View Full Version : Fuel pump issues :(
06-13-2009, 08:36 PM
Car has been sitting for a while.
Changed the engine harness with a good one, had some starter issues for a while, but now its just the fuel pump.
Not pumping anything.
I ran a hose directly from the pump to a bucket. Turned it on and nothing.
I had 2 spares so I swapped each in and same result, not fuel.
Checked the voltage at the wires at the pump, got some weird results.
Off, I get about 0.3V
First ign spot - 1.5V
Run - 3.5V
Start - 4.6V
I'm pretty sure I should be getting 12V or close to it.
Anyone know what will cause a no pumping condition?
I'm pretty sure my crank and spark sensors are hooked up right.
ideas on why I'm getting these voltages?
I dont have my bentley handy here.
06-14-2009, 12:17 AM
06-14-2009, 02:01 AM
fuel pump relay is something that very often goes bad. first off, swap the two orange relays by the AFM (under the black cover) and see if it improves. if so, replace the defect relay. (I think this is your problem.)
If you get the same result, measure V at the fuel pump relay harness. If you get voltage there, say on pin 30 is 12V, try jumpering pin 30 to pin 87.
DOUBLE CHECK THOSE PIN #s LOL. I have a terrible memory.
Anyway, that will jump the 12V directly to the pump and it should turn. If you get a V drop, bad wiring somewhere.
The pump can also exhibit strange resistance if it's partially seized up. Did you try hitting the top of the tank with a hammer? Seriously, try it. It got me home when my seized once.
06-14-2009, 03:36 PM
jumped 30 to 87 and the pump pumped fuel into the bucket i had beside the car. So pump works fine.
I swapped the relay with several spares i have. No dice.
Checked states of the voltage on pins 85 and 86 -
86 is 12V in run and start, so the only thing not letting the relay close is 85 going to the ECU. It needs to close to 0 or gnd in order for the relay to work.
Does anyone know what conditions need to be met for that circuit to close? I thought I heard someone say the ECU needs to see the crank sensor changing before that would work.
I'm so close to being finished this part of the project, help a brother out?
06-16-2009, 08:52 AM
'Main relay needs to function to make the fuel pump relay function. that's the white/metal one frontmost near the afm.
Pickups for the speed and reference sensors. Two on trans. bellhousing or 1 on front of engine with the later cars; which also have a pickup on the spark plug wire #1 I believe.
06-16-2009, 11:37 AM
main relay is working ok.
I think the issue is the crank sensor, but it was replaced with a new one same time as the harness(which was used - from my parts car 89 IX auto), I'm going to check it out this week to be sure.
Will the spark sensor cause the ECU not to allow the pump to work?
06-16-2009, 11:48 AM
AFAIK, if the car knows the vehicle has stopped running the pump power is cut. However, this is overridden during cranking. So, it would run while cranking then quit when the motor gets about cranking RPM.
06-16-2009, 12:05 PM
so, tell me this, do you see rpm on the tach while cranking(before it catches)? Because I don't.
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