2G No Start. Sensor Voltage and Harness Swap

[joshuah]

I'm having serious trouble getting my 95 Talon to start. As of now crank no start due to no spark.

I run voltage test on all the sensors and get 12v on all except TPS has 5v, CAM has 5v on one wire 12v on another, coil trigger power wire blk/w stripe has 12v the PTU has 12v on 3 wires 8v on 1.

The ECU right now is a black box, car is a 95 Talon. I have a EPROM ECU just cant afford ECMLink yet.

Just within last few months I had it tore down and put new rotating assembly in, forged H beam connecting rods, Nippon scat pistons, OEM crank, king bearing set, ARP 2000 cap bolts, ARP main studs, balance shaft delete, new valves and valve seals, ARP head studs, Cometic MLS head gasket, and HKS timing belt.

Please help I have no more knowledge about what to do.

 

[19Eclipse90]

Ok.

Sounds to me the new harness is not from a 1996, then, and you’d have been better off splicing on the 1995 relay to what sounds like a 1995 harness.

A 1996 harness should have 100% matched up with the pigtails of the two relays you have. The fact it didn’t and, specifically, you mentioned an extra black with white wire, which looks like it’s on the dual relays pigtails, not out of the harness, supports the conclusion it’s a 1995 harness.

So, easiest solution to this mess is to wire it back up with the 1995 relay. If you don’t have the 95 relay any longer, we can figure that out, if needed.

Either way, the black with white should not go to the black with red.

 

[joshuah]

Black with red supposed to be power supply but it only has 0.47 volts

 

[19Eclipse90]

It is a power supply to the rest of the ECU, not from the ECU to the MFI relay. The voltage gets to that point after the relay is activated. All of this is very well explained in the 2G MPI / MGI relay circuit explanation thread.

 

[joshuah]

Ok so is there any way to make this work or am I better off just pulling all the wires out and throwing it all away

 

[19Eclipse90]

In my opinion, the best thing to do would be go back to the 1995 relay if you still have it. That means every wire will have its own home.

If not:
1) Disconnect the black with white from the black with red.

2) Tape up the black with white and put it out of the way. Or tie it into the other black with white. Your choice.

3) Join the black with red to the thick reds (from the pin indicated below) you’ve already connected. So you’ll have three wires joined together.

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That will fix the wiring, as a start.

 

[joshuah]

In my opinion, the best thing to do would be go back to the 1995 relay if you still have it. That means every wire will have its own home.

If not:
1) Disconnect the black with white from the black with red.

2) Tape up the black with white and put it out of the way. Or tie it into the other black with white. Your choice.

3) Join the black with red to the thick reds (from the pin indicated below) you’ve already connected. So you’ll have three wires joined together.

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That will fix the wiring, as a start.

Still wont kick the fuel pump on when I turn ignition switch on run. If I jump a wire to fuel pump wire black / blue it comes on

At this point man I dont think it will ever start again it is so ridiculous. Everything I've tried doesn't change anything it just sits here and has me questioning my own ability. This year 2025 I've ha over 50 customers come with car problems and I have fixed everyone of them and they all are happy because they all passed emissions and safety. But my car the only thing I have, i cant get it to run anymore and it really doesn't make sense

 

[19Eclipse90]

Still wont kick the fuel pump on when I turn ignition switch on run. If I jump a wire to fuel pump wire black / blue it comes on

So, what did you end up doing to the wiring?

I never said it would fix your no start. But it should remove a variable if done properly and the wiring was otherwise good to begin with.

Again, I would point you to the article describing function of the 2G MFI circuit.

If the circuit isn’t switching on the fuel pump for you but you can jump it via the black with blue wire, then your issue is either the relay(s) itself, the ECU, the wiring in between, or the wiring leading up to the relay(s).

That article also provides how-tos for testing the relays which is a good place to start if you aren’t sure where to go from here.

 

[joshuah]

I wired the black red to the red wire

I wish when I bought this car it wouldn't have been so hacked up

Its so damn nerve racking mo being able to drive it. The f***er had only got maybe 50 miles on the rotating assembly and the entire suspension has maybe 10 miles on the whole system tire are brand new hks exaust still needs welded properly. Turbo new too

I have 2 sets of those relays neither make a difference

Even if I eventually get the pump to work I bet it doesn't have spark either

 

[19Eclipse90]

The CEL still comes on and turns off after 5 seconds when you turn the ignition to ON?

And still a crank no-start? It does crank, right?

If the ECU doesn’t see the CAS signal pulsing, the fuel pump won’t come on. What CAS are you using? 1G or 2Gb? How is it wired to your 2Ga harness?

 

[joshuah]

The CEL still comes on and turns off after 5 seconds when you turn the ignition to ON?

And still a crank no-start? It does crank, right?

If the ECU doesn’t see the CAS signal pulsing, the fuel pump won’t come on. What CAS are you using? 1G or 2Gb? How is it wired to your 2Ga harness?

Yea CEL comes on and off and yes it cranks . My cas is on the tranny end of the head and tge connector didn't match but wire were same so I spliced my cas plug from my harness

 

[19Eclipse90]

Only a 3-wire CAS?

