I unplgged the sensor and and inserted one VOM probe in.to the plug which has the lg/r wire which I beleive is going back to pin 38 of the PCM the other probe was connected to the battery ground the reading is 3.95V I'm looking for 5V. My next move wounld be to pull the PCM. Right now I'm running on defualt sensor unplugged. Thanks for your help that chart comes in handy.
I did ceck voltage from the 42 way connector to PCM got the same 3.95V I'v ruled out bad wiring between the two.

 

The 42 Pin Connector is NOT where you want to check first.

First, Back-Probe the PCM Pin. That being said.

***YOU DO NOT WANT TO USE TWO BACK PROBES ON A PCM UNLESS YOUR VERY CAREFUL.***

The chance of a short increases exponentially.

Use the Sensor's Ground to complete the Circuit. If you get 5v, the problem is in the circuitry ((+) wiring)).

If you don't, Back Pin the Ground on the PCM (-) and use the (+) in the Sensors Feed Side. if it increases, its in the Ground Side of the Circuit.

If you determine it's in the circuitry, then you begin checking circuits and junctions.

 

I went back to re-read the OP - I thought we were getting 3.95 volt output from thee sensor, which would be about right on a cold truck.

With my mental reset, I now wonder about the 5 volts. I have seen PCMs with max sensor voltages all over the spectrum, and I rarely see 5 volts anywhere. It's my understanding the PCM provides 5ish volts, and the PCM compares this voltage to the sensor input - automatically compensating for low or high voltage references.

I know from my own experience that 3.95 volts may be straight reference voltage, then it's a matter of learning what the sensor output is in relation to that and ground.

 

Yes, and No. The PCM uses "Substituted Values" during start up for example. The Engine would not run without these being placed in the Start Up Strategy. So, by him un plugging the sensor, the PCM uses substituted values such as un-plugging the ICP which is about 700psig.

There area a myriad of things that can affect the 5vR. As for a normal reading of 5vR, several things affect that. Batteries, Charging System, etc. For the most part "my rule of thumb is .5v. Anything greater than that, there is an issue. The great thing about voltage is it's either there, it's reduced, or its not there. It can't lie. All Scan Tools that display temperature and pressure are merely code written to use the voltage and convert it to another.

On the EOT, the three "key" voltage readings are for start up (Glow Plug Time On / Fuel Bowl Heater / and Fuel Delivery (keep it running). Of course there are additional sensors which al must have input such as the CMP and AIT.

I was attempting to get him to perform a few tests. First off he's getting a *F reading from somewhere. And, he doesn't say "how" he's getting it. Scan Tool, Gauge, etc. Un plugging the sensor improves performance. Well, that Sensor is a Thermistor.

A shorted thermistor will not pull-down the entire ref. circuit due to the internal resistor in the PCM for thermistor circuits.

While measuring reference voltage with the key on, (usually at the EOT or ECT because of easy access) start unplugging the sensors one at a time.

The System reference can be shared (externally from the PCM) with pots, psi sensors, and Hall effects but never with thermistors. A shorted pot., psi sensor, Hall Effect may pull down the entire System Reference Circuit, including all of the internal circuits that use this same reference voltage.

When he was testing, he was testing at the 42 Pin Connector and sensor. Grounds may be shared between any inputs, But, Signal wires are never shared between sensors.

The very simple test is to Find the sensor that causes the reference voltage to return to 5v when you unplug it.

If you still have no 5v ref. with the sensors all unplugged, then you must disconnect the PCM and measure for a short to ground on the reference circuit. (Sensors still unplugged)

No short to ground then you have a PCM problem. Make sure you check all PCM powers and grounds before replacing the PCM.

So, saying he has a "Bad Sensor or Circuit" is referring to something is "pulling the voltage down". He's got to find the offender before he knows what to fix.

 

Another thought on the 5vR Circuit I hope to prove or disprove is the misconception of the EBV Circuit.

One experiment I have been waiting a few years to do because I have not had an issue with EBV Sensor is that everyone states they adversely affect fuel mileage and performance when they're dirty or clogged.

I don't think its as much the sensor as it is the sensor is drawing the 5vR circuit down causing the vehicle to run in a different strategy than the warn engine mode because the sensor is commanding more current and the PCM can't maintain it.

So, If I ever get one (not likely in the deep south) I will scope it and analyze the data to prove or disprove my hypotheses.

So, if anyone out there is planning on cleaning the EBV because they're getting bad fuel mileage. Take a moment and send me the 5vR before and after for comparison.

 

I have a used ebpv, here are the AE readings I pulled before changing. I am willing to ship it to you.



Robert

 

Robert, that's great data. Do you have some after you changed it (same parameters)?

What was your reason for changing it?

Was your fuel mileage suffering?

Did it get better following the change?

 

Thank you guys for spending so much time helping me with this problem. I'v been checking the EOT with a Scangauge II reading 260*F cold engine. The voltage I get at the EOT unplugged is 3.95V I unplugged each sensor that shares 5v from the PCM pin #91 to see if one sensor is drawing the EOT sensor voltage down it had no change. Each was being supplied 5v (ICP,EBP,MAP,IAT. without the full 5v at the EOT the temperature scale is off. the engine runs better with EOT unplugged. I don't how one sensor could have less voltage then all the others. Thanks, Andy

 

The EOT, Engine Oil Temperature programming is:

TXD: C410F1221310
RXF: 046245130610
RXD: 3010
MTH: 00090005F060

If you by chance are referring to the ECT, Engine Coolant Temperature, the Scan Gauge II acquires that from several sensors as the ECT is not supported on Automatic Transmission equipped vehicles (the wiring is from the Thermister to the Gauge).

ETC Display on a Scan Gauge II is:
TXD: C410F1221139
RXF: 046205110639
RXD: 3008
MTH: 00010002007F
** It will read "out of range" 250*F + until the EOT (engine oil temperature reached 140*F or >).

 

Thanks ,Tom I have the same codes set in the Scagauge II. The gauge worked correctly when first installed reading max of 200*f but changed the next day I contacted the Scangauge people and after several attempts to correct the problem they said to send it back for repair which I did. When I got it back it still would not read the engine oil temperature (EOT) Thats when I discovered the lower voltage to the sensor I still have a issue with it not reading the codes. When I unplugged the ICP and the engine the SES light came on but Scangauge said there were no codes when I reconnected the ICP the SES cleared no codes were ever found.
Andy
Here's an update with the sensor connected the voltage input was 2.95v with 0 current

 

I apologize for the long delay on getting current data, I am willing to run any more test capable of AE that is . I answered your questions within the quoted area.

Robert

 

I found a good mechanic who knows 7.3's and the problem was the PCM I was thinking that way but wasn't sure where to get one, new one's are not available for my truck had to get rebuilt. The EOT was reading high on cool motor keeping GPR from working and voltage to the senor was low. Truck run great all is well. Hope this helps someone.