1UZ Code 14 and 15 but runs?

[Chiefkieff11]

Seeking help from the wise

I have a 1st gen 1uz in my 240sx on a 89661-50032 ecu (26 16 22 26 plug) with the KA Transmission.

I’m chasing a random miss that worsens as engine gets to temp. The only two codes i’m getting are 14 and 15, but the car runs???

Things i’ve done:
-All 8 injectors were professionally serviced by AUS Injection here in AZ, everything fuel side is good.

-I’ve tested primary and secondary resistance on ignition coils cold, all are within spec, i even tested my spares to compare.

-I have 12v going to both igniter connectors in the middle pin.

-I’ve checked wiring for primary 02 sensors (i only run these two)

-I’ve opened up the ecu to look for signs of damage, didn’t see anything out of the ordinary.

-I’ve pulled plugs one by one and it appears i’m getting good spark at each cylinder because each one made the motor run like absolute shit.


I’m going crazy trying to figure this out. Any guidance would be amazing.

 

[P Bateman]

Misfires are mostly due to fuel or spark dropping out, but can be caused by a range of issues like

• EGR leaks
• Vacuum leaks
• Carbon buildup
• Crappy fuel
• Cracked spark plugs

If you can get the engine to the point where its misfiring consistently, pull injector connectors off one by one and see which one makes the engine run the worst. Once you find it, focus on all the electrics, components and hardware related to the cylinder.

Happy hunting

 

[Chiefkieff11]

Misfires are mostly due to fuel or spark dropping out, but can be caused by a range of issues like

• EGR leaks
• Vacuum leaks
• Carbon buildup
• Crappy fuel
• Cracked spark plugs

If you can get the engine to the point where its misfiring consistently, pull injector connectors off one by one and see which one makes the engine run the worst. Once you find it, focus on all the electrics, components and hardware related to the cylinder.

Happy hunting

As far as my knowledge is concerned when code 14 and 15 are triggered, should this kill power to all 8 injectors? Every code 14 and 15 thread i’ve read have all had a no start condition. These are the only codes i got. I’ve pulled every spark plug and injector out one at a time and each time the car just runs shittier lol.

 

[P Bateman]

Looking at the DTC guide, 14 is triggered when the ECU doesn't get the IGF (Ignition Feedback) pulse from Igniter#1, 8-11 times consecutively.
Code 15 is the same thing, but for Igniter#2.
The ECU responds by stopping fuel injection as a failsafe.
Trouble areas can only be:

• wiring (open or short in the IGF/IGT circuit)
• igniters
• ECU.

The fact its happening to both igniters suggests the issue is common. The only common parts are the power supply and the ECU
Given the ECU is expecting to receive an IGF pulse from each igniter 4 times per full engine cycle, it would only need to occur for s spilt second for the fault to be logged. Once the pulse resumes, the engine should continue running.

I would suggest scoping the power connection to your igniters and see if it drops out momentarily when the fault occurs.
Failing that, do the same on the IGT (pin2) and IGF (pin1) to see if there are any glitches.

 

[Chiefkieff11]

Looking at the DTC guide, 14 is triggered when the ECU doesn't get the IGF (Ignition Feedback) pulse from Igniter#1, 8-11 times consecutively.
Code 15 is the same thing, but for Igniter#2.
The ECU responds by stopping fuel injection as a failsafe.
Trouble areas can only be:

• wiring (open or short in the IGF/IGT circuit)
• igniters
• ECU.

The fact its happening to both igniters suggests the issue is common. The only common parts are the power supply and the ECU
Given the ECU is expecting to receive an IGF pulse from each igniter 4 times per full engine cycle, it would only need to occur for s spilt second for the fault to be logged. Once the pulse resumes, the engine should continue running.

I would suggest scoping the power connection to your igniters and see if it drops out momentarily when the fault occurs.
Failing that, do the same on the IGT (pin2) and IGF (pin1) to see if there are any glitches.

