ECU Fuse Keeps Blowing after Trackday - No CEL - TT

JimmyK

TL;DR:

The 15A fuse (Fuse 50) that powers the ECU and other things repeatedly blows within a few mins of driving, but once replaced (stupid, I know), the car can idle perpetually without blowing the fuse, even if you up the revs to >4000 RPM. No CEL or BCM issue reported by the car.

The car was running hot on the track as expected when the fuse popped. After I found it and replaced it, the car ran for ~10 mins on the track before blowing again, when I decided to tow it. After a couple more fuses to get it off the track property for the tow and to get it to my garage, it seems like the runtime is ~2 mins before it blows, but I didn't want to keep testing to avoid damaging something. Turned off AC, radio, S-Mode, and anything else I could find before the last two fuse blowouts, so less likely that they're culprits.

Also, I'm going to put a bit more info than needed here for someone's sake in the future.

Tests Performed or Planned:

Did some mild continuity and grounding electrical checks with a DMM and a radio electrical fault finder to no avail, all harnesses seem okay to the components listed except the few I could not get to. Used an OBD monitor w/ an experimental CONSULT function to view live data while idling or w/ ignition on.

• Condenser
  - Harness under the Intake Manifold, so couldn't shake or inspect.
  - AC is off during event.
  
• Ignition Coil 1
  - No tests performed since car idles and revs well, no CELs.
  
• Ignition Coil 2
  - No tests performed since car idles and revs well, no CELs.
  
• Ignition Coil 3
  - No tests performed since car idles and revs well, no CELs.
  
• Ignition Coil 4
  - No tests performed since car idles and revs well, no CELs.
  
• Ignition Coil 5
  - No tests performed since car idles and revs well, no CELs.
  
• Ignition Coil 6
  - No tests performed since car idles and revs well, no CELs.
  
• Intake Valve Timing Control Solenoid Valve Bank 1
  - Violently shook cables while idling.
  
• Intake Valve Timing Control Solenoid Valve Bank 2
  - Violently shook cables while idling.
  
• EVAP Canister Vent Control Valve
  - Harness looks okay, will disconnect and test continuity.
  - OBD reads but no changes, possibly since the pressure isn't changing at idle without sloshing, etc.
  
• VVEL Control Module
  - VVEL position sensors and angle advance seem to be working w/OBD monitor, since they change values on idle/throttle.
  
• EVAP Canister Purge Volume Control Solenoid Valve
  - OBD reads % changes under throttle ups in idle that make some sense.
  - Electrical continuity of positive to ECU is good (Pin 21 on ECU), no shorts to ground of ECU or car.
  
• MAF Bank 1
  - Readings look okay in OBD.
  - Plan to check electrically per FSM.
  - Violently shook cables while idling.
  
• MAF Bank 2
  - Readings look okay in OBD.
  - Plan to check electrically per FSM.
  - Violently shook cables while idling.
  
• Input Speed Sensor (for S-Mode)
  - No tests done or planned, located on transmission.
  
• Crankshaft Position Sensor (not listed above)
  - Cables look frayed.
  - Violently shook cables while idling.
  - Electrical continuity of positive to ECU. No shorts to power from supply or sensor line, and no shorts to car or ECU ground.

Components Powered by Fuse 50:

Connector E5 (IPDM) Pin 10 (Unknown Color, will update if checked)

• Unlisted in PCS or EC FSM docs, untested, not inspected yet, no known connection.

Connector E7 (IPDM) Pin 49 (BG - Beige)

• VVEL Control Module [E7 Pin 49] -> [E15 Pin 8]
• ECM [E7 Pin 49] -> [E106] -> [M6] -> [M107 Pin 125]
• EVAP Canister Purge Volume Control Solenoid Valve [E7 Pin 49] -> [E106] -> [M6] -> [M116] -> [F103] -> [F7 Pin 1]
• MAF Bank 1 [E7 Pin 49] -> [E106] -> [M6] -> [M116] -> [F103] -> [F31 Pin 5]
• MAF Bank 2 [E7 Pin 49] -> [E106] -> [M6] -> [M116] -> [F103] -> [F42 Pin 5]
• Input Speed Sensor (for S-Mode) [E7 Pin 49] -> [E106] -> [M6] -> [M116] -> [F103] -> [F58 Pin 1]

Connector E7 (IPDM) Pin 53 (W - White)

