Fuel pump not getting electricity

[edward_rose_77]

1993 Mazda MX3... Manual... 1.6, 4cyl

Here's my problem. Drove to work the other day. Not raining. Parked at work. While at work it rained like hell. (South Florida) Came out from work after rain was over and my car wouldn't stay running. It starts for 2 seconds and then the rpm's drop and engine stops dead. (No sputtering down) The only reason I mentioned the rain is because I'm a techy guy, and sometimes a coincidence like that might mean something. By the way, never drove through any puddles all day.

So the tow truck driver calls his buddy. The buddy immediately says, "Air flow meter"

The next day... car sitting at home. I had this instinct that the fuel pump wasn't sending gas. As if the process of starting the car sucked some gas into the engine... just enough to start, and then the car would die like it was doing. So I yanked out the back seat and put my ear on the fuel pump cover while my girl turned over the engine. I didn't hear the whirring sound of the pump. I knew to do this because I changed the fuel pump recently. For some reason, as you'll see in the story, I doubted that maybe I just wasn't hearing it and that it WAS working.

So that day, I changed the fuel filter. (My neighbor's theory) Same problem. Started for 2 seconds and wound down quick. Then I figured that maybe this "Air flow meter" wasn't working, and that the AFM was assuming there was too much air coming in and wasn't allowing the fuel pump to turn on. So I called Advanced and ordered a $200 AFM.

Today the part came. Went and got it. Threw it in. Same problem. (Can't return AFM!)

Then I went back to the fuel pump theory. I took a little 12v battery pack and hooked it directly to the contacts above the fuel pump area and I could hear it turning/whirring just fine. Then I hooked a multitester up to the contacts that are supposed to SEND electricity to the fuel pump, and I got NO ELECTRICITY while starting the car and for the 2 seconds that it runs.

Next up. My electronics brain told me to just leave that 12 source ON the fuel pump so it's running, start the car, and see if it stays running. Well it does. Just fine. However, there's black water dripping out my tail pipe. (Car sitting for two days... don't know if this matters) The water is not coolant and doesn't have a gasoline smell. Just slightly black from running through dirty tail pipe. Also, no smoking out the tail pipe.

Already checked fuses and the Fuel Injection relay. I even hooked power to the relay (to hear the click of the coil/switch) and hooked a multitester to the switch side to confirm it is closing.

Questions:

1:Why the water?

2:Can I hook a direct 12v source from the car to my fuel pump with a switch, and drive around town like that with the fuel pumping running all the time?... or does the car's computer and/or Fuel Injection system constantly turn the fuel pump on & off during normal driving/running?

3: And most obvious... why the hell isn't my fuel pump getting electricity?

4: Anyone wanna buy an AFM? (Just kidding... had to give core to purchase)

Edward Rose

[edward_rose_77]

Well I figured out the water thing. Right now my car is parked in my car port 5 feet back from normal... so I could work on it.

Yesterday I got the car to run for a minute or two and black smoke came out the back for a few seconds. (Tail pipe got dirty) When I srted it today using the 12v hooked to the fuel pump, no smoke and normal run, but the water was alittle dirty from yesterday's sloppy run.

Getting to the point... I looked on the ground near the tail pipe but 5 feet up... where I normally park, and there is a light water stain from each morning when I start, warm up and drive off. So this is obviously the normal condensation thing.

But I still need to know if a fuel pump in a 93 mx-3 is always supposed to run when the engine is on, so I can at least get to work tomorrow until I figure out why the fuel pump isn't getting power.

Edward Rose

[mitmaks]

fuel pump should be getting juice to it once key is "ON" position. Have you tried bleeding fuel line, see if there's any air pockets in it. Water from exhaust sounds normal condensation.

[edward_rose_77]

No clogs. Like I said, with an external 12 volt source hooked directly to the fuel pump, the car runs fine.

In other words, I unhooked the wire harness from the fuel pump assembly. (Pump still screwed in and inside tank) This wire harness only has the fuel level detector and the fuel pump power contacts. I took 8 energizer batteries in an 8-battery battery clip and hooked that 12 volts directly to the power contacts on the fuel pump. Quickly turned on car. Runs perfect. But the car does NOT run for more than 2 seconds when the wire harness is clipped on to the fuel pump. This completely eliminates clogged fuel line or bad fuel filter.

I know my original post is long. But if you read it all, I go over and eliminate the most common possibilities.

Someone at another forum said to check the oil pressure switch. He doesn't know Mazda's, but said that this switch is commonly used to tell the car's computer "Engine is running," and consequently turns on the fuel pump. So I went out to my car just now with a flashlight to look at the oil pressure switch, and it's covered with oil gunk... aka: When it rained that night at my work, it may have been the final straw of moisture in the air that caused the oil pressure switch to malfunction.

But I won't know until tomorrow when it's daylight. I don't feel like going outside at midnight to clean gunk off that switch and off that part of my engine.

I'm still curious though if anyone knows if it's okay for the fuel pump in a Mazda mx-3 to run constantly as long as the engine is running. I may have to do this tomorrow afternoon when I leave for work if the oil pressure switch isn't the cause of the "No power going to fuel pump" problem.

