Need a second opinion! Help with fuel pump wiring

[psychlow]

OK guys, I'm needing your opinions on this one. I'm thinking this is simple, but I may be oversimplifying it.

The two stock power wires that go to the pump (one black, one black w/ white stripe) are both reading negative voltage - meaning I hook up my multimeter to a known good positive and either one of these wires, and I read +0.30V (battery is almost dead).

Does anyone know if, for some stupid reason, the positive wire switches to a ground wire when the ignition switch is off, or do I simply have a short somewhere?

ANY RESPONSE WILL BE HELPFUL - I have to get this car running within two days, otherwise my apartment complex is going to have it towed (bastards).

 

[psychlow]

Oh, I forgot to mention, 0.30V is the same reading at the battery itself (across the terminals).

 

[dave99gst]

not real sure about that one, but i do know the pump dont acualy get any power untill you turn the key to "start"

 

[psychlow]

Dave, thanks for the reply.

Yeah, I knew that the relay wouldn't engage until it was KOEO... but, here's a question you (or anyone) might have an answer for...

I tried looking ALL OVER, and CANNOT FOR THE LIFE OF ME figure out what relay the damned fuel pump wires connect to. There is evidently not a specific "FUEL PUMP RELAY" for our cars, according to the dealer and every parts store I've visited.

Aside from that, I haven't found a single damned wiring diagram that has the fuel pump circuit included in it - even on the DSM backup manual CD.

Any ideas?

 

[Aikouka]

Another good way to know if it works is if the fuel pump turns on when the car is turned to "ON". If someone stands out beside the car around the tank area, they should be able to hear the pump coming on and it will stay on as long as there is fuel pressure.

I also checked my repair manual for a wiring diagram for the fuel pump, but I was unable to find anything, sorry .

 

[psychlow]

That's OK, thanks for checking.

The problem I'm having is that I'm not getting sufficient voltage to those two wires to even activate the RELAY for the pump rewire. When I crank the engine (jumping from another car), voltage on those two wires cycles between 3-5 volts, and right when I stop cranking, it ups to 8.0+V, and then drops to zero.

I'm kind of at a loss for what's causing this ... I'm hoping it just a short somewhere, but I'm not finding any blown fuses, and that's concerning me.

Any other ideas? Anyone know much about the MPI control unit, what it does, or what wires go to it/come from it?

 

[Aikouka]

Okay, I actually found where the stuff is located. The fuel relay is by the ECU under the center console (I found it in the Haynes manual.) Also, you can try the fuel pump test connection and try running 12v through it (This will run the pump.) This site will show you where it is:

http://members.shaw.ca/dsm.1000q/Engineprimer/fuelpumptestconn.htm

If you have any other questions, let me know and I'll look 'em up in the manual.

 

[psychlow]

Awesome! Thank you, I had forgotten about that thing... it'll DEFINITELY help when I'm trying to diagnose this crap.

After studying the wiring diagrams futher, I did find that there are three relays near the ECU that control various things, one of those being the MPI relay that controls the fuel pump. So that might be a culprit - before that, in the wiring scheme, is the MPI control unit, which is another likely suspect.

So, my course of action either tomorrow or the next day is to cut the wiring near the MPI relay and see if I get the same results while the FP test connector is jumped. If so, I'll have to check/replace the MPI relay and/or controller... if not, it's just a short in the wiring to the pump.

Man, this is going to take forever. I'm almost ready just to hard-wire in a damned pump switch.

 

[shwinp]

Having the exact same problem. Since psychlow never found a solution, I'm renewing this thread.

- I tested the relay and it works fine with 12v to the switch terminal.
- measured voltage between new 10 guage and new ground (12+ volts as expected)
- measured voltage from stock plug during crank (not getting enough voltage to actuate the relay)

The relay is from radio shack and has a pull-in voltage of 6V (Which may vary on temperature).

Note that going back to stock wiring works fine.

Anyone have ideas as to why we can't get enough voltage from the stock plug?

I suppose my next step would be to try another relay.

 

[psychlow]

If you've tested the relay to be good, I somehow doubt that'll help, unfortunately.

Did you have any fuel supply problems on the stock wiring? That's originally why I replaced the pump and decided to do the rewire in the first place - my OEM pump was not supplying enough fuel to the engine.

Come to find out, the reason it was occurring was due to insufficient voltage at the pump.

 

[shwinp]

My reasoning for trying another relay is that the pull in voltage may not be to specs (relay may be defective in this respect).

Never had or have any problems with stock wiring - just want a little more fuel to play with my setup. Note: my car runs excellent with only 30k miles.

So you DO have the rewire working? If not, you're still running the new pump with the same "low" voltage?

If trying another relay doesn't work, I'll probably just go with a new 190 pump with rewire; and if that doesn't work, I'll have to go with a 190 pump with stock wiring.

I'll be updating this thread with results - it may take me some time though.

 

[psychlow]

The way I had to get the car to work was to just run my rewire straight to the pump, meaning I have to connect the pump before I drive and disconnect it when I get there.

Sure is a PITA. Can't wait to get it fixed, one way or another.

 

[shwinp]

ok - tried new relay - same result.
I can almost guarantee that a new pump will result in the same result.
I simply need more voltage to switch the relay on.

Found this link relating to the bigger dsm cars:
http://stealth316.com/2-fuelpumprelaybypass.htm

It details bypassing the stock fuel pump relay/resister to obtain more voltage and is apparently required for some to be able to rewire successfully (because they are not getting enough voltage to switch the new relay on).

I know on my 1g, the fuel pump relay is next to the ECU. Does anyone know how one might do the bypass for our cars? Our relay seems to be more complex than the ones on the stealth/3000gt.

Anyway, I'll be looking into this myself - as time permits. Will post back if I make any progress.

 

[shwinp]

Found a solution. Thanks to this article:
http://www.kydsm.com/article.php?a=7

Basically getting power source from fuel pump check connector to activate the relay.

I actually think this is the easier method of rewiring since you won't have deal with so many wires under the car. This assumes of course that you have the check connector. Some dsmers don't have this luxury as the check connect must be done at the stock FP relay itself.

 

[psychlow]

If you can post any pics or diagrams of your solution when you get it done, please do.

 

[shwinp]

I didn't see your request for pics until a few days ago, but here they are.

Source to switch the relay on using check connector (next negative battery terminal)

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Overview of rewire:

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