4JG2 EFI crank/cam sensor issues

[mr57757]

Few months ago, the car was having a "cranking but not starting" issue. It was more frequent during cold startups so I figured out it may be the glow plugs were going bad. Glow plugs were about 10 years old so that may be it

After inspecting, it seems all 4 glow plugs were good & checked it with a multimeter. Probably thought it was the glow plug's metal link connector (i don't know whats the name of it) corroding so I cleaned those out and assemble everything back together and the car still won't start

I've done some googling and I found out that before starting the car, if the CHECK ENGINE light flashes once and stays on, it shows that crank/cam sensor is faulty/error/no signal. So I decided to remove & inspect the crank/cam sensor which is located between the a/c compressor and alternator. It looks like it sticks into the back of the timing cover. I'm not sure whether the sensor is still good or not but it does seem to produce some weak AC voltage when I lightly tap it with any metal magnet. I could be wrong but I think tapping the sensor isn't the correct way to check it?

Sourcing for a used one is hard for now since this pandemic and even I'm still waiting for the shop to phone over (they didn't sell those so they had to order). I couldn't wait so I just reinstalled back the old sensor, cleaned all the connections and even the sensor itself since it was covered with dirt and stuff. and weirdly enough, before starting up, the CHECK ENGINE light doesn't light up. And yup, the engine fires right up. Seems to be a dirty connection I thought. So after all that, I think it was over.

Then the issue came back. Again. Cold startup, cranking but not starting. So I decided to figure out how to forcefully start this thing What I noticed was:-

1) When this issue occur, there is a clicking sound somewhere near the fuel pump. I'm guessing this is the fuel solenoid which controls the fuel to cut off or on. Along with the CHECK ENGINE light flashing once and staying lit up.
2) Normally, as far as I remember there isn't any clicking sound other than the glow plug timer and the CHECK ENGINE light will turn off after a brief moment.
3) The fuel solenoid will cut off fuel if it doesn't sense the crank/cam sensor or there is an error/no signal whatsoever. This is probably the clicking sound I guess.
4) I noticed that if I turned over the key to START quickly, it will start for a brief moment and dies.

Update: The steps below is useless and may kill your battery and starter motor. Read my 5th post instead.

After i fiddled around the car, I got it to start up eventually Here's what I did:-

1) Let the glow plugs to its job until it lights off. This will make the starting quicker. You may need it to light longer if you're in a very cold environment.
2) Turn the ignition back to OFF or ACC. Just back off from ON postion.
3) Get your foot ready on the throttle pedal.
4) Turn the key to START as quick as you can and start pumping or press the throttle pedal as soon as possible.
5) Maintain the throttle pedal or just pump it till there is no CHECK ENGINE light. (Normally it will turn right off if the engine fires up and you don't really need to press the throttle pedal for like more than 3 seconds)

As far as I know, if the crank/cam sensor position is toast, then it is toast. But for mine, it started to work when the revs are like more than 1200rpm~ maybe? As I pump the pedal while starting, the rev does rise up for a brief moment and that's where the CHECK ENGINE light turns off and the car idles fine after I let off the throttle. I tried turning off the engine and starting it up again, now the starting issue was gone... for now...

This is not a permanent solution obviously and you can try it with your own risk. I'm still waiting for a crank/cam sensor replacement anyways, but if anyone does experience this kind of problem and have some ideas about apart from a faulty sensor, do share Cause replacing the sensor is such a pain Also if there's any related post that I may have not seen, links are welcomed.

[Myarmila24311]

Crank sensor works to support the signal if the NP sensor fails. The NP sensor is located on the edge of the fuel pump with 2 connection wires. In my case before, the crank sensor was damaged due to a fracture while adjusting the alternator. But the engine is still alive as usual. Then I had a wiring problem that interrupted the NP sensor signal, the engine was dead and could not start. the engine check light is on. I replaced the crank sensor, the engine is on, idle is not stable, the engine check light is on, the rpm needle does not move. Then, the wiring problem is solved, the NP sensor works well, the engine lives on as usual. Same with rpm needles. There is 1 more case, the engine is running as usual, in a few minutes, the rpm suddenly goes up on its own, the engine check lights are on and the engine is off. Try restarting, the engine cannot start. The next day, the same thing happened again. The ecu problem. Change ecu, the problem is solved.

