sr20det injectors not firing

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RobbieSS
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Joined: Mon Mar 23, 2020 2:16 pm
Car: 1995 Nissan 240sx SE

sr20det injectors not firing

Postby RobbieSS » Fri May 22, 2020 2:44 pm

Im scoured every injector related thread on multiple different forums and still haven't found a solution so I decided to post.

My sr20det blacktop was running just a few weeks ago and I went to start it cranked but couldn't turn over. So I checked the injectors and they weren't firing. I tried spraying some ethanol into the throttle body and it started right up. So I hooked up a fuel pressure kit and it all looked fine so the only thing left was the ECU so i bought a new one and it still doesnt wanna fire the injectors. I know theyre good because I can hook gator clips to a battery and tap the connections and it'll fire. There is also plenty of fuel in the fuel rail and it has no issue building pressure. Any help would be appreciated.


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NukeKS14
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Car: 1995 240SX SE - KA24DE-T
2014 Camaro SS 1LE

Re: sr20det injectors not firing

Postby NukeKS14 » Fri May 22, 2020 6:28 pm

sounds like an issue with your CAS. either bad CAS or wiring from CAS to computer.

RobbieSS
Posts: 8
Joined: Mon Mar 23, 2020 2:16 pm
Car: 1995 Nissan 240sx SE

Re: sr20det injectors not firing

Postby RobbieSS » Mon May 25, 2020 3:32 pm

NukeKS14 wrote:
Fri May 22, 2020 6:28 pm
sounds like an issue with your CAS. either bad CAS or wiring from CAS to computer.
I ran through all the cas wiring and all seems fine. How do i go about testing my CAS?

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NukeKS14
Posts: 144
Joined: Wed Apr 10, 2019 2:50 pm
Car: 1995 240SX SE - KA24DE-T
2014 Camaro SS 1LE

Re: sr20det injectors not firing

Postby NukeKS14 » Mon May 25, 2020 7:44 pm

RobbieSS wrote:
Mon May 25, 2020 3:32 pm
I ran through all the cas wiring and all seems fine. How do i go about testing my CAS?
If it's the CAS you'll also not be getting any spark so if you have someone to help, you can pull a coil pack and test for spark while they crank. No spark, no fuel, you've nailed your issue; the ECU isn't getting a signal from the CAS for whatever reason.

Here's a link to the English-translated FSM from our own site;

https://www.nicoclub.com/service-manual ... R20DET.pdf

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It's that easy. You're simultaneously testing the CAS and wiring to the ECU here. If you don't get any response from the injectors, it could be bad CAS or wiring. How did you test the wiring between the CAS and ECU? What do you mean by 'seems fine'?

Also, try pulling codes from the ECU and let us know what you're getting. The computer will tell you what it thinks is wrong. The procedure for this begins on page EC-50 of the previous link.

RobbieSS
Posts: 8
Joined: Mon Mar 23, 2020 2:16 pm
Car: 1995 Nissan 240sx SE

Re: sr20det injectors not firing

Postby RobbieSS » Wed May 27, 2020 5:05 pm

NukeKS14 wrote:
Mon May 25, 2020 7:44 pm
RobbieSS wrote:
Mon May 25, 2020 3:32 pm
I ran through all the cas wiring and all seems fine. How do i go about testing my CAS?
If it's the CAS you'll also not be getting any spark so if you have someone to help, you can pull a coil pack and test for spark while they crank. No spark, no fuel, you've nailed your issue; the ECU isn't getting a signal from the CAS for whatever reason.

Here's a link to the English-translated FSM from our own site;

https://www.nicoclub.com/service-manual ... R20DET.pdf

Image
Image
Image
Image

It's that easy. You're simultaneously testing the CAS and wiring to the ECU here. If you don't get any response from the injectors, it could be bad CAS or wiring. How did you test the wiring between the CAS and ECU? What do you mean by 'seems fine'?

Also, try pulling codes from the ECU and let us know what you're getting. The computer will tell you what it thinks is wrong. The procedure for this begins on page EC-50 of the previous link.
I looked over all the wires from the cas and none of them looked corroded or bad but I took a multimeter to it and wasn't getting anything but I could've tested it wrong. I have spark i just checked it but still no fuel. I'll run codes here in a bit and keep you posted, thankyou so much for your help by the way i appreciate it.

