Weak Spark from SR20DET distributor

Hi Folks,

I recently installed and wired a SR20DET from a Nissan liberty into my Nissan Sunny B14. The engine cranks over fine, fuel pump primes, injector pulses but no spark or to be more specific a very weak barely noticeable spark.

The spark is literally a hair thin and orange in colour. I checked the spark by using a test light just off the distributor cap and also with an inline tester and both reflects a very thin weak spark. I took a spark plug out and grounded it at the top of the engine and realized the spark is too weak to jump the gap of the plug.

Here is a wiring diagram I found from another site as reference:



It is a 8 pin distributor and I have confirmed the following pin outs checking continuity between the ECU plug and the distributor plug:

1. Black - Ground
2. White/Red - 12V (Pin 38/47)
3. Black/Red - 5V (Pin31)
4. Brown - 5V (Pin 22/309)
5. Green/Black - 11.7V (Pin 3) *Does not light the test light up.
6. White/Black - 12VB (ECCS relay) *Coil +
7. Orange/Black - (Pin1) *Control Wire
8. Black/Yellow - Ground *Possibly coil -

*The only discrepancy I see between my setup and the diagram is that the switched 12V for coil + comes direct from the ECCS relay instead of pin 36.

Steps taken so far:

I have tested and confirmed 12V on coil +.

Due to the coil, condenser and ignition module being internal to the distributor, I was only able to test the negative side of the coil after the ignition module going to the ECU. I get no light from my tester when I probe this wire (black/yellow) on crank. I also tried connecting my multi meter and it reflects 4mV on crank. Based on troubleshooting steps of chapter 22 in the book this should indicate a faulty igniter? What confuses me is the fact that I do get a weak spark from the distributor so even though my test light does not light up when probing after the ignition module, I still expected the multi meter to reflect some voltage reading on crank at least higher than 4mV.

I also double checked all my wiring of the ECU. Power (12V on pin 36,46,38,47 and 9-10V on pin 34 while cranking) and grounds (both on harness and engine bay).

I scanned the engine via the consult port which reflects a code 21 "ignition signal missing" every time I crank. The software I use to scan is "ECU Talk" and can display outputs from the sensors. Oddly enough I can bring up a display for base ignition timing and get a reading while cranking....

Finally I tried replacing the distributor with a used one I bought but I still get the same problem! I am a bit skeptical that I now have 2 distributors with faulty ignition modules but I will be getting the one I bought replaced for another next week just in case.

Any ideas or suggestions into this issue, maybe something simple I am overlooking?

I just edited my last post as I realized that I mixed up the coil - and control wire.

I was not 100% sure whether the solid black or yellow/black wire was the coil - as both were ground so I checked voltage on crank for both:

4mV on black/yellow
8mV on black

Unfortunately I am testing after the ignitor because everything is internal on the distributor.

check your crank sensor signal... the ecm looks for the signal from the crank to fire the power transistor. without the power transistor you do not get the proper coil voltage to fire the plugs.

Thank you for your response. The crank sensor is housed in the distributor as well. I believe the first 4 wires of the distributor plug is the crank sensor:

1. Black - Ground
2. White/Red - 12V (Pin 38/47)
3. Black/Red - 5V (Pin31)
4. Brown - 5V (Pin 22/309)

I am aware a 3 wire hall effect sensor but not 4. This particular diagram refers to it as a crank angle sensor but I saw some other diagram referring to it as the Cam angle sensor but regardless of what it is referred as, it is the same pin connection to the ECU.

When I look at a ECU pin out reference I see it as:

1. Black - Ground
2. White/Red - 12V (Pin 38/47)
3. Black/Red - 5V (POS) Camshaft position sensor
4. Brown - 5V (REF) Camshaft position sensor

I have not tested the REF and POS on crank but will do that next.

I believe pin 31 is your crank signal (5v ref). pin 1 has to receive the crank signal in order to energize the base of the power transistor to allow the release of the high energy voltage to the coil. while cranking, should have a 5v on off signal a pin 1.

I will double check voltage on pin1 on crank. Last time I checked i got no reading at all from pin 1 but maybe I did not have proper connection. I will work on this tomorrow.

What confuses me is that the injectors are pulsing and I am getting spark, just too weak of a spark.

DVOM will not show the signal, you need to use an O scope to see the square wave on off 5v.

I managed to get access to a scope yesterday but had some difficulties getting the signal off pin 1 to be displayed properly. Using a 1 Volt division on the vertical I can see the signal however it seemed to intermittently cut out. I did notice afterwards that the voltmeter displays a 0.3V on pin1 during crank.

While not the greatest troubleshooting method I am aware that the GA16(1.6) ECU is the same pin outs as the SR20 so I decided to do a quick and dirty test of swapping the SR20 ECU with the 1.6ECU. The engine still did not start or catch at all. This indicates to me that I may have some issues with the wiring conversion. Will double check this once I get a chance.

Finally got back to this today. I have double checked all my wiring for the engine swap. All power and ground connections are where they should be.

Interestingly after adding more ground connections from the chassis to engine, the spark has now gotten a bit brighter. I tried grounding the spark plug to the valve cover and I can now see spark jumping the plug gap, although still too weak to start the engine.

We had tried another distributor which of course made no difference. I had also tried adjusting the distributor while cranking but no luck.

I went back to the distributor plug to check voltages on crank:


1. Black - Ground

2. White/Red - 12V switched (Pin 38/47)
Around 12V on crank. Test light dims when cranking.

3. Black/Red - 5V (Pin31)
2.6V on crank.

4. Brown - 5V (Pin 22/309)
I realized it reads 0V with disty plug connected and 5V with it connected??

5. Green/Black - 11.7V (Pin 3) *Does not light the test light up.
10V on crank and then after a while I see voltages in the 20s on crank...

6. White/Black - 12VB (ECCS relay) *Coil +
Around 9-6V on crank. Test lights blinks then seems to remain dim on crank.

7. Orange/Black - (Pin1) *Control Wire
Unfortunately I don't have access to the scope anymore. But I did get a display on crank when I had it. Unfortunately I did not take a picture of it.

8. Black/Yellow - Ground


*As for my power and ground connections:
I have switched 12V on pin 36,38 & 47.
Constant 12V on pin 46.
12V on crank on pin 34.

All grounds where checked for continuity to chassis with a reading of 0.4 to 0.5 ohms (pin 6,13,21,39,48,108 & 116)

Summary of steps taken since:

Camshaft sensor and ignition components checks out OK except for secondary coil resistance. US FSM states that is should be 25K ohms but I get 16 and 15K ohms on the distributors I have. This distributor is different fro the US so It could have been possible that the resistance is within spec. Cannot confirm as I cannot source this info or a FSM for the Nissan liberty.

I tested an external coil using a direct feed from the battery for positive and connecting coil negative internally to the distributor. Success! On crank I have a bright spark from the external coil.

Almost thought that the internal coil was faulty but then realized that I used a direct 12V feed from battery to power the coil instead of the feed from the engine harness. I then tested using this direct feed to the distributor instead and success! The engine fired right up.

I am assuming that I have an amperage issue on this wire as voltage checks out OK on switch and cranking. This feed comes from the ECCS relay which is a 6pin double switch relay as opposed to the US diagrams I saw which comes from pin36 or a switched 12 V source. I have checked and changed the relay which did not make a difference.

While it may be a workaround, I will be connecting a separate relay to power the coil feed as I do not have a wiring diagram specific to this engine.

I'm impressed and you didn't throw any more parts at it. Good job!!!

Thank you, got a lot of guidance and direction from the youtube videos.