What size injectors do you have?

bo0st2 said:

What size injectors do you have?

Click to expand...

450cc. Number 4 is dumping fuel into the cylinder. Did compression test everything only leaves MFI/ads relay or the multi function relay ground and my ECU.

Memory says when injector is closed the 1 side of the wire is powered 12v via the MFI. Both pins will read 12v as the ECU is floating open. When it fires it the ECU then grounds the wire and the injector opens. Do you have injector Noid lights? This would confirm the 12v is there and ECU is grounding to fire it. That would then tell you if its wiring, ECU or a stuck injector.

jed344 said:

Memory says when injector is closed the 1 side of the wire is powered 12v via the MFI. Both pins will read 12v as the ECU is floating open. When it fires it the ECU then grounds the wire and the injector opens. Do you have injector Noid lights? This would confirm the 12v is there and ECU is grounding to fire it. That would then tell you if its wiring, ECU or a stuck injector.

Click to expand...

I changed the injectors all 4. I have 12 power from green wire that goes to MFI and I tested the green/red wire to ECU, it’s not damaged. The ECU isn’t grounding the green/red as it should.

What is the resistor and where is the MFI relay located in a 1997 TSi?

The MFI is located under the dash behind the radio on 2g's.
The injector resistor box is located on the firewall in the engine bay.

So you have 12v at the injector pin. Then tested the other side pin from injector clip to ECU pin for that injector and have continuity? Then I am a little stumped if you also tried different known good injectors. I have yet to see a car with known good injectors and 12v and good continuity to ECU not fire a injector.

jed344 said:

The MFI is located under the dash behind the radio on 2g's.
The injector resistor box is located on the firewall in the engine bay.

So you have 12v at the injector pin. Then tested the other side pin from injector clip to ECU pin for that injector and have continuity? Then I am a little stumped if you also tried different known good injectors. I have yet to see a car with known good injectors and 12v and good continuity to ECU not fire a injector.

Click to expand...

Correct that’s exactly what happened

Have you tried a Noid light?

Last time we came across this kind of issue a week before shootout we tore the car apart and testing everything we could think. We then tried a Noid light and it flashed showing injector was being sent signal to fire and it turned out to be a injector issue with the replacement set we had tried. They pulse so fast you cannot tell if it does with a multimeter but the noid light will flash and tell you. When that flashes it has to be a injector issue.

This car also had the results your's had with what I asked is only reason I ask. Then if it does not flash and you know you have 12v and continuity to the ECU on the other side I would have to think a ECU issue. I have zero idea what would cause just the 1 injector circuit though in that case. I thought the ECU uses one of the ground wires into it for the circuit when it grounds the injector and causes it to fire. So if it was a ground issue then it would be more then 1 I would think.

The resistor pack on the firewall by my understanding takes the low impedance of the factory injectors and raises the resistance so the ECU thinks they are high. Had to do with back in the day you could not get enough injector flow from high vs low. I am not familiar enough with that part of the circuit to say a issue there could cause 1 injector a issue.

I know from the past tuning cars with high Z injectors and guys did not delete it as suppose to that it still works quite well other then random strange part throttle things and it did not throw a code at ECU.

Essentially everything now is just high impdence injectors and that pack is gone so never learned exactly the ins and outs of it. Could just be ECU is damaged and the noid light would show this so I would try that.

jed344 said:

Then if it does not flash and you know you have 12v and continuity to the ECU on the other side I would have to think a ECU issue. I have zero idea what would cause just the 1 injector circuit though in that case. I thought the ECU uses one of the ground wires into it for the circuit when it grounds the injector and causes it to fire. So if it was a ground issue then it would be more then 1 I would think.

The resistor pack on the firewall by my understanding takes the low impedance of the factory injectors and raises the resistance so the ECU thinks they are high. Had to do with back in the day you could not get enough injector flow from high vs low. I am not familiar enough with that part of the circuit to say a issue there could cause 1 injector a issue.

Click to expand...

Each injector has it's own driver circuit inside the ECU. They do share the ECU's ground but if you have a problem with that it would show up in a more substantial way.

The injector resistor is there for current control. The ECU doesn't know if the injectors are low or high but the drivers (same ones as on the NA ECUs that use high impedance injectors) can only switch so much current and low impedance injectors draw more when they are turned on and quicker than high impedance ones. In the past that meant low impedance injectors were better performing with less deadtime required and usually had more expensive peak and hold drivers but technology marches on.

okay I’ll buy the injector light nodes to confirm the ECU is the issue but I tested it every other way and changed them all around and got an extra set I suspect ECU as well as my local DSM group

I’m stuck I have looked everywhere and maybe found my concussion I have an open circuit on injector 4 giving code P0204.
If the resistor pack went bad would that cause the code or does the ECU cause the problem? I tested my wires to the ECU and it’s good, no damage.

Off to the left of your diagram you'll see that the Injector Resistor gets power from all four injectors from the MPI Relay so it's common to all 4 at pin 3 of the resistor pack. Inside the metal shell are 4 power resistors, one end of each connected to that pin 3 and the other end goes to one injector. 4 resistors, one for each injector and yes one could go bad causing the P0204 fault.

From the diagram you can see which pins on the resistor pack goes to which injector. (#4 would be pin 6). Check to make sure you have battery voltage there when the ignition is on. (good idea to check all of them)

Then make sure you have battery voltage on the pins at the injector.

Lastly measure the resistance of each injector at it's pins to make sure none are shorted or open.

