Hey everyone,

First of all I hope all of you have had a great holiday season!

My 94 Bronco, 5.8 E4OD stock, has been having problems for about 2 months now. I need some input from the experts here.

I have done the following:
Starter relay was bad - replaced with new $27
Battery not holding charge - new battery N/C under warranty
Starter was bad - replaced with rebuilt lifetime from Napa $120
Coil yellow/orange spark (weak) - replaced with new $30

With every repair the truck would run fine for a couple of days and then not start in the morning. I could jump it or wait until it warmed up in the afternoon. I think I have checked everything in the starting system.

After searching here and Google I found that the ECT or ACT sensors could be a problem. So I checked the ECT today, KOEO, and got these numbers -

Cold - air temp today around 73* -
34.5 k ohms 4.57 v

Warmed it up to about 160 - 180* (guessing on the temp)
3.3 k ohms 4.57 v

I am not sure about the volts - I don't think I am doing it right. With the harness disconnected I put the red lead from the multimeter in the harness and black lead to ground? I am not very experienced with electrical stuff.

I have power, the starter spins, I am getting spark and I hear the fuel pump running. So, I need your advice! I appreciate any and all info!

Thanks
Mark

Edit: I pulled codes just got 111 = pass

 

Your resistance readings from the sensor itself at the temperatures given are right on target. However, you cannot take voltage readings with the sensor disconnected from the harness. The reason you got the same voltage every time is because you were reading the only harness terminal that would give any voltage with the sensor removed. 4.57 VDC is reference voltage or VREF which is generated by the EEC-IV computer power supply. The nice thing is that 4.57 VDC is exactly what VREF should be.

Given that the resistance readings are correct for the sensor, there is less concern that the ECT sensor itself is the problem. Do the same thing for the ACT sensor. The readings for the ACT should be nearly identical to the readings you got from the ECT at the temperatures you already mentioned. If they are not, your problem lies in the ACT.

If the resistance readings are similar enough you can double check that voltage coming through the sensor is correct by taking voltage readings at the signal return side of each sensor while they are still connected to the harness. The ECT sensor should be read for voltage between ground (negative) and the LT. GREEN/RED wire at the sensor. The ACT sensor should be read for voltage between ground (negative) and the GREY wire at the sensor. The attached file lists approximate resistances at certain temperatures. (Note: 195º F should read 0.60 VDC and not 0.06 VDC as shown).

 

Greystreak thanks so much for your response! I will check the ACT tomorrow and report back.

As far as the voltage is concerned - I want to be sure I understand what you are saying. Multimeter black lead to ground and red lead to correct wire you listed with harness connected. I am guessing I need to make a small cut in the wire insulation in order to make contact with the wire?

Thanks again,
Mark

 

Correct. Try not to cut the insulation... use a straight pin or a sewing needle to poke all the way through the wire. This will give you a metal "test point" in the wire that you can easily seal up with a small piece of electrical tape after you have taken your readings and removed the pin. Don't want those wires to corrode from the inside out in the future.

 

Thanks again Greystreak! I really appreciate it. Like I said I am not very good with electrical issues.

I will report what I find tomorrow.

Mark

 

OK - numbers from today.

ECT v following Greystreak's instructions - 2.84 v cold.

ACT v 2.92 v cold (temp the same as yesterday - 73-74*).
31.8 k ohms cold
7.2 k ohms warm (about 160-180*) this number seems high to me.

Both tests were done the same time of day - 2 PM - and same outside temp. I did not check the volts when warm.

What do you think?

Thanks
Mark

 

Can anyone confirm that the warm ohm number on the ACT sensor is out of spec? It is about 4 k more than the ECT sensor when warm.

If it is what size socket will I need to replace it?

Thanks

Mark

 

So, I replaced the ACT sensor - 1" socket in case anyone else needs that info. Same thing happened - fired right up and then would not start 2 days later. I decided to take it to a shop - I was out of ideas. Of course, it started for them so they could not find anything but told me if the no start condition came up again replace the #1 & #2 relays in the power distribution block. #1 is powertrain control system and #2 is the fuel pump. I did that and it would not start early in the day. Later in the afternoon it started. Needless to say I am very frustrated!

Does anyone have any ideas or suggestions? I don't know what else to check.

Thanks,

Mark