charliegt

Every car I've driven primes the fuel pump for a couple seconds when you turn the ignition to on. I've been having problems with my FD starting and I noticed that the pump does not come on when I turn the ignition on. 0 fuel pressure, 0 volts at the fuel pump relay terminals. If I remove the fuel pump relay and hard wire the fuel pump by jumping terminals, the car starts up perfect and runs perfect. With the relay back in, it stalls out when it starts hot, and runs like crap when it starts cold.

I've tested the relay and it seems to be working. I also replaced the fuel pump. When I crank the car the fuel pump relay terminal (the one that energizes/closes the relay) sees 7-10 volts.

Any tips about where to look would be great.

Thanks,
-Charlie

charliegt

Can someone at least tell me if THEIR fuel pump comes on for 2 seconds when they turn the ignition to the on position?

-Charlie

c00lduke

Yes, they all do.

charliegt

Thanks duke, I guess now I need to find out why the ECU isn't closing the pump relay to prime the pump.

-Charlie

mad_7tist

you know the ecu will control the ground side of the relay correct? in any 4 post relay you need 2 powers. one for the load side, one for the solenoid side. usually the ecu willl provide the ground side to the "solenoid or switch" side or the relay.

that said, there is a pump speed control relay, is that the one you are testing because it is non-active during idle,key on light load

Gadd

As mad_7tist said, the "fuel pump relay" controls the pump votage, The "circuit opening relay" turns the pump on and off. The Factory Service Manual will show you how to test the system step by step.

mad_7tist

yes if you are jumpering the fp spped relay and getting power i would look into the fp resistor under the cruise control motor. it may be open thus not completing the circuit to the pump

charliegt

Thanks for the responses guys. If I'm reading Mad7tist's response correctly it is the fuel pump (speed relay) that should activate the pump for the 2 second prime?

I've been looking over the factory service manual and the diagrams, I have a pretty good idea of the basic layout. Here is a more detailed explanation of what is going on.

When I turn the ignition key on the fuel pressure remains at 0. I've tested both relays and they are working. When I crank the engine or jump f/p and gnd I get fuel pressure. I just replaced the pump.

The voltage at the switch part of the fuel pump relay terminal sits at 0 when I turn the ignition on. I have not checked the fuel pump relay (speed) terminal for voltage yet.

What I've done to get the car to run correctly is jump the power/load terminals for the fuel pump relay so that it is supplying constant power to the pump when the ignition is on. So, for one reason or another the relay isn't closing for 2 seconds when I first turn on the ignition.

Gadd - I've looked through the pump diagram in the FSM and don't see the "circuit opening relay", only the fuel pump relay, fuel pump relay (speed), and the fuel pump resistor. Were you refering to one of those, or am I missing something?

Thanks again,
-Charlie

mad_7tist

no the speed relay does just that controls the speed ~ 8v to batt volt. sorry if i confused you. the manual calls it 2 diff things. circuit opening and fp. they are the same. the speed relay is seperate. the relay you jump is in the front of the car by the fans?

charliegt

Yes, it is in the relay box next to what I think is the EGI main relay.

Gadd

Sorry to misdirect you but you must have a 94 or newer car, at some point Mazda changed the name of that relay.. but yes it's the one next to the EGI relay. the speed relay is in the box by the intake box........ That cleared up, I've never confirmed that the pump runs before the engine is turned over, but if you suspect your having fuel pressure problems I would perform the fuel pressure tests in the FSM

charliegt

Gadd, yeah it is a 94 (sorry I should have specified). I've performed the FSM tests and it checks out OK. But, for one reason or another the car has trouble starting (rough starts cold and usually stalls out a few times when hot). When I remove the fuel pump relay and jump the terminals as I described above, the problems go away and the car runs perfect. Normally I would suspect the relay, but I've tested it twice and it is working.

I haven't seen anything in the FSM about the 2 second prime, but I'm almost positive that it happens. If someone could check on it and let me know for sure then I would know if there is a continuity problem between the PCME and the relay, or if the PCME is intentionally not turning on the pump due to a sensor failure somewhere else.

Thanks again,
-Charlie

Gadd

So I checked my car and the pump does not run untill the key is in the crank position.

mad_7tist

mine does... so do at least 3-4 i have worked on for sure.

