire system instead of just fixing it for a $15 part and a service call charge.

 

[Schurkey]

Pull the relay, put in the jumper wire (that I now carry with me all the time), and it starts fine. Put the relay back and it won't start. OK, so I've narrowed it down to the relay,

No, you haven't.

You may have more than one issue, but you know the relay is bad.

Mistake in logic. The relay MIGHT be bad...or the ECM and it's wire harness may not be triggering the relay. A faulty ECM might not send the power to the relay to turn it on; or the wire harness may not pass current to the relay (or from the relay to ground) causing it to not turn on. And of course, either could be intermittent.

Without diagnosis on the trigger side of the relay, there's no guarantee that the relay is defective.

 

[mudpie]

No, you haven't.

No, clearly I haven't. If I had, my truck would be running without issue and there would have been no need to post this thread. As I mentioned, when I went to the parts store to get a relay, I put the relay back in and the truck ran fine, clearly indicating that it wasn't the relay, but you wanted to grab that little tidbit to scold me on my roadside diagnostics. Thanks. Similarly, when I posted for brake help a couple weeks ago you decided to give me a lecture I didn't need instead of helping answer the question. I don't need lectures, and I don't need scolding, so I'd appreciate if you could just step out of this thread.

 

[mudpie]

Can somebody tell me how these pins come out please. There appears to be a little plastic tab that holds them in. First one seemed to just fall out, but the other 4 drop about 3/4 of the way out when I release the tab, but they won't come out completely

 

[Erik the Awful]

Don't be so fast to push Schurkey away. Yes, he can preach, but he knows his stuff.

@Schurkey, yes, it might not be the relay, but my rule on relays is "when in doubt, throw them out". They're electro-mechanical. The fact that it's intermittent points more towards the relay than it does the ECM. Troubleshooting sticky relays sucks, and I err on the side of replacement.