Edward Rose

[Ryan]

I work at mazda, and recently we have a B2200 come in. It wouldn't run, and it ended up being a mix of both the fuel pump relay and the ECM both malfunctioning. The ECM because it's located behind the fender and met the weather when they rusted out, and the fuel pump relay because its old.

I think the relay is right beside the ECM on the pass side, its a 4 wire plug that simply goes into a cubic black box. Try swapping that out with another Mazda and see if it fixes the issue. Maybe a $10 junk yard steal, or pocket loot if you wear enough sweaters.

I'm sorry I didn't read thoroughly, but did you check for fuel pressure by unhooking the send line and holding it in a bucket while cranking? You should get substancial flow. send line is the one... oh shoot. umm. well, its the one NOT on the FPR side.


Edit:

Yeah, I was right. Here you go: http://www.mx-3.com/manuals/showimg.php ... F1-109.gif" onclick="window.open(this.href);return false;

Also, you can troubleshoot the pump by jumping GND and F/P in the DIAGNOSIS box found agaisnt the firewall on the driver side of the engine bay. that will make it run untill you pull the jumper out. Use something more substancial than a paperclip because it does draw a fair ammount of current.

[edward_rose_77]

Thank you. Never would have found them or guessed where they were. Going to check them out now.

Edward Rose

[edward_rose_77]

Not the fuel pump relay. Maybe ECM. How about the fuel pump cut off switch? Could that be it?

Well, gotta go to work. Using direct voltage to fuel pump and hope all goes well.

Edward Rose

[Custommx3]

the Fuel pump relay is attached to the side of the ECU under the center of the dash.

Check that one?

[edward_rose_77]

Yeah I checked it. I confirmed right above your post that it wasn't the problem.

I bought a new oil pressure switch today. The one in my car... even after cleaning, looks like it still has grit in between the outside contact and the ground of the switch. Might be shorting. But still not even sure if the ECM uses oil pressure to figure out if the car is running to turn on the fuel pump.

Driving today with direct voltage to the fuel pump was weird. All went well, but I had more horse power. Felt like a sports car. (I know it is anyway) Also, my idle in each gear was different. Normally I go from 3rd to 4th gear around 30mph. Today it was 35. And normally I go from 4th to 5th gear around 40mph, and today it was 45. I hope I'm not sending too much voltage to the fuel pump... hope I don't burn it out while using this quick fix.

Edward Rose

[Ryan]

You're probably just running the pump at full duty the whole time. You're probably richer than a rotary.

You should be able to jump F/P and GND in the diagnostic box instead of running leads through the cab.

[wytbishop]

Same affect. The F/P runs continuously when jumpered from the DIAG box.

[Ryan]

That was my point

Its got to be the relay because if that works, you know its not the wiring. The F/P runs with ignition on. The F/P apparently runs at the same pressure all the time, and the FPR regulates the pressure at the rail. (says Mazda) So maybe the solenoid controlling the FPRis bad? Is on the pass side of the intake mani, the one with the vac line running to the FPR. Try replacing that. Try replacing the FPR while you're at it.

Bad MAF/VAF? Maybe try swapping that out for a known good unit. Although it says you bought a new one?


I seriously doubt the oil pressure switch has anything to do with it because the oil light stays on for 1-2 secconds after you start and the car is clearly getting fuel in that time, that and it runs before there's any pressure in the vehicle at all. They are independent systems. Also, Mazda has desined some stupid things, but that seems too over the top stupid for them. Using a single wire sensor for a dual unrelated (and unfit) purpose?

[edward_rose_77]

Okay. I just removed my 12v-to-fuel-pump rig, plugged the cable harness back in, and then put a jumper wire on the switch contacts of the fuel pump relay. Car runs fine. But the FPR is making constant clicking and vibrating noises. Today for the trip to and from work, I'll be using this simpler jumper wire on the FPR. Didn't like the other rig because the wires I had crammed in the wire harness socket near the fuel pump, ran the risk of popping out while driving... or moving slightly and losing contact.

Tomorrow I'm off work again and I guess I'll waste another day off checking the other things mentioned by Ryan.

Quick Q Ryan...
What is the MAF and VAF you mentioned?

If one of them is the air filter that looks like a giant fuel filter near the passenger side mirror, I removed that on day 1 and it's fine. (Thought it was a fuel filter ) Blows through fine when I put my mouth on it.

Edward Rose

[Ryan]

The MAF/VAF are the airflow sensors found in the intake system... which one depends on the year. trapdoor style are VAF, round ones are MAF.

They shouldn't be affecting your problem, I forget why I mentioned it.

I wouldn't be putting my mouth on that, its the charcoal canister. I bet it tasted awesome.

so:

The car runs with the f/p jumped. This rules out bad pump and most of the wiring.

Have you replaced the relay yet? I'd try that next.

The pump runs constantly at a constant rate as soon as the ignition is turned to the "on" position. The pressure is regulated by the FPR, which I described earlier. If this had failed open, it would be letting your pump do circles, effectively giving you near 0 PSI at the rails. I'd check this too.

Can't imagine much else.

[Dark_Rider2k3]

sorry if this has been done before but did he check the the connector to the fuel pump to see if it was getting any power? And trace it back to see if maybe a fuse is blown, or if the wiring shorted?