Fuel delivery

Check the voltage on the plug.while someone is trying to start the truck

8.5 volts with switch turned on and while trying to start it.

That's your problem there your pump is 12v should be getting above 12. Did you test the ground also

Yes, ground is good. Even ran a temp wire from battery to pump to make sure. If I am only getting 8.5 volts then where am I losing power? Where do I even begin to check? Possible ECM fault maybe?

You need to do a fuel pressure test on the line

Possible or maybe a brake in the wire.check fuseable links make sure there are good

Ok I will check them in the morning and let you know where I stand. Thank you very much for your input and entertaining my ignorance.

also check your main bus fuse in your panel under the hood, also here is a common one you can do on your own. unplug the map sensor and disconnect the battery for the 30 minute period to reset the computer. then reconnect map sensor and battery and see what happens.

Ok, I'll try that also. Thanks.

No problem.

the pump needs 12v. You have resistance somewhere. Check the relay connections

Electricity is fun if you can understand it. Finding a short is really hair pulling, short of replacing the entire wire. Use a volt meter to see if your getting a 12 volt draw when trying to start the engine. If everything up to the fuse box is good, it is after it leaves the fuse box and connects to the pump. Will the pump operate if there is a block in the gas line? Check the filters.

Ok, I checked all grounds, all are good. Re-set computer tested voltage at the pump and have 8.5 still with switch on and 13.1 while cranking but the pump still will not kick on. The pump still does work when I hook 12 volts directly to it. I hooked a new pump to the harness and it will not kick on until you try to crank the motor nothing when the switch is turned on. I am completely lost here, I have voltage where I should and ground where I should. Whats next?

Fuel lines and filter are free, I hook 12 volts directly to the pump and it fires right up.

I'm not familiar with the new computer hook-ups to all things electrical in the newer cars. Is there a chance the line goes through a computer module that is not sending the correct voltage and or signal to the pump the work? If you directly hook it up by by passing everything and it works, than it stands to reason when the key is turned on and the engine is cranking, there should be power to the unit and it will work. Hook a line from the tank to the frame, independent of the wiring to the pump. Perhaps the ground from the tank is not strong enough to complete the circuit. If the pumps works by hot wiring it, does not when re-connected to the correct wires, than there is either a backward connection, ground is hot, hot is ground, or the circuit is not being complete. Read the instructions on the new fuel pump and make sure it is wired correctly, it is the fuel pump replacement for your year and make of truck. Be careful as your dealing with a tank of gas, and stray sparks can cause intense heat if it goes wrong. Th9nk of electricity as water running. To get to where you want it to go, the valves must be open. In DC circuity, there must be a complete circuit back to the battery, and that is through ground.

There resistance somewhere. Check the power before and after the pump relay. Ive seen the connectors and the relay develop resistance and bring the voltage down. Also bad grounds and any connector

Ever consider the replaced pump relay may be bad? Re-check all the connections on the relay, spray them with either acetone or WWD-40 and hit them with a clean toothbrush to clean all the contacts. It sounds like your dropping voltage somewhere. If the voltage is low, the motor/pump may not have enough juice to function. If your not versed enough in checking for this, my next suggestion is to find a garage that specializes or has someone that is knowledgeable in car electrical issues.

The pump and relay are getting the 12 volts needed. I am well versed in using a multi meter and reading schematics, that's why I am seeking advice from someone that may know of something I am overlooking.

I goggled 1990 Chevy fuel electrical and got a diagram, I'll try to add it to the picture part.

The diagram came through. Hope that helps.

