Question for Steve (wiring guru!) 2g 6 bolt swap, no fuel pump, no fuel, no spark.

[-TunedDSM-]

First let me state the research i have done on this.

From steve:

Can we stick to super95awd questions?

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Like the 1G, the 2G DSM has two main circuits for the engine. The MPI circuit and the Ignition circuit.

The ECU is connected to both but powered from the MPI circuit.

Power for the MPI circuit comes from the MPI fusable link #4 (30A) in the relay box under the hood to pin 3 and 4 on the MPI relay and should be present all the time. Power for the Fuel Pump and the rest of the ignition circuit comes from the Ignition fusable link #6 (30A) in the relay boxl and for the fuel pump winds up on pin 3 and 4 on the FP relay.

On the 2G the MPI relay and fuel pump relay are two seperate relays unlike the 1G where they are combined. The FP relay only has one trigger input and the MPI relay one. Pins 3 and 4 are the power inputs for both relays. When the control line (pin 2) to either relay is activated (pulled to ground) the relay switches the power from the input (pin 3) to the output (pin1).

The ECU receives backup power on pin 80 (red with blue stripe) from dedicated fuse 11 in the relay box under the hood. This is used to maintain the RAM in the ECU's CPU and allow the ECU to power itself up. Backup power on ECU pin 80 should to present all the time even with the car off.

The ECU sits dormant in a powered down state waiting to see pin 82 (IG1 from ignition switch) go high to battery voltage. When pin 82 goes high the ECU pulls pin 38 (MPI relay pin 2) (blue with green stripe) low (to ground). This causes the the relay to activate and switches the MPI power from MPI pin 3 to MPI pin 1 providing power to the ECU on pins 12 and 25 (red) along with various sensors, solenoids, injectors, ISC, and O2 Heaters in the engine bay.

Shortly after battery voltage shows up on ECU pins 12 and 25 the reset circuit in the ECU wakes the ECU up and if it boots the CEL will come on for about 5 seconds, the boost gauge will display 0 (Stock ECU software on turbo cars) and the ISC on the throttle body will move in and out to rehome.

The next interesting condition is when ECU pin 71 (yellow) (indirectly START from the ignition switch) goes high (to battery voltage).


I hope I got this right.

Steve

Now. Here lays my problem.

I get 12v on pin 80, and 12v on pin 82 when ACC position.

However, i get a knocked down .02-.07 volts at pin 12 and 25. No more than that.

My fuel pump does not turn on, i am getting no spark, my 1g CAS is only registering .02 volts on ACC, no fuel. It cranks but that is about all it does.

I am thinking it is something with the relays, but im really quite lost.

Its a 1997 GSX with a 95 ECU w/ dsmlink and a complete 6 bolt swap with ISC block off blate.

 

[-TunedDSM-]

Alright, at the MPI relay i am getting 12v ffrom the constant 30A fuse -> mpi relay.

The fuel pump relay is getting nothing in any PIN's. I get maybe .02 v in one of the pins and that is it.

So i have ecu power, but im getting a severly knocked down/non existent power supply back to the ecu after traveling to the relay's.

What can i do>

 

[steve]

I get a knocked down .02-.07 volts at pin 12 and 25. No more than that.

My fuel pump does not turn on, i am getting no spark, my 1g CAS is only registering .02 volts on ACC, no fuel. It cranks but that is about all it does.

Pins 12 and 25 are the +12v power feed from the MPI/MFI relay. Without power there nothing else interesting is going to happen. You can make sure that relay is getting 12v from the fusable link and check that the relay works by grounding pin 2 on the relay to see if the power gets switched to the output and to the ECU.

If you don't have a Factory Service Manual with the wiring diagrams you'll need to get one or a ManualCD.

Steve

 

[-TunedDSM-]

i have the DSM CD i am using for reference. (manualCD).

So i am getting a full 12v at the Red/blue wire to the MFI, as well as 12v on the B/W, and 12v at the R/B wire. I do not have power to the wire BL/LG (according the manualCD wiring diagram). Which is correct.

The MPI/Fuel pump relay has no 12v at all (i get ground on one pin, 0 on 2, and a .02v on one).

Thanks steve, I have never tackled wiring before and i had to read the manualCD "how to read" for about an hour learning the diagrams

 

[lucasto34]

okay, i had the exact same problem. i will say it's highly unlikely that it's your relay that the problem. if it is then you're probably going to have to go to the dealer to get the relays ### i've searched all the regular autoshop stores and they don't stock the correct ones.

the chilton/hanes manual tell you how to test them differently than you described. i used their diagram and found out that mine were fine.

you're probably not going to want to hear this either.. i'm going to go ahead and say that your chip is backwards or your ecu is fried. i also have a 97gsx with a dsmlink in it that didn't get any fuel or spark. you can try one of two things. 1- flip your chip around and see if that solved it. if not, then 2- swap your ecu out with another one and see if that starts your car. if 1 doesn't work, then 2 will most likely work and that will tell you that your ecu was bad to begin with or fried bye, most likely, whoever socketed it. also, when you stick your test ecu in make sure to swap your spark plug wires as per what dsmlink says to do. you may have heard of the CAS inversion!http://www.dsmlink.com/faq.html#cas

 

[steve]

I have the DSM CD I am using for reference. (manualCD).

Good

So I am getting a full 12v at the Red/blue wire to the MFI, as well as 12v on the B/W, and 12v at the R/B wire. I do not have power to the wire BL/LG (according the manualCD wiring diagram). Which is correct.

The MPI/Fuel pump relay has no 12v at all (I get ground on one pin, 0 on 2, and a .02v on one).

