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Chevrolet S10 4x2: 98 chevy s10 2.2 4 prong relay. No power

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98 chevy s10 2.2...
98 chevy s10 2.2 4 prong relay. No power to fuel pump on grey wire at fuel pump relay. I have 12 volts on dark green/white wire from pcm to relay with ign on, I have 12 volts on orange wire to relay, constant. Looking at the bottom of the underhood fuse block where the fuel pump relay is theres only the three wires, orange, dark green/white, and grey. How come there is no ground wire to the relay? Is the relay grounded inside the fuse block? Why do i have 12 volts where it seems ground should be? The relay will not energize but the pump will come on and run if i jump the relay. Also my headlights will not come on at all unless I jump the relay at hdlp relay or the ground relay. Im thinking theres a shorted groun in the fuse block or something else isnt grounded.
Submitted: 6 years ago.Category: Chevy
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Answered in 9 minutes by:
11/30/2011
Chevy Mechanic: Tim's Auto Repair, mechanic replied 6 years ago
Tim's Auto Repair
Category: Chevy
Satisfied Customers: 16,171
Experience: Have owned a repair shop for 25 yrs.
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hi

it sounds as if you may have a bad pcm[computer] here....the ground is the green/white..you should get a ground signal on this wire from the pcm for 2 seconds when you first turn the key on,..and a constant ground when the engine is turning...,this activates the relay...the gray is the hot o the pump after it is activated..the orange is the hot to the relay...if you have a bad pcm,this may also be the reason for the light problem

thanks

Please ACCEPT my answer by clicking the accept button, so I can get credit for my work.i don't receive commission unless you do ..I'm not always going to be giving you good news,so please don't let this stand in the way of you accepting my answer.it does not cost you more money.we will still be able to communicate.please understand,i can not see,hear or touch the vehicle and only know what you tell me. Bonuses and positive feedback are appreciated!if you are not satisfied with my answer,please do not leave bad feed back,i will gladly opt out and let another expert handle the question.if i have sent any diagrams,please print them.they will only stay on here for an hour or so...sometimes you may need to right click the image,then save picture as]to save it to your computer so you can open it with your picture program...PLEASE ASK IF YOU NEED MORE HELP

 

1998 Chevy Truck S10/T10 P/U 2WD L4-2.2L VIN 4
Powertrain Management Diagrams, Electrical: Fuel Delivery & Controls, Fuel Controls
46_gc98stbok_6-595.png Wiring Diagram
1998 Chevy Truck S10/T10 P/U 2WD L4-2.2L VIN 4
Powertrain Management Diagrams, Electrical: Fuel Delivery & Controls, Fuel Level and Fuel Tank Pressure Sensor
45_gc98stbok_6-594.png Wiring Diagram
Please ACCEPT my answer by clicking the accept button, so I can get credit for my work.i don't receive commission unless you do ..I'm not always going to be giving you good news,so please don't let this stand in the way of you accepting my answer.it does not cost you more money.we will still be able to communicate.please understand,i can not see,hear or touch the vehicle and only know what you tell me. Bonuses and positive feedback are appreciated!if you are not satisfied with my answer,please do not leave bad feed back,i will gladly opt out and let another expert handle the question.if i have sent any diagrams,please print them.they will only stay on here for an hour or so...sometimes you may need to right click the image,then save picture as]to save it to your computer so you can open it with your picture program...PLEASE ASK IF YOU NEED MORE HELP
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Customer reply replied 6 years ago
This is the third PCM in the truck and its still doing the same thing. The first PCM read 6 volts or .6 volts cant remember which one, the second and the 3rd PCMs are both reading 12v. Could there be another underlying cause? Also when i turn the ign on the dark green/white wire is constant 12 volts.
Chevy Mechanic: Tim's Auto Repair, mechanic replied 6 years ago

well

the green/white should be your ground from the computer..this activates the relay..other than the pcm,there is nothing else there exept the ignition switch,,that may cause this..you may want o check the wiring harness for damage

thanks

Please ACCEPT my answer by clicking the accept button, so I can get credit for my work.i don't receive commission unless you do ..I'm not always going to be giving you good news,so please don't let this stand in the way of you accepting my answer.it does not cost you more money.we will still be able to communicate.please understand,i can not see,hear or touch the vehicle and only know what you tell me. Bonuses and positive feedback are appreciated!if you are not satisfied with my answer,please do not leave bad feed back,i will gladly opt out and let another expert handle the question.if i have sent any diagrams,please print them.they will only stay on here for an hour or so...sometimes you may need to right click the image,then save picture as]to save it to your computer so you can open it with your picture program...PLEASE ASK IF YOU NEED MORE HELP

Tim's Auto Repair
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Customer reply replied 6 years ago
I disconnected the green/white wire and connected it to ground. I can hear the relay click but im still not getting power to the grey wire. The relay makes a clicking sound but the points arent contacting, I pulled the top off one of my relays so i could see in it. I tried swapping it out with another relay and same thing.
Chevy Mechanic: Tim's Auto Repair, mechanic replied 6 years ago

ok

when the relay clicks on...it sould connect the orange and the gray...the orange is hot,,,the gray gos to the fuel pump........if it is making contact the the gray should be hot

thanks

 