Check the map sensor. everything has to go through the map sensor before going into the main board

I've got the same problem changed the pump fuel filter both of them and pulled the gas lines off to try and get fuel out of them and nothing but will try y'all methods in the mornings thanks

I have seen this happen and it was the ignition switch and or the cable in the steering column. They could start the suburban priming it but it wouldnt turn the pump on initially. Check voltage while pump is plugged in at the plug. Check while turning key etc key check all wiring and connections for resistance dropping the voltage. See if can prime and start and stays running. No dealership was smart enough to find this. Rob Sandera The peoples choice for President

Is fuel pumps will not deliver pressure unless oil pressure is registered from the sending unit behind the intake. If the ECM or PCM whatever you want to call it does not register fuel pressure it will not allow the fuel pump to turn on. If you crank the motor and see no oil pressure on the gauge then you know that is your problem

fuel pumps will not deliver pressure unless oil pressure is registered from the sending unit behind the intake. If the ECM or PCM whatever you want to call it does not register fuel pressure it will not allow the fuel pump to turn on. If you crank the motor and see no oil pressure on the gauge then you know that is your problem

Hi 304brad38: I also own a 1990 chevy 1500K. Had the same problem. After three weeks of no driving and extensive research on my year and model, the problem was with the oil pressure sensor (OPS) located on the block just below the carb. As soon as the new OPS was installed the engine fired up like a champ. The OPS is a safety mech mandated by Feds for safety during front end collisions. When the OPS goes bad or fuel source is shut down, look first at the OPS for it just may be your villain.

Hi 304brad38. I had the same problem with the same truck. After three weeks of no driving, I found my solution. The culprit was my "oil pressure sensor" aka OPS. Truck engineered to shut down fuel supply after head on collision, Fed mandated. However, the draw back to this design is when the OPS is defective or wears out, you're dead in the water because the OPS controls the fuel pump. After installing a new OPS, varoom! old girl fired up like the space shuttle. Fuel flows like great now. Talk about being mad. All the time I spent trying to figure out the problem, finally decided to spend the effort and research the cause. check it out my friend; it's the OPS.

My 95 chevy is not running right if im on the gas just trying to cruise it will for a second but then the truck acts like im not on the gas when i am and i have to gas on it to keep going?????

rundo123453. Sound like a plugged fuel line or filter right off. change the filters and have the jets checked for buildup. If you can, have a computer readout of the fuel delivery system and ignition to make sure they are working correctly. Timing, fuel pressure, etc.

i have the same damn problem with my 1996 1500 4.3-----replaced the tank and pump replaced all fuel lines with fuel hose- replaced fuel regulator- come to find out it was the ground so i drilled a hole in frame and ran negitive from bat to frame to pump--worked for 6 months---now its acting up again sometimes pump kicks on sometimes it dont---

havent multimetered the fuel pump connector yet--but its possible the fuel pump went bad again?---next step checking connector voltage then running 12 from bat direct to pump of course just filled the damn tank with 30 gallons

What type of car and year do you have. Check if this may need a computer rebut to engage it. More and more everything runs through the computer and either disconnecting or replacing may need a rebate to mate it with the existing computer. Just a guess? I know in my GMC Terrain, if I replace or disconnect the battery, it needs to be rebutted to match it with the computer.

GURUZ59BC, recheck the wiring. You may have corrosion or a lose/broken connection. If it is spotty, I'd venture to guess a bad connection or a broken line.

I have a 1991 Shevi suburban 350 four-wheel-drive I thought I had a bad fuel pipe I change the fuel pipe find out the fuel pipe is not bad but I did find was that if the sending unit shows a full tank the fuel pump doesn't work on alright so I took the float off and pushed it down so it shows the tanks empty and then it works on an auxiliary battery but won't stay running. But if I plug it in to the harness nothing. There is no constant power at the fuel pump relay. I need help

ECM

So if I turn my key and I have no movement on my oil gauge my ops is bad

I have a 2004 Chevy Silverado truck I put a new fuel pump in it cuz that wat I think was the problem but my truck will still not start my battery will not all ways hold a charge on it

GuruY58HC, if you battery will not hold a charge, pull the battery and have it tested. If the battery is bad, replace it. If the battery will hold a charge when removed from the vehicle, there is something draining the battery. Make sure all the positive wires are not shouting out. Is the connections clean to the battery hookup? Someone suggested if the bluetooth is not turned off before turning off the engine, it will remain on and drain the battery. (In GMC Terrains) so if you use bluetooth in the vehicle, turn it off before turning the vehicle off. Try that.

ok brad I am dealing with the exact same problem on my 1992 gmc 1500!! im going to work on it today . I am starting at my fuse block. mine has a constant 12 volts to the relay which is an orange wire. should be 12 volts on it all the time. my control wire is a green/white wire this is what trips the relay when being primed and when motor is running. I have a grey wire that comes out of the relay that runs to my pump. in the line there is also a oil pressure cutoff switch which should be supplying 12 volts as well if operating correctly and with enough oil pressure in the motor. I will let u know what I find out and hopefully we can both get this pesky issue resolved!!!