ARMAN

I got the same problem and my car doesnt prime at all, and my pump is getting a straight 12V feed, but when i test the speed relay box it is recieving 8.8V from the resistor. the relay stays open. Got a Fault check done, #51 description: Fuel pump relay Ground short circut. what ever that means i also changed my ECU with another standard one same thing happens, cant find the problem car runs too rich in low rpm. Keep us updated on ur progress i might try somethings you have to try and sort myne out. Cheers

charliegt

I still haven't progressed much since my last post. What I know for sure is that the car starts and runs PERFECT when the fuel pump relay is removed and a paperclip is used to close the circuit to the pump.

So, this means that the problem is being caused by 1 of 2 things:

1. The fuel pump relay is not closing properly, or not supplying good voltage to the pump.

2. The ECU is not closing the pump relay properly, either due to a bad connection or maybe intentionally due to a bad sensor somewhere else.

When I turn the ignition to ON, the relay does NOT receive voltage from the ECU. I have verified this with a volt meter. When cranking, the relay receives 7-10 volts. So, before I do much more work I need to definitively know whether or not the relay should close for a prime when the ignition is first switched ON. Several people have answered several different ways about this subject. I have not been able to find a definitive answer in the FSM either.

-Charlie

ARMAN

Like wise, if your car is running perfect with a paper clip that means the resistor is working properly, there are 2 wires that come from the ECU- one goes to the actual fuel pump relay and the other goes to to fuel pump speed relay, i havnt got a straight answer either i dont know if my car is supposed to prime or not because it start ok. can u test your Fuel pump resistor and see how many ohms your getting? also when the car is on, the fuel pump drains some of the current so the voltage you are getting isnt the true voltage the pump is recieving.

You are using a paper clip in the main fuel relay not the SPEED relay yes?

charliegt

Arman,

That's correct - I'm using the clip on the main fuel pump relay. Unfortunately, I can't test the resistor for you because I'm not in town. If you don't have it already, I'd recommend downloading the factory service manual. Section F-109 details testing the resistor. The resistance should be 0.57-0.70 at 68F.

Have you tried using a paperclip in place of the main fuel pump relay - and does that resolve your problem as well?

-Charlie

ARMAN

I have tested the resistor I think its Stuffed its not cutting down the voltage it seems pretty heavy duty tho I dont know how it could stuff up, but im replacing it tomorrow.
No my problem is with the Speed relay and the resistor because im getting a direct 12V feed all the time, If your car is working fine with the paperclip then the relay is stuffed. mayb the coil is burnt out or the resistor in between under the coil is burnt. try another relay.
I played around with my ground wires today and my car wasnt boosting past 4000RPM now it is boosting fine but not till 4000 due to the constant 12V feed. Ill let u know what happens tomorrow mayb u can try somethings I have. Thanx for the help.

charliegt

I've found a few people that say that the fuel pump DOES prime for a couple seconds when you switch the ignition on.

If that is the case, then what would cause it not to? More specific, what would cause the ECU not to? I get not voltage at the fuel pump relay terminals when I flip the ignition on, so the ECU is not sending the signal - or it is not getting there. Since I get voltage once I crank the engine, I'd say the wiring is OK. So, what type of input would cause the ECU not to prime the fuel system with the ignition on? Or is it just a faulty ECU?

-Charlie

Gadd

Somebody else need to check to see if there car primes for 2 secs when the ign. is turned to the on position, before the ign is turned to start. It's easy to do, just check for votage at the connector at the tank. My car does not, and starts just fine hot or cold. Now the f/p relay should have battery voltage when the ign. is in the on position, the ecu grounds the relay to energize it. Have you checked for voltage from the relay to ground with key on?

charliegt

There is no voltage coming from the ECU to the relay when I turn on the ignition and the engine is not running. Voltage shows up when the car is cranking though.

If the fuel pump is supposed to prime when the ignition is first turned on then my problem is with the ECU. If the pump is NOT supposed to prime, then the problem seems to be with my relay.

-Charlie

ARMAN

Yeah same problem as me, there is voltage at the relay terminals but the relay doesnt kick in till i crack the car and still no prime i have changed my ECU with another stock one and same problem happens, mayb the car is not meant to prime.. but what would cause my fuel pump to recieve 12V all the time i checked the resistor and there is a terminal that does cut down the power to around 8.81V im guessing thats from the resistor but still no good, i changed all the relays in the car and same problem. Is there anywhere else that i need to check mayb something on the actual engine? ??

Gadd

I'm not sure I being clear... +12v to the relay comes from the ign switch. The ecu grounds the relay to turn it on. Anytime the ign switch is in the on position there should be 12v at the relay.

Gadd

Charlie, if you have confirmed you have proper pressures discribed in the FSM, I think your barking up the wrong tree. Have you done a compression test? Low compression can cause similar problems.