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NukeKS14
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Car: 1995 240SX SE - KA24DE-T
2014 Camaro SS 1LE

Re: sr20det injectors not firing

Postby NukeKS14 » Wed May 27, 2020 5:47 pm

visual inspection almost never tells you anything. to test the harness you need to disconnect the battery AND the ECU, and check resistance between the component end and the ECU. NEVER do continuity checks on a live circuit. low resistance (<100 ohm at absolute worst, ideally <10) tells you the wire is good from the component to the ECU. It's important to move the harness around while you're checking to simulate engine movement and vibration. A wire can become brittle and break inside the insulation, making intermittent contact.

So the way the Nissan ECUs work is by a ground switching approach. constant voltage is supplied to the controlling elements (coils, injectors, solenoids, starter, etc...) and the ECU operates them by completing their circuit path to ground.

Next thing I'd do is turn the ignition key to the on position and check voltage at the red wire on the injector clips to ground. You SHOULD be seeing near 12v. The injectors have a common 12v supply so if you're finding it on the first one it's on the rest of them. don't test BETWEEN the wires. Test red wire to ground. If you're not getting that, the second picture shows the path from the ignition to injectors. Something is broken faulted or disconnected between there and the ignition. no fuses between the ignition and the injectors. Wouldnt hurt to double check that 30A ign fuse though.

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RobbieSS
Posts: 8
Joined: Mon Mar 23, 2020 2:16 pm
Car: 1995 Nissan 240sx SE

Re: sr20det injectors not firing

Postby RobbieSS » Wed May 27, 2020 8:05 pm

NukeKS14 wrote:
Wed May 27, 2020 5:47 pm
visual inspection almost never tells you anything. to test the harness you need to disconnect the battery AND the ECU, and check resistance between the component end and the ECU. NEVER do continuity checks on a live circuit. low resistance (<100 ohm at absolute worst, ideally <10) tells you the wire is good from the component to the ECU. It's important to move the harness around while you're checking to simulate engine movement and vibration. A wire can become brittle and break inside the insulation, making intermittent contact.

So the way the Nissan ECUs work is by a ground switching approach. constant voltage is supplied to the controlling elements (coils, injectors, solenoids, starter, etc...) and the ECU operates them by completing their circuit path to ground.

Next thing I'd do is turn the ignition key to the on position and check voltage at the red wire on the injector clips to ground. You SHOULD be seeing near 12v. The injectors have a common 12v supply so if you're finding it on the first one it's on the rest of them. don't test BETWEEN the wires. Test red wire to ground. If you're not getting that, the second picture shows the path from the ignition to injectors. Something is broken faulted or disconnected between there and the ignition. no fuses between the ignition and the injectors. Wouldnt hurt to double check that 30A ign fuse though.
Okay so I just tried checking the resistance between the ecu and the cas harness. I tried all wires on the harness and i tried pins #30 and #40 on the ecu but there was no resistance. Was I doing it wrong or is that the issue?

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NukeKS14
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2014 Camaro SS 1LE

Re: sr20det injectors not firing

Postby NukeKS14 » Wed May 27, 2020 8:31 pm

: Wrong pins.

White wire on cas harness (pin 4) goes to pin 51 on the ecu

The black wire on the cas harness next to the white one (pin 3) goes to pin 42 on the ecu.

Ec-109 for the cas wiring

The white/black wire at the cas plug (pin 1) is your 12v in.

If youre getting spark the cas is working. Did you pull codes before disconnecting the battery? If not theyre gone. They live in the volatile memory.

Also, overload means infinite resistance. Opposite of no resistance.

RobbieSS
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Joined: Mon Mar 23, 2020 2:16 pm
Car: 1995 Nissan 240sx SE

Re: sr20det injectors not firing

Postby RobbieSS » Thu May 28, 2020 3:50 pm

NukeKS14 wrote:
Wed May 27, 2020 8:31 pm
: Wrong pins.