• Condenser [E7 Pin 53] -> [E3] -> [F1] -> [F8 Pin 1]
• Ignition Coil 1 [E7 Pin 53] -> [E3] -> [F1] -> [F11 Pin 3]
• Ignition Coil 2 [E7 Pin 53] -> [E3] -> [F1] -> [F12 Pin 3]
• Ignition Coil 3 [E7 Pin 53] -> [E3] -> [F1] -> [F13 Pin 3]
• Ignition Coil 4 [E7 Pin 53] -> [E3] -> [F1] -> [F14 Pin 3]
• Ignition Coil 5 [E7 Pin 53] -> [E3] -> [F1] -> [F15 Pin 3]
• Ignition Coil 6 [E7 Pin 53] -> [E3] -> [F1] -> [F16 Pin 3]
• Intake Valve Timing Control Solenoid Valve Bank 1 [E7 Pin 53] -> [E3] -> [F1] -> [F28 Pin 2]
• Intake Valve Timing Control Solenoid Valve Bank 2 [E7 Pin 53] -> [E3] -> [F1] -> [F29 Pin 2]
• EVAP Canister Vent Control Valve [E7 Pin 53] -> [E3] -> [F1] -> [F103] -> [M116] -> [M7] -> [B1] -> [B31 Pin 1]

Connector E7 (IPDM) Pin 55 (SB - Sky Blue)

• ECM Power Supply

Connector E7 (IPDM) Pin 69 (BR - Brown?)

• ECM Relay Control

Connector E7 (IPDM) Pin 70 (BG - Beige)

• Throttle Control Motor Relay Control

Request

Please recommend any tests, ask for test results, suggest issues, etc. I'll also be sure to update the page once it gets solved, be it by me or my mechanic. I'm avoiding the obvious ECU swap since it works well when idling, and also I don't want to have to deal with re-tunes.

Anything will help! Going to tow the car to the shop that put the mods in soon, but figured I'd try as much as I could with my time off during the holidays. I did try a dealership in case they had some better diag tools, but they couldn't figure it out (and didn't charge me) since it was "too modified" for them, whatever that means .

Reference Information

FSM Pages:

• Power Supply & Grounding - PG-7/8/23 (Shows Fuse 50 relative to Power & Grounding and Harnessing)
• Power Control System - PCS-26 (Harness diagram shows additional Fuse 50 connections rel to IPDM)
• Engine Control System - ECS-XX (Lots of harness diagrams show this connection)

Car Details:

• 2014 370Z Base - 29XXX miles
• Fast Intentions GT2860 RS Complete TT Kit
• TurboSmart E Boost 2 Controller
• Zeitronix ECA-2
• (Can add more, lmk what you want!)

Spooler

You have an intermittent short. Grab the schematic and see what that fuse runs. Then, start tracing from there. Is your grommit behind the battery that feeds the main engine harness into the interior in good shape. Wondering if you have a water intrusion issue where water has gotten to the ECU and damaged it. Check your ECU connectors for any signs of green corrosion.

JimmyK

Hey Spooler, thanks for the reply man, I recognized your name from the many threads I've seen over the years!

I inspected the grommit and quite a bit of harnessing with a snake cam and it looks great*. The harnesses also have continuity from the IPDM E/R to the ECU where they need it or makes sense, but I didn't get to shake the cables in all the areas or vibrate it the way the car does. I also didn't get to check all the connections to the ECU from the IPDM E/R of course, since it doesn't seem to be shorted when idling.

The ECU connectors all look brand new thankfully, no green corrosion. I will take the camera and inspect the top, sides, and back side of the ECU to see if there's any sign of water getting in. Thanks for the suggestion.

Could it be something that doesn't get actuated until the car starts moving? I suspected the EVAP Canister Vent Control Valve since that seems to be static while idling, and logically should start venting when fuel sloshes or builds pressure in the canister or tank.

Beyond what's listed in the General Information portion of the FSM, do you have any better ways to test for Intermittent failures/shorts? I have a data record function on the OBD tool I use, I could record the data and see what changes right before the ECU stops communicating but that's a stretch.

Thanks again for the reply and thoughts, if you have any other ideas let me know and I'll keep checking them. I can also take some pictures with the snake cam.

*Looks great aside from the Crankshaft Position Sensor (which comes off the ECU and was tested from the ECU pins for short-to-power & short-to-ground. I also shook the crap out of that one by its jacket using a snake grabber tool to see if it was an intermittent short caused by vibration, but it didn't cause any failures while idling or didn't short while the car was off and being electrically tested.