Does the pump run when it is hooked up at all. Ran in the problem of the wires on the pump itself was backwards. Pump turned in reverse

Same problem if you're getting 8.5 volts you're probably checking the gas gauge wire the fuel pump wire is on the side of the connector I followed it down to the pump my connector at the pump was corroded the wire on the side as soon as you turn the key on you get 12 volts then it goes away so you got to check it quick or when the key turns off it turns the pump on sounds like connector on top of your tank is bad if you're putting voltage cheer and the bump is starting up means the tank assembly is good replace or splice this connector

Chevy 1500 no start, fuel gauge sitting at 3 o'clock issue. I found this site easydiagnostics.com, followed steps to check crank sensor, ignition module, coil. With their easy steps I found out it was my ignition module in 15 minutes. Guys I don't know if I'm allowed to give a site out but this site really helped me, check it out. This was after a garage told me it was the fuel pump and they wanted almost $900 to do it, so I had it towed home and had it running in 30 minutes, and only spent $75.

Oil pressure sensor, Chevy put a safety feature on there cars. If the oil pressure sensor is no good the fuel pump will not work, sounds crazy but it's a fact. The feds made them do this.

Everything goes through the crank sensor before the computer, not the map sensor.

Yes if you crank the motor and your gauge does not show oil Pressure then your ops is bad and this will cause the fuel pump to not work.

My engine starts then dies. It seems to get fuel to the carborator jets to prime them but nothing when engine starts. I have a new fuel filter that quickly fills with gas and will change the pump relay. The oil pressure guage has been quite erratic so I am suspecting the ops may be my fuel problem. Is it possible to bypass the ops by shorting it out, crossing the wires, to see if the truck will run?

Does the OPS gradually go to s#*t, or does it just die quickly. I have had an intermittent fue; loss issue, eg. truck just dies after a minute, sets for 30 seconds, then fires up again. Last week it did this 3 times during a 4 mile trip, and now it’s just not getting fuel to the carb. Filter, pump and sending unit replaced 1 week before total shut down .... any help would be greatly appreciated.

I just had the same exact problem and finally figured it out. 1990 gmc sierra 1500 5.7l tbi. Crank no start. After finding that the fuel pump fuse was blowing every time I turned the ignition on and tracing wires all day I finally pulled the pump and to my surprise I had a short in the tank at the float. It was burned up causing a hot to ground. What I did was wired a jumper from the 2 little torx screws at the top and bottom of the float switch, broke the float and tied it at 3/4 full. Bench tested the pump. It was good. Jumpered the fuel pump relay and tested voltage at relay then at tank connection. Both tested 12v. So reinstall pump assembly and checked the tank ground. Turned the ignition and pump kicked on. Fixed it. Only problem now is no fuel gauge but I can live with that for a while. It was a real pain guys but thank you all very much for your tips they all helped me so I thought I should share and help someone to. Hope so.

Find the emergency shut off switch that will be it

8.5 V is likely the line that communicates the fuel level to the gas gauge in your instrument panel . Try the other sure. In my S10, grey is 12 V power from FP Relay to FP, purple is resistance signal from Float to Gas Gauge.

Have you checked the oil pressure switch (not the sending unit sensor if it doesnt sense oil pressure the fuel pump will not run its located near the distributor

My Silverado fuel pump gets juice from both the ops and the fuel pump relay . I'm wondering if they work all the time. It's a diesel that can run on the injector pump alone. 8.5 volts is weak.

