Fuel pump issue

My Brother-in-law has a 1996 s10 blazer - Started hard one day at work, made it home, would not fire the next morning. He says it spits and chugs with starting fluid, so he thinks no gas - fuel pump. I did quite a bit of reading here and found it could be several other things.
I went over to his apartment and had him turn the key on - no noise at all from the fuel pump. I found a red wire with a connector under the hood on the driver side near the fire wall that I assume is the test wire for the pump. We ran power to it and nothing.

I read this could be a relay or fuse issue? The only relays I could find behind a cover in the glove box. Is one of these the fuel pump relay? There were three in a line, all the same part, so I re-ordered them to see if this would make a difference. We turned the key to on and the pump still did not run.

I don't see any mention of a fuel pump fuse in the owners manual, and it seems if it was a fuse issue the truck would have died immediately wouldn't it?

What do I try next? He is at an apartment and it is very cold in MI right now, so we towed it to my place where it will be in my garage until we get it fixed - help please!

There should be both a fuel pump fuse + relay!

My original OEM fuel pump died suddenly too. We drove to breakfast one morning, and when we came out, nothing. If you cannot Hear the 2 second prime cycle when standing at the gas cap door while someone turns the key, that pretty much tells the story. You can try a fuel pump gage to see if there is any pressure. But the only thing I could suggest is a new fuel filter, which you will need anyway. When you have the old one off, and before you put the new one on, turn the key and see if it pumps anything. It probably won't but it is worth a try. If you do need a new fuel pump PLEASE buy an AC-Delco Delphi pump only.

Where is the Relay? Under the hood, or the ones I found behind the glove box? There is no mention of a fuel pump fuse, but I've seen some posts about testing the ECM fuses.

The relay is behind the glove box, I am pretty sure the one on the left, towards the driver side if I remember correctly. if the relay is clicking after you turn the key your fuse is fine and the relay for that matter too. As for the fuse itself, its on the driver side fuse panel, side of the dash, when the door is open. Its the ECM BATT fuse, I think, its fuse #9, but ECM BATT for sure.

Thanks, fuse is fine and I hear the relay click when I turn the key on. So, that means power should be on its way to the pump right?

If the relay/fuse check out alright chances are its the pump. You can test just to make sure its getting power once you pull the tank down and unplug it. You can probe the connector at that point. Chances are though, its the pump. When you go to pull the tank be careful with the assembly and connections at the top of the tank, they break very easily, and cost a pretty penny to replace. This applies even more for the 4 door versions, as it can be tricky to get to these. Either way, jsut take your time as the plastic can easily break.

Ok, Thanks, sounds like we'll be pulling the tank tomorrow.

Ok, Thanks, sounds like we'll be pulling the tank tomorrow.
Again AC-Delco only stay away from Airtex.

Sometimes one that does like yours, if you can tap on the fuel pump, maybe the fuel tank, a few times it might start working. That worked on my 1st fuel pump that went out and it got me home.

One person said his would do that and he got about 3 more months out of his fuel pump. I did not dare do as he did, I quickly replace mine.

Please, I'm not saying beat on the fuel pump or tank with a big hammer, just tap on it. And it may take several taps.

Had to wait a couple of weeks so he could afford the pump. He had to work till noon today so I pulled it in my garage and got the garage all heated up. I started with the fuel filter, won't budge. I'll let him try it. So I took the plastic cover off the tank, and got one hose clamp loose, can't get the other one.
I got frustrated and took a break, I started looking at the Haynes manual and saw something about testing the connector at the pump. So I turn the key on and the damn pump runs. Started up and ran fine.

Could it have been frozen, it wouldn't run at prior to this. Or is it just going to be an intermittent problem and we should change it now? (I have to add, we are in MI and it has not been above 32 in weeks.

Had to wait a couple of weeks so he could afford the pump. He had to work till noon today so I pulled it in my garage and got the garage all heated up. I started with the fuel filter, won't budge. I'll let him try it. So I took the plastic cover off the tank, and got one hose clamp loose, can't get the other one.
I got frustrated and took a break, I started looking at the Haynes manual and saw something about testing the connector at the pump. So I turn the key on and the damn pump runs. Started up and ran fine.

Could it have been frozen, it wouldn't run at prior to this. Or is it just going to be an intermittent problem and we should change it now? (I have to add, we are in MI and it has not been above 32 in weeks.

I've heard that the pigtail from the fuel pump to the connection in back of the gas tank when the pigtail hooks up goes bad quite often.

I might add, to loosen the connections on top of the gas tank you need to drop the fuel tank down just a bit. Of course you need to get as much gas out of the tank that you can before dropping it down.

We decided to wait, he drove it home and of course it wouldn't start this morning.... Guess we'll be putting the pump in after all. Damn

Jumper the red connector under hood and whaaaap the bottom of fuel tank- pump will most likely come on-- then you can drive it to the repair area and change out the fuel pump-

If above does not work- check the plug in near the tank for melted connector.

The red "pump prime" wire is only connected to the fuel pump when the fuel pump relay is deactivated. Whenever the relay is activated by the ECM, the red wire goes to nothing!

Just an FYI, something to keep in mind when testing the pump.

The red "pump prime" wire is only connected to the fuel pump when the fuel pump relay is deactivated. Whenever the relay is activated by the ECM, the red wire goes to nothing!

Just an FYI, something to keep in mind when testing the pump.

Hate to disagree but actually- I've always seen the red wire (on GMs) to be continuously connected to the fuel pump- the Mitchell-on-Demand wiring diagram shows it connected at the relay in the same terminal as the fuel pump lead. I have often used the fuel pump primer lead to drive myself somewhere when a fuseable link (one that feeds the relay and FP) feed is bad. I also used to install daytime running signals on various GM cars and used the fuel pump primer lead to backfeed as a relay source to determine engine running, not just ignition on. Hook a test light to this red lead and you'll see it is on anytime the FP is running, as a matter of fact, they (test light and FP) will often stay on 2-3 seconds after engine shut-off due to oil pressure bleed down holds the oil pressure switch on till system oil pressure drops below 4 psi.

The tricky thing in your circuit is the oil pressure sending unit switch which sends a 12 volt signal to the fuel pump in parallel to the FP relay. If you have a 3-wire oil pressure sending unit, then this is the case. There are some single wire sending units on particular years.

Just my experiences- always best to study the wiring diagrams when diagnosing....

1992 through 1997, (S&T body GM) use a 5 terminal fuel pump relay. The red pump prime wire goes to relay terminal 87a. Battery voltage is applied to terminal 87 at all times. The fuel pump is connected to terminal 30. When the relay is deactivated, 30 and 87a are connected together. When the relay is activated, 30 and 87 are connected together and 87a is removed from the circuit, (dead ends inside the relay).

http://i561.photobucket.com/albums/ss58/cwhook/ISO_Relay_Fig_11-9.jpg

1998 and newer use a 4 terminal relay with a take out terminal in the underhood fuse panel that goes directly to the fuel pump.

The parallel fuel pump circuit was used from 1992 through 1997, (same ones that use the 5 terminal relay). 1998 and newer do not use the parallel circuit. I agree that the oil pressure switch can keep voltage applied to the fuel pump until residual oil pressure drops, but keep in mind that certain ECM's are programmed to keep the fuel pump relay activated for 2 to 3 seconds after the ignition is shut off to prime the system for the next start.

He got it to start and was able to drive it over and get it bakc in my garage prior to blizzard we got Tuesday and Wednesday.
Last night We drained the 15 gallons of gas he put in it after the "we thought it was frozen" incident and we have the hoses from the fill to the tank disconnected.

I can see three lines on top, there are two with black plastic connectors with little square holes on the sides, are these the pinch to disconnect type, or the type that need the plastic sleeve tool? (1996 4.3 two door blazer)

There is one other skinny line, I havent followed it yet to see where it goes, does one of the brake lines cross over the top of the tank?

Thanks,
Steve

The 5/16" line is fuel return from the fuel pressure regulator and the fitting is round. The clip is released with the "sleeve tool". You can do it with a small screwdriver, but take your time and be careful not to break the fitting.

The 3/8" line is fuel pressure from the pump, it is also round. The clip is released the same way as the return line clip.

The 1/4" line is fuel vapor to the canister. It is a more square shape and you pinch it to release it. You'll feel two sides of the fitting are "checkered", that's where you pinch it.

These lines tend to stick to the module fittings so make sure you rotate each one first to break it loose before you try to remove it. When removing the pressure and return lines: Push them onto the fuel pump module all the way, then release the clip. Then rotate the fitting back and forth while pulling it off. Same program with the vapor line, push it on, pinch, rotate and remove. Before installing the lines, coat the module fittings with oil so the O rings slide on easier, and don't rip or tear. If you coat the fuel fill pipe and vent line fittings with grease or oil, the rubber hoses will slide on much easier too. Use anti seize on the tank strap bolts.... help the next guy out, it might be you!

No brake lines above the tank. The skinny line you see might be the vapor line.

We got it done yesterday. Not a fun job, everything is so heard to reach, and many times working byt feel alone. One of the lines just dd not want to release, my fingers are sore as &^%$ from pinching the release clip. I dont understand why two of the three lines can be released in fornt of the tank and the other one has to be disconnected at the pump either. We were pretty much positive the old pump was bad, so we eventually ended up just snapping the plastic finger off of it instead of disconnecting it.

The pump was held in with a snap ring also, no tapping and turning counter clockwise like the haynes manual stated we had to do.

I missed the post about oiling the lines, I hope he doesn't end up with any leaks. Installation was a heck of a lot easier than removal.

..... I dont understand why two of the three lines can be released in fornt of the tank and the other one has to be disconnected at the pump either.

Al three lines are different diameter so they can't get connected incorrectly. The pressure and return flexible lines are easier to replace than steel lines, and it allows you to drop the tank down to get at the fittings.
[/QUOTE]


....We were pretty much positive the old pump was bad, so we eventually ended up just snapping the plastic finger off of it instead of disconnecting it.

Common practice ;) Much easier to remove the lines when they're right in front of you.


....The pump was held in with a snap ring also, no tapping and turning counter clockwise like the haynes manual stated we had to do......

Aftermarket shop manuals are good for general repairs, that's about it.


....I missed the post about oiling the lines, I hope he doesn't end up with any leaks....

That is a precautionary measure, if they do leak, which they probably won't, you know how to get at them now!

Is the original problem solved?

Yes, the problem seems to be fixed, at least for two days now. Now that I think about it we may have been lowering the tank incorrectly. What I mean by this is we put a jack and a 2 by 6 under the tank and were lowering it straight down. we couldn't lower it very far at all before the lines were beign pulled too tight. This really didn't give us much more room to work. Maybe if we lowered only the passenger side straight down we could get more room without stretching the lines? Or should we have only removed the back bolts on the straps and lowered the rear of the tank only?

I doubt I will ever have to do this again, but this may help for someone else.

Thanks,
Steve

.....I doubt I will ever have to do this again, ....

If you installed an AC Delco or Delphi pump, you're probably right. If you installed an aftermarket pump, ya better think about getting rid of it soon, they don't last ;)