Troubleshooting Problems
Troubleshooting Problems
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With any engine, especially 30+ year old computer controlled, you will have an issue pop up. Misfires, no start, running rich, weird noises, etc. it is part of being a car enthusiast. This page covers common issues found on RB20s (applies to most RBs) and how to diagnose and fix them.
All of these engines, especially modified ones, need to have a proper ecu with a good tune and quality electronic components to run flawlessly. A cheap tune and cheap non OEM electronics makes for a massive headache trying to diagnose issues. I always recommend a modern ECU with good tune and new sensors and electronics where you can afford them.
***Disclaimer: I am not an expert. Follow these recommendations with caution. Use manufacturer recommended instructions and techniques along with logic and critical thinking when working on your car. I am not responsible for any injuries to yourself or your car.***
Table of Contents
Table of Contents
Common Issues
Coil Packs / Igniter
MAF
CAS
Idle Air Control Valve (IACV)
TPS
Factory ECU Diagnosis
Common Issues
Common Issues
Once you can check off these main items, the issue is likely something that will cause any engine to run poorly. Vacuum leak, bad fuel pump, clogged injector, old spark plugs, old wiring etc. These are just a few common issues with RBs and how to diagnose them.
Coil Packs / Igniter
Symptoms
Single cylinder misfire
Misfire under load
No spark at all (igniter)
Diagnosing Issues
Have the car running at idle and try to find the cylinder misfiring. Once located unplug the coil pack while it is running. If the misfire is exactly the same then try to unplug another coil until you find one that causes the misfire to get worse. Now that you have identified a known good and a known bad cylinder, swap the coil packs and try the unplugging them again. If the misfire moves with the questionable coil pack then you have successfully found the issue is the coil pack. If the misfire is still on the same cylinder with a known working coil pack more diagnosis is needed.
Inspect the connector for the misfiring cylinder and all the sub harness wiring. It is very common for the connectors to fall apart or wires get cooked. I would recommend replacing the entire sub harness. If the cylinder continues to misfire, look into the injector.
If multiple cylinders are misfiring or if you have exhausted all other options, but have identified the issue is spark related then the issue is likely the igniter or wiring from ECU to igniter.
In some cases an igniter failing and ECU internal failure have the exact same symptoms.
MAF
Symptoms
Random misfires
Hesitation under throttle
Jerky under throttle
Running rich or lean
"Limp Mode" - 3k rpm limit
Idle hunting
Diagnosing Issues
Have the car running at idle and unplug it. The car should run much worse and idle hunt and be limited to 3k rpm. Plug it back in and it should run much better. If no change when unplugged this may be your issue.
If the hesitation/ issue is random while driving, it still could be your MAF and is much harder to diagnose intermittently.
CAS
Symptoms
Random misfires
No start
Injectors not firing
No spark at all
RPM gauge does not work
Diagnosing Issues
If no start (but will crank) issue is occurring, the easiest thing to check is if the RPM gauge is moving. You should see it reading 150-250 rpm while cranking. If its dead still when cranking then its a sign pointing to a bad CAS.
Mark the CAS orientation with a sharpie line on a bolt or the cover. Carefully remove the CAS.
Unplug the CAS and spin it by hand, there should be no binding, scratching noises, and should rotate smooth.
Plug the CAS wire in (but do not reinstall) and turn the key to the on position. Slowly rotate the CAS by hand and you should hear each of the 6 injectors click and each spark plug should fire. If you do not hear clicking then the CAS or CAS wiring is likely bad. *note do not spin it too much as it is still injecting fuel and spark so combustion could occur. You can unplug the igniter and spin as much as you want to test injectors just know it will be injecting fuel.
IACV
Symptoms
High Idle
Poor Idle
Idle Hunting
Diagnosing Issues
Let the car idle (or hold throttle) till it is warm. If its a high or poor idle, unplug the IACV and monitor for a change. If there is a change then adjust the idle air screw on the valve. If no change then remove the IACV and clean thoroughly and repeat the test. If still poor idle then could be bad IACV or IACV wiring.
TPS
Symptoms
Poor Idle
Hesitation under throttle
Diagnosing Issues
Verify the TPS voltage is 0.48V when closed. Loosen the TPS position screws and rotate till it reads 0.48V when fully closed and around 4.5V at full throttle.
Factory ECU Diagnosis
Factory ECU Diagnosis
Diagnostic Mode RB20DET ECU:
The ECU is in the passenger footwell, behind the plastic kickplate to the left of your feet. You'll have to remove the computer from the mounts in the footwell, as the led/leds you'll need to see are pointing towards the front of the car. Switch on the ignition but don't start engine, the led on the ECU will begin glowing turn the selector screw clockwise all the way.
There's three types of factory ecu in Skylines, One type has two LEDs and five modes, the other type has one LED and two modes and the last type has no LEDs, the output is done with the engine check light in the instrument cluster.
For two led ecus the led will flash once, pause, flash twice, pause... all the way up to five this is the diagnostic mode Mode 1 = one flash, mode 5 = five flashes. When you reach the right mode, turn the screw back counter-clockwise. Mode 3 is what most people use.
For one led ecus wait a couple of seconds, and turn the screw back counter-clockwise, the ECU is now in mode 2 the engine check light on the dash will mirror the LED on the computer.
The led will flash out a code or series of codes if there is more than one fault More recent ECU's have two LED's red is first digit, green is second digit, eg red 2x flash, green 1x flash = code 21. The ecus on most R32's have one LED, long flash = first digit, short flash = second digit, eg long, long, short = code 21.
Codes:
11 Camshaft position sensor
12 MAF sensor circuit
13 Coolant temperature circuit
14 Vehicle speed sensor circuit
21 Ignition circuit
31 ECU
34 Knock sensor
43 Throttle position circuit
45 Injector leak
51 Ignition circuit
54 Auto signal to ECU
55 All OK Turn the ignition off to put the ECU back to normal
There is also a O2 sensor test in real time available - do the above to get the ECU into mode 2 (single LED ECU) or mode 1 (2 LED ECU's) Start the engine. Warm the engine, and then run under no load at 2000 rpm for the test. Single LEDs: on = lean, off = rich Dual LED's: green LED on = lean, green LED off = rich
This info is found here written by LO CEF, Thanks for the great write up!
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