[Myarmila24311]

NP sensor responsible for give signal to ecu to drive rpm and injection timing. If it is damaged, the ecu will use the signal from the crank sensor to start the engine. But in case NP sensor fails, crank sensor works, rpm needle does not move, engine idle is unstable but can still be driven, engine check light is on. If both sensors are damaged, the engine cannot start

[mr57757]

Hi there, really forgotten this thread since no one bothered to reply at all...

Recently, my previous problem (from the 1st post), I actually managed to start it by letting the ignition key to stay at 'ON' position for at least 5 minutes. Definitely the CHECK ENGINE light came on even though the glow plug has gone off... but after letting it at 'ON' position for 5 minutes, I turned the key back to ACC and then ON position, the CHECK ENGINE light is gone and the engine fired right up. Weird issue... but at least the engine is running... so I figured out probably its just some wiring issue that I'll solve someday...

Until now, it really has gotten worse. Now it does start as usual but only for few seconds. It revs up on its own and dies. Then the CHECK ENGINE light came on again just as you mentioned previously on your first reply.

I've also been suspecting the ECU was actually the main culprit because, as much as I understand, if the sensor failed completely, it wouldn't have such weird issues like the CHECK ENGINE light is gone after letting the ignition position set to ON for like more than 5 minutes. If a sensor fails, then it the engine should've just stayed dead. I've also tried checking out the wiring looms around the injection pump and there's no signs of oil or water at all. Even the cable connections are pretty clean.

Anyway, I appreciate your reply. I actually didn't know about the mechanism of the injection pump and the existence of another NP sensor. I've read somewhere a facebook post where a guy said that he had the same issue and tried to replace two capacitors on the ECU and it worked. Probably I'll try that out before sourcing another ECU because its really pricey.

[mr57757]

I noticed that this thread has a lot of views so maybe I'll try to share some of the progress I've made resolving this 4JG2 Check Engine light/cam sensor issue

To recap from 1st post, I was having issues with starting up the car especially when cold. It has the 'CHECK ENGINE' light flashed once after I turned the ignition ON and a click somewhere from the fuel pump area. This led to endless cranking. I've mentioned on the 1st post that I tried to 'quick' starting it by directly cranking the engine before the check engine light comes on and clicks off the solenoid in the fuel pump. This isn't a practical solution since it kills the battery super fast.

After few weeks from my 1st post, I found out how to get it started which is by letting the ignition stayed 'ON' for about 5-6 minutes and turning the ignition to OFF and back ON and the CHECK ENGINE light is gone (I was able to get it running ). Once started and after a few minutes of driving, it doesn't emit any problems until the next morning or any random day.

As of now, the ECU finally gave up and decided to rev up, cut off every few seconds and gave a CHECK ENGINE light after starting. Sometimes it just shows CHECK ENGINE and clicks off the solenoid in the fuel pump.

I'd like to add that the ECU was replaced back in 2016. The original ECU was holding probably about 20 years and it started giving problems like revving on its own, and it was towed to a workshop since it couldn't start. I've actually tried plugging the old faulty ECU back and certainly it does emit the CHECK ENGINE light and flashes once. Tried the 5-6 minutes trick, didn't work. I've done some research on this issue and the closest one I can get is a fellow from facebook which he states in his comment/post that, he also had the CHECK ENGINE light issue. According to him, he had replaced 2 capacitors on the ECU with a PW series capacitor. Both of them are 16v 10uF.

So I ordered some capacitors, and instead of replacing only 2, I decided that I'll just replace all of the caps. After it came, I soldered them off on the faulty ECU (the original one) and guess what, it did started. BUT... the engine was knocking the hell out and I instantly turn it off. Maybe its just the ECU sorting itself out? So I dared myself to start it back it up and let engine knock and after few seconds, the knock was gone .

Did I actually ended up fixing the faulty ECU? Nope.

After few revs and idling, the engine misfires, the tachometer dies out even when the engine is still running and boy, I turned it off instantly and felt pissed . So I moved on to the 2nd ECU and soldered only 2 capacitors which were the 16v 10uF. Results? It started fine on the first attempt, but it still revs out, dies and gave a CHECK ENGINE light. Not good

Much much more research, I found out that I did not realized there are specific types of capacitors which are only used for ECUs. Yep, I misunderstood the 'PW series capacitor'. I actually thought that was just another brand name or whatnot. Turns out, Capacitors on ECUs should be low ESR type or something? I'm not an electronic expert, but that is what I can interpret so far. Another thing, even other vehicles in the 90's also have similar problems where these ECU capacitors are known to have a limited lifespan.

I've already ordered low-ESR types capacitors and we'll see how it goes this time...

