fuel pump relay

[Mitsu_dude]

lemme start off by saying what my car is doing. it feels like its sputtering and i found out that it was from lack of fuel. obd1 reader came in handy. so now i will give you the in depth story...

well a couple days ago my fuel pump went out so i threw in a walbro 190. got the cel checked before hand and all it said was fuel pump. so i crank the car thinking the problem is fixed but no. its still not getting fuel, i can tell because the car is still sputtering from lack of it. so i replace the fuel filter thinking okay, the filter could be clogged. crank it, and problem is still there, but now, the cel says fuel pump circuit?????? WTF why would the code change if all i did was put in the new pump and filter? im so confused. and i dont even know where the fuel pump relay is to check it. i did some searching and i think i read something about it being behind the radio and something about it being under the center console. so my question is, does it sound like the relay went out? if so, where is it and how do i go about fixing it?

 

[bomper04]

If it were a fuel pump relay gone completely bad, you would not be able to start the car, you wouldn't even have any fuel pressure. And at that, how is your fuel pressure? If you want to test fuel pump circuit then you can check for continuity of your wires to the fuel pump and then check for voltage and ground as well. When you say "sputter" do you mean it's missing?

 

[Mitsu_dude]

it feels like a misfire, yea, but the only code its throwing is fuel pump relay or something like that. and i have no idea how to do the whole voltage check thing. my room mate has that little tool to check it, but i have no idea how to use it, and he doesnt know what he needs to check

 

[yokotabrat]

The fuel pump code is thrown when the ecu doesn't see the proper voltage on pin 13. Since you've replaced the fuel pump, that should rule that out. The only other things are the mpi relay, wiring, or the ecu itself. The ecu activates the mpi relay which also powers the fuel pump by pulling pin 56 low. If you stick a volt meter on pin 56 and see 12V there all the time, the ecu is damaged. This is probably the result of leaking capacitors. Let us know what you find.

 

[Mitsu_dude]

how do i test the mpi relay? and another thing i still dont get is why would it throw the relay code after i replaced the fuel pump. i dont get that because at first the only code was the fuel pump itself. then when i replaced it it threw the relay code??????????

 

[yokotabrat]

Check out post # 5:

http://www.dsmtuners.com/forums/newbie-forum/263224-mfi-mpi-relay.html

Is this a 1g? There is no relay code that I'm aware of:

ECU Code Checking

It sounds like you're getting code 42, correct?

 

[Mitsu_dude]

yes. its a 90 gst. i was getting a "fuel pump" code at first. but now im getting a "fuel pump circuit" or "fuel pump relay" code. cant remember which it was. but i know for a fact its not just saying fuel pump anymore. thnx for all this help btw. and one more question, if i do the fp hotwire or rewire whatever it is, doesnt that give the fuel pump a new relay? so my question is, if in fact the relay is messed up, then would doing the rewire fix that problem?

 

[yokotabrat]

The fuel pump rewire does give the pump a new relay, but it still uses the old mpi relay to activate your new relay. You'll still run into the same problem unless you activate your new relay using some other power source, although I wouldn't recommend that.

There aren't too many reasons to get this code and it usually occurs because the caps in the ecu have started to leak. If that's the case, you could have other issues down the road. It's easy to crack open the ecu and look for signs of leaking caps.

 

[Mitsu_dude]

k. ive heard to look at it and look for fried connections or see if it smells like fish(wtf? ). is it under the center console part that lifts up, or back behind the radio?

 

[okm12346]

Did you check out the links above?

Its behind the radio at passenger side. remove the panel to access the bolts.

 

[Mitsu_dude]

yea i just read it. even printed all the pages. . its storming like crazy here so i cant go outside to check it out right now, but i will keep you guys up dated when i get a chance. probly later tonite

 

[yokotabrat]

Check out this link for examples of leaking caps (look under corrosion examples):

ecurepairhome [ECMTuning - wiki]

Yep, if it's been leaking for a while it'll smell pretty bad.

