rotorypolo

iTrader: (1)

Guy,
I am sure some of you like Dale, Phil and others were aware of my broken signal from the watertemp sender to my pfc. Well to make a long story short, I tested the current to my watertemp from the stock harness clip, and got about 5 v of current, and I think just about right. Therefore, I went and got a new watertemp sender, and thought that would resolve my problem. When I plug in the new sender physically w/o having to remove the alternator to get to the old sender, my PFC reading is still nothing. Now I am puzzled. Can anyone tell me why I am still getting zero readings? Do I physically have to plug the watertemp sender in to get a reading? I highly doubt it is the watertemp sender now. Can anyone explain why I am getting current from the harness, but no reading from pfc? What can I do @ this point to get my computer to read my watertemp? My last resort is to bypass the harness and splice a wire to run form the computer to the sender itself. Any help would be great.
Dale, let you a message last night, but if you can give me a call today if you get a chance would be great
404-423-6460

Marco

DaleClark

iTrader: (55)

I'll try and give you a holler tonight - had a busy night last night.

Anyhow, it's most likely a break in the signal wire going back to the ECU. The 5v signal to the sender doesn't come all the way from the ECU - there's a 5v wire in the harness that branches out within the harness to feed the various sensors that want a 5v signal. So, the 5v wire has much less length to fail - the wire feeding the signal back to the ECU runs the whole length.

Might be worth pulling the upper intake manifold and unwrapping the harness coming from the water temp sender to look for breaks. Most times breaks are near the sensor, as that part of the wiring gets the most abuse. If you can't find it, might be time to just run a new wire. Also, make sure the connector itself isn't damaged, like pins backed out of the connector or something.

I don't think the sensor has to be grounded to read, but all you'd have to do is touch the metal body of the sensor to the water pump housing to test that theory.

Good luck,
Dale

cewrx7r1

iTrader: (2)

There is always two sides to any circuit. And you only mention testing the 5V side from the ECU. Have you tested the ground side from the sensor to insure it is going to ground?

Did you test the original sensor to verify if it was really bad. The manual shows how and all it takes is an ohm meter, thermometer, and hot water.

rotorypolo

iTrader: (1)

cewrx7, I am not sure what you mean, how do you ground the sensor? I assume it is grounded by just plugging into the sensor location behind the filler neck? In that case, maybe I did it wrong. I only plug the new sensor into the harness and checked to see if I am getting signal, which I didnt get a signal indicating from the PFC the sensor is working. Maybe I need to put the sensor in its proper location, plug in the harness and try again?? I assum by the metal contact from the sensor to the filler neck, it is grounded?

twokrx7

iTrader: (1)

You don't have to ground this sensor, it makes a circuit back to the ECU and not the engine block.

rotorypolo

iTrader: (1)

Well in this case, can someone tell me why I am not getting a reading?

DaleClark

iTrader: (55)

It's gotta be the wire that takes the signal from the sensor back to the ECU. If you have enough jumper wires, you could test continuity on that wire.

This circuit is VERY simple - 5v in one side of the sensor, the sensor has variable resistance with temp, giving a 0-5v output back to the ECU. That's it. The sensor body might have to ground to the water pump housing just by being screwed in - that's the only variable.

Since you know the sensor is good, it's one of three things -

- bad connector to the sensor
- bad signal wire from sensor to ECU
- sensor needs to be screwed in/grounded to give a proper reading, which is semi doubtful

That's the only thing it can be.

Dale

cewrx7r1

iTrader: (2)

OK, the foolishness has gone on long enough, DAPDAS!

First you all need to look at the wiring diagram in section F-250 of the manual, and understand a little about electronics.

The ECU supplies voltage (+5vdc) to one side of the sensor from pin 3E and the wire is green with a white stripe. This is the hot lead/side of the circuit going to the sensor connector. The other wire from the sensor connector is brown with a black stripe. This wire goes to ground, or as some might call it the negative side of the battery.

The sensor is a thermistor (a resistor that changes resistance with temperature change). See page F-183, at 68F it is 2.2-2.5Komh, at 176F it is 290-350ohm.

The ECU monitors the voltage drop across this resistance that varies as the water temperature varies. Hot sesnor means low resistance thus the voltage is closer to ground or low voltage. Cold sensor is opposite thus a high voltage at or near 5volts.

Thus there are three components of the circuit to test. Does the sensor connector have the 5volts from the ECU? Does the sensor resisitance vs temperature match the specs? Does the gound side lead go to ground(no voltage and almost no resistance between the connector and the wiring harness ground.

A final circuit test can be done with the sensor plugged into its connector but not screwed into the waterpump housing. Cool the sensor in ice water, plug it into the connector, turn on the key and observe the voltage as you heat the sensor with a hair drier. The voltage should drop from 5 volts as the sensor warms up.

If the first three test past and this final 4th test fails, the PFC or the commander are bad.

I should get paid for this crap!

DaleClark

iTrader: (55)

Thanks for that, Chuck - I learned a little somethin'. I was a bit backwards on how it works. I'm sitting here with the shop manual in my lap and verified what you're saying - the BrB wire is common ground for all the inputs (intake air temp, MAP, fuel thermosensor, etc.) and the GW wire is the signal back to the ECU.

Regardless, a break or a failure of the connector will cause the problem. That's the only explanation, unless something is REALLY hosed with the ECU.

Dale

rotorypolo

iTrader: (1)

problem solved. I ended up jumping the wire from the back of the ecu to the water temp sender and boom, the magic number came up on the Commander. Thanks for all the help guys, I guess the stock harness 5v wire was disconnect somehow. Now my question is, I better go get a wideband and recheck my A/F ratio since I believe my tune was based on a broken water sender, and my car was running a little rich. Technically, when my computer senses a stone cold motor, it gives more fuel correct? Does that mean a bad sender will give the computer a cold reading, 5v, meaning bad gas miledge? I think with a working watertemp sender, it will be probably running alot leaner? I wonder if I need a retune?