White wire on cas harness (pin 4) goes to pin 51 on the ecu

The black wire on the cas harness next to the white one (pin 3) goes to pin 42 on the ecu.

Ec-109 for the cas wiring

The white/black wire at the cas plug (pin 1) is your 12v in.

If youre getting spark the cas is working. Did you pull codes before disconnecting the battery? If not theyre gone. They live in the volatile memory.

Also, overload means infinite resistance. Opposite of no resistance.
Sorry for making this difficult im new to this but i'm a little confused because the ecu pinout sheet you sent doesn't match my ecu but i tried anyways and I got the same result. Heres a pic of my ecu and my cas plug.
And before i posted on the forum I tried a different ecu on the car so it's gone.
IMG_1308.jpg
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IMG_1307.jpg

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NukeKS14
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Car: 1995 240SX SE - KA24DE-T
2014 Camaro SS 1LE

Re: sr20det injectors not firing

Postby NukeKS14 » Thu May 28, 2020 6:58 pm

Ill try to make some time this weekend and find the pinout for that ecu. You said blacktop so i assumed s14 notch top. Apologies.

RobbieSS
Posts: 8
Joined: Mon Mar 23, 2020 2:16 pm
Car: 1995 Nissan 240sx SE

Re: sr20det injectors not firing

Postby RobbieSS » Thu May 28, 2020 8:40 pm

NukeKS14 wrote:
Thu May 28, 2020 6:58 pm
Ill try to make some time this weekend and find the pinout for that ecu. You said blacktop so i assumed s14 notch top. Apologies.
oh no man it's alright you've already done so much to help me. It's weird i looked up all the sr20det pinouts and it matches the one for the kouki but im running a blacktop zenki

RobbieSS
Posts: 8
Joined: Mon Mar 23, 2020 2:16 pm
Car: 1995 Nissan 240sx SE

Re: sr20det injectors not firing

Postby RobbieSS » Mon Jun 01, 2020 4:06 pm

NukeKS14 wrote:
Thu May 28, 2020 6:58 pm
Ill try to make some time this weekend and find the pinout for that ecu. You said blacktop so i assumed s14 notch top. Apologies.
Did some more rooting around in my car this weekend and I found so many issues. There is a green and black wire and a orange wire that were cu t right next to the driver side fuse box & 2 different harness connections with no where to connect to right next to the ecu. I tried to figure out what they were but I had no luck

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NukeKS14
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Car: 1995 240SX SE - KA24DE-T
2014 Camaro SS 1LE

Re: sr20det injectors not firing

Postby NukeKS14 » Fri Jun 19, 2020 7:22 pm

Sorry for the delay. I found a few pinouts that could be it. Check the sticker on your ECU for what number it is, that'll let you know which of these is the right one.

Source: https://www.wiringspecialties.com/ecu-p ... u-pinouts/
sr-ecu-pinouts-t495077.html

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It can have whatever ECU that matches the engine wiring harness used, honestly. Case in point; I did a motorswap on my first 1990 240sx; I used a 96' KA24DE with an S13KA24DE lower manifold/wiring harness and just swapped over the distributor and sensors that needed converted (TPS, CTS, etc...) So I had an S13 SOHC chassis with an S14 KA24DE motor running on an S13 KA24DE ECU.

You could have a zenki engine with a kouki wiring harness, if whomever did the swap used the matching sensors for that harness/ecu.

Green and black wire sounds like someone defeated the clutch safety switch. (switch that requires you to have your clutch engaged to start the car.) Orange wire... I have no idea. Picture would help on that.

You can test the clutch safety switch if you MAKE 100% SURE THE TRANSMISSION IS IN NEUTRAL then try to start the car without touching the clutch pedal. If it will turn over, then that switch is defeated.

The other black wire w/ green stripe goes to the cruise control defeat. Basically if you have cruise control and touch the clutch it'll disengage cruise control. THAT is a separate switch on the top of the clutch pedal. But same wiring color. Thanks for that Nissan.

The unused harness connections you're talking about, are those on the ENGINE wiring harness or the chassis side? Pictures would help.


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