I searched this forum and didn't find an answer so,,,,

My '87 SE 5-speed with 215K miles failed smog. Its HC (Hydrocarbons) are high. I've replaced plugs and the O2 sensor. I checked the ECU codes and got a 44 which is "no fault". I went through the factory service manual trouble shooting section and checked the input voltages for each sensor at the ECU. The CHTS was bad so I replaced it and now get proper voltage at the ECU. It still fails smog!

The O2 sensor is putting out 1 volt which indicates a rich condition. The ECU shows both red & green lights on steady at idle in "mode 2" which indicates a lean condition.

So it looks like the ECU thinks the engine is running lean and increasing the injector pulse to allow more fuel in. The O2 sensor says it's running rich (as a result of the extra fuel). I've adjusted the air bypass on the AFM to try and get the mixture right (following the FSM), Still no change.

Does anyone know why the ECU would think the engine is running lean when it's not?

 

check your MAF other then that if you run around 1/3 E85 it should drop your HC enough to pass, other then that be sure to take it out and get it good and warmed up, make sure all the vacum hoses are good, be sure the recall has been done, if it should have been, I think your car is going to fall into the ones that should have (my 87 did) if you call nissan and give them the VIN they should be able to tell you.......

 

I took out the MAF and cleaned it when I removed the plug to be able to adjust the bypass air. The EFI recall was done a while ago (I'm the original owner). All the voltages to the ECU from all the sensors are correct...

It's frustrating. Three years ago it passed with flying colors. A year ago it failed the first time. I put a new CAT on and it passed. This time it won't pass at all. I know it has a lot of miles, but has been well taken care of. I'm thinking something (solenoid, etc) went bad. I just can't find it.

 

I would go though and replace vacum lines, if you have the time run the 1/3 E85 run the first tank down then change fuel filter and run that for the test, I have ran it alot and when I had mine done she passed at less then 1/2 on the high rpm and passed really well on low idle even though she was on high idle due to the cooling fan coming on...... another old school trick that might help is, with it running and warmed up take a spray bottle with water in it, pull the air filter out and spray water in the intake, not enough to kill it might want to rev it up a little, that will clean a bit of the carbon out, you will want to do that till you have black water coming out of the tail pipe and then a bit more, then take it out and drive it a bit to get the remaining water out of the intake, just be sure not to spray so heavy that you would hydro lock......

 

Bad IDEA !!
Water going into the AFM could damage the anemometer wire.


Check to see if the thermotime switch is functioning correctly. You may be getting excess fuel from the cold start valve not shutting off.

 

In all 3 cases of my 86se with 165k miles failing CA smog it boiled down to being the CAT not hot enough to do it’s job. I still have the original CAT which I should have replaced long ago. I have gone over the car after each failure finding nothing out of spec so took the car back for a retest. Different machine, different technician, same machine , same technician….never the same condition. Each retest the car passed.
On the 2nd retest the tech did put more effort than usual to pass my car. He had my car at high rpm for over 5 minutes before running the test. Later told me these old cars needed the CAT to be very hot to pass. He was right as I haven’t seen the smog numbers this low in years.
3rd time barely failed but also failed visual smoke in the exhaust. Used two different magic stuff in a bottle to fix the smoke problem. Had to get the CAT hot on my own as the tech said he preferred I did it before the retest. He wasn’t as helpful this time.
I would run your car at high rpm for 10 minutes at the smog shop just before the retest. Hope this helps.

Oh what kind of gas mileage do you get on your 87se?