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2G Test fuel pump/mfi relay

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JGeezyyy

Proven Member
46
2
Feb 2, 2015
Naugatuck, Connecticut
Diagnosing a no-start. Fuel pump isn’t turning on. Tested the fuel pump by directly connecting power to it and it turned on. Trying to test the relays. In the picture below it’s sayingto test the continuity between 2-4. Do i have them labeled correctly in the pictures? And this is just with the multimeter correct? I’m not good with this kind of stuff. I connected the black end of the meter to “3” and the red to “4” as I have in the pics. On the left terminal it’s only showing 1.xx. The terminal on the right isn’t showing anything for a reading. I know it’s supposed to be 70 if done correctly but I just want to make sure I’m testing it correctly so I can rule it out.
 

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The manual usually shows pin numbering looking from the top (where the wires go in) of a connector. So I think you have them labeled incorrectly. You are measuring the relay and not the harness, correct?
 
The manual usually shows pin numbering looking from the top (where the wires go in) of a connector. So I think you have them labeled incorrectly. You are measuring the relay and not the harness, correct?
Very easy to just jump the test connector on the firewall. Might help rule out relay
 
The manual usually shows pin numbering looking from the top (where the wires go in) of a connector. So I think you have them labeled incorrectly. You are measuring the relay and not the harness, correct?
Sorry for the labeling I should have labeled the relay.

At first I’ll admit I was testing the harness. But I’ve been testing the relays out of the car for the past day or 2 and can’t get the multimeter to give a solid reading. It’ll flash a random number, sometimes 30, sometimes 90, then drop back down to 0.

I’ve been testing them per the manual in the picture. Am i testing it wrong?

Very easy to just jump the test connector on the firewall. Might help rule out relay
On 2gs is it the black or blue connector? I’ve been getting mixed answers. When I tried this last week nothing happened on either connector so again I wasn’t sure if I was properly testing.
 
Last edited by a moderator:
There are two parts to the relay, the coil and the contacts.

The coil will have a fixed resistance between it's two connectors (pins 2 and 4).

It's the coil that gets battery voltage fed to it which creates an electromagnet that cause the contacts to connect. When there is no voltage across the coil, the contacts are not connected (Infinite ohms between pins 1 and 3) and when there is voltage across the coil, the the contacts are connected (0 ohms between pins 1 and 3)

Looking down into the relay with the ridge that the connectors snaps on facing away from you the pins are:

1 2
3 4

On the 2g's that use these two relays rather than the old MPI relay both relays are the same, one's for the car MPI circuit and the other for the fuel pump.
 
There are two parts to the relay, the coil and the contacts.

The coil will have a fixed resistance between it's two connectors (pins 2 and 4).

It's the coil that gets battery voltage fed to it which creates an electromagnet that cause the contacts to connect. When there is no voltage across the coil, the contacts are not connected (Infinite ohms between pins 1 and 3) and when there is voltage across the coil, the the contacts are connected (0 ohms between pins 1 and 3)

Looking down into the relay with the ridge that the connectors snaps on facing away from you the pins are:

1 2
3 4

On the 2g's that use these two relays rather than the old MPI relay both relays are the same, one's for the car MPI circuit and the other for the fuel pump.

Okay so I think I’ve been testing correctly then. The way I have it in the picture is the correct orientation if I’m not mistaken?
 

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I have the red on pin 4 (bottom right) and the black on pin 3 (top right). When I try to test the ohms on one and 3 it’s always a different number, sometimes 30, sometimes 90. But it always goes back to 0 if I keep the test leads on.
 

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The next test as shown in the FSM is to apply battery voltage to 2 and 4 and see if 1 and 3 switch.

I don't have access in the mountains to my FSM so I can't say what color wire the Fuel Check Connector under the hood is. But to use it you apply +12v to it and the pump should run.

However that test bypasses the ECU and fuel pump relay operation, it's just feeding 12v to the same place after the FP relay.

Without DSMLink it's difficult to get the ECU to force the fuel pump on. You can check to see if by grounding the FP relay pin at the ECU that the relay activates and runs the pump which leaves the ECU as the last unknown.
 
The next test as shown in the FSM is to apply battery voltage to 2 and 4 and see if 1 and 3 switch.

I don't have access in the mountains to my FSM so I can't say what color wire the Fuel Check Connector under the hood is. But to use it you apply +12v to it and the pump should run.

However that test bypasses the ECU and fuel pump relay operation, it's just feeding 12v to the same place after the FP relay.

