Possible bad ECU

Hi, maybe you guys can give me some advice with the following situation. As you might know, its always hard to know for sure if the ECU is bad, since there is a lot of other factor which may give a "false" sign that the problem is the ECU. The car I working on is a Mitsubishi Lancer 2008. VIN: JMYSRCY2A8U000844 Engine 4A91 1.5cc. The car starts fine when cold, after a few seconds it start misfiring. the misfiring is due not working of injector number 1. Injector is fine. ECU will not enter Closed Loop. It stays in open loop. O2 sensor stuck at 0.02vlts and no fuel trim data! O2 sensor is OK. DTC Stored: P0122, P0223, P1233, P1234, P1235, P1238, P0350, P1235. P0350 again, ignition coils are ok. Based on my experience, since so many DTC are present with no obvious reason, the ECU may be bad. Further, the car may stall, and not able to idle. Throttle may become non responsive. When cycling the key, after a few seconds, car may start fine and start misfiring again shortly after start up. I was almost convinced that the fuel injector driver chip in the ECU is bad. But since it start up firing all the four injectors fine and short after that only the number 1 stops firing, made me doubt about my diagnosis. I am about to call this a bad ECU. ECU Part No: 1860A799 it seems to be very hard to find a used one. Any help suggestion will be highly appreciated. Best Regards, RP

Nice list of codes! :woohoo: I'd say stick with the P0350 code, as it's an ignition system circuit code, and could very easily explain why the #1 fuel injector is getting turned off.

For example, if the ECM sets the P0350 for something it recognizes as wrong in the #1 ignition circuit, it's common for ECM's to respond by also turning off the #1 injector to save the catalytic converter. Intentional shutdown. The fact that you can bring the #1 injector back to life after a key cycle supports this.

SD covers this very phenomenon in one of his videos:



If the P0350 resets immediately after clearing, then that's the place to start. What kind of ignition system does this engine use? Waste spark, COP? Can you move coils around and get the disabled injector to move with them?

Thank you so much for your reply, it make sense what you told me about the injector being shut down due P0350. It refers to the primary side of the ignition coil. I will try swapping see what will change. I am still concern about the ecu not entering the closed loop and no ST data. When the engine just start up with no misfire, the O2 is cycling and ST data is present! only a few seconds and when the injector #1 shuts down (car starts misfire) the O2 values jump immediately to 0.02vlts and no ST data is gone! 0 value.

Cool, let us know what you find.

The O2 and trim reaction you saw is anther typical reaction to a primary ignition failure or dead misfire. The ECM will usually give up fuel control and lean things out in hopes of preventing the cat from melting down. :silly:

I don't believe we get the 4A91 in the US market? Correct me if I'm wrong. I'm gonna figure it's pretty similar to most other Mitsu aluminum block DOHC engines.

Do you have any readings from downstream O2 sensor?

Ok thank you so much for your advices. It all make more sense for me now. I will keep you posted when I have some updates after checking out the root cause for the P0350. Its gone take some time since the code does not specify which coil. What weird to me is when the injector number 1 is shut down the ignition coil is sparking normal. I took it out and use a spark tester on the coil and at the same time a test light connected on the B+ and the signal wire of the injector. While my test light is not giving any activity and the engine is misfiring, the ignition number one is firing fine on my spark tester. You are right, I don't believe you will have this engine in the US, its a Korean engine made for export. The VIN number is not even valid for most of the online decoders.

Well.. that is another strange case with this car. There is only one O2 sensor on this car. Only one before the CAT. Its a 4 wire O2 sensor. # 1588A192. Its actually the first time I am seeing only one O2 installed on a car.

Only an upstream O2 sensor used to be normal, the downstream O2 was introduced as a check that the cat was working. It is still the case on the vast majority of cars that the downstream exists only to flag up a fault code if the cat isn't lighting up for whatever reason.

In open loop at idle and for the first injection shots, ECU stays focus on LTFT, MAP/MAF, IAT, ICT and engine speed (CKP/CMP)

For instance siemens sim32 ECU at 23°C, shots for every injector 32,21,16,13,10,9 ms. Then stays adjusting pulse width according to desired engine speed.

At aprox. 13°C injection schedule is 51,37,24,18,15,11 ms.

I still cannot explain whyu is not switching to closed loop (neither why only cyl #1 is misfiring), but i would discard first all sensors mentioned before and check injection pulse width in every injector.

This could just explain no misfire at start.

Here some update regarding this issue. After verifying the wiring, injectors and coils I did not find anything wrong. Good continuity from coil and injector connectors to the ECU connector. So, as last check, I decided to take the plugs out for visual inspection and some measurements, (I have seen plugs gone bad before) There was nothing wrong with the plugs but what I have noticed that cylinder number one plug came out like it was soaked in engine oil!! that was not oil dripping from the valve cover. The piston at cylinder one is completely wet of engine oil while the rest are dry!!! I believe that might be giving the P0350 code, since the oil is preventing the plug to spark or spark as It should be. P0350 refers to a primary OR secondary abnormality detected. So in this case it might be a secondary issue. Pls advice what you guys think of this. I did not start the car after this findings, I will re assemble everything back tomorrow and focus on the oily cylinder number 1 issue. Unfortunately, this might be worn rings related.