Reviewing what I wrote earlier again, the “extra” black with white wire - what did you do with that? And which position is it on the relay connector? Continuing to try wrapping my head around your situation, it does need to be connected to the other black with white if it isn’t already. It cannot be left disconnected. That was my error mixing up which harness and relays were being used.

 

[joshuah]

I did wire the blk and wht stripe to the other one both are on the fuel pump relay

Yea 3 wire cam angle sensor

 

[19Eclipse90]

And both black with white wires from the FP relay pigtail attach to the black with white in the harness?

So, using that thread I keep referring to, do you see battery voltage at ECU pin 71 when cranking? What about the voltage at ECU pin 8? Does it differ when not cranking vs cranking?

 

[joshuah]

Pin 8 fp with ignition on i get 12 volts

 

[19Eclipse90]

Ok. And with the engine cranking, what does voltage at ECU pin 8 read?

 

[joshuah]

Id have to check again. I verified spark too

finally getting codes

When I crank pin 8 drops . 0.08v

And not sure why but crank sensor red wire has 12v with ignition on getting codes for cam tangle sensor and the manifold absolute pressure sensor

 

[19Eclipse90]

Pin 8 fp with ignition on i get 12 volts

When I crank pin 8 drops . 0.08v

If you still aren’t getting the circuit to switch on the fuel pump, these results along with being able to jump the black with blue and get the pump to turn on suggest that there is an issue with the fuel pump relay. Measure voltage at the black with blue while cranking to see what you get.

 

[joshuah]

The fuel pump connector had a bad plug, it was rusted don't know why but I replaced with a new pin plug and my car finally fired up. It didn't run very long and I have codes for TPS, CAS, and MAP.

I'll have to test each one and inspect wires and plugs to determine if the sensor is actually bad or not. BUT SHE DID FIRE UP AND I WAS LIKE "YEAHHHHH bi***!"

 

[Maxicarlos]

¿Un tienes el problema? Tengo un defecto muy similar.
I have spark. Fuel arrives, I have current in all the sensors, new crankshaft sensor, camshaft sensor works, mpi and gasoline relay they lent me one that works. Control unit looked at the components visually and they look perfectly. Still don't inject gasoline! I'm already going crazy!

 

[joshuah]

The wires going to/from the MPI or ignition switch get 12v the wire connecting to ECU pin 81 get 5v. Do you get a CEL turned on for 5 seconds when you turn the ignition on?

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Yes Steve I've went through all these I have them printed out. Where i screwed up was i bought a 96 engine harness

The wires going to/from the MPI or ignition switch get 12v the wire connecting to ECU pin 81 get 5v. Do you get a CEL turned on for 5 seconds when you turn the ignition on?

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Yes cel comes on 5 seconds goes off

Yes Steve I've went through all these I have them printed out. Where i screwed up was i bought a 96 engine harness

Yes cel comes on 5 seconds goes off

I dont get it i have them wired exactly the same as diagram

maybe this was already asked but what happens when key on? Does the ECU light come on for 5 sec then go out? When you do crank it does fuel pump turn on? Those are two big indicators. You already said tach does not twitch? Is that correct?

Now jet turned on fuel pump comes on until I turn to run then I goes off and starter doesn't engage

95 eprom ecu with the 95 cam sensor now and trigger wheel installed timing done yesterday

Ok.

Sounds to me the new harness is not from a 1996, then, and you’d have been better off splicing on the 1995 relay to what sounds like a 1995 harness.

A 1996 harness should have 100% matched up with the pigtails of the two relays you have. The fact it didn’t and, specifically, you mentioned an extra black with white wire, which looks like it’s on the dual relays pigtails, not out of the harness, supports the conclusion it’s a 1995 harness.

So, easiest solution to this mess is to wire it back up with the 1995 relay. If you don’t have the 95 relay any longer, we can figure that out, if needed.

Either way, the black with white should not go to the black with red.

Yes what i did was wire the black and white back to other black and white and tge black with red same thing

 

[pauleyman]

Now jet turned on fuel pump comes on until I turn to run then I goes off and starter doesn't engage

I assume you mean key on? Fuel pump should only fire for a moment with key on if memory serves. Stays on when ecu has CAS signal.

 

[joshuah]

I assume you mean key on? Fuel pump should only fire for a moment with key on if memory serves. Stays on when ecu has CAS signal.

Yes mine comes on and stays on when ignition is on

 

[steve]

Yes mine comes on and stays on when ignition is on

Since it's not supposed to do that, that would indicate a problem most likely a wiring issue.
The fuel pump circuit is pretty simple, shouldn't take more that an hour to figure it out.

 

[joshuah]

Since it's not supposed to do that, that would indicate a problem most likely a wiring issue.
The fuel pump circuit is pretty simple, shouldn't take more that an hour to figure it out.

Maybe if I knew how to figure it out

 

[steve]

Maybe if I knew how to figure it out

Given that you have a multimeter you were using to take voltage measurements and post #6 in this thread shows the basic wiring for the pump the first thing I would do is check the car to make sure the wiring matches and start taking measurements at each point to see what/why things are doing what they are doing.