The Nissan Path

Hello all,
I'm new to the forum and have recently acquired a 91 pathfinder V6 with 33,000 original miles. Everything looks like new, but runs ruff and rich at idle. I tried to pull codes from ecm. However, only the red light is on. Green light does not come on and the ecm does not go into diagnostic mode. Can I assume the ecm is shot, or did I overlook something. Also there is not CEL to be found on the dash. Thank you for any help.

The only WD21 Pathfinders that had CEL's were California emission models and I think it was just the last year or two of that model run. Which ECM do you have: a two-mode or five-mode? A two-mode has a toggle switch and the five-mode will have no toggle switch, but a mode screw.

I have a 5-mode.
After turning ignition to ACC and turning the mode screw fully clockwise, nothing happens. Only the red light is on. I think the green and red lights should both blink together to indicate the mode, and when the desired mode flashes I need to return the mode screw to full counterclockwise. I was hoping to go into mode 3 to retrieve any possible codes. No dice!
Thank you for the quick reply

Ignition should be in the "ON" position.

http://www.troublecodes.net/nissan/

Sorry for the confusion. I did have the key in the ON position. This vehicle had also sat with a dead battery for several months before I picked it up, and it only drove about 4 miles before I parked it. Not sure if the ecm has to relearn after power is restored and that is what might be causing just the red light to be on?

Those ECM's had a base setting so it wouldn't matter if it was left without power for an extended amount of time. With the mode screw turned full counter-clockwise, turn the ignition key to the "on" position and check the LED's. This is the bulb check and both LED's should be illuminated. If they are not, there is an internal problem with the ECM. You will need to either replace it or send it out for repair.

When I have the mode screw turned to the "normal" full counter clockwise position and the ignition in the "on" position, there is only a red light, green light is not on. Can you suggest a good place to send the ECM off for repair, or give me an idea about what I might be looking at cost wise to have it repaired. Thank you for your time.

Circuit Board Medics is pretty well known. You will have to contact them for a quote:

https://circuitboardmedics.com/nissan-ecm-repairs/

If you have an automatic transmission with Federal emissions, Rockauto.com has an A1-Cardone reman for $242+core.

You could also opt to go for a used ECM. Get the Nissan part # off of the top and try searching for it on Ebay or use www.car-part.com. The part # will start with "23710-" and be followed by five more digits. Used unit probably fall in the $75-$100 range, but keep in mind they are 25 years old.

There is a blank box on my ecm where the 23710 # should be located. The other box does have a MECM -V181 but not sure this helps. A large #37 is also stamped on the placard. After calling Napa and giving them my vehicle info, the call for a 23710-88G71. I'm stuck on which way to go without a definite # on my ecm.

Go to www.NissanPartsDepot.com and look up your vehicle by VIN # and then search for the engine control module and it should give you a part #. 23710-88G71 would be the ECM for a 91 Pathfinder with automatic transmission and Federal emissions certification.

Thank you for all your help. I will let you and any others that are interested know how everything turns out.

Just an update to let everyone know. I picked up a used ECM on EBay and I was able to enter the diagnostic mode. Luckily, the only code received was a code 55 which is " no malfunctions". Once the pathfinder was started up, I could immediately tell the difference at idle. There is no longer a rich running condition. Thank you again for your help.
I'm now planning on changing the timing belt.

Good to hear! I've done a lot of VG timing belts. I usually go to Rockauto.com and get a Gates Timing Belt Component Kit w/ Water pump and Bando brand drive belts. Not a "must," but they also sell Pentosin Permafrost A2 green anti-freeze, which is exactly the same as genuine Nissan green anti-freeze. I get the thermostat, front cam seals and front crank seals, coolant bypass hose (and radiator hoses, if needed) from Nissan. While the rear belt cover is off to replace the bypass hose and cam seals, I'll check the welch for any coolant seepage around it; if there is, I remove it, clean the threads and coat with RTV sealant, and re-install to a torque of 50 ft/lbs. You need a 17MM hex socket to do this. Do all that and you should be in pretty good shape for a long time.

I'm a little up in the air about how deep to go with the timing belt change. This pathfinder only has 33000 original miles. That's right "33,000". I was just thinking about changing the belt and possibly the tensioner. Do you think I should do the whole kit regardless of mileage?

Well, if you want to rely on 25 year old seals, hoses and belts lasting until the next time the timing belt is due, that's on you! I know what I would do..