You have me confused. I can't remember if all 2Gs use two relays or if some years use the old combined MPI relay.

If your car matches the setup like shown inon the ManualCD then there whould be two big red/black wires from the underhood fusebox. These should have 12v all the time if the fuse is good. You see that there is one red output wire from the relay that branches off to feed the ECU and solenoids. That will only have 12v when L/G (Blue/Green) wire is grounded. (It's one end of a coil and the other end is connected to the battery via the MFI fuse.) That's the pin the ECU pulls to ground to switch the power on.

On the fuel pump relay, the power feed comes from ignition circuit on the two Black/White wires. The output to the fuel pump is black/blue wire and the coil is activated by the white/red wire being pulled to ground by the ECU.

Steve

 

[luv2rallye]

I can't remember if all 2Gs use two relays or if some years use the old combined MPI relay.

Only the 95 2g used the combined MPI/FP relay (according to each year's manual 1995-1999 of "Mitchell Engine Performance & Service Repair" manuals anyway). If someone knows otherwise please correct me.

 

[-TunedDSM-]

Thanks steve, and yes, i have 2 seperate relays just as you described.

Is there anyway to bypass the relays themselves for testing's sake?

The relay is definetly not functioning because i get all the sources for power but it will not ground the BL/LG (pin38), therefore leaving barely .02 volts to go to the ECU pin 25.

And on the fuel pump relay, i do not get ANY 12v source, at ACC or not.

 

[-TunedDSM-]

Steve,

Is there any way to bypass the Relays with a fused power source straight to pins 12 and 25 to see if the relays are my probelm?

I am only getting 6 volts via the yellow/black wire at the fuel pump. I still have no spark/fuel and the ecu is dormant (CEL light just stays on with ACC turned, doesnt flash)

ALso dsmlink wont connect.

The ecu/dsmlink was working properly all year last year and it did nothing but sit covered in my bedroom since decmeber, i doubt my ecu blew up randomly and we all knwo 2g ecu's dont blow capacitors often

 

[-TunedDSM-]

Also, even when using the fuel pump jumper connectiono n the firewall, i only get 5v to the fuel pump

 

[steve]

Is there any way to bypass the Relays with a fused power source straight to pins 12 and 25 to see if the relays are my problem?I still have no spark/fuel and the ecu is dormant (CEL light just stays on with ACC turned, doesnt flash)

I wouldn't go bypassing the relay until you know why they aren't working.
Did you ground the pin like I suggested? You can activate the relay with the ECU unplugged. Assuming you have 12v to the input and one side of the relay coil then grounding the other side of the coil will trigger the relay.

Once your sure the problem is the relay you could bypass the relay using a fused jumper between the input and output pins.

I am only getting 6 volts via the yellow/black wire at the fuel pump, even when using the fuel pump jumper connectiono n the firewall, I still only get 5v to the fuel pump.

Worry about one thing at a time but make sure that the battery is fully charged.

ALso dsmlink wont connect.

The ecu/dsmlink was working properly all year last year and it did nothing but sit covered in my bedroom since decmeber, i doubt my ecu blew up randomly and we all knwo 2g ecu's dont blow capacitors often

If the MPI/MFI relay isn't switching on then DSMLink isn't going to work for the same reason that your not getting any spark or fuel, the ECU isn't powered up.

Steve

 

[-TunedDSM-]

disregard this post, check the one below!

 

[-TunedDSM-]

Ok steve,

I grounded the BL/LG pin that the ECU would normally pull to ground to open the relay.

When grounded, the audible click occured.

But heres the part where im lost:

Im only getting 5 volts at the ecu pin 12 when the relay is grounded (open)

Same with the 5 volts im getting at the fuel pump...

 

[steve]

Ok steve,

I grounded the BL/LG pin that the ECU would normally pull to ground to open the relay.

When grounded, the audible click occured.

But heres the part where im lost:

Im only getting 5 volts at the ecu pin 12 when the relay is grounded (open)

Same with the 5 volts im getting at the fuel pump...

So your relay works but you have a very low voltage under load. 5v isn't enough to power the ECU up.

So now it time to look at the battery and it's cables and terminals. With a fully charged battery you would have to be pulling a lot of current to drop the voltage to 5v, enough current to blow fuses. If you have a bad battery or poor connections to the battery it might do this.

Steve

 

[-TunedDSM-]

I have a worn out battery and the negative terminal will not go any tighter, its really loose. I bought all new terminals and a new battery and i will go at this again

Thanks steve

 

[-TunedDSM-]

! this is driving me nuts.

I bought all new terminals, new cables, even ran 4 more grounds from the battery (extra ones)

Still nothing.


No ecu on (CEL doesnt flash, just stays on, no spark/fuel)

No spark/fuel (due to ecu not coming on)

12v TO the relay's... 5-6 volts to the ecu and the fuel pump

 

[-TunedDSM-]

I have a wiring short somewhere, i believe the leads for the MPI relay and the headlights got switched when the fusebox was rewired.


When the key is turned the headlights come on, and then shortly after my light switch on the steering column begins to smoke/caught fire. This happened twice, with 2 light switch levers.

I need to completely redo the fusebox..

 

[steve]

This is really critical information that should have been in your first post. I wish you luck getting to the bottom of all these problems.

Steve

 

[-TunedDSM-]

Thanks steve, you were right. I found the headlight and Engine fuse wires mixed up. I rewired it and everything works beautifully, although your help couldnt do much since i left that out, I have learned far more about wiring and electrical in my car than i ever thought i would, and im sure it will come in handy in future issues!

Feel free to lock

 

[steve]

Congratz on wiorking through the problem to a successfull conclusion. I'm glad I could help the little I could.

Steve