Faulty Air temperature sensor

[EuroDat]

Last weekend I had trouble with water in my fuel tank, so I started cleaning the fuel system and did some other checks while I was at it.

The engine had developed a hesitation and sometimes backfiring.

The fuel pressure was ok so did some further checking of the throttle switch and the AFM using the EFI Bible. The throttle switch checked out ok, but the temperature sensor in the AFM was measuring 4ohms.

According to the manual is should be reading about 2500ohms at 20degreeC:disappoin

As a temporary fix Ive fitted a 2250ohm resistor to simulate 20degrees C. We are having a very mild winter here atm.

I don't think the sensor is available anymore, if it ever was available. Now I have to find a more permenate fix or wait for Lenny's Hellfire and goto MAP or MAF:bulb:

An alternative would be to fit a temperature sensor used for the water temperature and wiring it in the back of the terminal block. You could fit it in the flat section on the throttle body side of the AFM. The sensor has the same temperature/resistance curve, but I don't know if it would have the same response time.

Chas

Edited April 6, 2014 by EuroDat

[Zed Head]

I accidentally ripped apart a coolant temperature sensor trying to get the plug off. It came right out of the top with the EV1 connector attached, just minus the threaded metal portion. The actual sensor is just a blob of semiconductor on two pieces of wire, surrounded by a gel, probably silicone, inserted in to the brass housing. If you have an old coolant sensor it might be worth an experiment. I'm sure it would have a fast response time out of its housing.

[Zed Head]

No editing allowed, so here's another post. A picture of the guts.

You might also check the wires at the AFM sensor haven't rubbed through their insulation, causing a short. A piece of heat shrink, or tape or some glue might solve it.

Edited April 6, 2014 by Zed Head

[bartsscooterservice]

Hi Chas,

Can't you get another good AFM somewhere ?

Gr Bart

[EuroDat]

Quick Status update.

I found a thermal couple for a floor heating system I had left over from our central heating. It has a quicker response time than the water temp sensor and the same resistance span over the temerature range. Thats comparing the water temperature sensor (out of the engine) with the thermal couple using a hair dryer.

Its a little different in shape and I had to make a plate to get it to fit in the AFM. Its now glued in the plate and drying. Only thing left is to trim the cable to length, fit the crimp termanals and install it in the AFM. That will be tomorrow.

Here are some photo's to give you an idea what I mean.

ZED: I checked the wiring and couldn't see any damaged, so it looks like its in the sensor itself. Thanks for the tip on removing the sensor. I managed to get mine out undamaged so I could compare it to the AEG sensor. Mine looks pretty scruffy, but it works and came out in one piece.

Bart: Trying to fix the temp sensor first before replacing the whole AFM and these things are not so common here in NL.

Chas

Edited April 9, 2014 by EuroDat

[bartsscooterservice]

There's a guy in Groningen who has 280Z parts. Look under " Datsun 280Z " in Markplaats, he's called Peter I believe.

I like your creativity here

[superlen]

Chas,

I have several AFMS if you need me to pull an air temp sensor for you, just yell. I've never had one off the AFM meter and never heard of one that confirmed failed. Lucky you. Nice hack with the floor thermocouple. As long as the Resistance vs Temp is the same, you're in good shape.

Len

Edited April 13, 2014 by superlen

[EuroDat]

Hi Len,

It seems to be working fine now. The thermocouple had a similar resistance to the Fuel injection bible and response quick enough.

I would have thought the sensor would open circuit, but mine shorted and had less than 200 ohm.

Chas

[superlen]

Chas,

Interesting failure mode for sure...especially for something that is essentially a resistor. I would have put money on open circuit or abnormally high resistance as well.

Len