My Tach and therefore my transmission is not working. I have replaced the tach sensor ($85 at Ford) but still no reading. I tested the old and got no ohms but should have tested it on the vehicle as it may have been OK. The new sensor is giving a good .5 volt AC reading.

The tach needle moves during start up but falls dead when the engine starts. All other gauges are functioning. So it appears the failure is some where between the gauge and the sensor.
Is there another common failure point? Where do the wires connect to the transmission controller? I want to test for .5 at the controller.

 

what year truck? if it's a 9th gen era idi (92-94) check for blown fuses in the power distribution box.

 

Yes it is a 94 IDI. I checked and did no see any blown but the radio fuse and on other have been patched by the PO. I pulled the tach fuse (17 if i remember) and cleaned it. The other guages are working so that was not it. The OD off light does not come on when I push the button. Now that you mentioned the fuses, I need to find the transmission fuse, clean it a check for power to it.

I remember some old post mentioning the transmission and the fuel heater share the same fuse. My "Water in Fuel" light came on and blinked and went out last week. It does not have the water sensor installed so there may be some wiring issues. The truck is new to me and I am trying to get her road ready.

 

Checked the fuse and the relay in the power distribution box. The relay clicks when the fuse is removed (key on) and there is continuity across the switched connectors.

All the fuses inside and are good and all other functions are working on the truck.

Now to locate the TCM and test the connections. I keep hoping for a cheap and easy fix. I bought an automatic in hopes my wife would drive it to the lumber yard for supplies. At the moment a 5 spd is looking good.

 

so fuse #17 is ok? that's for a few things but two of which are your issues; no tach and no od indicator light.
when you press the od cancel button,does it function correctly and lock out OD even if the bulb doesn't illuminate?

manuals trans are not exempt from failures brother.iv had my share of those too.the trucks are 20-30 years old.even these legendary engines need maintenance and replacements.if all we had to do was buy old trucks and simply run them like new trucks,then who in their right mind would spend 60 grand for a new one right?

 

I found another one your post related posts and have checked the PCM diode and Fuse "I". both have power. Fuse "I" has 13 volts on the hot side and .6 on the out going side. I read another post for the TPS indicating the trace voltage is an indicator of a bad ground. Where are the other end points located?

The transmission starts in 3rd, moving the shift lever to 1st and second will give you those gears. There is no OD shift at all and no OD light.

Thank you for your current help and all of your previous post. I would be lost without your help.

I loved the auto when it was working even though is shifts hard. I am just frustrated. The truck ran great last week. Now, everywhere I look there is more to do. I have a 64 F100 I have brought back to life. When I can drive them all is good. When they are stuck in the drive, life is bad. Both are stuck in the drive today.

 

oh that's vital info.this changes things.that means your TECA doesn't have power (or the solenoids in the pack i guess more importantly.) so you need to insure those fuses are good.none blown.

so with no tach,no od cancel light and no normal 1st in D this all points to the fuse or the TECA (pcm as noted in the gas trucks) relay.
i would suppose however the od light and the tach would be ok still if the TECA relay went bad? (easy enough to experiment to find out if ya wanted) but with the fuse "I" there blown,that kinda narrows it down.

so you found your issue.fuse "I" as noted there in that chart OR 3rd position down from the diode is bad.it should have full power of course going through it not just on the supply side.so the TECA relay,thus the TECA and solenoids are not getting power.so swap that fuse "I" out and all these things should clear right up.

no problem.nah,you'd find your way through it.it can seem a bit daunting at first,but after awhile you learn the system is only so complicated and becomes very simplistic to ya after a bit.

TECA = transmission electronic control assembly.
TCM = trans control unit.
PCM = powertrain control module.
all the above = the same basic thing. the control box that operates the trans (pcm would be a multi unit which handles the engine as well,but term is often used loosely in idi trucks too.)

whatever ya wanna call it,she hasn't got enough power captain!

 

My apologies for not being clear. Fuse "I" is good or at least looks good. When I test the fuse Bus the hot side has full power and the output side has .6 volts. I expected the out put side to be 0. Not sure if that is the case. All of the fuses inside and under the hood are good. Many are the incorrect size which I will correct tomorrow. That also leads me to believe there have been electrical problems in the past.

The there is no change. No signs of intelligent life from the transmission or tach.

I loosened the connection to the PCM or TCM, the one located on the firewall below booster. I did not get the connection all the way off but it come out about inch. Tightened it up with no change. I will check the the TPS, and the two connections on the transmission tomorrow.

I did fix the shift indicator and unplugged some of the PO's bad wiring. I think it goes to the aux fuel tank in the bed which being removed. At least some progress was made. I also converted my '64 F100 to a dual master cylinder and replaced the hard lines. I will fabricate a brake light switch tomorrow and She will be back on the road so my spirits will be better.

 

This says fuse I is bad, this fuse has constant power going to it for the TECA "Keep Alive Memory" and also feeds the TECA relay contact side only.
You should be getting the same voltage on both sides of the fuse, the 0.6v your reading tells me your seeing a feed back voltage from the TECA that would not be there if this fuse was good.

The TPS grounds into the TECA and the TECA has its own dedicated ground to the rad support, this isn't causing you problems.

The tach doesn't go "through" the TECA, the TECA takes the tach signal and buffers it and the sends it back out to the tach. Same thing goes for the OD light, the TECA grounds the light turning it on, so no TECA power, no tach or OD light

Fuse I supplies a yellow wire to the TECA plug for keep alive memory, it also feeds the TECA relay which supplies two red wires to the TECA plug and one red wire to the solenoid pack.

 

Today:
1. Cleaned all the fuses and change the ones that were the incorrect amperage.
2. Check the PCM relay and it has 13 volts
3. Check the TPS and it had 5 volts. ( 1.3 -4.2 and smooth through the range. The idle is high, I tackle that tomorrow.)
4. Cleaned the solenoid pack connection with cleaner and compressed air. It had 2 connector with 9.8, one with 10.8 and the remainder only a trace voltage. All increased 1 volt after cleaning, but I could have just had a better ground.
5. Cleaned the MLPS connection with cleaner and compressed air. It looks like the top in not on correctly. see below.

Cranked her up and nothing. No tach and no shifting from the transmission. I put her in 1st and drove around the block manually shifting. Pulled in the drive and the tach came to life. Pulled back on the road and she found 1st on her own as well as 2nd and 3rd, LU. My front axle made a bad noise before OD speed (another thread). And the shift were smooth, not harsh as before.

The problem can and went with no explanation. That makes me very uncomfortable. At least I know I can manually shift to get home if it happens again.

Thank you for the help. I am comfortable I can take care of the obvious problems if they do occur in the future.

 

you can't give up.you need to find the corrosion or the break in the wires.it's vital the TECA receives a clean power signal with no off/on issues.
sometimes the trans harness can fray right where it runs up from the trans along the frame on drivers side and or that plug where it goes into the power distribution box.if you find no issues there,then you may want to unclip and flip over the power dist box to inspect the pins on the under side.
one things for sure,the issue will return if you don't fix it.the question when it happens again will be if you let it hurt the trans and then require a rebuild plus resolve the issue.don't give up.there's only so much that can be wrong.

you did pull the TECA harness clip with the 10mm and cleaned that right?
but i would say,your issue is with that fuse or dirty pins in the power dist box since you found less than 1 volt at it once,but then now get full bat voltage latter on without doing anything to it.you've got it pretty much narrowed down.don't loose focus on the issue you found.that's very good info you found with less than a volt on the one fuse side.investigate further here,and i think you'll find your issue.
you may just want to pull all the relays and fuses in the power dist box and spray all the pins with e-cleaner and then apply some dialectic grease.that's just good maintenance with 20 yr old trucks anyway.

 

I will continue to look for frayed wires in the places you mentioned. I also rotated all the 20 amp maxi fuses in the distribution box. They all look good but I have had the small one fool me. I will double check the voltage across all the fuses. I have not cleaned the TECA connections but will do so tomorrow.

I was afraid to start it up today and see if the tach was still alive. The delay in tach coming back make me think the cleaner finally dried. I would feel better to find a frayed wire.

 

Checked the PCM connection and looked for chaffing. The wiring across the transfer case has been re-wrapped and secured. I did not take it a part to check the quality of the work. There is power on the connector so it must be fine. Nothing. I tried to check the back of the power distribution box but could not get the relay tray up. I did not want to break it. There is power at the TPS and solenoid. Still no tach or shifting.

It is beginning to look to the PCM is dead. Otherwise, I would expect it to go into limp mode or flash the OD. I saw another post where this was the case. Rock auto has TCM/PCM for $125+core. I will try to locate a ODB1 scanner and see it there is any signs of life then order a PCM. I need to get the truck running.

 

The PCM test port is always 12 volts. I started a new thread to see if there is a way to test the PCM.

https://www.ford-trucks.com/forums/1...l#post14499469