Item Posts    Sort Order

86 vette fuel pump

 
Cartero
I love my Chevy Chevette!
Posts: 14
Joined: 09/09
Posted: 02/11/12 08:07 PM

Just bought this 86,the problem is the fuel pump does not turn on with the ignition,Checked all the fuses and replaced the relay.In the 3 wires at the pump i get dc power at  the red wire but no at the Brown one.Put a voltmeter at terminal D and  E of the relay plug and i get a volt measure for about 3 seconds then back to 0 volts.If i run 2 wires straight from the battery to the brown and black wires at
the pump,it runs fine.Tried to jump the red and brown wires at  the pump but did not worked,nor enough amps i guess.HellllllllllllllP Confused  

Post Reply
waynep7122
I have an SS396 tatoo
Posts: 262
Joined: 08/09
Posted: 02/12/12 12:31 AM

here is a partial wiring diagram for the fuel pump...  i say partial as its NOT complete..

the section is in the upper right.....

86 88Corvettestarterwiring

the fuse powers not just the fuel pump relay..  but one of the outer terminals of the 3 on the oil pressure sending unit..

so the oil pressure sending unit and the fuel pump relay work in parallel.. either can power the fuel pump...

the insides of the oil pressure switch fail.. sometimes get bent when installing the oil pressure switch.. i have one on my desk right now..  that the cap got pulled off by my oil sending unit socket and it shorted out.. eventually causing the fuel pump to run for days.. draining the battery almost to the point of a no start each night..   i will pull the top off and snap some pictures...

you might also have a bad wire connection somewhere between the back of the car and the fuel pump relay or the oil pressure sending unit...

depending on the production date of your car..

you could have a single wire oil pressure sending unit like this...



if you have the ONE wire switch like above.. you will also have a 2 terminal switch like this..




this is the dual sending unit...

the outer two terminals are for the fuel pump circuit.. its totally isolated from  the center terminal...   the center is just for the oil pressure gauge..

 

Post Reply
pepsi1
V-6 Camaros rule!
Posts: 88
Joined: 01/12
Posted: 02/12/12 12:36 AM

Have you looked for a seperate fuel pump cut-off switch. Some guys were doing that to detour the bad guys. If you don't find a seperate switch, why not install one of your own. Just get a power line a HD switch and HD wire and wire it up.It's not hard to ***

Most electric fuel pumps will run when there is NO resistence. If you have a tank full of fuel it's harder for the pump to work....so it won't. Good Luck,,,,,
Thank's
Bob  

Post Reply
waynep7122
I have an SS396 tatoo
Posts: 262
Joined: 08/09
Posted: 02/12/12 12:50 AM

this is the fuel pump relay for an 86...



please be very careful that you do NOT probe or Short the wire to the ECM to either ground or power...

this relay .. unlike almost every other relay used...    has the coil winding grounded. and the ECM sends positive voltage to control it..      short that out..  blow the power transistor in the ECM...   they are only rated for 1 amp...


i could be totally wrong..   i know the relay terminals are lettered.. not numbered.. but i don't have a delco relay in front of my right now..

terminals 1 and 5 are the fuel pump circuit..    orange is constant power from the battery..  the other wire will be to the fuel pump..

terminals 3 and 4... are the control winding..    one of these will be grounded..   the other is the ECM control..   the Dark Green with a white stripe wire is the ECM control wire.. ...


if you have purchased a new relay..    find the old one..    pry the cover gently off it..    this will allow you to view the relay action as you turn on the key..   the relay should be commanded closed for 2 seconds when you first turn the ignition key on..   then not again until you start to crank the engine..   it may stay closed while the engine is running.. or it may open up depending on the oil pressure switch to take over the control of the fuel pump...

this also allows the engine to be shut off if the oil pressure drops..  

Post Reply
waynep7122
I have an SS396 tatoo
Posts: 262
Joined: 08/09
Posted: 02/12/12 12:52 AM

i hope this helps...


the oil pressure switches are usually hidden under the distributer.. really close to the back of the block.. in a horrible spot that if the wires have fallen down.. can easily get pinched by somebody installing the transmission..  

Post Reply
waynep7122
I have an SS396 tatoo
Posts: 262
Joined: 08/09
Posted: 02/12/12 01:05 AM

one last thing.. if you have to pull the sending unit to get at the pump.. you will need to order a gasket in advance.. they are all mangled after all these years... and don't come with the fuel pumps..


 i would also like you to drop a magnet into the bottom of the fuel tank..   yes.. i know its a rubber lined fuel tank.. so rust should NOT be an issue.. but the fuel pump  hanger can rust...   the inside of the fuel lines..      the gas station pipes..

this prevents any rust from getting pulled in through the pump...   also keeps your fuel filters cleaner longer..

make sure to use a strong one....  

Post Reply
waynep7122
I have an SS396 tatoo
Posts: 262
Joined: 08/09
Posted: 02/12/12 11:19 AM

bypass the relay...

or bypass the ECM control of the relay????

you could disconnect the dark green and white stripe wire..   and connect  a wire from a switched ignition source...

this will make the relay turn on when ever the ignition is on..

the first or last pin is the fuel pump.. orange wire is usually constant voltage..    grey wire is usually to the fuel pump..

you could go direct on that wire ...

check your messages to the left of where you log out at...  

Post Reply
waynep7122
I have an SS396 tatoo
Posts: 262
Joined: 08/09
Posted: 02/12/12 11:39 AM

here is a much better diagram for the fuel pump relay

Fuelpumprelaywiring747ecm4


pin A on the relay.. is an orange wire.. constant power...

pin B on the relay is not used

pin C on the relay is the normally open contact.. is connected to PIN G of the aldl connector under the dash board...  or to the fuel pump prime connector.. this allows you to send direct power to the fuel pump with the key off.. for testing..

pin D  on the relay is the control wire from the ECM.. this gets power for 2 seconds when you turn the key on.. and again when the ECM sees the engine is being cranked...  also while the engine is running...

pin E on the relay is the output voltage.. to the fuel pump..

if you notice..  the tan and white striped wire also is connected to the oil pressure switch...  so when the oil pressure is up.. the oil pressure switch can also supply power to run the fuel pump..

there is also on some models.. a HOT FUEL module... i don't have a clue where this is stashed.. it seems to keep the fuel pump running or possibly turns it on for a few seconds when you open the door... so the engine is closer to the proper fuel pressure for easy starting...  

Post Reply
TO TOP