90 Nissan 240sx ignition/computer

Reply

  #1  
Old 03-31-02, 05:16 PM
wyres
Visiting Guest
Posts: n/a
90 Nissan 240sx ignition/computer

I just replaced the distributor cap, rotor and plugs as a preventative measure, I was not having any trouble. I drove it for about an hour on the highway, got into stop and go traffic, and it died. After a short time, it re-started. I drove a few minutes, and it died again. There appears to be no spark. I put a new coil on it, same problem. Put the old rotor and cap back on, same problem. The power transistor passes a continuity test according to the Nissan shop manual test procedure. The engine computer gives error code 21, no feedback from ignition circuit. I connected a general purpose oscilloscope to the ignition signal lead from the computer to the transistor. When the car is cranked, the voltage jumpes up to about eight volts, but I don't see anything that looks like pulses, just a very "noisy" eight or so volts. Anyone know what that signal is supposed to look like, or a different test procedure? Does this mean the computer is bad?
 
Sponsored Links
  #2  
Old 04-01-02, 04:44 PM
Joe_F
Visiting Guest
Posts: n/a
You seem to have access to the Nissan shop manual, have you checked all your grounds and so forth? What does the manual say?

That being said, the easiest thing to do is to send the computer out through a parts store's reman electronics supplier for testing to confirm fault. Could have a bad solder joint inside from age. Common problem.
 
  #3  
Old 04-01-02, 11:02 PM
wyres
Visiting Guest
Posts: n/a
Yes, I have a Nissan shop manual for it. I never cared for the Chilton or Hanes books, think it's worth the extra bucks to get a factory book.
All the grounds are good. The supply from ignition switch has 12V.

The manual says to check the signal from the computer to the power transistor with a "logic probe", which has a light that is supposed to blink to indicate the presence of a signal. What I normally think of as a "logic probe" in my line of work is used to look for high/low logic, and low frequency pulses in TTL circuits. (normally 5V) I suspect that the device they are describing is essentially the same thing, (probably a factory issue gadget) but I don't know what voltage levels you should see on that line. (Thus, I don't know what would constitute a compatible logic probe) So, I used the oscilloscope to see what was there. I tested with the connector removed from the transistor. Don't know if that is a valid test, or if the line requires termination.

If the computer is generating an error code because it is not getting a feedback signal from the ignition circuit, and the computer is not sending out an ignition signal, but that problem does not cause a fault code for an internal problem in the computer itself, it would suggest a problem somewhere between the actual CPU chip, and the output pin on the box. (probably some sort of buffer circuit in there?) Is there any chance I might find a schematic and/or service information for the guts of the computer box itself?

I was also wondering, apparantly, some of those cars had distributors made by Hitachi, and some by Mitsubishi. Any chance that the parts store gave me the wrong flavor, that this could have fried something?
 
  #4  
Old 04-02-02, 06:58 AM
Joe_F
Visiting Guest
Posts: n/a
If the service manual doesn't have it, it's not a "service oriented" item. It's a factory type service that requires special equipment to test. My guess is even Nissan farms out their rebuilt computers to someone .

I think you are thinking like how a GM computer is set up with a PROM. I do not think Nissans are set up like that. There is no removeable in a Nissan computer. It's a sealed box. Most parts stores test them fairly cheap through their electronics suppliers. If you suspect fault there and your service manual points you there, it's worth it to have it tested.
 
  #5  
Old 04-02-02, 03:08 PM
chadtoolio
Visiting Guest
Posts: n/a
Good luck on finding the schematics on the inside of a Nissan ECU! Even when I worked at a Nissan dealer their technical hotline would not give them to me! Sounds like you might have a faulty distributor... You said that the ECU is not getting the Ignition signal from the hall sensor of the distributor, have you tested the distibutor yet?

Good luck
 
  #6  
Old 04-03-02, 05:32 AM
Joe_F
Visiting Guest
Posts: n/a
Right. Because it is not a field serviced item. It is a FACTORY serviced item .

Nissan does not break down the module into serviceable pieces. It's the whole or nothing.

It would be great if cars included the wiring diagrams like appliances do . In fact, when I wanted a wiring diagram for my machines, I just called Whirlpool and they faxed it to me. That's cool beans .
 
  #7  
Old 04-03-02, 11:26 AM
wyres
Visiting Guest
Posts: n/a
I just got the car towed back home. As soon as time permits, I want to re-test everything, including the crank angle sensor. It will be a little easier here than on the side of the road an hour away from home.

This car apparently has an optical crank angle sensor, a slotted disk in the distributor, as opposed to a Hall effect sensor. Having recently messed with the distributor cap, I suspected dirt getting into the sensor. I gave it a shot of compressed air, but that is all I have been able to try up till now. However, there is a separate error code that is supposed to indicate a problem with the crank angle sensor. The error code I am getting is no feedback from the ignition circuit. In this car, there appears to be no connection between the crank angle sensor and the ignition circuit, other than through the ECU.

I know that the ECU is not "normally" a "field repairable" unit. However, I are un elektrikawl injuneer, and am good with that sort of stuff. (cars however, are not my specialty) You can take the cover off of the unit, it has a clear coating sprayed on the circuit board, but it is not "potted", so a component level repair may be possible. Unfortunately, it is all surface mount components, kind of tricky to work with. And yes, the PROM is soldered in, not removable without some delicate soldering.

The shop manual does have pretty good schematics of the electrical system. Thus my preference for a genuine Nissan book, as opposed to a Chilton manual. I swear, I think all Chilton manuals have the exact same "beginners introductory overview of engine re-building" which accounts for half of the manual, with a few pages of info added that is actually specific to the car that it is supposed to cover.

Thanks for the info, lemme run through everything again, and I'll let you know what I find.
 
  #8  
Old 04-03-02, 12:00 PM
Joe_F
Visiting Guest
Posts: n/a
My coworker had this same problem with his 200SX and a rebuilt distributor was the solution. Probably the same here, but make sure it checks out.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes