Something doesn't look right. Your voltage for water temp and fuel temp look way off. It's odd because the water temp is showing operating temp. Double check the wire colors on the connectors. The 2 plugs are long enough to be swapped around. Although it would be extremely unlikely you have a 80c+ fuel temp

 

I can't find the temp sensor that I was referring to in the FSM. But it was mentioned in a thread, that I can not now find.

Your intake air temp seems low for a car that may only have been idling. Are you in North UK?

 

On the power fc, the thermoswitch serves no function. Fan controls are controlled by the power fc. That's on the back of the filler neck. The sensor on the rear iron under the oil filter is for the temp Guage on the cluster. It has no tie in to the ecu. The main water temp sensor that does feed the ecu is also on the back of the filler neck above the thermoswitch.

Air temp I wrote off as it being actually cold wherever he is. Typically when they fail, they go -40c and stay there. It would be a good idea to verify that's accurate though. How is the weather in that part of the world

 

I am trying to find the thread, but changing out that rear sensor fixed the guy's problem. I was remarked that it was a very unusual problem, and something not many would have guessed at. The sensor malfunction was showing on the datalogit read-out.

 

Do we know the year and model of the car? Jdm or LHD?

 

There must have been some funky wiring or something because fuel, air and water temp are the only temp sensors the power fc and stock ecu reads. Oil pressure goes directly to the cluster and the cluster water temp has its own sensor. There are no sensors on the engine itself that feed the ecu. All the metrics are in actual parts.

His car is a 93 rhd

 

https://www.rx7club.com/3rd-generati...1167435/page3/

 

He could put the OEM ecu back in and run codes.

 

Yea, water temp on the back of the filler neck fixed his issue. The voltage of the water temp sensor at 80c should not be 0.49v so he has an issue there somewhere. Likewise, the fuel temp voltage should not be 4.xxV. so I think his problem is in there somewhere. At the same time it's odd because at 0.49v you shouldn't have an indicated 80c water temp. It doesn't match.

 

FDAUTO the voltage for fuel temperature you are saying is not correct , ??? not sure,, when i start car (please bare in mind outside temperature is 3 degrees) the voltage for water is like 3.7 and air temperature about same say 3.8 fuel temperature is 4.6.
As the car comes up to temperature the water voltage is dropping gradually to 0.49V and the air temperature down to 2.2 (which sort of read correct as water is now 82 degrees and air has come up to 17 degrees on the inlet manifold) the fuel voltage stays the same,, presuming that as fuel moves through the fuel rail the temperature should remain cold, so 4.6 sort of sounds correct,,, or am i wrong??


id be curious to know what voltage should be on someone else commander at certain temperatures,, maybe the sensor is out of range.
but the apexi is using the temperature sensor to give me a reading of 82 degrees and my gauges on the dash read 85 like 3 degrees different??

 

I think there is a spare bung on the upper filler neck. You can stick another temp sensor in there to check it out. Cheapo temp sensor /gauge sets should be available at any automotive hardware store.

Is your RHD a UK spec car or a grey market JDM import?

 

i made a mistake. voltage drops as temp increases. sorry. so that is working correctly. i defer back to my original suggestion of pulling the pump to inspect the hose

 

Thanks FD auto was scratching my head about that,, i searched for photos on google of sensor check screen and all things looked pretty much same as mine,,
So now I'm gonna pull pump over next week and do the fuel pressure checks (see if we have good pressure hot and cold and see if rail holds pressure, i.e no injector leaks).
I will dig out factory ecu and see if the hot start is still exactly the same,, (i still keep thinking it something in the tune for hot start)