[geeves]

Its an interesting problem and not one that has come up before here. I saw your post on facebook as well but not a lot of help there either. Its tempting to try a known good ecu but who would loan you theirs when a fault in the car might fry any ecu. A trip to an auto sparky who has proper diagnostic gear might be in order

[mr57757]

My ordered capacitors have just arrived and I rushed to get it, came home and directly soldered them into both of my ECUs.

1st ECU (the original one which was announced dead on 2016):-

I've replaced ALL capacitors... 16v 10uF x2, 50v 100uF x1 and 50v 220uF x1. Except that I've replaced the 16v ones with 50v 10uF. (According to my research, a higher voltage rating of the capacitor can be safely use). The vehicle started, but with a brief knocking sound (probably less than 10 seconds) and idles pretty normal. However, after few minutes, the engine starts misfiring with an unstable idling. The tachometer stopped working reading 0 rpm, and the 'CHECK ENGINE' light appears... Engine doesn't turn off immediately though. A bit of hesitation when I tried depress the accelerator pedal.
Video link: https://www.youtube.com/watch?v=2XngckAdOJI

Turned off the engine and restarted it, directly came with unstable idling with CHECK ENGINE light (during the glow plug period, there is no CHECK ENGINE light). I tried shifting to reverse or drive (its an auto) and somehow the engine became smooth until I shift back to Park or Neutral.

2nd ECU:-

Replaced both 16v 10uF with 50v 10uF first. The other 2 capacitors were untouched. First start, it also idles normal except that it doesn't knock just as the 1st ECU did. Few minutes later on, it emits the same problem. Rev up, and dead with CHECK ENGINE light. I tried restarting it, and this time, it stays quite awhile but there some noticeable unstable idling. No CHECK ENGINE light. Turned off the engine and tried starting it back up, and it revs the shit on its own with some serious black smoke . Not good.

This time, I tried replacing the remaining 2 capacitors. Same results unfortunately . Rev up, and dead with CHECK ENGINE light. Tried restarting it, and it just clicks off the fuel pump solenoid with the CHECK ENGINE light.
Video link: https://www.youtube.com/watch?v=hueXKX8oSwI

Conclusion:-

Both ECUs does work NORMAL for few minutes. After that, they will produce their own problems. The 1st ECU was unstable with 0 rpm reading but engine doesn't turn off. The 2nd ECU still revs up and dies out.

Now, if I were to use the 1st ECU, the NP sensor might be the problem (as mentioned by Myarmila24311)... but if it did, then why does the engine idled fine for the first few minutes? As of now, I'm thinking of inspecting the NP sensor and might as well try replacing it if it doesn't cost as much as another ECU .

[mr57757]

New update here and this will the last (probably)

I've finally bought a used ECU off from a half cut JDM shop. Back to home and plugged in the 3rd ECU now. It finally works. No abnormal operations even after few minutes of idling and test driven. Hell, it kinda performs smoother now (still the same power tho).

Unfortunately, I could not solve the ECU issue just by replacing those capacitors. Maybe my ordered caps are just shitty? Because they are labeled 'low ESR' but no brand name like NIchicon or something... who knows . Some more bad news, according to the owner of the half cut shop, these ECU's have a lifespan of about 20 years. Therefore, buying off a used ECU will approximately run the vehicle for just another 3-4 years . If anyone has the schematic, pins or any relevant diagrams, information on these 4JG2 ECU's, do share

There's an option for converting to mechanical, but will have a lower power output. Not sure about upgrading/tuning the fuel pump though, but if the time comes... maybe swapping in a 4JJ1 will open some more opportunities...

[geeves]

I wonder if a link computer could be tuned to work?

[mr57757]

Not sure about that one, geeves. Do you mean by running a standalone ECU similar to megasquirt or something? I liked that idea too but from what I've researched so far, customized standalone ECUs for diesel aren't alot... I may be wrong though. Even if it did exist, I'll probably take ages to figure it out or bomb few engines before I could finally made a proper one .

[geeves]

Link and megasquirt are much the same (in the same way as Mazda and Mitsubishi) Beyond that I have no knowledge

[Myarmila24311]

Probably the circuit in the ecu of the Np signal reception part is faulty. But to find it you have to have expertise in electronics and eye acuity. For me, it's hard.

[Myarmila24311]

Thankfully, the problem is solved. greatly appreciates the partnership in finding its solution

[Natek235]

Any chance you took photos of replacing the caps in the ecu? Cheers