Hey guys, I need all the help I can get. I have been over and over this truck.

Inital Problem: Truck wouldnt start. When I turned the key on I couldnt hear the fuel pump prime.

!st try at fixing it: I waited a week and thought "hey maybe my fuel gauge isnt working" so I added a couple gallons of gas and it started up. I figured that was the problem. Truck ran fine for a month.

Seconded time: Drove truck to the store, came out to start it after shopping and same thing, I couldnt hear the fuel pump prime, the engine would only turn over. So I towed it home.

2nd time trying to fix it: I figured fuel pump must be going bad and I dropped the fuel tank and pulled the pump out. I took the fuel pump around to the front of my truck bolted the ground wire to my negative terminal, and ran a jump wire from the positive terminal to the power wire on the fuel pump and it cranked up. So I figured the fuel pump must be fine and maybe its ground was bad. So I cleaned and sanded the grounds connector and the contact area on the frame and put it all back together. The truck fired right up, and I could hear it prime before I started it like its supposed to. SO I THOUGHT IT MUST HAVE JUST BEEN THE GROUND.

Third time: the next day my mom drove the truck to work with no problems....until she went to go home, she got in and it wouldnt start. She said she didnt hear the pump priming. I got a ride down to her work and brought a long peice of wire. When I got there I confirmed the fuel pump wasnt priming, so I ran a wire from the positive terminal through the inside of the truck out the back window, cut the fuel pumps power wire between the connector and fuel pump, and connected my new wire to the fuel pumps power wire. The pump started hummin and the truck fired up, and I drove it 45 miles home.

3rd try at fixing it: I figured it must be the fuel pumps relay. So I found the relay on the drivers side on the firewall mounted with the a/c relay (I belive). I noticed and confirmed with the Chevy parts dealer they are the same relay ( A/c relay and fuel pump relay) so I swapped the a/c relay for the fuel pump relay to see if maybe the relay was just bad. Well I turned the key over and the fuel pump started hummin and the truck fired right up. My dad came down and said "are you sure it not just magicaly starting again" and told me to put the relay I thought was bad and confirm it wouldnt start, so I did that and it wouldnt start with the original relay back on. Thought it must be just the relay, and went to put the a/c relay on so I could drive down to the parts store and buy a new one, but when I did this it wouldnt start again, no pump priming........Nothing. Figuring maybe I blew the a/c relay some how I ran a wire through the truck again and attached in the back to the fuel pump by the connector again and when I do this the pump starts humming and the truck starts. So I dorve down to the parts store and bought a new relay, detached my jump wire I ran through the truck and I get no humming, no starting.

I have also attached a jump wire to the test wire by the trans dip stick and get nothing.

Sorry this post is so long, I am not a mechaniac and didnt want to leave any details out that may give the problem away. One more little detail, I live right outside sacramento Ca. and its been cold latley, seems this all started on a cold day in Novemeber, but not cold enough to freeze the fuel if thats possible.

Any help or advice would be appricated. This is my only vehicle for me and my wife and kids, and I am so exhausted trying everything to fix this. Everytime I think I have fixed it and it runs the pump quits pumping. I hope my post is clear, its been a long cold day working on the truck.

 

Did I miss something or is there no year, make or model to this. But some old body styles(83-94) used to have sending unit issues-sounding similar to this. The newer ones that have pump and module all in one(96 and up)-haven't as many sending unit issues as the first design.(my experience) This may be a first generation based on where this is posted but....who knows. JP

 

Your right, I forgot that.....Its a 1993 chevy blazer 4wd with a 4.3ltr.

So a sending unit you think....is there anything I can to confirm that? Any tests I can try?

 

A couple of things before you jump to dropping the tank(again). If/when it fails-no pump hum at all? If that's correct...on a 93 the plug to the pump should be up behind the rear bumper, near the license plate light. Two wire(gauge and pump-the ground is two wires not clearly visible at this point-with tank in place). Probe these two wires with either a multimeter or you can do it with a 12v test light. When it fails, one of these wires should have 6ish volts constant to it, the other 12 volts for 2 seconds key on to prime. Have someone help you if possible as by the time you get back there the 2 second prime signal is history. If alone there are creative ways to do but a partner is best. Keep in mind that the gauge wire is a 6 volt signal-constant and will only half light a 12v test lamp. We/you need to see when this thing fails whether the issue is from this plug back of from here forward. It's possible that removing the pump the first time-it got bumped and started working again. At this point although not 100% sure of your problem, I am suspicious of either the pump/sending unit. If that pans out the good news is that they are no where as expensive as the units in a 96 up. But....there is a remote possibility of something else...example-the oil pressure switch is tied up into this circuit but rarely fails(although possible-not probable). Also had one once with a wiring problem between the relay and the rear of the truck. This will show, though, when you check for your 12 volts a key on. Keep us posted. JP

 

another thing to consider (but I wouldn't do this unless you end up having to drop the tank again) on my 1st gen as well as a few other 1st gens i've worked on the wiring inside the tank (from sending unit to pump) gets broken inside the insulation first time i ran into this it took me days to figure out the problem (continuity tester found it) these short wires are readily available at napa for very cheap ($15-$20 iirc).
Definitely do the other tests JP posted first and if dropping the tank becomes a necessity look at these wires (i'd advise replacing em along with the pump just to be safe if you end up having to replace the pump).

 

def sounds like its ur fuel pump. just happend to me not that long ago. how many miles do u have? cuz it is very common on all GM vehicles for the fuel pump to go around 150k mi. just my fuel pump went but when i went to drop the tank the lines were all rusted and corroded and they twisted so i had to get a new sending unit. its kinda a PITA to drop and install the tank. its prolly just better to get the sending unit since u have to do the pump any ways so u dont have to drop the tank again. if u go to buy both the sending unit and pump buy them as seperate items cuz then its only like $130 instead of the $300 package of both of them together. other than that its not bad. just take the old sending unit and pump w/ u when u pick up the parts to make sure its the right one. they gave me the wrong one the first time.

 

Your jumper wire is clever. Wish I would have thought of that. Kind of works the same as a blower motor.
Slick.
Its in the vault now.

 

A while ago I posted on here with suspicions that the problem with my truck not starting was the fuel pump. I have a 1993 chevy s-10 blazer 4X4 with the 4.3ltr.


Since this I have installed"
new fuel pump with bottom filter, and sending unit, new wires also from pump to rear connector.
fuel pump relay
$100 battery

I replaced the fuel pump the truck ran and started for 1 day before it wouldnt start again. It would turn over but not start. I also wouldnt be able to hear the fuel pump run either.

Then I replaced the relay and that didnt fix it.

Then the battery, and that fixed it for a few months.

Now it wont start again, turns over fine but I cant hear the fuel pump kick on.

I have replaced the fuel pump module again and still only the engine turn over and I cant hear the fuel pump puzz.

I bought a computer code reader, and disconnected the negative trminal to get the "hard Code" and it gave me a code 12 [Diagnostic mode; no distributer signal electronic control module; System Pass]

Can anyone please help me out on this, I have tried everything I can think of seem to fix this. I also dont understand what to interpet that code's meaning.

Any idea's?

I really appricate any help, while im at work this is the only vehicle my wife has to use for her and the kids. I also cant afford to take my truck to one of these California rip off Mechaniac shops.

 

I have combined your two threads to make it easier for folks to see what you have done on this matter.
The '12' code you get means that the diagnostic system did not detect any fault.

 

thanks riddle. So what does that mean if it didnt detect anything? Would it detect a shorted wire?

Is there items the diagnostic system wouldnt detect?