Hello all my 7.3l 2wd F250 E4OD is having some issues. I know big surprise lol. Trans seems like maybe it is in limp mode. When put in drive it is stuck in what feels like 3rd or 4th, takes off in that gear and does not shift out of it. If I move the shifter to 2nd or 1st it will shift into what feels like 2nd gear. So basically I can shift manually between what I think is 2nd and 4th gear. My O/D off button does not work and the O/D light on the dash does not work/does not do anything/doesn’t flash. My tachometer is stuck at 250 rpm. I learned through searches that tach signal is needed for E4OD to operate correctly. So I looked into it and tach sensor is good. (2500 ohms resistance through terminals, also puts out constant .5 AC volts at idle, which steadily increases with engine rpm) After verifying sensor is good I pulled the gauge cluster and measured voltage between the tachometer’s ground and signal terminals, it is a constant 2.6v DC regardless of engine rpm, it does not change no matter what. So something is not right here. From there I disconnected the TECA (tcm) connector and checked to see if tach signal was there. Had same AC voltage reading as tach sensor did, so signal from tach sensor is getting to the TECA. Also checked all grounds in the TECA connector (good) and checked it was getting power through the power wires (good). So the TECA is getting all power/ground/signal it needs. ALSO when I hook up my obd1 ford scanner to my obd connectors under the hood, the scanner will act like it is not even connected to anything, as if I hadn’t even plugged it in. This is Very odd and makes me suspect TECA is failed internally. Yes all my fuses and relays are good. I am suspecting a bad TECA (tcm). What are all your thoughts? What should I check to be double sure that the TECA is toast? Should I go to the connectors on the trans and check for any voltages/signals to see if they are correct? NOTE: this truck just sat for 12 years and I was told everything worked fine when it was parked. Thank you from Washington’s state.

 

I'd work the TACH signal first (it will put you in LIMP MODE in a heartbeat and could be symptomatic of problems elsewhere (e.g. PCM) -- I've had plenty of E4ODs and on the older ones the TACH signal heads directly to the dash, newer ones it heads over to the PCM first...............

 

When the transmission doesn't have power from the TCM it will operate in fourth gear only when in D, and in second gear only when in 2 or 1. That's what you have, so that tells me there is no power at the transmission connector on the passenger's side of the trans.

 

Hi maybe I was unclear I am trying to work out the tach right now. The TECA is sending a constant 2.6v to the tachometer regardless of engine rpm. This is causing the tach to sit at 250rpm. However the TECA is receiving a correct signal from the tach sensor, and has good power/ground. So I’m suspecting the TECA is faulty. Just looking for opinions of others and what they think, maybe I should check something else to be sure.

 

Mark thank you this is helpful information do you have access to a connector view of the connectors on the transmission so I can get down there and test for power? Do you think based on these symptoms the tcm is suspect for this condition?

 

Mark thank you this is helpful information do you have access to a connector view of the connectors on the transmission so I can get down there and test for power? Do you think based on these symptoms the tcm is suspect for this condition?

 

I do not have a wiring diagram. The two red wires are +12 to the solenoids.

 

First off it's a "Digital Signal" to the Tach from the PCM you cannot test it with a Volt Meter, you need to use a Scope to watch that signal.... it's a Square Wave that varies in Frequency....

 

hi im sorry but that is not correct the tach sensor is a hall effect sensor that produces a pulsed DC voltage- too fast for a multimeter to read on DCV setting but it can be read with multimeter set to ACV. in this case i can measure .5 ACV at idle that steadily increases as engine RPM increases. (which is correct) This pulsed DCV signal is sent to the teca which computes it and then sends a DC voltage to the coil within the tachometer which then creates a magnetic field and moves the needle in the tach gauge to display the correct RPM. The TECA is doing all the computer work on this vehicle, there is no PCM; the 7.3l idi is completely mechanical.

 

the Sensor on the 7.3 IDI is nothing more than a coil of wire wrapped on an Iron Core it produces an AC signal to the PCM mounted behind the firewall under the brake booster the PCM takes that signal and conditions it then sends it to drive the Tach ... the tach sensor is a simple Proximity sensor and has no electronics in it.

what I told you is 100% correct for an IDI 7.3 BTW I calibrate these Tachometers using a Certified Wavetek FG, Freq Counter and a Scope.

your Engine RPM sensor is connected to Pin 4 and pin 44 of the PCM Pin #36 of the PCM drives the Tach....

 

Hi again lone wolf pin #36 of the pcm is sending out a constant 2.6v DC. Is this correct ?

 

as I said earlier the voltage is not important as it is a Pulsing signal that the electronics in the Tach converts to a Voltage to drive the D'Arsonval meter movement
IF you look at that signal with a Scope you will see ... and IF it is not Varying in Frequency to follow the signal from the Tach Sensor then you might have an issue within the PCM (Powertrain Control Module) IF that signal is Varying in Frequency then you may have failed wiring to the Tachometer or a failed tach ...

Easy way to test the Tachometer is apply 12 volts to it on the Bench and use a signal Generator set to Square Wave at 3 to 5 volts Amplituide and apply about 1khz

now on Pin #36 IF you just have a constant DC voltage with no AC Component to it ( varying frequency) and you have a Tach signal across Pin 4 and 44 then the PCM has an Issue.......
the Tach sensor has a resistance of between 2400 and 2800 Ohms ...and produces a sine wave output since pin 44 is considered the Logical Minus and Pin 4 is considered Logical Plus .... AKA signal return and Signal + it can be considered as a Pulsing DC signal... but one really needs to watch it on a Scope then you will be CornVinced

 

search some of my posts because I think I have posted the 93 and 94 E4OD schematics and also the pinouts for the bulkhead connectors... they would all be in the Pre PowerChoke forums.

the only difference in the wiring of the 93 and the 94 is a Splice between Pin 1 and pin 12 on the solenoid connector.... the 94 powers the EPC off Pin 37 on the PCM instead of pin 35 ... either way works on the Latest PCM

 

OP -- you're getting close / in the ballpark and I'm still thinking the confuzer (TACH signal, power, etc) and/or wiring, connectors................Dr in Residence on Ford Transmissions (Mark) nailed it earlier......

I use o-scopes, would use my 60-pin breakout box (and my E4OD test harness) on this issue and I'm not sure what your MM can do by way of triggers, thresholds so it can give "counts" , but some do a decent job of measuring frequency--- was doing that with my Fluke 88 Automotive decades ago...........

 

Yepper X2.... I'm an Old TEK Guy (retired electronics engineer) ..... but Kudos to some of the newer MM's Scope meters are reasonably priced now and many of the older meters I have still had nice functions .. I use an old Metex M-3640D it has a nice Freq Counter in it.

I wish I had a Breakout box or even a DIY Test harness