Which ECU can I use on my engine?

[Teknogaeque]

I confess, this question isn't from my '94 Pathy...it's from the VG30i in my 86.5 Hardbody...that has a few replacement parts from sadly junked Pathfinders. I've been troubleshooting a problem that's come down to a code 43 [injector Failure]. I replaced the injectors, and the injector circuit tests correct. Now, even though the ECU says Normal Operation before I try to start it, the engine will not start, and afterward the ECU shows Injector Failure again.

 

I have nothing left to test, so I'd like to try a replacement ECU...and that's where I ran into a question. I've done some looking and searching, and it looks like there were 4 parts used on the MT model trucks. My ECU is Nissan part #23710 12G00, Hitachi part #MECS-G001 D1. Can I use a the (all of these numbers start with 23710) 12G60, 42G00, or 42G01, which were evidently all used that year, or are there differences?

 

Also, some posts here seem to indicate I could use the AT model ECU, which opens up the 12G10, 12G70, 42G10, and 42G01 models. Does anyone know what the specific differences are, and whether they'll interchange and allow me to test whether my ECU is the problem?

[GrimGreg]

That code can come from number of sensor malfunctions. Basically, the ECU is getting bad readings in the O2 sensor or MAF, etc and blaming the injector for the fault.

[Teknogaeque]

That code can come from number of sensor malfunctions. Basically, the ECU is getting bad readings in the O2 sensor or MAF, etc and blaming the injector for the fault.

 

Thanks for your reply, GrimGreg. I really appreciate the information, but it doesn't really match what I've seen in the FSM. Is there some known issue where ECUs generate unexpected codes for specific failures?

 

The FSM indicates that there is a separate code for the O2 sensor (Exhaust Gas Sensor on this vehicle), as well as a separate code for the MAF (Air Flow Meter on this vehicle). Even though an Air Flow Meter problem can cause the ECU to go to Failsafe mode, it doesn't appear to cause the engine to not run...even the test procedure, if I remember correctly, requires the engine to be running, and my engine won't start. Even a bad Exhaust Gas Sensor reading would be ignored at startup.

 

I have tested another, not necessarily known-good, Air Flow Meter, and the behavior didn't change. Based on the information in the FSM about the inputs the ECU uses, the Injector Failure code, what can cause failsafe mode, and what a low-resistance injector can do, the best theory I have is as follows.

 

I'm guessing I had an intermittent injector failure (when operating in alternating mode, an injector fails to inject 4 times because of an electrical problem - that triggers injector failure and causes failsafe mode to be activated) that caused the initial symptoms. Over the course of a week, the injector probably failed with a short in its coil, resulting in low impedance, causing it to sink too much current, thus damaging the ECU (the FSM says this will happen if resistance is too low). This would explain why, after replacing the injectors, my ECU still senses incorrect behavior on the ECU circuit; because its circuitry is damaged...and that it what's driving me to try another ECU.

 

I wish I could close this thread by providing the results of what I've found on which ECUs interchange...just to help the next guy. Unfortunately, I can't find a scrap of information. The best thing I've got is a link to this document, which details which ECUs were used in which vehicles. I've found another ECU with a part number that was used in 86.5...hopefully it works in my truck. Good luck to anybody else trying to answer the ECU interchange question.

 

http://maxima.theowensfamily.com/tsb/NTB94-097.pdf

Edited October 20, 2009 by Teknogaeque

[Precise1]

I do recall reading something similar to what you are describing, the injector malfunctioning and damaging the ECU, but I can not recall the exact context. I know several people have needed 'new' ECUs due to theirs not functioning correctly but I can't help with what units will work for your truck. There is an airplane mechanic in Hawaii with whom I was talking about selling him my EUC and he seemed to have good info about which ones he was looking for. I'll see if I can contact him again, he may be a good resource and/or Morpheus or Alkorahil who both work in dealerships may be able to provide you with some info??

 

B

[Teknogaeque]

Sorry, was just throwing out sensors as example, not specifics.

 

What I was trying to get across is the fact our ECUs are dumb, it may get an injector code, but it could be something completely different causing the problem.

 

I can certainly agree with you on that...especially when one thing depends on another. I got a replacement ECU, and my engine will run now...but it still doesn't want to rev up to higher RPMs. It's not failsafe, it's just genuinely confused when I try to zip up past about 2200 RPM. Even the tach bounces around like mad, in a way that the engine can't physically do. I think the crank angle sensor may be the culprit here. I need to do a little more reading in the FSM, but that's my guess. Injector timing depends on engine speed, so that would make sense.

 

Woohoo...progress is good!