Please Help Me With Fuel Problem

[1badtsiawd]

Hello everyone,

Okay, first thing first. Just so everyone knows, i have searched for this topic of a couple of hours and can't seem to find what i am looking for. I'm sure it has been gone over before but i am unable to locate it. Here is my situation.

I recently just dropped a new engine in my car and after i did so it the fuel pump would not turn on. Used to be when i would turn my key to the start position the pump would prime. You could hear it plain as day because i have a upgraded fuel pump. I do have a fuel pump rewire mod and i am getting voltage from the battery. i tried bypassing the fuel pump rewire to see if the relay on that was bad and i still had no luck. And i put direct power to the fuel pump and it kicked on. I checked the mpi fuse and it is fine, i also checked the mpi relay. I did this by using this check that steve put on the board:

To check the fuel pump circuit first measure the resistance between 9 to 6, and 3 to 7 on the MPI relay to make sure the coils haven't opened.
Make sure MPI relay pin 6 is grounded.
Check for 12v at pin 3 on the MPI relay when your ignition switch is set to RUN. (this comes from IGN fuse to the ignition switch to the MPI relay)
Check for 12v at MPI relay pin 9 when your ignition switch is set to START. You should also see 12v on pin 2 at this point and the pump should turn on. If you have 12v at pin 9 but not at pin 2 the MPI relay isn't switching. If you have 12v at pin 2 but the pump isn't running you have a bad pump or the wiring is open.
With the ignition switch in RUN try grounding pin 7 and check for 12v at pin 2. This is the other way to switch the MPI relay and how the ECU keeps the pump on after you release the starter.

Steve

I checked the resistance between pin 6 & 9 and got about 250. then i checked the resistance between 3 & 7 and got about 1250. Thats a pretty big difference between them. My question is, what are the numbers suppose to be? and i also found that i have no power at the #2 pin when the key is in the run position as well as the start position. I am not sure if i should have power when it is at the run position. Can someone elaborate on this? When i turn the key from run to start the mpi clicks over( i can hear it). I also checkedto make sure i have spark at the plugs, and i do. Also i took out the ecu and opened it up and everything seems to be fine, no leaking or bad smells. And the ecu turns on and shuts off like it should. If anyone can help me with this i would greatly appreciate it.

Thank you
patrick

 

[steve]

While this shows the automatic version of the 1G MPI circuit you should be able to figure out what goes where.

The FSM says that the wire to pin 3 (power feed from the ignition switch) is a thick black w/white stripe and the wire to pin 2 a thick black w/green stripe until C-54 in the harness at which point it is also a thick black w/white stripe wire all the way to the fuel pump.

 

[1badtsiawd]

Steve,

Like i said in the above post. i checked the resistance between pin 6 & 9 and got about 250, then i checked between 3 & 7 and got about 1250. Should there be that big of a difference between them? also From the diagram you provided would i be correct to say that in the run position i should have power to the #3 pin and to the #7 pin which would in turn prime the pump. and then when the key is turned to the start position pin 9 should have power and that would supply pin 2 with the constant power while trying to start? Please correct me if i'm wrong. If i am testing the mpi right then it seems to me it would be bad and is not switching over to provide power to pin 2, unless something else would keep it from switching over like the ecu.

thanks
patrick

 

[steve]

i checked the resistance between pin 6 & 9 and got about 250, then i checked between 3 & 7 and got about 1250.

Should there be that big of a difference between them?

From the diagram you provided would i be correct to say that in the run position i should have power to the #3 pin and to the #7 pin which would in turn prime the pump.

then when the key is turned to the start position pin 9 should have power and that would supply pin 2 with the constant power while trying to start?

Please correct me if i'm wrong.

If i am testing the mpi right then it seems to me it would be bad and is not switching over to provide power to pin 2, unless something else would keep it from switching over like the ecu.

thanks
patrick

1. I don't have an extra MPI relay handy to measure and the FSM doesn't provide a specification but I would have expected the two coils to have the same resistance.

2. Unless the engine is running (CAS turning) the ECU isn't going to be pulling pin 7 low so you will see pretty much the same voltage on pins 3 and 7 since no current is flowing and therefore no voltage drop (read about ohms law).

So there shouldn't be any voltage on pin 2 unless the ignition switch is in the start position or the engine is running.

3. Yes, the ignition switch should be providing pin 9 with battery voltage when it's turned to the start position and that should activate the relay.

 

[1badtsiawd]

okay, when i have the ignition turned to the start position i am not getting any voltage to the # 2 pin. at no point in time can i get any voltage out of pin 2, no matter where i turn the key. Would that accompanied with the resistance difference between the 2 coils mean that the mpi is bad? or might i have another problem. It seems to me that everything going into the mpi is giving the correct voltage and is putting the voltage out when it is suppose too. So at this point its looking like i have a bad mpi to me, but there may be something that i don't know about that would keep it from working correctly. Am i over looking something that would keep the mpi from working properly? or am i just over analyzing things and trying to make it more complicated than it really is?

thanks
patrick

 

[steve]

If your not getting power to pin 2 anytime and you have power at pin 3 then your MPI Relay may be bad. I can't make it any clearer than I have in the post you quoted or from the diagram I posted.

P.S. I can't read big run on paragraphs anymore. If you want me to help you, have to help me by formating your questions.

 

[1badtsiawd]

sorry if the reply is to long or if i you think i am dragging this out. i am just trying to gather as much info about this as possible so i know i am doing things correct and have everything covered. thanks for the help so far.

patrick

 

[1badtsiawd]

there is one more question that i have and can't seem to find a answer too.

I found a guy who has a mpi relay, it's out a the same car as mine which is a 92' talon turbo 5spd. the number on his relay is:

E8T07071
1911

and the number on my relay is:

E8T07071
1531

My question is what is the bottom number for and does it matter or is it just the top number that matters?

 

[steve]

My question is what is the bottom number for and does it matter or is it just the top number that matters?

It's just the top number that matters.

 

[1badtsiawd]

Cool, thank you for all the help!

 

[1badtsiawd]

okay, so after testing my mpi and finding out that i was not getting any power out of the #2pin(leads to fuel pump), i decided to buy another one. i put that one on the car and same thing no power on pin 2. I tested the resistance between pins 6 & 9 it was 250, and between 3 & 7 it was 1250. This was the numbers on both relays. My question is: is that what the numbers should be or are they off?

If anyone knows the answer or would even be willing to take theres off the car to test it( would take about 5 minutes) i would appreciate it. I'm trying to find out what the numbers should be from someone that has one on a car presently that is running. Maybe i just got another bad one or maybe it may be something worse like the ecu. let me know if you can help.

thanks
patrick

 

[1badtsiawd]

Okay, I decided to buy another ecu because i found one that was cheap. When i put that on my car nothing changed. I still do not get any power to the fuel pump. Does anyone have any help they can offer because i am stumped on this.

I have checked the mpi fuse, mpi relay, changed ecu's, applied direct power to pump( works fine). Everything seems to be okay. The only problem i am having is that i don't get any power out of the #2pin on the mpi relay which leads to the fuel pump. It seems to be getting power into it, just not out. I replaced the relay and nothing changed. Maybe i got another bad one, i'm not sure.

Please if you know how to check the relay and would do so for me i would appreciate it. I hate to just buy another one if that is not the problem. And there maybe something else that i am not thinking of or i don't know about. I would appreciate any help.

thanks
patrick

 

[steve]

Steve,

Like i said in the above post. i checked the resistance between pin 6 & 9 and got about 250, then i checked between 3 & 7 and got about 1250. Should there be that big of a difference between them?

Also from the diagram you provided would i be correct to say that in the run position i should have power to the #3 pin and to the #7 pin which would in turn prime the pump.

Then when the key is turned to the start position pin 9 should have power and that would supply pin 2 with the constant power while trying to start?

I pulled the MPI relay from my parts car and measured it.

From pin 3 to pin 7 I get 128 Ohms.
From pin 6 to pin 9 I get 26 Ohms.
Measuring across pin 10 to pin 8 is effected by the diode that blocks current in one direction but also has a voltage drop that will fool the DVM measuring resistance.

In the run position you should have power to pin 3. If you see power on pin 7 then the ECU isn't pulling the pin low and the fuel pump shouldn't be running. The coil just looks like a long piece of wire so if you have a voltage on one end and the other end is floating (basicly disconnected) you will also have the voltage on the that end too. Since the circuit isn't completed, no current is flowing there won't be any voltage drop. When the ECU decides to turn on the pump it will pull pin 7 to ground and make circuit flow in the coil.

You can test the functions out of the car if you have access to 12v to test with.
Connect pin 3 to 12+ and pin 7 to the ground/negative. The rleay should click and you should see 12v at pin 2.

Connect the battery across pins 6 and 9, again the relay should click but because the battery isn't connected to pin 3 also you won't see voltage at pin 2. Instead you'll be able to measure continuity (0 Ohms resistance) between pins 2 and 3.

That tests the function of the fuel side of the MPI relay.