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Customer reply replied 6 years ago
Thanks for helping. Im still having problems though and have a few questions. With the ignition on and the green/white wire connected to ground from the relay. I can take the relay out and stick it back in and the fuel pump will kick on sometimes. Sometimes just tapping on it or jiggling it around will make it come on. The relay will not kick on by itself when I turn the ign to on. Also, when I get the relay to turn on the fuel pump i can pull the hdlp power relay and the fuel pump relay will shut off. These two circuits are not connected at all in the fuse block are they? Should I be looking at getting a new fuse block or do you think this has something to do with the ignition? Its frustrating the hell out of me. Ive been messing with this for a month.
Chevy Mechanic: Tim's Auto Repair, mechanic replied 6 years ago

i must admit..this makes little sense

sense the relay works sometimes when shaking/jaring it..the problem may be your power distribution center.[relay box]..i also dont understand why the computer is giving a hot on that wire,if the pcm is good..the head lights shouldnt have anything to do with this

1998 Chevy Truck S10/T10 P/U 2WD L4-2.2L VIN 4
Fuel Pump Description and Operation, Components: Electric Fuel Pump
Description



DESCRIPTION
An electric fuel pump (2) located in the modular sender assembly is used to provide fuel pressure.

OPERATION
To control fuel pump operation, a fuel pump relay and fuel pump switch are used. When the ignition switch is turned to RUN position, the fuel pump relay activates the electric fuel pump for approximately two seconds to prime the fuel injectors. If the PCM does not receive reference pulses after this time, the PCM opens the fuel pump relay ground circuit. The relay will reactivate the fuel pump when the PCM receives reference pulses.

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Customer reply replied 6 years ago
I dunno what the hell man. I dont understand why theres only three wires hooked to the fp relay going into the fuse block. Is there supposed to be a forth?
Chevy Mechanic: Tim's Auto Repair, mechanic replied 6 years ago

please tell me how and when the truck quit running??

 

 

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Customer reply replied 6 years ago
Long story. I bought the truck off my buddy who let it set for a few years. The fuel pump was froze up in it so i put a new pump in. it ran for a month or so and quit running. I went to put another pump in it and couldnt get it to come on. My uncle said it wasnt getting enough power from the green/white wire so he jumped the green and white wire to an ignition wire so the pump would come on when you turned the key. But this doesnt make sense to me if the green and white wire is supposed to be a ground, but thats what he did... it ran for a while like this but i had to put a new pump in every 5 or 6 months. I think because the pcm runs the pump at a duty cycle and it was just running constant. Im tired of dropping the tank so i installed an inline fuel pump on it using the original grey fuel pump wire and grounded the pump to the frame. the sending unit is still in the tank. I purchased a PCM off ebay but didnt know it had to be programmed to my vin for the passlock. It wouldnt start even with the fuel pump jumped so i left it in the closet for a while. I found a PCM reset/relearn procedure online one day so I stuck the PCM in and i got it to work without having the PCM flashed with my vin. I noticed the headlights wouldn't come on just after that. I ordered another PCM off ebay that they programmed to my vin. I had to do the relearn procedure on that one also. Now im worse off than where i was in the beginning. Fuel pump doesn't work and now my headlights dont work.
Chevy Mechanic: Tim's Auto Repair, mechanic replied 6 years ago

well

the inline pump may not have enough pressure to start this truck,,it must have no less than 42psi at all times.........this sill puts me back to the pcm....you need to use a stock pump here

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Customer reply replied 6 years ago
The truck fires right up and I can drive it when the relay is jumped. Its an msd fuel pump I purchased from jegs. Several other people have been using the same pump online and seem to be having no problems.
Chevy Mechanic: Tim's Auto Repair, mechanic replied 6 years ago

ok

i would think the pcm is bad

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Customer reply replied 6 years ago
Yeah, it has to be something with the pcm. I dont understand why all 3 pcms are doing the same thing though. Could there be something in that circuit that is shorting out the pcm? Is it possible I lost some kind of ground to the pcm and its not able to send the correct signal to the fp relay or the headlights? I hate to buy another pcm only to have the same problem.
Chevy Mechanic: Tim's Auto Repair, mechanic replied 6 years ago

yes..it is possible to have something shorting it out..you do need to check the wiring harness for damage...the pcm should be grounded when it is bolted in

 

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Customer reply replied 6 years ago
The PCM isnt grounded when its bolted in. Its mounted on plastic... Also the PCM is fine. The problem was the fuse box under the hood has a short in it somewhere. I bypassed the fuse block and connected the fuel pump wires straight to the relay and ran a ground wire from the relay over to ground on the firewall. The fuel pump kicked on for 2 seconds to pressurize and its running fine now. The headlight relay lost ground in the relay box. I grounded it by sticking a wire on the ground side where the relay goes, stuck the relay back in, and ran the other end of the wire to the firewall also. This will get me by until I can get another fuse block. Hopefully this will help someone if they run into a similar problem. Thanks for the help.
Chevy Mechanic: Tim's Auto Repair, mechanic replied 6 years ago

yes,,it will help..it is not common for the ipdm to go bad in this model,,,strange,,,,i am glad you got it though

thanks again

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