Computer control unit

[da_viper_1999]

I am new to this forum and am looking for some assistance from people who know what they are talking about. I have a 78 280z and I can't get it to pass smog. It always comes accross too rich i.e. too many CO's. I changed the water temperature sensor after running the tests in my Factory Service Manual and tried again and no good. so I ran some more tests and changed the throttle position sensor and the Mass Air Flow meter and now the car will not run for a long enough period of time for me to get it to the smog shop. I set the timing to 10 btdc and I also did all the tests I could find on my Mass Air Flow meter and everything looks good. The funny thing is when I have the car running it's fine at first, then after it appears to warm up it begins to die. If you diconnect the temp. sensor the car kicks up and runs fine, but you can look at and smell the exhaust and gather that it is running REALLY rich. when you plug the temp. sensor back in it will jump up in rpm for a split second then begin to run crappy again. My Dad and I think it might be the computer is bad? I would appreciate any constructive thoughts.

Travis

[sblake01]

I doubt that the computer would be bad as it isn't really a computer per se. It's an electronic control unit. It doesn't do any computations or or anything like that nor does it have any software programmed into it. It simply patches electronic signals from one place to another. I've never had a problem with one. Just make sure that it's the one that belongs in that car as there are different ones for different models, years, and equipment i.e auto trans or manual trans., and that it's connection is clean. At the point you seem to be at, I would be checking fuel pressure, the fuel pressure regulator itself, cold start vavle and thermotime switch, air temp sensor, and even the water temp sensor since there are several that will fit but only one that right for a particular application. Not only check the function of these items but also make sure that they have clean, tight electrical connections. How old is you catalytic converter?

[e_racer1999]

heh.... when i first saw this topic and saw who wrote it, i thought it was me! i was like "when did i write this?"

anyway, i'm thinking maybe an injector or two? what do your plugs look like?

[TomoHawk]

I'd add that the 280Z doesn't have a mass air flow meter- it's just an air flow meter.

You should also make sure that the connections to the ECU are good by tracing the lines to it. The way I did it was to connect a wire from the Pos. battery post to one end of a sensor wire, and a lightbulb (test light to the pin on the ECU connector( test lightg clip to the chassi). The bulb should light up it the wire is good.

Also, get yourself a copy of the 280Z fuel injection book, you will learn how simple it really is and how to check the important stuff. The problem you have isreally very simple, once you find it.

thx

[Pennyman]

The air flow meter may be out of whack. Check the seal around the plastic cover on the side. It should be a tight seal. If the shop which is smoging your car is an actual mechanic's shop, you might want the head mechanic to take a look at the air flow meter. Speaking from experience, this may be what is causing your car to fail. Bring it to a shop where the guys who know WHY your car is failing are the SAME guys who can fix it for ya.

[TomoHawk]

If the shop which is smogging your car is an actual mechanic's shop, you might want the head mechanic to take a look at the air flow meter. Speaking from experience, this may be what is causing your car to fail. Bring it to a shop where the guys who know WHY your car is failing are the SAME guys who can fix it for ya.

Due to the age of the car, it will be difficult to find "a mechanic" who can diagnose the problem accurately. Current mechanics can measure the CO or HC content and tell if if it's in out out of spec, and they can only speculate on the problem, because their knowledge is only for the newer fuel injection stuff- even though it's similar to yours. I doubt of they can correctly diagnose the problem with your older car. I think your best bet is a certain Nissan dealer- call around to see if there is one with a guy that has "30+ years" experience with the older Zs.

[BullsEye]

1st:Is your car a Federal or Calf. model?

2nd: Is it being tested to the standards posted for the year model, and see above "model" of your car.

If not, it should be. It is highly unlikely that is will pass the "newer" smog limits.

3rd: Which one of the 3 senors did you replace?

Single wire goes to the gauge

Smaller 2 wire is the temp sensor for the ecu

Larger 2 wire is the thermal time switch. This is the one used for warm up

4th: Make sure ALL grounds are clean and tight.

Which plug are you disconecting?

If it is the larger one the thermal time switch is bad.

If it is the smaller one then it is either a bad sensor or a loose conection.

[TomoHawk]

I took my 78 280Z to the local Nissan Dealer, who has a couple old-timers, per se, and the one guy hooked up the temp sensors and tuned up my air flow meter to where I'm getting 22 MPG! No gas smell out the tailpipe!

Money well spent, even though I went through the service manual myself. I think they have a service manual with some 'extra info' in there. It was money very well spent.

I hope you have such experts in your area.

thx