Get an 87 ECU if you can, pressty sure they have the fail safe CHTS/FTS warm up problem soloution.

 

When you ran the diagnostic on the ECU for codes, was the engine already hot and the car exhibiting issues, or was the car cold and still running fine?

Whatever the problem, its only showing itself in closed loop mode, which means its gotta be related to a sensor somewhere, whether its the sensor itself or old corroded wiring to the sensor thats causing the problem. Since you've already replaced just about everything I would be prompted to suggest looking at, I'm going to suspect you have poor wiring somewhere.

One thing you can do is check the FSM wiring diagrams for the EFI harness diagram, and check the wiring to things like the CHTS harness, O2 sensor harness, etc, for too much resistance. If you're getting more than just a few ohms on any given length of wire, you could have corroded cables leading to poor quality signals going to the ECU.


Also, unfortunately since you're an 85 turbo vehicle you are going to be restricted to using only either the 84 turbo ECU or the 85 turbo ECU. The 87 ECU will not work with your O2 sensor. Since you have three ECUs, I would probably not bother getting a new one again at this point.

 

Thanks for the suggestion, phx. I'll get the ohm meter out, some paper clips, and start digging. Yes, I look at the ECU codes after the failure, when the engine is warm. Then, I switch with a "cold" ECU to see if there is any improvement. Sometimes there are slight differences in the way it sputters and stumbles, but for the most part, it doesn't make a difference.

Can you explain exactly what "Open & Closed Loop" means, and what happens when it changes over? I cannot find a reference to that in the 85 FSM. I think the ECU had 4 test modes in later years, but in the 85, it just has the one (or two if you include the fuel mixture test). Even though my FSM doesn't mention this, would this "closed/open loop" still be relevent to my '85? If so, I can download a later FSM and read up about it, but I wouldn't quite know what the differences are between years.

 

open/closed loop refers to the usage of mixture ratio feedback sensors.

 

The FSM covers open and closed loop modes in great detail, but here's a simplified version of it:

1) open loop, happens when the car is warming up, not at proper temperature, or when certain sensors report certain engine conditions. In open loop mode, the ECU is ignoring mixture feedback from the O2 sensor and various other engine sensors, and running on a pre-programmed map for fuel and ignition. In this mode, basically only the CAS and MAF are important for keeping the engine running, while the CHTS is being monitored for engine temperature so that the computer knows when to switch to closed loop.

2) closed loop happens once the engine has reached full operating temperature. It is triggered by the CHTS sensor primarily, among others too. In closed loop mode, the ECU is monitoring the CHTS, FTS, O2 sensor, knock sensor, CAS, MAF, etc. It uses values from all these sensors to calculate the most appropriate amount of fuel and spark advance for the current conditions. This is where the car normally runs, but where yours is failing to run correctly.

 

Thanks for the explanation. So it seems that I'm not looking for an intermittency, but a failure when it goes into the “closed loop” (which I swear I cannot find this expression used in the EF & EC sections of the 85 FSM). Since the ECU isn’t giving me any clues to follow, I’ll just work though the various sensors and the wiring to/from them. But some fixes in the FSM leave a little to be desired, for example, checking the detonation sensor consists of “check harness for continuity”, that’s all. If I’m not getting a code 34, how would I know if the knock sensor is truly malfunctioning? Could I ground it, or leave it unplugged to test? Has anyone put together a more comprehensive test of these sensors than what appears in the 85 FSM?

In the FSM, the AAC test says to check for 12V between terminals 2 & 28/36 when the connectors are still plugged in to the ECU and the engine is on. Has anyone else tried this test? I mentioned in my original post that it failed, yet I’m almost positive that that the valve and circuit are fine (12 v going to the valve when ignition is on, Continuity on the valve and wiring to back to the ECU.)

I haven’t checked for updates or modifications to the FSM. Is there a good site to check for this?

Again, thanks for any help.

 

open and closed loop are common terms. The FSM may not make much of an effort to define them, but it does use them frequently.

There is a mention of the "Mixture Feedback Control" in the 1984 FSM, EFEC-21, under the heading "ECCS Description, Fuel Injection Control." It goes on to say how the mixture feedback system uses various sensors to keep the A/F ratio closest to the stoichiometric point. It then says that the system will "open" under certain various conditions. I'll see if I can find other specific references if you'd like.

