So 2 nights ago, I had to get home on a flatbed again. My fuel pump stopped working while driving again. At the beginning of the summer, my fuel pump died, so I replaced it with a Bosch universal pump. Worked great until 2 nights ago.

The same thing happened as last time. Fuel pump quits, I call a for a tow truck, and as soon as it drops me off at home an hour later, the pump starts working.

Is there something else that could cause my pumps to stop working? Has anyone ever had any experience with bosch pumps? Maybe the pumps are unreliable, poor quality? I don't want to get stuck again, I might just order a better pump with regulator.

 

wiring to the back goes intermittent on many older rx's , certainly very common on 70's mazdas
not entirely sure what the issue is,, ignition barrel or issues in the loom make for sporadic low volts


always fixed with a fused relay that takes fresh power from the battery , use the old wire to switch it

 

yup , pull the carpet in the rear next to the bins and follow the harness, my buddys gs use to do the same thinfg and it turned out one of the sharp ends of the metal bpdy cut in to the harness

 

I'm still an electrical noob.
If my old wiring voltage is sporadic, would it not be also unreliable to use it to switch the relay on and off?
I have an extra relay laying around, so I can try it. How would I wire it?

Thanks for the help

 

Yes you could still have issues if the current wire to the fuel pump does not always provide a proper voltage to trigger the relay. However, you can always jump the relay to override and turn on the pump.

Here is your basic wire up:
Pin 30: +12V from battery (fused)
87: +12 on fuel pump
85: Existing stock wire for fuel pump
86: Ground of some sort. I would imagine one of the stock wires is a ground.
87A: No connection

If for some reason your fuel pump does not turn on while on the road, you could just connect 30 to 87.

 

Thanks Sgt Fox, but I have another question. With the relay, if my car is already started and running, and I lose voltage in the signal wire, will my car die or will it keep going? Does the relay need a constant signal to keep it switched on?

 

sa7 - yes, your relay needs a constant signal to keep the power to the pump on

What you can do is use a signal that is working consitantly, like say your switched power to the radio, as the signal for the pump to run, the only problem with this is that you would then lose the ACC position on your ignition switch

 

Thanks!

 

Just curious - so you have confirmed the pump has actually STOPPED running? I ask because if the fuel system is getting clogged, the car will stall even if the pump continues to run. So you actually have checked to see that the pump is not running by getting down near it and listening for its operation (or not).

I have had a situation where my SA would stall out (no fuel) then, after sitting, would start back up again and run for a while, repeat... traced to a clogged fuel filter and internal shedding of fuel tank, repeatedly clogging the filter. The pump was running the whole time, but acted like it was "dead" (since no fuel).

Just a thought-

Stu Aull
80GS
Alaska

 

I'd have to agree with 7all. Best to fix the actual problem instead of a bandage fix. Personally I wouldn't use a relay unless I was upgrading to an aftermarket pump with a higher current draw than stock. Using a relay connected to the ignition also defeats safety shutoffs.

 

+1 with Sgt

 

fuel pump cut off is a feature on FB ( or series 3 SA22 as known in other countries )
but AFAIK is not a feature of an earlier rx ( at least where i come from )

issue is the age of the loom and its connections ,, and or wear in the ignition barrel contacts

issue presents as LOW volts , not NO volts , usually the stock ( s1 /s2 ) facet pump requires a little tap to start moving and off it goes again

volts are still low,, and as such the pump is derated
and you are pleading for a lean out at revs


relay is the proper fix for the issue
adding a carotor or gerotor ( Carter P60504 ) type fuel pump ( which will run even with low ish volts )
is a small but recommended upgrade over the facet pump which is likely getting long in the tooth


either that or spend $1000 in labor to totally rewire the rear of the car and replace the ignition barrel

what to do is an easy choice for me,, and a solution i have used in literally dozens of old rx's

 

True, but he should at least determine if his problem is insufficient voltage to the pump, before tagging some relay off a controlled 12VDC source. Additionally, while the stock wiring may not be able to provide enough power for the pump, it very well could trigger the relay, with the pump's power coming from a dedicated fused line.

I do remember there being a Mazda service bulletin about chaffing wiring harnesses in the bin location. Something to check for. Time to get out your multimeter and inspector's cap.

 

+1; there's no inherent design issue with the SA fuel pump system; it's simple and reliable.


*Check voltage at the pump.
*Check quality of ground connections.
*Check condition of ignition switch - SA fuel pump is directly driven from the same switch contact that powers the ignition system. Positive voltage at the coils is derived from the same source that provides voltage at the pump, absent two lengths of wire and two connectors.
*Check for frayed wiring under the carpet, but keep in mind that if you are shorting to ground due to wire chafing, you'd be blowing fuses. If your problem is electrical, it's most likely an under-volt or open-connection problem, not a short.

 

7aull- When I was waiting for the tow truck to arrive after I broke down, I kept turning the key every few minutes to see if I could hear the pump turn on. I even got out of the car a couple times to listen close to the where it's located. I couldn't hear the pump turn on at all. I can usually hear it from inside the car when I start it.

I took the bins out, and took everything off of the steering column to get to the ignition switch. I followed the wire from the ignition switch all the way back to the connector in the rear bin, and it looked fine. I tested the voltage at the column and at the connector, and they both read about 11.1V.

I still need to raise the car to check all the connections and wires from the connector to the pump. I also still need to check the ground.

 

Did your tach stop working at the same time. If so, then the problem is with the ignitor (trailing, I think). I had exactly the same symptoms/problems as you. The ignitor can fail intermittently and can temporarily "fix" itself.

The ignitor is tied to both the tach and the fuel pump (at least in the later 1st gens). If it goes, neither works, although the car will still run if you can get fuel to it.

I suggest swapping in a different ignitor. You might try swapping the leading to the trailing just to see if the pump will come on if you don't have a spare. If the ignitor is the problem you can switch wiring and pumps forever, unless you wire the fuel pump directly to the ignition system.

Carl

 

You need to compare that to voltage direct across the battery (assuming the engine was off at the time) to really know what it means, but you should be seeing something at or above 12V. You're dropping 8% of your voltage (at least) in your wiring just between the battery and the column. May not be the total cause of your problem, but it's not helping.

If your battery is also reading 11.1V, you have a bad battery, or your alt is not charging it properly.

 

Carl- my tach was still working when the car died. I'm sure I was watching the needle slowly start going down, as my car was dying. The car didn't suddenly die, it took a few seconds, so when I was giving it gas, my tach would momentarily jump up.

I just checked the voltage at the battery, and it read 11.51V. I also tested the voltage at the fuse block under the hood to see if it was the same, since my battery is in the bins. It was also at 11.5V. I'll have my battery tested tomorrow, looks like I might need to replace it.

 

Yeah, 11.5 would say you've probably got a dead cell... Do yourself a favor and have your alt tested at the same time. Half of all battery failures are due to alternator/voltage regulator failures.

On an SA (at least, with stock wiring) there's no relation between the tach, fuel pump, and trailing ignitor. SA fuel pump wiring goes directly from the ignition switch to the fuel pump, no intervening relay or other switching components. key on = pump on.

And on the SA, the tach is connected to the leading (not trailing) coil signal, since the trailing ignition is shut down under certain conditions by the ECU, for emissions purposes related to the function of the thermal reactor exhaust.

FB's use the trailing signal for the tach, and also for the fuel pump control signal.