 

[Mitsu_dude]

well it was pretty simple to get to. like 3 screws. i got the relay out. should i just go ahead and replace it, because the dealer said it was only 5 bucks, or just test it? i havnt tried the ecu yet, but if the relay doesnt fix it, then i will

 

[GooeyGus]

They say an MPI relay is only $5? That doesn't sound right.

I would pop open the ECU first. Damage will usually be obvious.

 

[Mitsu_dude]

yea, i went up there to get it and they said 95, not 5. . BIG difference. so i didnt get one just yet. but i pulled out my ecu and looked at it and it looked fine. didnt smell at all. im about to upload pictures now..

here they are

 

[yokotabrat]

That brown stuff in the first picture indicates the lower capacitor had leaked at one time. Someone attempted to clean it up and replace the caps, but it looks like they didn't do the greatest job. It's possible some of that residue was left behind and still killed the ecu. Do you have a way to get a hold of another ecu to test?

 

[Mitsu_dude]

most likely not. i just moved to nc so i dont know anybody with a dsm. and also, i tested the mpi relay by taking the cover off and turning the keey to each thing like on accesories and start, and one of the two things didnt spark at all. its the one on the relay that onnly has 4 prongs in the back, not the one with 5 prongs. the one with 5 prongs sparked each time i tried to start the car, but the other didnt??????

 

[yokotabrat]

That's the portion of the mpi relay that powers the fuel pump that's not working. If you have a multimeter, measure pin 56 of the ecu or pin 7 of the mpi relay. If you see 12V there all the time, the relay is fine and the ecu is bad. A good ecu will pull those pins close to 0V to activate the fuel pump.

 

[Mitsu_dude]

so that means that my problem is in fact either the mpi relay or the ecu? as in those are the only 2 things it could be?

 

[yokotabrat]

Or the wiring between the two. It's more common for the failure to be in the ecu, though. If you measure right at the ecu and see that the voltage doesn't drop, your ecu is definitely bad.

 

[Mitsu_dude]

i just got a multimeter and tested the pins 1-10. the only 2 that had voltage were 3 and 10. they both had over 12 volts. 10 had voltage all the time, and 3 had voltage when the car was in the on position. no other pins had voltage. i hooked the multimeter positive end into the fuse connector thing that the mpi relay plugs into, and tried each pin hole. i grounded it by touching metal. did i do it wrong? and if not what do these results mean?

and also i dont know if its important but my car has a push start wired.

 

[yokotabrat]

That's good. Pins 3 and 10 should have voltage. Was the mpi relay plugged in while you were measuring? You have to have it plugged in to see voltage on pin 7 and have the ecu control the relay.

 

[Mitsu_dude]

no, it wasnt plugged in. i had the relay out, and tested the little slots where each of the pins of the relay would plug in. how do i test it with the relay in? and just from checking it the first time does it show whether or not its the relay or the ecu? but like i said before, when it was plugged in and the cover was off only the part of the relay with 5 prongs sparked made contact whatever you call it. wouldnt that mean that pin 7 isnt getting voltage?

 

[yokotabrat]

You might be able to jam in the red multimeter lead into the back of the plug (where the wires go into the plug) and be able to touch the contact that mates with the relay pin. That's your best bet.

Yes, if you measure with the relay plugged in and you see voltage on pin 7, the ecu is bad.

There are 2 relays inside the mpi relay. The side with 5 prongs is for the fuel pump, the other one is to power the ecu. They both are activated at separate times. The ecu power side will be activated when the key is turned to ON. The fuel pump side will actually be activated when the starter is engaged. This is probably what you are seeing. However, after the starter has engaged the fuel pump relay, the ecu is supposed to pull pin 56 low (pin 7 on the mpi relay) to keep the fuel pump powered. If you are seeing the fuel pump side click off a second or two after the starter turned over the engine, the ecu isn't keeping the fuel pump side of the relay on like it should. Measuring pin 7 will tell you for sure. If you see it at 12V all the time when the relay is plugged in, the ecu is not working properly.

Hope this helps explain it better.

 

[Mitsu_dude]

so in theory, with the cover pulled off the relay, if i start the car then the fuel pump relay should click once and the little contact thingy should be down the entire time???? and also i was reading somewhere that a kinked fuel line from the fuel pump might throw a code as well. is this true?