Spooler

Get DMM out and start testing every leg that the fuse feeds. You are looking for a short. Use the continuity test on the DMM so you can hear the beep when you come across the short. It takes time, patience, and a little bit of luck.

Spooler

Maybe a little more direction. Disconnect from the battery. Plug in DMM leads to the fuse and ground. Start fiddling around with the wiring harness to see if you can locate the short. You may need to disconnect the wiring harness from the ECU if you have continuity.

JimmyK

Thanks again for the response! I started to do this but after a bit I looked at the schematic and saw that all the components, ECU included, are downwind of the ECU Relay which is in the IPDM box. Without the battery plugged in and the key in the ign position, the harness won't be live unless I get that relay to close somehow, or at least that's what I think is the case.

I confirmed this by purposely connecting a known component's harness to ground on both terminals and got no hits as well. The component was the EVAP Purge Solenoid.

Edit: Correction, there is one power line to the ECU that is pre-relay, but everything else including back up power supply to the ECU are all post-relay.

JimmyK

Update: Got past the relay by just using the lines downwind of the IPDM (from the connectors on the IPDM). I confirmed that this works by purposely shorting that same solenoid to car ground (not the battery) and heard the beeps loud and clear.

So far I have tested two of the four lines, but of course the tests are not comprehensive because it's really really hard to get to all the harnessing to rattle it. Still no luck unfortunately.

As ridiculous as it sounds, I can rent a trailer and tow my car around while listening for the shorts with a few DMMs so I can at least narrow things down.

Averying

So if you just leave the car idling it would still die after a few minutes? Or is it only once you get driving the car?

Maybe the drivetrain movement is causing a short and that’s why you’re not picking it up when testing with a DMM and the battery unplugged? I see that you shook the cables though which would be more movement than from the engine/transmission rocking around during load…




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JimmyK

Hey Averying, thanks for the reply! I can leave it idling for longer than 30 mins, blip or hold the revs, etc without it blowing the fuse. Once i start driving it blows the fuse within a few mins, and that degraded from 10+ mins on the first fuse.

Agreed, though the movement I made still doesn't shake everything everywhere, only where I could reach. I'll keep hunting for a short, but that could be a long long search, and it feels like I'm chasing a ghost.

Averying

Sounds like the Crank position sensor is the only wire that visually looks like it could be the culprit. Some more info about that might be good to know.

Where it’s frayed.. how close does it come to a surface that would ground it out? What is it fraying on? How bad is it frayed? Hopefully no exposed wire.


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Jhill

Ok so I’m a bit out of practice since I’ve been out of the industry for about 6 or 7 years now but it sounds like your chasing an intermittent short with a fuse that feeds a bunch of parallel circuits. It sounds like it’s at least consistent enough you can get it to blow reliably so that’s a good thing. So what you could do is use a recording dmm or scope with an amp clamp on and you’ll have to monitor each branch of the circuit while the fuse blows to see which one is spiking.

The other option which I’ve had to do for a customer that would blow one fuse every 4-6 months so very intermittent and that fuse fed 5 wires which then each split into 3 other parallel circuits so there was no way I was going to find it. In a situation like that or what you can do since most likely don’t have a way to record amperage is go get a bunch of in line fuse holders and fuses and you’ll have to cut and wire in the in line fuses on every branch that fuse feeds. Once you have the branch with the fuse that pops you’ll have better isolated the components and wiring path you need to inspect (took a while but finally found a hairline crack in a wire that would intermittently touch the window regulator channel).

JimmyK

Hey, thanks again for the reply!

So at the point at which the jacket/heat insulation is melted/burned away, there isn't anything that close by, but it's definitely about 24 inches between the tie-down or stake points so that harness could move.

That said the three cables are not frayed or exposed. I also, while idling, used a gripper tool to grab the insulated portion that wasn't burned away and shake the wire very extensively to see if I can get it to pop the fuse, and I didn't get any short. That said, even though this is not on fuse 50, it's still tied to the ECU so I can figure out what pins it connects to the ECU on and possibly to the IPDM on, and test it. I'll let you know how that goes as soon as I can do the test. Thanks for the suggestion and I'll try to test it is extensively as I can.

JimmyK

Hi Jhill, thanks for the reply!