Without DSMLink it's difficult to get the ECU to force the fuel pump on. You can check to see if by grounding the FP relay pin at the ECU that the relay activates and runs the pump which leaves the ECU as the last unknown.
When 2 and 4 are getting power, do I test ohms on 1 and 3? If so, it flashes random numbers but eventually go down to 0. I have dsmlink, but I can’t get my cable to connect anymore. Also, when I tried the check connector last week, nothing happened. So it’s confusing me :banghead:. My check engine light did come on with the key turned to on as it’s supposed to, then turned off. So no clue why the cables not working. I even sent it in to ECMlink and they said the cable was fine. Just received it back the other day actually. I have a video of the car trying to start last week but can’t seem to figure out how to upload it. (Stupid iPhones LOL)
 
I’m helping my cousin fire up his 97 GST.
After a head job and wire harness tuck, the fuel pump doesn’t get power. Cranks over has spark and no fuel.
Crank position sensor, trigger plate, plug wires and fuel filter are brand new.
Coil pack & igniter, MPI relays, CPS, Engine fuse, fuel pump and coolant temperature sensor either have continuity, power or ohm tolerances on point.
I stumbled on the following thread.
http://www.orldsm.com/archive/index.php/t-12221.html
And will definitely start tracing ground from the fuel pump to beyond the firewall.
I’ll probably do this on Thursday night.
The only plug on the harness I didn’t get any power or any type of reading was the triangle coil pack one.
 
I’m helping my cousin fire up his 97 GST.
After a head job and wire harness tuck, the fuel pump doesn’t get power. Cranks over has spark and no fuel.
Crank position sensor, trigger plate, plug wires and fuel filter are brand new.
Coil pack & igniter, MPI relays, CPS, Engine fuse, fuel pump and coolant temperature sensor either have continuity, power or ohm tolerances on point.
I stumbled on the following thread.
http://www.orldsm.com/archive/index.php/t-12221.html
And will definitely start tracing ground from the fuel pump to beyond the firewall.
I’ll probably do this on Thursday night.
The only plug on the harness I didn’t get any power or any type of reading was the triangle coil pack one.
I found a local guy who’s gonna let me use one of his spare ecus to see if that is the issue since I also can’t connect to dsmlink. Hopefully that’s my issue. If not I’m gonna have to chase the fuel pump wiring to make sure it’s all good.
 
It's the black connector on the firewall

2g only sends power to fuel pump when key is at start position unless you jump the connector on the firewall

The pgmfi relay controls more than the fuel pump, you could always just make your own fuel pump hotwire kit with a seperate relay like the do on a hotwire kit
 
I found a local guy who’s gonna let me use one of his spare ecus to see if that is the issue since I also can’t connect to dsmlink. Hopefully that’s my issue. If not I’m gonna have to chase the fuel pump wiring to make sure it’s all good.

You’ve inspired me. One of the clerks at our San Bernardino 40th street Autozone has a 97 as well. I’m tempted to ask him to let me connect our ECU in his car, just to rule out a bad control unit as well.
 
Very easy to just jump the test connector on the firewall. Might help rule out relay

When you do jump this black test wire,

It's the black connector on the firewall

2g only sends power to fuel pump when key is at start position unless you jump the connector on the firewall The pgmfi relay controls more than the fuel pump, you could always just make your own fuel pump hotwire kit with a seperate relay like the do on a hotwire kit

is it safe to crank the engine to see if it will fire up, or is this test connector only intended to just rule out bad EFI and pump?
 
on these relays, the silver pins are for the trigger (coil) and the copper pins are for the load

You must be logged in to view this image or video.
 
JGeezyyy: You do know, right, that on a 2g turbo (but not 2g NT) the fuel pump is only powered when the engine is turning getting CAS pulses (like cranking or running). With engine not turning and key in "ON" position, the fuel pump does not get power.
 
JGeezyyy: You do know, right, that on a 2g turbo (but not 2g NT) the fuel pump is only powered when the engine is turning getting CAS pulses (like cranking or running). With engine not turning and key in "ON" position, the fuel pump does not get power.
Yes I have read that, it wasn’t turning on while I was cranking.
 
JGeezyyy: You do know, right, that on a 2g turbo (but not 2g NT) the fuel pump is only powered when the engine is turning getting CAS pulses (like cranking or running). With engine not turning and key in "ON" position, the fuel pump does not get power.
After reading this response I remembered reading the following awnswer from Tuff4x4 on cargurus.
https://www.cargurus.com/Cars/Discussion-t8186_ds573815
What is the relay module he is talking about?
Also, how does the ignition coil’s harness tie in with the MFI and the relay module in correlation with fuel pump power.
 
So to correctly check the relays, do you need to crank (turn key to start) to get an accurate reading?
I don’t think so. I was able to get a reading by connecting power to pin 2 and 4 ( in the picture above ) while they are connected you test the ohmswith a multimeter, should be around 70
 
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