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jazzmaster
jazzmaster, ASE Certified Tech
Category: Buick
Satisfied Customers: 2951
Experience:  ase certified
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We have a 1985 Buick Century Limited (vin E) 3.0L carbureted

Customer Question

We have a 1985 Buick Century Limited (vin E) 3.0L carbureted engine. We have had fuel delivery problems for some time. So far we have replaced the fuel pump with sending unit and the fuel pump relay. What we are experiencing now is the engine will start for a few second then stall. The way we understand the system is that the relay starts the engine and that the relay switches over to the oil pressure switch to keep the engine running. What we are seeing on voltage is dropping from 12v to 3v when the vehicle switches from start to run thus no fuel pressure. Please help we are a our wits end.
Submitted: 1 year ago.
Category: Buick
Expert:  K. Wiggins replied 1 year ago.

Hello, where are you measureing the voltage at?

Customer: replied 1 year ago.
There is a test lead just off the fuel pump relay that goes to the pump . When the key is in start we have 10+ volts and after it's running it's at 3+volts.
Expert:  K. Wiggins replied 1 year ago.

Thanks, that's after the oil pressure switch. With key on in start the voltage is coming from the relay.

To test if the oil presure switch is bad you can unplug it and use a sumper wire from the pink and black to the tan and white wire. I'll post the wiring diagram below. Let me know how things go with the test.

Expert:  K. Wiggins replied 1 year ago.

Sorry meant jumper wire

Customer: replied 1 year ago.
We have jumped the oil pressure switch connector with the same results. We have 12v from the fuse through the connector and up to the relay but once the engine goes form start to run the voltage drops to 3v.
Expert:  K. Wiggins replied 1 year ago.

Thanks, ***** ***** pump being new that has me stumped as well. Let me open this back up to other experts, someone should be with you shortly.

Expert:  jazzmaster replied 1 year ago.

hi, do you have continuity from the fuel pump prime to the fuel pump ?

Customer: replied 1 year ago.
I don't know if this has anything to do with what is going on but can somebody explain the reason behind the 2 wires coming into the fusible link before entering the relay. I know 1 is coming from the starter is the other coming from the ignition switch.
Customer: replied 1 year ago.
Where is the fuel pump prime?
Expert:  jazzmaster replied 1 year ago.

the fuel pump prime is that tan/white wire ,it comes from or near the fuel pump relay wiring .it has a connector end on it ,

or you can check from the fuel pump relay the tan/white wire ..to the fuel pump ..

Expert:  jazzmaster replied 1 year ago.

that I dont think is a fusible link but a joint connection for the relay -fuel pump prime and the wire going to the fuel pump

Customer: replied 1 year ago.
That is the wire we have been using to check the voltage. We have been getting 10+ volts there in start and only 3+ volts in run.
Expert:  jazzmaster replied 1 year ago.

I know ,,on the pink/blk wire that goes to the oil pressure switch ,does that stay a consistant 12 volts or battery voltage ...

Customer: replied 1 year ago.
with the oil pressure connector jumped it's 12v to the relay.
Expert:  jazzmaster replied 1 year ago.

when the oil pressure switch is jumped the voltage goes directly to the fuel pump as well.,so at the fuel pump with the presssure switch jumped does the voltage change too

Customer: replied 1 year ago.
it's only 3 volts.
Expert:  jazzmaster replied 1 year ago.

so with the key in the rum position and not running the voltage is 3 volts ?

Customer: replied 1 year ago.
the engine will start with the little bit of fuel it's pumped in start but will die after it's gone into run mode.
Customer: replied 1 year ago.
only 3 volts in run
Expert:  jazzmaster replied 1 year ago.

it only shows 3 volt key on/engine off at the fuel pump ?

Expert:  jazzmaster replied 1 year ago.

also, at the fuel pump relay the pink/white wire does that show 3 volts

Customer: replied 1 year ago.
Ok, here's what we have done. First there is no pk/wht wire. We have checked voltage at the exit of the red fusible link at the pump relay engine in start with 10+ volts. We have the same voltage at the tan/wht wire at the pump prime connector and the engine will start but only run for a few seconds because the carburetor runs out of gas after the ignition key is in the run and the voltage at the prime connector is only 3 volts. We measured the voltage at the brown wire before the oil pressure switch KOEO showing 12 volts. We jumped the switch connector and had 12 volts at the tan wire but only 3 volts at the prime connector. Is it possible to be losing the 9 volts in the pump relay connector? I ohmed out he relay on the oil press side with no loss.
Expert:  jazzmaster replied 1 year ago.

ok, I was going by the other persons wiring schematic.

I have mine up and I see the right colors ..the wire coming from the fusible link into the relay ,does that show battery voltage in the start position ?

and if you jump a hot wire to the fuel pump does the car now run ?

Customer: replied 1 year ago.
Ok Jazz, we have 10+ volts at the fusible link in the start position. I'm going to run a jumper from the brown wire, on the hot in run, to the tan/wht pump prime connector going to the pump. I'll let you know.
Expert:  jazzmaster replied 1 year ago.

ok,thanks ..jazz..

Customer: replied 1 year ago.
Ok, with the jumper wire installed the engine ran without stalling. Now what we need is, what do we need to fix this so all the connections are back to OEM and the engine will run. There must be something that has to be replaced.
Expert:  jazzmaster replied 1 year ago.

you haven't changed the oil pressure switch ?

Expert:  jazzmaster replied 1 year ago.

what are the colors at the fuel pump relay ?

Expert:  jazzmaster replied 1 year ago.

I want to make sure we have the same colors

Customer: replied 1 year ago.
Ok, we have changed the oil pressure switch. Our problem has been that once the engine starts and switches over to run, the voltage out of the relay on the tan/wht wire drops to 3 volts but it's reading 12 volts on the tan wire going into the relay. The wire colors going to the relay are red fusible link, black ground, tan in from the oil press switch, tan/wht going to the fuel pump and a ppl that loops in the relay connector. I asked this before, but can the connector we have to the pump relay, which looks like something has melted on the wires input side of the relay, cause the voltage drop to the relay when it switches to run position? Also it's 2:30pm here in Nevada. What time are you closing for the holiday?
Expert:  jazzmaster replied 1 year ago.

that purple wire should be hot in the start position ,as far as a relay should work ,then once the oil pressure takes over or reaches around 4-6 psi then the circuit is run through the oil pressure .

I think the fusible link is bad ,you should measure the voltage coming out of the fusible link ,if fact both sides of the link when in the start/crank position ..that may be where you are losing the 12 volts needed ..

Expert:  jazzmaster replied 1 year ago.

If I helped you please rate me positive and we can still continue on if needed ;

this is the only way I receive credit ,,thank you ...jazzmaster .