One thing I discovered today was that while the engine is running, i’m only getting 11.7 votls at idle. Under load there is no change in voltage.

 

[P Bateman]

Where did you measure the 11.7 volts at?

 

[Chiefkieff11]

Where did you measure the 11.7 volts at?

Directly on the battery with it idling, and under load. Got it charging now (12v switch was bad) and now it’s running much better, but still missing ever so slightly. Gonna check codes again tomorrow.

 

[Chiefkieff11]

Update:

-New spark plugs
-Plug wires
- Alt is charging properly

Codes 14 and 15 are still present. Even tried a new ecu and no changes. Is there a way to test the ignitors? This misfire is driving me up a wall. It starts up absolutely beautiful when it’s cold and starts to miss only a few minutes later, worsening as it gets up to temp. As it gets up to temp it’ll randomly drop idle down and pick back up. Not consistent at all.

 

[Chiefkieff11]

Update:

Replaced coils because the primary windings were a little high. No change.

I found a video on youtube on how to test these igniters and it appears the transistors are working.

I really need some help guys. Loosing a ton of motivation at this point…

 

[P Bateman]

If the ECU is registering a loss of signal on IGF, it will cut the injector until the signal returns. It's programmed to do this to protect the cat converters from melting.

ECUs, coils and igniters aside, this can be caused by a poor connection, open circuit or short circuit on IGF. Get a scope onto the ECU and see what the IGF pulse looks like when the misfire occurs.

 

[blinkerfluid]

Check wiring from igniters to ECU, should be faily simple to do.
Also keep in mind that the igniter bodies need a good solid ground, make sure they are fitted well and not insulated from ground

If you've replaced the ECU and still have the same problem, its likely the wiring...

 

[ivan129]

If your only measuring 11.7 - 12V at the battery terminals when the engine is running then you either have a bad connection or buggered alternator. A charged battery will start the engine, drop to around 10 - 11v when cranking and then recover to around 12V.
If the aternator is playing its part, the Battery voltage should be around 13.8 - 14.5V (measured at the battery terminals) when engine running at 1500 RPM or above even when headlights are on.

 

[Chiefkieff11]

If your only measuring 11.7 - 12V at the battery terminals when the engine is running then you either have a bad connection or buggered alternator. A charged battery will start the engine, drop to around 10 - 11v when cranking and then recover to around 12V.
If the aternator is playing its part, the Battery voltage should be around 13.8 - 14.5V (measured at the battery terminals) when engine running at 1500 RPM or above even when headlights are on.

i replaced the switch i was using and now it’s charging at a solid 13.9v

 

[Chiefkieff11]

Check wiring from igniters to ECU, should be faily simple to do.
Also keep in mind that the igniter bodies need a good solid ground, make sure they are fitted well and not insulated from ground

If you've replaced the ECU and still have the same problem, its likely the wiring...

I tore the entire harness out of the engine bay and had a look through of everything and didn’t find anything suspect, additionally i also have the igniter mount attached to a dedicated cable that is fastened to the body from the chassis. I pulled some igniters off a new arrival at my local pull n save and those didn’t change anything

i’ve got good continuity through all igt and igf circuits. I went ahead and did a compression test for shits and giggles and had 190-210 psi across all 8 so i’m good there.

 

[blinkerfluid]

Have you confirmed that the IGT and IGF connections are correct? for example they are at correct pin numbers for both sides?

 

[Chiefkieff11]

Have you confirmed that the IGT and IGF connections are correct? for example they are at correct pin numbers for both sides?

Yes. All the pins are correct.

It’s an intermittent fuel cut, so it’s going through fail safe deactivation. Why would the signal be intermittently lost if it’s not grounding out anywhere ?

 

[blinkerfluid]

Ground and Power to coils ok?

 

[Chiefkieff11]

Ground and Power to coils ok?

Are you referring to the voltage of the two pins that attach to the primary windings ?

 

[blinkerfluid]

yes and their connection stability

ie it could be an intermittent connection on either of those coils