CHTS Need help

[gryt57]

New Z owner here, car is having problems passing emissions. After searching every forun I could find, it seems the chts is a reason the car would run rich. I think I located the chts, passenger side, cylinder head, between #5 and 6. The problem, there is no wire anywhere in sight to attach to the sensor. Previous owner changed all fuel injectors cutting wires to redo them. Is this where the wiring should come from?

[gryt57]

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Car is 1978 2.8L I think it is the original engine.

New Z owner here, car is having problems passing emissions. After searching every forun I could find, it seems the chts is a reason the car would run rich. I think I located the chts, passenger side, cylinder head, between #5 and 6. The problem, there is no wire anywhere in sight to attach to the sensor. Previous owner changed all fuel injectors cutting wires to redo them. Is this where the wiring should come from?

[sblake01]

If you have a cylinder head temperature switch in a 78 S30 you do not have the original engine. The CHTS didn't appear until later on the ZX and Maxima. Not having it hooked up shouldn't affect antying since it's not in the cars electronic circuitry. ZX engines have slightly different electronics. I'd make sure all of the components that should exist on a 78 are there and working properly.

[gryt57]

So what I'm looking at is either a different motor or a different head? Is it a possibility that this is a different, later head and the rest of the motor is the original 78. If this is the case, is it going to matter that my newer head has a CHTS on it? Is this CHTS node that is inactive causing any problems? I wouldn't think that it would considering that the ECU doesnt even have a connection for it right?

In either case, If I do have a later head, and my car originally did not come with a CHTS, I have a Coolant Temp sensor instead? Is this the same as the Water Temp Sensor?

[sblake01]

Look on the drivers side of the block just behind the motor mount and you'll see the block number. If it's N42 it's the stock motor. 78 had an N47 head on a N42 block. The CHTS should make no difference as long as you have the correct 78 components hooked up. The coolant temp sensor is the same as the water temp sensor. Located on the water neck beside the thermotime switch which are both below the temperature sender for the temperature guage. Confused yet?

[gryt57]

I went out and checked for the stamp on the motor, and it is stamped F54

followed by the numbers 1022A. If I am looking at the right # for the head it is stamped P78. I thought the motor was the factory motor, and I think the previous owner thought so to. New injectors were wired on by PO, and I put in Plugs ,wires, and cap thinking it was the original motor. What now?

[gryt57]

THe head is stamped P79, it looked like an 8, but is a 9. sorry

[sblake01]

That's a ZX motor.

[gryt57]

So, now Im thinking when the motor was changed did they change the ECU? Is there a marking on the ECU that will help me?

Then, If they did change both the motor and the ECU, this is what I think is going on. The previous owner did the fuel injectors and changed that entire wiring harness. He wasn't aware of the motor swap so he used a harness for a 78z. Which is lacking a connector for the CHTS. Is this even possible? If this happened would the car still run?

Thanks for all your guys help so far. Much appreciated!

[sblake01]

I doubt if he changed the ECU but he may have changed the AFM. My ECU is marked A11 601 000 and my AFM is A31 605 000. Stock California 5 speed 1978. They've never been changed. The CHTS is not necessary if you have the stock 78 electronics. When you say "The previous owner did the fuel injectors and changed that entire wiring harness", I doubt that. He probably changed the fuel injector part of the harness to replace bad connectors. That's somewhat common and would have no bearing on what ECU was used. Forget the CHTS. It does nothing since your cars circuitry doesn't include it. The car will run without it and your problem is likely elsewhere.

[gryt57]

See I thought that a different ECU was used because when I bought the car he gave me an extra ECU but they both have the same model number A11 600 000. They have different 4 digit numbers one is 8331 and the other is 79--.

So now Im forgetting about the Cylinder Head Temperature Sensor.

Should I focus on the Water Temp Sensor. Im guessing that that is what is getting the Head to proper running temperture if there is not a CHTS.

Thanks again Blake!

[sblake01]

Actually the water temp sensor monitors the water temperature and transmits a signal for the fuel mixtue and pulse duration the change during warm up. It has nothing to do with geting the head to operating temperature. A bad water temp sensor or a bad connectiion to it can cause the car to run rich. There is a test procedure in the FSM for that and the other sensors.