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fuel pump issue

J

jester1614

NAXJA Forum User
Location
ventura california
89 xj 4.0 newly swapped 94 motor

fuel pump is not priming

batttery is brand new

I have 12 volts at terminal 30 at the fuel pump relay. when i jumper the relay I hear another relay (havent figured out what one, i think its by the radiator passenger side) clicking

swapped the relay with the ac relay, no change

at the ceramic resistor on the foward terminal i have .240 volts rearward terminal .172 volts

with the ceramic resistor bypassed i see 6 volts at the connector going to the fuel pump with key on engine off

any ideas (i am searching as well)
 
Last edited:
The fuel pump ballast resistor is bypassed until the engine starts IIRC. There are three routs to the Renix fuel pump, one is a prime timer stage just before cranking, then cranking which both bypass the resistor, then the run circuit goes through the resistor once the engine starts.

The fuel pump relay is on the passenger side!!!!! So I am confused as to what relay you were jumping or exactly what you were doing? Are you jumping a relay on the drivers side, the O2 sensor heater relay, or???
 
Last edited:
jester1614 said:
also i have diagnosed my cps as bad, but am i correct in assuming that that wouldnt cause a no prime, but would cause a no start.
Click to expand...

Correct, it will prime with a bad, or even disconnected CPS on 89 Renix. Why do you think yours is bad?
 
jester1614 said:
sub .150 volt ac reading while cranking.

sorry i meant relay clicking on the drivers side, i noticed it but cant edit it.
Click to expand...


OK, IIRC that driver's side relay goes to the electric heater inside the O2 sensor.

Did it suddenly or gradually get hard to start, the sign of a bad CPS?

I had a CPS that was only .17 V that worked fine. And a new one that was .25V that worked sometimes and not others, LOL. That is why I asked. If you have no spark, then the CPS IS BAD!!!! Or bad enough that it needs to go. But be sure to get a good one and mount it closer the flywheel (we can discuss later).
 
I have had to clean the male and female contacts on the fuel pump relay and the male female contacts at the harness / fuel pump connectors at the gas tank on both my Renix rigs at one time to get the pumps working again, several years ago!!!! I used solvents and q-tips, and sandpaper to get them clean. Also try bypassing the resistor, it may be bad.
 
jester1614 said:
also what terminals to use to put power directly to the pump (under the car at the connector in front of the axle)
Click to expand...

I would run a jumper to the wire at the resistor from the battery, only two wires at the resistor to try, as one should go directly to the fuel pump, I think ??? One should run the pump to where you can hear it running.

That resistor if good, should ohm out at about 8 ohms when isolated from the harness.
 
Ecomike said:
I would run a jumper to the wire at the resistor from the battery, only two wires at the resistor to try, as one should go directly to the fuel pump, I think ??? One should run the pump to where you can hear it running.

That resistor if good, should ohm out at about 8 ohms when isolated from the harness.
Click to expand...


tried running a wire from the battery to both wires at the resistor, nothing happened.

thanks for the ohm spec
 
jester1614 said:
tried running a wire from the battery to both wires at the resistor, nothing happened.

thanks for the ohm spec
Click to expand...

I take it that means the fuel pump did not make a sound?

Try it again, but this time use a volt meter across the connector contacts at the gas tank-fuel pump harness contacts to see if 12 volts got that far!!!! That will tell you a lot!!!! Clean those contacts while you are at it, and verify that one contact is actually a good ground!!!!!

You could have 12 volts at the pump and a bad ground!!!! Renix is notorious for bad grounds!!!
 
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