My C4 is a great car. Best "toy" money I've ever spent.....on my C4. OTOH, my kids' '03 WRX with COP ignition died on him driving to work. Has no spark .

I'm trying to test to see why. Each coil has three wires:
1. Ignition on/Power
2. Ground to engine block
3. "Signal wire" (the switched ground through the ECM for each coil)

All 4 of the "xxxx/Yellow" wires go to the ECM ....to ground and open the primary circuit in the coils, I'd assume.





1. We have good power, all the time that the key is ON or CRANK positions.
2. We have good ground all the time
3. Here is where things get confusing. If I probe the signal wire (the yellow or xcolor/yellow wires) to the ECM, I get a high resistant "short to ground"; about 5.9 M ohms. If I crank the engine, I get no on/off pulse of the signal wire. Key on/off/cranking doesn't matter, it's all the same. If I disconnect the ECM, the 5.9 M ohm "short" goes away; circuit is open. My son has a spare ECM...swapped it...same/same.

Here is another weird one; I back probed the signal wire on the 3 pin coil connector, plugged the connector into the coil and tried to monitor for pulses on the signal wire while cranking....WITH the coil all hooked up. No change, but when I was dicking around with that arrangement, I inadvertently put batt power to the signal wire back probe; I had a test light connected to B+ and I touched the back probe. When I removed the test light tip from the back probe....SPARK. Wha!?... That ain't how coils work!?






What am I being dumb about? What am I missing/forgetting about how coils work.

 

You have no spark on any coil? A bad coil can cause the rest to not fire but thats rare...I assume it has a crank position sensor? That will cause no fire at all. A cam position sensor if it has one shouldn't cause a no fire, it only fine tunes the ignition. On some engines there is also a separate fuse for the injectors, or injector driver....
keep in mind I know crap about that engine, but they all work basically the same.

 

I agree that they all work basically the same and that's why I posted here. I posted on Subaru forums but it's just a bunch of kids and they don't know how anything works. So that's going nowhere. Thanks for all the replies so far.

That's right, no spark on any cylinder. The car just shut off on him and hasn't run since.
Crank position sensor was my first thought. There was actually some sketchy wiring there from the previous owner. We rewired the crank position sensor and can see RPM on the scan tool while cranking. About 120 rpm.

the cam position sensor appears to be working. When I bring it up on live data stream on my scan tool it only shows off or on. While not cranking it says off. When I crank it mostly says on but flashes to off somewhat randomly.

 

thanks for both of the replies. It is not a waste spark System though, since it has four coils for four cylinders. There is literally a coil on each Spark plug.

 

First, when 'rewiring' the Crank position sensor--polarity is critical Is polarity correct back to ECM? Would look here as a wiring/issue fix in past
The ECM "looks" for the slope on the leading or trailing side of the wave form to ECM.
Try getting into the IATN library for waveform patterns or Google search
Do you have a way of "scoping the wave form" of the Crank position sensor at the ECM?

The ECM needs to see "the space" (missing tooth) to "know" which cylinder to fire. "indexes firing order"--generally not an issue unless tooth is "lost/damaged" or "gap" is filled due to lack of oil changes and is filled with sludge and debris. ECM will not "fire" as it does not know really where the cranks is, as the missing tooth index is missing or not enough "pulses" between the "gap"--caused by an additional "gap".
Depending on the logic in the ECM, a cam sensor signal MAY also be required to fire ignition

 

Quick update. My wife and I are about to embark on a 5-day backpacking trip in the Wind rivers. I won't be able to respond to this thread until we get out at the end of the week. Just wanted to let everyone know. I will dive into this thread and reread everything carefully and any new posts when we get back on Friday so feel free to add anything you may think of and thank you all so much for the thoughts so far. Catch up in a few days!

 

Did you unclip the wiring harness connectors when you were looking at the crank and cam sensors? I had an 02 WRX that developed timing and AFR issues because the the sensors leaked internally and oil actually wicked up through the wiring all the way back to the ECM. I assume when you swapped the ECM you would have noticed oil wicking at the ECM end or the sensor connection end of the harness, but I figured Id throw it out there. My car never died completely though. Those cars were pretty notorious for doing that from what I came to find out. Mine was a JDM swapped engine with 35k miles and the sensors were bad.

 

Hey everyone I'm back. A bit sore in the hips, quads, calves and shoulders but what a hell of a trip! Here's a picture of where we were camping two nights ago. Absolutely unbelievable...









Back to ignition systems. Unfortunately I do not have a scope. That is an excellent suggestion that I would love to explore but I don't have one. It's on my list of tools I need to buy. It's annoying to me that scan tools don't have a scope feature built in.

That's funny, this was a JDM swapped car as well. The kids who had it before my son bought it did the swap. They must have been the ones who chopped up the harness and butt connected things. Tonight I threw my scan tool on it and graft the crank RPM while cranking with the starter and the spark plugs removed. It showed a peak of 134 RPM which seems about right to me.




Maybe a bit low but not too far off. That's about the most detail I can get from the crank position sensor with my scan tool. For the cam sensor, it simply shows on or off and it shows mostly on while cranking. Occasionally it will show off for a split second. Not sure what that means. Would love to see a waveform on that as well but I can't.

I'm sure the cam sensor is critical as a otherwise the ECM wouldn't know which cylinder to fire.

Also tested shorts to ground in the harness and checked for shorts to ground at critical places. Didn't find anything. Put the plugs back in and checked for spark again, no spark.

 

Ok. There are many “options” for these swaps. Unfortunately, all options included axing the main wiring harness at the firewall. Best practice is to use your own USDM main firewall harness and buy the adapter harnesses necessary for connecting the main harness to the main engine harness (if the engine was bought with engine harness intact). Point I’m trying to make is that there was the potential for very much teenage wiring depending on what they got with the swap vs what they purchased to make it work. If they didn’t get much as part of the swap and didn’t buy the supplemental harnesses from companies like IA Performance in Cali, it could be a wiring disaster. Matter of fact, you might want to call the guy that runs IA and check out his site. It’s all about JDM swaps and the pre made harnesses, aftermarket, and OEM new old stock parts that make the JDM swap world turn. I forget his name, but he is the most knowledgeable Subaru geek on the planet. He can probably make some very good suggestions as to what to check and where to go from nowhere. Also you might want to Google search your issue with the term nasioc forum in it. I found nasioc to be way more helpful than the other Subaru and WRX forums.

 

Hey there...been busy and haven't been able to look at this more until now.
This car appears to have one harness from the ECM, through the firewall, to the engine's sensors. I don't see a firewall plug. Whatever the case with the OEM>JDM swap arrangement, the car has run great for the past year. So whatever "they" did when installing the JDM engine, it worked fine. Car ran great until a couple weeks ago, then just shut off while my son was driving it to work. Hasn't made a spark since.

Never heard of IA Perf, but I'll give 'em a ring and see what they say. Thanks.
A google search brought up several hits on broken teeth on the crank reluctor wheel (how that happens, IDK)...we've already pulled the crank gear and checked the reluctor wheel; it's fine w/no missing teeth.

NASIOC....Eh. I already posted this issue there and have gotten squat for good advice. That's why I posted here....I feel that folks here are more.....knowledgeable about how engines work.

 

Honestly I’d have a hard look at the cam sensors especially since the diagnostics with them have been erratic. The problems with them can range from what I understand. On my car, they were causing a bad reading so it messed up the fuel curve which caused the ECM to put it in limp mode with limited boost and retarded timing. From what I understand, if they get weak enough, the ECM will just shut spark down completely to save the motor. On the JDM there should be two cam sensors as opposed to the one with USDM engines. As of 2018, IA Performance carried new OEM JDM cam sensors for the EJ205 WRX engines. I can’t remember, but maybe the dual cam sensor engines were engines with AVCS (Subarus variable valve timing like Honda’s V-Tech). The AVCS motors definitely have two sensors which is what mine was. Non AVCS, similar to USDM, only had one I believe.

 

Thanks again. I think it's time for me to buy an oscilloscope. Cam sensor investigation to ensue....

 

I Googled the ignition system on the car which brought up several PDFs which I didn't download as my laptop quit and phones don't have enough memory. Anyway it's out there
. The spark by the 12v test light. Test light clamped positive post and probe on pin P of hei ignition module should cause a spark from coil when probe is removed. So it may be normal. The probe is energizing primary when it's removed primary collapses and secondary discharges a spark.

 

Copy....that's what I was sort of guessing, thanks for the confirmation.


My problem is that I have no grounding happening on the ECM side. IDK why. I'm stuck. I think I may try switching the polarity on the crank sensor. Maybe it got mixed up when my son spliced it back together.

 

I'm sure you know, but most Japanese systems will switch the ground. Its actually a better way. Just FYI

 

Yep...that is how most work everywhere. That's the part I'm not getting through the ECM. I'd think the "ECM must be bad!"....but we swapped ECM's...same thing.

 

Gotta be a connection issue id say then. Most sensors (and again no clue the engine your on) will set a code, go to a default setting, but won't not let it run. Only a serious fault will cause it not to run, or, a connection issue...and its a swapped motor..look at ALL the connections....I'd trust no one with a swap like that . Electrical is most peoples fear for some reason, and thats usually the issue.

 

Yep...The cam and crank sensors were butt-connector'd by the PO. Car's ran great for the past year like that, but then died suddenly. My FIRST thought was those butt connectors, and I had my son tug on the wires...crank sensor wire pulled right apart. "That's it!"

So we spliced them proper, heat shrink'd them...but still no start. That is why I'm starting to suspect rev polarity on those wires. I was going to work on it last night but by the time I got home, walked Emma, cooked dinner, ate....it was bed time.

 

FIXED. We got spark, and it runs again.

Wires were backward on the crank sensor. MAN...I'm glad that it's running again! Now he can take it out of my garage and bring it to college.🤣

Kids before my son didn't leave us much to splice with...hacks.