So many different things can be the problem with such an issue. UGH. So frustrating. Yet another "simple" thing that no one mentions - BAD FUEL. If you let your fuel level almost run out, then you filled up at a "questionable" gas station - it is very possible you purchased 20 or so gallons of crappy gas. Has happened to me before as well. Especially if your truck was running perfectly fine until this occurred. Just a thought. Don't eliminate BAD FUEL from the equation. It has happened. Also, simple things like the fuel filter. If it hasn't replaced in forever, replace it. It is very easy to do, and not expensive. Mine looked very old on my 1990 Chevrolet K1500 5.7 truck. (in 2020). And you would not believe what poured out of my old fuel filter - almost BLACK looking solvent-smelling liquid. EVEN THOUGH my fuel was new. Just filled up a couple of days prior (at a questionable non name-brand gas station.) But the odd thing is, the fuel in the gas tank looked and smelled "normal." Replaced the fuel pump, sending unit - did not resolve the No Start problem. Did all sorts of common old school "tests" to ensure spark, fuel, etc (compression is good.) and what got my truck running again was to simply pour a little fuel straight into the throttle body, truck fired up, was sounding rough, kept it running, it eventually cleared up and idled normally. Mind you, this truck had NEVER shown this issue before. Never. It always cranked right up, ran fine. This issue appeared ONLY AFTER I FILLED UP WITH QUESTIONABLE FUEL. So, before you go tearing into everything else (including your hair,) consider two simple and obvious things - related wiring, fuses, relays, old fuel filter and/or bad gas in the tank. IT'S POSSIBLE!

I have a 1990 1500 chevy truck. The fuel gauge does not read the gas. I thought it was the fuel pump so i replaced it and still, the gauge does not read the gas.

If the fuel pump is not the problem, it could be the ground wire going to the trucks computer. Or it could be the fuel gauge itself. It is not that difficult to replace just the gauge. You don’t have to place the entire cluster. The good thing about these trucks as you can replace each individual gauge pretty easily. Well you have to take apart most of the driver side dash to get to it. But you can do it. I’ve done it several times to my 1990 K 1500

I know this is an old post, and I have not read all comments, but I'll out this here in case it helps someone else. I had the same issue. Put in three pumps in 3 months. Finally tracked it down to a faulty ignition switch. Replaced the switch and all has been perfect ever since.

I have a 1992 that has shorted out fuel pump and relay have tried everything still don't know what is going on

My 1993 Blazer Silverado K1500 bogged down at a light a couple of days ago and then would not get up to 60 MPH on the freeway. I'd press the gas peddle and no acceleration. Got off the freeway and drove fairly well on side streets to home. Does a fuel pump relay ever flake out intermittently? Replacing the pump looks to be a PINA project, but I do have tools and some skills. My baby does have 218K miles and I love it. Any input is appreciated.

possibly need to look at the oild pressure switch ,when hooking up new not original equipment direction is given to use a 3 post oil switch so the pump only works when engine is calling for fuel, therefore the reason it will work with direct power ,so with original equipment perhaps you need to replace the factory oil pressure switch as in the harness there should be a wire from it to switch and then to pump ,maybe worth a try

I ran into same problem, the Problem was the plastic connectors themselves that the wires run into from the fuel pump if you will take those two plastic ends off that connect together about 3 ft away from the gas tank and just hard wire the wires together then your fuel pump will work I bought a brand new fuel pump and it wouldn't work either and I got to play in with the connectors where you plug them in together and I would hear the pump go on but then when I would let the connectors go it would go off so I took the connectors off and just hardwired the wires together and the pump started working

93 Chev K2500, 5.7L. been sitting 3 years. New battery, cranks but no start. Engine started with Starting fluid, so has spark. Unhooked fuel line from TBI & it's dry. Fuel pump fuse is good. Bench tested Pump Relay and it actuates, but not sure if it does when installed. Will investigate OPS, but I thought that was a safety issue that kept the truck running if Relay failed. I didn't think it would prevent starting. And yes, tank is 3/4 full, and had stabilizer in it when parked. There has not been any service on fuel system prior to parking. No critter damage that I can see, either (live on a farm). What direction should I go next?