I have a 1990 Ford f350 Dually with 7.3 Diesel and Banks Sidewinder turbo. What has been happening lately is that I cannot start out in Drive. If I put it in low second it will go and then manually shift it then will go into drive. Also when this is going on the factory tachometer does not work. But then the next day it will start out in drive and be fine all day long. Also when it working the tachometer is working fine.
So what going on here? I'm Lost. Please give me some guidance.Thanks.

 

Only achieving drivability by starting out in Second then shifting to Drive is what's known as the E4OD's "limp mode". You've got a problem with the communication between the PCM (Powertrain Control Module) and the transmission.

The first thing I'd try is to remove the solenoid block harness connector (located on the passenger side of the trans. just above the pan) and see if any water is in the connection. If so, dry it out, clean the pins, apply some dielectric grease, and see if it shifts properly.

Are the locking tabs on the connector still there and functioning correctly? How about the first 6 inches of the wires? Is the insulation burned or corroded off. If so, you need to go to a local tranny shop and buy a new harness connector. Will set you back about $30.00.

The tach. not working might be the RPM sensor not functioning. Click on my "profile" in blue at the bottom of my reply and send me an email and I will send you a zipped file of info which will hopefully help you diagnose your problems inexpensively. It also has a picture with a pin-out of the Sol. Block Harness Connector if you need to replace it.
R.A.

 

I will check out your idea tomorrow. I think the transmission thing and the tach problem are related because everytime the tachometer stops working it won't start out in drive.

 

To check the functionality of the RPM sensor:

1. Remove two wire connector end.

2. Hook DVOM meter leads to pins on sensor. It doesn't matter which way you hook up the red and black leads.

3. Set DVOM scale to AC voltage, 0 to 40 volts.

4.Start engine in Park. Raise RPM's while watching DVOM.

5. Voltage must increase or sensor is bad.

The RPM sensor is located in the Injection Pump housing, on the Driver's side, below the Oil fill spout. "Jens" posted a picture of it in this thread (down towards the bottom):

https://www.ford-trucks.com/forums/s...hreadid=157482

This sensor test as well as several others are included in the zip file I have free for the asking.

I don't understand how a bad RPM sensor could cause you to go into limp mode. Symptoms of a bad RPM sensor are: cause no LU (which can cause setting of code 62/628 TCC slippage), shifts and LU cycle back and forth, and erratic shifts. May or may not set the code 14/211 RPM sensor circuit failure.

The tach. not working and the limp mode coinciding hint that the T.E.C.A. relay is either bad or is not grounded properly. I don't know what type of vehicle you have but assume it's a truck. You might want to find the T.E.C.A. relay and verify the ground is good. If all of the above don't get results, and you still don't want the zip file, write, and I will type out the T.E.C.A. relay test procedure.

R.A.