cooldatsun

Hi, I am new to this site. My 1982 280zx turbo sputters and sneezes when the Cylinder Head Temp. Sensor (CHTS) is plugged in. When I unplug the sensor, the car runs perfect, but the timing retards 10 degrees and the idle goes up to 1000. I replaced the CHTS with a new one and that did not do anything. I adjusted the distributor so that now the timing is at 20 degrees at idle when the chts is unplugged, and the car seems to be running and idleing correctly. Is it OK to run the car without the CHTS. Does anybody know why unplugging the sensor would make everything run fine eventhough the sensor is ok.

iestyn.lewis

The connections to the CHTS are supposed to be easily corroded - maybe clean the contacts with a little screwdriver and contact cleaner - and i guess on some models there is another inline wire connection (bullet-type?) right behind the sensor connection.

NismoPick

Welcome to ZDriver!

It actually might be the AFM, or TPS, or a corroded connection like iestyn said. Or a combination of them. Check the AFM & TPS.

duowing

Although it's not very likely I had this bizarre problem. It plagued me and the previous owner, actually part of the reason why he ended up selling the car. The CHTS went bad and the O2 sensor crapped out. So he didn't have the O2 sensor to help correct the awful rich mixture of the bad CHTS. Anyway he bought a new CHTS from Black Dragon Auto. Turned out that one was bad. He didn't know it and neither did I. He even had the receipt and everything to prove it, plus the part looked shinier and not coated with years of dirt and grime. I ended up replacing it with the CHTS from my old 83' 2+2 non-turbo which ran perfectly. Turns out that CHTS was on it's way out. It was odd because the first time I put in the CHTS from my old 2+2 my Turbo car ran perfect. Then it crapped out immediately afterwards. Finally I went ahead and bought a new CHTS through MSA. It came in the Nissan packaging and everything. I went and tested the two CHTS that were causing me problems and they had similar readings where as the new one I got from MSA had a drastically different reading. Finally the horrible CHTS problem was solved. Although as said your problem could be something else, this is one thing I love about the Z31 ECU. It can at least provide you with codes when these sensors go out of range.

cooldatsun

Thank you everybody for responding so quickly. I found the car starts with the CHTS unplugged when it is cold, but not when it is warm. When I unplug the CHTS after i get it to start it runs very well except the mixture becomes too rich. I have swapped the AFM with one from a well running 280zx turbo, and that did not change anything, and the connectors are all clean. I have also swapped the TVS and that has not changed anything either. I have not checked the O2 sensor yet, nothing changes when I unplug it, tomorrow I am going to swap it with a good one and see if that changes anything. I will check the readings on both CHTSensors and see if they are the same.

duowing how do you get the codes from the Z31 ECU?

Thanks!

duowing

It's a diagnostics procedure in the ECU itself. Unfortunately it's not going to help you in this situation. It requires a little bit of re-wiring, the 300ZX MAF and the plate from a 300ZX crank angle sensor.

As for your O2 sensor though, there's a little LED on the bottom of your ECU. You'll have to remove the kick panel down on the driver's side to get to the ECU. Anyway what you want to do is with the O2 sensor plugged in take your car for a drive get it nice and warm, come to a stop and rev it a few times, then either with a mirror, or get out and get your head down in there to see the LED check to see if it's flashing it's supposed to flash 5 or more times in a 10 second period. If it does this it indicates your O2 sensor is working as it should be. If you don't have a light or the light is just staying lit and not flashing it means your O2 sensor is dead, or maybe not dead, but not working properly.

Should you feel like testing them the Factory Service Manual has a procedure for testing the CHTS. It involves putting them in water and checking the resistance at various temperatures to see if the sensor is in range or not.

cooldatsun

Thanks duowing, I found out that the o2 sensor was bad, so I removed it, and boy that was a pain, and I actually broke one o2 socket trying to get it out. After I replaced the o2 sensor the LED under the ECU blinked about 6-7 times in a ten second period, however it does not blink steady it blinks sporatically, is that ok?

I went through and thoroughly cleaned every electrical contact, unplugged the battery for 30 min, plugged it in again and started the car. And I am happy to say the car is running just like new and is not running rich.

The only thing that it seems to do wrong is struggle shifting from 2nd to 3rd gear, it seems to want to stay in 2nd until a very high RPM and then shifts to 3rd. Does anybody know what could be causing this? thanks

duowing

it could be the tranny? From what I know is that 3rd gear on the T5 seems to be the problematic gear.

Anyway yeah the sporadic blinking is fine. As long as it's blinking it indicates it's working. Glad to hear the problems have been worked out. It is possible too that the O2 sensor was causing you problems entirely. If it fails and is giving out say a constant lean signal the ECU is just going to continue to keep trying to richen the mixture. I also wonder if then unplugging your CHTS threw the car into open loop so it was ignoring the O2 sensor?

lww

I'm going to assume this is an automatic 280ZX? Check the fluid level in your tranny. If it's low, it will take longer and require more rpm's to build up enough pressure to shift into the next gear.

It might be time for a tranny fluid flush if it hasn't been done in awhile. It's a PITA because there's no drain plug in the auto tranny! You have to drop the whole pan. If you do this, I would recommend having someone weld in a bung and a drain plug so you don't have to drop the pan the next time. Make sure they know what they're doing or they could ruin your pan and then you'll be in a world of hurt.

cooldatsun

Thanks duowing and lww, I got underneath the car and cleaned all the electrical contacts to the transmission and made sure the vacuum line was secure on the transmission and engine. I also checked the transmission fluid level and it was good. Now the car shifts perfectly, I took it on the freeway and it does great, just like new. Thanks everybody for the help.

Tib78z

So I’m planning on getting this zx motor and I saw it has a chts, My question is will it run without that sensor or would I have to get a zx ecu. My Z is a 1978 2+2.