Renix fuel pump ballast resistor voltage

My '88 XJ just up and quit on me this afternoon. The first thing I looked for was fuel pressure, which there was none. I next bypassed the ballast, but still no luck. With the key in the run position I'm only seeing 0.3 volts to the resistor, so I'm now smelling a rat. What is the next logical thing to check? Just how much voltage should be available to the fuel pump ballast resistor?
Thanks!

BTW, I just swapped out the FP relay. Still no joy.

OK, with the key in the run position, there's no power coming off the Fuel Pump Ballast Resistor terminal of the starter relay. Any thoughts?

I don't have my wiring diagrams handy, so I can't tell you exactly which relay to check, but if you do a search for "RENIX Relays" or something similar I know it was posted recently.

You may have lost the fuel pump relay, which is in the group of four on the passenger fenderwell behind the start relay. They're standard Bosch relays, which you can get pretty much anywere for less than $10. Keep spares, just in case (I tend to use them for pretty much any mod I do that draws more than a couple amps, just because I'm cranky and like things to last a while. I can usually swap a relay faster than changing a switch...)

I *think* it's the second relay back, but you should find that post to make sure (The FSM pic was posted as well, so you'll know what they all are!)

5-90

I've swapped both the fuel pump relay and the starter relay, but still no luck. I then ran 12 volts straight to the FP ballast and still nothing. I can see the pump giving up the ghost, but why no power to the fuel pump ballast?

Are you measuring across the ballast or from chassis to ballast? From chassis to ballast is about 12 VDC, across the ballast would be about .4 VDC. You can also jumper the fuel pump relay and listen for the pump to hum. Fuel pump relay is 2nd in from the front on the passenger side bank of four relays. Make sure you jumper across the relay contacts and not the coil . The diagram is on top of the relay.

I'm measuring voltage to the ballast, not across it. I'm not even seeing 0.3 volts now... All of the 4 relays have been swapped, along with the starter relay. Like I said earlier, even when I hook it directly to the battery, nothing. Bad ground at the FP? :wierd:

gator_grabber said:

OK, with the key in the run position, there's no power coming off the Fuel Pump Ballast Resistor terminal of the starter relay. Any thoughts?

Click to expand...

You have 12 volts into the relay, and no volts out?

Replace the relay would be my response to that one.

As stated earlier, the starter relay was also replaced today. I'm now in the process of replaceing the pump with a working OEM unit. We'll see soon...

Is the relay closing? If you dont have voltage at the ballast, then maybe not. Just a thought. I just replaced my pump and it worked for two days then low pressure again.

Mr Gator, I just measured my voltage out of curiosity, and got near 0v on both ballast resistor wires with the key on. Mine runs perfectly.

I remember reading in a repair manual that the Renix ECM cuts power to the fuel pump after it's initially energized, and then re-powers it when the engine starts. That must be what's happening with yours. You can check it by touching the voltmeter probes, one to the ballast wire, one to a ground, and then having an assistant turn the key. The wire should be energized for about 2 seconds, and then drop to near 0v, if the pump relay is working OK. You should also hear the pump running for that time.

I think your pump has died.....

Yes thats correct, jumper the relay and you should get 12vdc and pump running. Ive been playing with mine for a couple weeks now, gonna drop the tank again tomorrow. Either the new pumps gone bad or somethings clogged, maybe I should check the new filter first just in case its clogged already.

Problem found...loose wire (in tank) to fuel pump. Wow, now that was fun! Thanks for all the advice.