With everything connected (the connectors locked in place) and the ignition on engine off you should measure battery voltage on each of the injector pins at the ECU. They will float high like that until the ECU tries to fire the injector by pulling the pin to ground.

Clear the fault code and see if it returns.

Thanks so much the Mitsubishi manual says it’s only ecu and not anything else following the diag process I know it’s common but I have black box and it was inspected before it was installed and I know I’m missing something it randomly died at idle after I just drove it a bunch and finished my restoration

The alternator killed my battery and I changed both drove it for 2 weeks no issues disconnected everything it started right up after doing some welding then injector 4 got that code I changed injectors same thing bought new ones same thing wires have connections no breaks so it’s not shorting like normal leading me to believe a relay or resistor and worst case ecu

Sorry, my age and ADHD make it difficult to figure out what you were trying to get across in your last post. I'll be happy to mail you some periods and commas if you have run out.

The site lets you edit for while after you post and you should do so rather than quote your last post to follow up.

Have spent more time in the past diagnosing injector issues then I would like to admit. Like stated when key is on both pins at each injector plug will show 12v when plugged in. The MPI supplies power to one side and ECU floats open. Then grounds to fire injector. We always confirm 12v at the injector plugs on the one side, Then continuity test from the other pin on the injector plugs to the ECU pins. This at least rules out wiring issue. Then if injectors are confirmed good I would suspect ECU issue. I am not 100% but I would guess if ECU had ground issues so it couldn't ground the circuit there would be much more issues at hand too.

steve said:

Sorry, my age and ADHD make it difficult to figure out what you were trying to get across in your last post. I'll be happy to mail you some periods and commas if you have run out.

The site lets you edit for while after you post and you should do so rather than quote your last post to follow up.

Click to expand...

I don’t know how to use them sorry i would if I knew how thanks. School is useless

Then if you have 12v at the injector plugs and continuity at the plugs from other pins to the ECU pins that means no broken or open circuit in wiring. I would have to suspect ECU.

I do not think a issue with resistor pack would toss a code, especially for 1 injector circuit. I once years ago tuned a car that ended up having a strange stumble cruising and it was due to him using high impedance injectors without ditching the resistor pack. The tune looked normal and no code's where thrown. Same when you go to high impedance injectors those wires all just get connected to each other at where the pack used to be, Still no code thrown. The ECU has no idea in this sense.

The ECU is designed to drive high impedance injectors just at the time these car's where made you could not make decent sized injectors in high impedance. So they used that resistor pack to bump up the impedance the ECU saw.

Did you ever try the NOID light I recommended? Like I said before I know for a fact that will 100% show if the ECU is trying to fire the injector or not. Happens too fast for a multimeter to pick it up correctly.

jed344 said:

I do not think a issue with resistor pack would toss a code, especially for 1 injector circuit. I once years ago tuned a car that ended up having a strange stumble cruising and it was due to him using high impedance injectors without ditching the resistor pack. The tune looked normal and no code's where thrown. Same when you go to high impedance injectors those wires all just get connected to each other at where the pack used to be, Still no code thrown. The ECU has no idea in this sense.

Click to expand...

The ECU will if there is an open in one of the resistors but it's not going to catch the case of high impedance injectors and a injector resistor.

If injector 4 is constantly dumping fuel into the cylinder it would either have to be stuck open or the ECU side pulling (shorted?) to ground. Assuming the injectors have been changed that would eliminate it being stuck open. Assuming #4 is still dumping fuel, something is up on the the ECU side of the circuit. It's possible to have continuity from the injector to the ECU and still have the wire shorted to ground. That's a quick check with the multimeter, unplug both the injector and ECU and see if there is any resistance on that wire to chassis ground.

The injector drivers on a 2G black box ECU are different than the metal 1G and 2G ECUs. I'll look and see if I have one to see what might fail there.

If you pinched wire somewhere then you will still have continuity to the ECU because the ECU will be connected to the pinch point as well as the injector side of it. The ECU is calling it an open circuit because it's expecting to see 12 volts returned to it when it's not attempting to ground it. I commonly see these codes described on newer cars as "open OR short to ground". The ECU is looking for the voltage feed back, when it doesn't see it, it usually cannot determine between a short to ground or open circuit.

The only way for an injector to be open all the time is for it to be stuck or to have power and ground on both pins at the injector all the time.

To make it simple and clear, do you have ground on the green red wire at injector 4? If yes, Does it go away when you unplug the ECU? If yes, you have a bad ECU. If no, then the wire is shorted to ground somewhere and you need to trace it out.

If you do not have ground on the green red wire all the time but the injector sprays full all the time then your injector is stuck.

Diamond Star Werks said:

If you pinched wire somewhere then you will still have continuity to the ECU because the ECU will be connected to the pinch point as well as the injector side of it. The ECU is calling it an open circuit because it's expecting to see 12 volts returned to it when it's not attempting to ground it. I commonly see these codes described on newer cars as "open OR short to ground". The ECU is looking for the voltage feed back, when it doesn't see it, it usually cannot determine between a short to ground or open circuit.

The only way for an injector to be open all the time is for it to be stuck or to have power and ground on both pins at the injector all the time.

To make it simple and clear, do you have ground on the green red wire at injector 4? If yes, Does it go away when you unplug the ECU? If yes, you have a bad ECU. If no, then the wire is shorted to ground somewhere and you need to trace it out.

If you do not have ground on the green red wire all the time but the injector sprays full all the time then your injector is stuck.

Click to expand...

I’m going to test everything here next weekend it’s not raining thanks everyone.