rx7vadim

What voltage should ecu see when engine is cold, at the 2i wire? i did search.

HAILERS

It depends on the water temperature. I'd GUESS that at around 32*it MIGHT read as high as 3.5vdc.

When the engine is up to full temp of 180*, it will read approx a half volt or 0.50 vdc if you will.

I don't have a stone cold car right now so I can't go out and read off a car.

The colder the water temp, the higher the reading will be to 5vdc. Seeing as how your in Miami, I'd guess you'll see approx 2vdc. That would be normal. Like I say, depends on water temp.

Most of the large changes made to the fuel amount by the water thermo sensor seem to happen around 120-125* and 150* F.

This does not count the effect of water temperature on the amount of Starting fuel. Start meaning rpms below 500rpm and the key HELD to Start.

rx7vadim

getting water thermo error right now, i took it out and ohmed it in cold and hot water and its withing spec. 2I getting 5volts with engine cold. What else can i check?

arghx

iTrader: (3)

dude if you took it out, just buy a new one while it's out. You can get an OEM one for like $35 or $40 or you can get one at an auto parts store for $15. if it doesn't break now, it will break later.

rx7vadim

Hailers said they dont go bad.........I want to run new wire to ecu. The ground on the sensor can it be ran srait to ground?

HAILERS

Look at the water thermo sensors electrical connector. See if one of the two terminals inside the plug are or are not pushed back where it won't make contact.

I think you have a meter. So. Get something like a paper clip or piece of wire the size of a paper clip. Now leave all the plugs on the ECU, but take that straightened out paper clip, and shove it up the backside of pin 2I on the plug. Should be a green/white wire.

Put your negative lead to a good grounding point. One of the studs/nuts that hold the ECU in place will do. Now turn the key to ON. What does the meter read????? IF the car is fully hot, it will read approx 0.50vdc.

Seeing how you get a fault code, maybe you do have a open wire. It's a straight run from the ECU to the water thermo sensor. No plugs inbetween, so there won't be a connector inbetween unplugged. You should be able to ohm out from one end to the other but you need LONG meter leads to do so. You could just get a piece of electrical wire and tape a meter lead on one of its' ends and then probe the water thermo sensors plug with the other end of the wire (green white wire).

The other wire is the gnd wire for the sensor. It is spliced to several other wires inside the harness and you won't be able to fine that splice. But all those splices end up at the ECU at pin..........eh, no manual here.......I think 2C.

So now that I think of it, you could put one meter lead on 2C and the other on 2I, and ohm out the circuit inside the water thermo sensor. I'm not sure what it'll read though. Temp dependent. But should ohm out. That would be with the middle plug off the ECU and ohming out the wires in the harness plug, not the ECU itself (just in case).

The sensor would have to have a *open* inside it for the ECU to kick a fault. Your ohm'd the sensor out already and KNOW it does not have a open winding. So forget a new sensor.

And just in case>>>>...the water thermosensor is on the back of the water pump housing. Has a somewhat square jack and is usually green in color. Some people go to the wrong connector.

Does this car run??????

rx7vadim

Thanks Tha car runs, hot start is a lil pain but u have another thread on that.
It runs but seem rich. I have dmm but i dont know how to check the wires continuity. Should it read 0ohms? or what will it read if its broken? Do i just place a lead on unluged connector G/W and other on ecu pluged in connector g/w? What does it have to read?

HAILERS

You'd go to the sensor and pull the plug off. You'd put one meter lead into the socket on the plug where the green white wire is. Then with the other meter lead you'd go to the ECU and pull the middle plug off and put that meters lead into the socket on the plug where the green/white wire is. Meter on ohms and it should read about a ohm or less.

You'd do that if you suspect the wire was broken b/t the sensor and the ECU plug. NOt a likely scenario.

Personally, I'd just go to the ECU. Put the meter on dcvolts. Negative meter lead on a ground point like one of the studs that hold the ECU bracket to the floor. Then I'd get a piece of bare wire like a paper clip or such and with the plug attached to the ECU, shove the paper clip into the same socket as the green/white wire. Now touch the positive meter lead to that paper clip and turn the key to ON with a hot engine. It will read appos 0.5vdc or a half volt if you will.

But let me tell you this. Lets say the green/white wire was broken and not sending a signal to the ECU. What happens is the ECU sees this and it Defaults the signal to 178* F. Now that temp is the running temp of a RX-7, so it seems to me a broken water thermo sensor cannot cause a rich condition when the engine is fully warmed up.

Also a broken wire would cause a really hard start from a stone cold engine for reasons I'm too lazy to write about Again. At least right now.

arghx

iTrader: (3)

dude i really think you should replace the sensor, it's cheap and won't hurt anything. I had hot start problems with my car, and once I got an aftermarket ECU i figured out that the thermosensor was reading 50 C too cold compared to my aftermarket gauge in the waterpump housing. So I replaced it and now it's accurate.

It's hard to know if it's in spec unless you know EXACTLY what voltage it should read or you have something to do the conversion and tell you what degrees the thermosensor is saying. What could be happening is that your sensor is still sending a voltage to the ECU (and therefore the ECU is not defaulting to 176) it just happens to be wrong.

HAILERS

Or do this. Fully heat the engine up.
Engine turned to OFF.
Pull the middle plug off the ECU.
Meter on ohms.
One meter lead on the green white wires socket on the plug.
Other meter lead on the brown/black wire on the plug.
Meter should read 0.320 K ohms or, depending on the meter and its range, might read 320ohms. Same thing as the .320K ohms.

In other words the same numbers as in the FSM when you check out the sensor in a pot of water at different temperatures. The 0.320 K ohms (or 320 ohms) is the equiv of a 176*F water temp.

The brown/black is pin 2C or the second pin over on the top row counting from your right. The green/white should be the fifth wire over on the top row counting from your right. I just did this and know it works just fine and dandy.

There's no need to remove the plug off the water thermos sensor if you do it this way. No intake to be removed etc. Only heating the engine up and then turning it off and then removing the middle ECU plug. Meter on ohms.

rx7vadim

Thanks hailers. i got it fixed, it was pushed in connectors.
Now my egts went up 100-200 F, before it was too low. And my car doesnt stink.
Thanks alot. I got a air temp error and got that fixed also, now i cant believe no more error codes. Does some1 know safe afr numbers WOF and Cruise.

rx7vadim

Related issue came up, hot start problem. I follow hailers solution, cut the 3b B/L wire and makes no difference, Starts cold and very hard start when hot. Compression is decent and no error codes. Got new plugs and wires.

rx7vadim

3B wasnt recieving 12v at cranking before i cut it. There is an issue somewhere i need to figure out how to decrease fuel amount at hot start.

kjdakilla

wow, gud stuff here

rx7vadim

kinda old thread.

HAILERS

Wires can be depinned from a plug. You don't have to cut any wires. Just depin and tie back to the harness with tape over the contact.

galaxy convoy

iTrader: (12)

Just curiousity what is the thermo switch look like?

HAILERS

It's not a SWITCH, it's the water thermosensor which is a thermistor. It's located on the back of the water pump housing. Has two wires. It's plug is green if memory serves.

It works somewhat like the jpg attached.