I was thinking of doing a test like that but with cheap DMMs; I was going to put the vehicle on a trailer and have someone drive it around until one of the DMMs shows a short. Your test makes things even easier since the amp clamps are not invasive, so the harnessing can be plugged in and the car can be on. I would probably label the few multimeters that I use and record it with a camera so that I can be sure I don't miss the fuse popping if I do this.

I'm glad that you also mentioned the in-line fuse method because I was thinking of doing that since it's only a few lines coming off the fuse to the parallel circuit, so I could try to isolate things by only popping two or three fuses. I'm worried about cutting the wires and installing those because they're a future failure point, and because I was worried about resistances or impedances being a little off before going into the ECU (I'm less worried about that now though since I know they are all power lines).

Sounds like this is gonna be way harder than it has been regardless.

JimmyK

Update, still no luck, not even with the Crankshaft Position Sensor or EVAP Canister Vent Control Valve, and no luck with the continuity checks while shaking the harness and the whole car (not out of frustration, I swear).

Here are the updates to the tests performed:

Tests Performed or Planned:

• Condenser
  - Harness under the Intake Manifold.
  - AC is off during event.
  - Inspected with scope and by shaking from where accessible, no shorts.
  
• Ignition Coil 1
  - No tests performed since car idles and revs well, no CELs.
  
• Ignition Coil 2
  - No tests performed since car idles and revs well, no CELs.
  
• Ignition Coil 3
  - No tests performed since car idles and revs well, no CELs.
  
• Ignition Coil 4
  - No tests performed since car idles and revs well, no CELs.
  
• Ignition Coil 5
  - No tests performed since car idles and revs well, no CELs.
  
• Ignition Coil 6
  - No tests performed since car idles and revs well, no CELs.
  
• Intake Valve Timing Control Solenoid Valve Bank 1
  - Violently shook cables while idling.
  
• Intake Valve Timing Control Solenoid Valve Bank 2
  - Violently shook cables while idling.
  
• EVAP Canister Vent Control Valve
  - Disconnected at canister and checked continuity to ECU on pin 2, and to the IPDM on pin 1. No other pins exist, continuity was good even with some shaking.
  - Possible candidate since there's lots of harness spidering its way through the body to get to the canister.
  - OBD reads but no changes, possibly since the pressure isn't changing at idle without sloshing, etc. Less worried about this now since it has continuity at rest.
  
• VVEL Control Module
  - VVEL position sensors and angle advance seem to be working w/OBD monitor, since they change values on idle/throttle.
  
• EVAP Canister Purge Volume Control Solenoid Valve
  - OBD reads % changes under throttle ups in idle that make some sense.
  - Electrical continuity of positive to ECU is good (Pin 21 on ECU), no shorts to ground of ECU or car even with violent shaking.
  
• MAF Bank 1
  - Readings look okay in OBD.
  - Plan to check electrically per FSM.
  - Violently shook cables while idling.
  
• MAF Bank 2
  - Readings look okay in OBD.
  - Plan to check electrically per FSM.
  - Violently shook cables while idling.
  
• Input Speed Sensor (for S-Mode)
  - No tests done or planned, located on transmission.
  - Only one not tested so may check continuity. Don't want to jack car up again for this but might.
  
• Crankshaft Position Sensor (not listed above)
  - Cables look frayed.
  - Violently shook cables while idling.
  - No shorts to power from supply or sensor line, and no shorts to car or ECU ground.
  - Check all pins directly from the ECU to the connector, no shorts to power or ground, neither sensor power or sensor return.
  - Will repair nonetheless.
  
• Continuity Tests
  - Performed continuity tests on all pins coming out of the IPDM (45, 53, 55, 69, 70, all from E7) to the components while shaking the harness up and down the car wherever I possibly could, and no continuity was found so the intermittent short culprit was not located.
  - Components less affected were the EVAP Canister Control Valve and the Input Speed Sensor.

Averying

Sounds like it’s time to bust out the amp clamps / recording DMMs

How many 15a fuses have you gone through now? Lol


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2009 Sport Touring | Platinum Graphite | GTM Stage 1 Supercharger | BC BR Coilovers | Hotchkis Swaybar | Z1 FUCAs | AME TM-02 Wheels | Z1 2-piece Front Rotors | Z1 Clutch & Flywheel | Invidia Gemini Catback | GTM Resonated Test Pipes