Hello all,

I'm trying to fix an issue on this 1997 E250.
Engine, 4.2L V6
2wd,

I replaced the engine due to a failed oil pump gear, installing a rebuilt engine.

Everything was fine, I'm 90% positive that the temp gauge worked at this time. Took vehicle for a test drive and stopped about 4 miles out. Turned out to be a blown fuse (cannot recall which one, sorry).
After this point in time the temp gauge on the dash has not worked.

I have tried new sensors (3x), no change,
I have gone to the junkyard and confirmed the new sensors had the same resistance as the new ones.
Tried another used instrument cluster from a junkyard van, same inop gauge.
Measuring the pins at the sensor, 1 pin does get voltage (10.3 when battery is at 12.3 ish), with key in on position.
Bridging the two pins together the needle jumps to max temp.
Sensor being used looks like this

I cannot seem to locate wiring schematics for this vehicle to be able to further trace the wiring, or know what pin to even do an ohms check at the instrument cluster for.....

Any help to further diagnose this is most appreciated. Vehicle runs fine, no overheating, but really want this gauge working so I can tell if/when a problem is occurring.

 

Does anyone have the wiring schematic at least so that I can do a few resistance checks?

 

I don't have a schematic but would look on the Internet. However, the 4.2 engine did not appear in the E vans until 1997 so it might be helpful to either correct the year of your van or correct the engine size.

Good luck,
George

 

I don't have a wiring schematic, but I'll give you a few things to check.

Edit: I'm assuming you have a 1990 van with the 4.9L inline six, not the 4.2L V6 that was introduced in 1997 as YoGeorge mentioned in his reply.

1) If you haven't yet, pull codes using the EEC IV KOEO and KOER tests. All it takes is a paper clip or small jumper wire, a pen and pad of paper, and watching the Check Engine Light. Code 21, 61, 117, and 118 are related to the ECT. Code 11 indicates the system passed the test. EEC-IV Testing

2) Are you sure your engine is full of coolant? These sensors only work when in contact with coolant. If there's an air cavity where the sensor is inserted, it will not register temperature properly.

3) I believe that the reference voltage from the EEC IV computer to the ECT should be 5 volts, so I'm surprised you're getting 10.3. Where were you measuring between? If you weren't measuring between the ECT wiring harness pins or the corresponding computer harness pins, you probably weren't using the computer signal ground, so the voltage value may not be accurate. ECT reference voltage should come from pin 7 of the EEC IV computer harness and be measured against pin 46.

4) ECT resistance should be around 470k ohm with the engine cold and 1k ohm hot. You can test this with an ohm meter and either the sensor unplugged while the engine is warming up, or the sensor suspended in a pot of water on your stove. Resistance should consistently drop as the ECT reads warmer and warmer water or coolant.

5) Voltage drop across the ECT sensor with the sensor hooked up should be about 4.5 volts with the engine cold, and under .5 volts hot. You should see virtually the same voltage values backprobing wires on the ECT sensor connector as you do across pins 7 and 46 at the EEC IV computer harness.

Here are a few links for EEC IV troubleshooting. You might have some luck looking for generic EEC IV wiring schematics. You will definitely find plenty of EEC IV information related to 5 liter Mustangs. Most of that general information is valid across all EEC IV systems, though there are some differences through the years, especially between older speed density and newer mass airflow based systems. Backprobing the EEC IV computer harness can be a PITA, but much easier using an EEC IV breakout box. You can get those on eBay, though it’s probably overkill for a single vehicle.

EEC IV Trouble Codes
EEC IV harness pin outs
EEC IV Inner Workings
EEC IV Operation and Testing - (direct link removed, Slideshare embedding fails). Go to http://www.slideshare.net/ and search for "EEC IV". It should be the first link.

Good luck!

 

Thank you both,

I'm sorry I missed up the year. It is a 97, not a 90.

I'm certain that the coolant is full as coolant does come out the hole when I pull/move the sensor.

packmule, are those resistance values good for the 97 w/ 4.2 as well?

 

The resistance values for OBD2-era Ford V6 and V8s should be ~55k ohm cold, ~2 ohm hot. Here's a good article re: troubleshooting OBD2-era Ford ECT issues. The article focuses on 4.6/5.4 V8s but the information is the same for the 4.2 V6.

Part 1 -Troubleshooting P0117 and P0118 ECT Sensor Tests (4.6L, 5.4L)

Most of the general suggestions in my previous post are still good. Use an OBD2 scanner to check for ECT codes such as P0117 and P0118 and start your troubleshooting efforts there. Reference voltage for the ECT is still the same (5V) and voltage should still be measured between the reference voltage signal wire and the computer ground.