 

Yes, I see that. It's on the same page 21 in the 85 FSM. I see the diagram showing the infamous "closed" loop. Curious that it says below the diagram that it will be "open" if certain conditions are met. One of these is when the car is in idle. I know that the idle switch is working, so it would seem that it is not supposed to go to the "closed loop" if it's still at idle. Unfortunately, that is when my engine dies!

I'll still continue checking the electrical and EFI circuits. Any more suggestions would be very welcome.

 

So your car will run when warm if you give it throttle? It only dies at idle and when warm. Correct?

 

Yes, that's correct. I can keep it running when warm and I give it throttle. The lower the rev, the more problems (backfire, not responsive, sputters) until it dies at idle, so the throttle position switch doesn't seem to make a difference when warm.

When cold (and for 10 minutes) I can drive the car without problem. It runs great, in fact! (It's good for very small trips.)

 

AFM can give that type of problem. Test the AFM via the FSM directions on the EFEC section. Check ECU input voltage at terminal 31 and ground of the ECU. All you have to do is use a simple multimeter, if the multimeter has good probes you can push the metallic pin probes into the wire to pierce the rubber. Idling 2-3V and revving the engine high 3-4V.

Have fun, try it out.

 

Yeah I would have suspected the MAF too, but since he's got two of them now and its highly unlikely that the two would exhibit the same malfunction. Unless neither is bad, and its bad wiring going to the MAF......

 

Did he check it or replace it?

 

I did both. The one I have in there is only a few years old and tested good with the external test. But it was high on my "most likely list" also, so I borrowed a known good one and swapped it. No difference. But I don't think I tested the wiring that well besides seeing that 12 volts was being delivered to the AFM. And I know I didn't try the test back at the ECU. Swampman, is that test described somewhere, besides reading it off the schematic?

I'll setup the voltage meter on pin 31 with everything plugged in and run the engine cold and hot and I'll throttle it up to see if I'm getting proper readings today and let you know what happens. Good suggestion. Geeze, you would expect the ECU to give at least one code 12 the 100 times that I've checked it, if the AFM was faulty.

 

Yes the test I described is in the EFEC section under Air flow meter. It may not be the AFM at the end of the day but it is good to check the inputs that would effect the ECU like pin 31.

 

What year FSM do you have, Swampman? I'm looking for all tests possible, and the one you describe makes sense to run, but I don't see it being described specifically in my 85 FSM. I see on page EFEC-14 a good description and pinout diagram, and on page EFEC-43 an external test that requires you to take the AFM out of the car (which I've done), but I don't see the one you're describing. (Basically the same information that appears here: www.xenonz31.com(forward slash)sensors.html

I'm just wondering if there is a supplemental source that shows more tests that I can run on other sensors that might not be in the FSM for the '85. Thx.

 

The 89 FSM. EFEC Pgs 86-87.

Maybe Nissan thought of better ways to test them.

 

Just downloaded and printed the '89 FSM EF & EC section, It has tons of additional info & tests. I'll be busy again! It looks like they did a much more thorough job than the 85 FSM (They even added little cartoons). Section went from 77 to 159 pages! I just need to ignore the parts that do not pertain to my vehicle year, and I'll double-check the schematics to make sure things are the same. Thx for the lead to this. Hopefully I'll post the fix soon!

 

For my 1985 NA, I always use a combination of the 84, 87 and 89 FSMs. I find pretty much whatever I need in those. The 1985 FSM that I downloaded was incomplete, but otherwise completely identical to the 1984 FSM.

(unless you have a 1986 vehicle, in which case the 1986 FSM is definitely required)

 

Double and triple checked sensors. I'm going to look at electrical next.

 

It seems that the injectors stop working, when the engine warms up. I hear a loud click on each injector when cold, and either nothing or barely nothing when the engine warms up. I still get a healthy spark.

I am wiggling wires & connectors everywhere along the EFI harness, all the way to the ECU. I have already replaced or repaired most connectors. I wiggle them when the engine is cold and running fine to see if I can make it quit, and then I wiggle them after the engine is sputtering and ready to die to see if I can hear an improvement. All fusible links are in great shape. Engine grounds (at least the ones that I know about) look fine. I have I even rewired the injectors back to factory (before the injector campaign), even though that shouldn’t make a difference.

So what would be some more good tests to try related to the injectors quitting when the engine reaches operating temperature?