A compression and/or leak down test will give you a clue about the rings etc. It might be a damaged head gasket as well, especially if this started all of a sudden.

well... last night I was working on this car again and there is nothing wrong with the cylinders, compression reads Ok. Leak Down test OK. After that I checked the crank position sensor since it has a main role in the ignition system. I found that the connector is broken and the three wires were very loosen and wiggling freely. Although the car starts fine, Its very obvious that there might be a connection issue. I am now fixing the harness connector in the best way possible. What I found is just the three bare metal plugs which are supposed to be locked in a housing. I believe this might affect the ignition system and make the ECU throw the P0350 code and disable the injector. What is not so clear to me is why the ECU always shuts down only the number one injector. I will put an update when so far today. Thanks

Hello, unfortunately fixing the crk sensor connection did not fix the issue. I don't have a automotive scope yet. But I used a old school conventional Oscilloscope used back in time to repair electronic devices. What I could see is a normal square wave pattern for the crank sensor and for the cam sensor. I also look at the control wires of the coils, the number one coil looks different than the 3 others. Numbers 2, 3 and 4 has a flat on top pattern while the number one coil has a slight larger amplitude and like a drop of voltage at the top. Its very hard to see any further details with the scope I used. I am not sure how a input to the ECU can bring a abnormal wave for only coil number 1 but I believe the ECU is bad in this case. Switching the coils and injector did not change anything, it keeps killing the number one injector circuit. Cycle the key, will bring it back to life just to kill it again after about 20 seconds. P0350 keeps showing up persistently. Any comment will be appreciated, I will call the customer on Monday and tell her she needs a ECU.

What about the oil issue?

Compression and leak down test can be fine, even if you have oil inside cylinder.

Where's the oil coming from would be interesting to know. I'd be interested to know what he finds. With the oil in the cylinder could it be a cam related issue? I'm just giving it a shot in the dark as I'm learning from this post.

HE never mentioned that he watched the scannerdanner video that one of the replies refers to.

Which video would this be by chance as I do want to watch it and see what I can glean from it in regards to this guys situation.

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Would it be possible to post the ignition coil waveforms you saw? #1 and one of the others, preferably. I dunno that it's gonna change your diagnostic direction? :silly: But I think it'd be beneficial for the group to see what the PCM is seeing.

I was going to suggest using a spark tester on the #1 coil to see if it was something about the spark in the cylinder that the PCM doesn't like, but I see you've already done that. :silly:

You might be down to a PCM? I'd love to know more about the exact criteria on this P0350 code, but I can't see that the US market Mitsubishi's use that code. Before you pull the trigger, it's worth trying a hard reset. Disconnect both battery cables, jumper them together and have a cup of coffee. Come back and see if the symptom remains.

Hi guys, thanks for your attention on this issue, well to be honest, I don't see the oil on the number one spark plug anymore. My first guess is that the oil I saw in the beginning of my diagnosis was just oil build up during all the days/months that the customer kept driving this vehicle with the engine running on 3 cylinders.. No combustion firing, no oil burning! hence the oil observed earlier on the spark plug and the wet piston top. Since I cleaned up the spark plugs and swapped them, no oil was observed. This car went to several service centers for this issue without any success. Even the local Mitsubishi dealer kept this car for a week long and called a bad ECU! Many cars drove in my shop having the same call out from dealers and other service centers and drove out fixed without replacing the ECU. This one is kicking me in the bud!!. I watched the video of ScannerDanner Tyler sent me earlier. As a matter of fact I watch all the scannerdanner videos and learned a lot of him, he is a great teacher!! The video is about the same situation I am having with this car, but in his case there was an obvious issue which was a bad/damaged spark plug. In my case, I am no seeing anything wrong that could be affecting the ignition system what so ever!

Thanks for the updates! Besides the hard reset with the battery cables, I think you're on the right track with the ECM.

Excellent observation with the #1 plug, BTW. It figures that miles and miles of driving around that way would end up with a wet plug. I was about to suggest an oil control ring issue, but I think your suspicions are closer to the mark.

Well, like I said before the scope device I used has a 4"x4" display with a green tiny fluorescent line which can barely seen, there for very little can be seen in a picture. Its time to get my scope right away. The 4 channel PICO is in my mind! Anyways, I could see some difference in the wave form of the number one coil in comparison with the rest. My question would be, if there is any bad and/or erratic input information to the ECU that might be affecting only the number one ignition circuit. Further observation, scan tool data shows me a jumping RPM that varies very rapidly from 7K to 9K at idle and the spark advance jumps 6 to 14 degrees just idling. The Tachometer in dash stays firmly on 8K, no jumping. I have seen RPM scan data jumping before, but I believe this one is jumping to far, and I don't trust the spark advance data jumping in that way without even touching the throttle pedal. The P0350 so far I could read refers to a discrepancy of more than 10% of the voltage readings by the ECU. Its a COP engine 3 wires ignition coils all of them shares the same (chassis) ground and the same B+ voltage from the Relay. Like you sad Tyler, I did the spark tester on cylinder one and it sparks great. I don't if it would be of added value to take all the plugs out, connected the coils grounded together and crank the engine just observed and compare the spark with each one. Maybe four spark tester will be better for this test. This may sound crazy but at sometimes you will reach a point that you have to do the uncommon things to try figure out what exactly is going on! I don't care so much whether I fix this car or not but what matters to me is that I can say for sure "this is the problem" . A bad ECU was my first guess rom the start, but as we all know, its not easy at all to call out a bad ECU!! And... unfortunately I can not find a replacement ECU for this car, not even on Ebay!!

Just last idea before kill that ecu.

Have you checked resistance in wiring hardness (injectors and coils connected) from ecu connector?