No overdrive

[callcameron]

Ok, I just had my transmission rebuilt (radiator blew and warped the heads and burnt the transmission). Before it was rebuilt, it stopped going into overdrive and reverse. Since it's rebuilt, it won't go into overdrive. I put my $20 walmart code reader on it and it gave me a Vehicle Speed Sensor code. I replaced it. Still no overdrive. The code reader still gives me the same Vehicle Speed Sensor code. I've been told that regardless of whether it is good or bad, it shouldn't keep it from going into overdrive. Can somebody PLEASE tell me what to look for? Gas milage is TERRIBLE at 4,000 rpms!!! Any help is appreciated.

By the way, I have a 1992 Explorer XLT with 4WD, 4.0L V6

Cameron
callcameron@hotmail.com

 

[MrShorty]

4000 RPMS? Are you sure it's getting from 2nd to 3rd (has to get to 3rd before it can go into 4th)?
Bad speed sensor will definitely prevent it from going into 4th gear. 3-4 shift is electronically controlled by teh computer, and one of it's main (if not the main input) it uses to decide when to shift from 3 to 4 is vehicle speed. If the computer doesn't know how fast you're going, it's not going to shift into 4th gear.
Since the only VSS code I see listed is a CM 452, I'm going to assume that's what you're getting. The thing to remember about any code is that the computer can't see past the end of its nose. It doesn't know the difference between a bad sensor and a broken wire between it and the sensor. You said the transmission was recently rebuilt, make sure the sensor is plugged in. Make sure there is continuity between the sensor and the computer.
In addition to testing the VSS circuit, you might also check the wiring between the computer and the 3-4 shift solenoid.

 

[callcameron]

more help please

Yes, it is going into 3rd. 4000 rpms was freeway speed (or should i say freeway TRAFFIC speed). I already thought about the computer not being able to see past it's own nose. I personal changed the sensor so I know that it is plugged in at the transmission. Where do the wires go so I can trace them to see if they are severed? Or what's the best way to check continuity? Also, what is involved in checking the wiring to 3-4 solenoid? Please tell me that it doesn't involve removing the entire transmission again. Thanks for you help.

 

[MrShorty]

Do you have a wiring diagram? If not, that's the first thing to get. Wiring diagrams in the vehicle repair guides at www.autozone.com (same as Chiltons) seem adequate for this.

Best way to check for continuity is with an ohmmeter. Unplug the harness at the computer and at the VSS (or whatever sensor/solenoid you want to inspect), then measure the resistance of the wires (should be near 0 ohms in most cases).

 

[Glacier991]

Callcameron, PM me, I'm in Sacramento. I might be able to give you a hand after this weekend. We can pretty quickly rule out any mechanical problems using the transmission tester. Then it's just working out any electrical issues. And even then we can test for resistance and find shorts etc without even removing the pan. What speed is giving you 4000 rpms? I find 60-65 is 3000 to 3200 RPM or so on my 92 in 3rd gear. 4000RPM? Sounds high to me....

The only computer controlled shift is 3/4 and the Torque convertor clutch is also computer controlled.... hmmm.. if you lacked BOTH, hmmmm maybe you'd get 4000.....both at the same time..... hmmmm curious. Could be a starting diagnosis... both rely on Speed sensor input..... this would be a case tailor made to use the Trans tester on... it relys on no inputs other than the operator....

 

[callcameron]

Hey, thank you. I'm sorry that I don't come on here often enough to know how to PM you. My email address is: callcameron@hotmail.com or you can call me at 916-265-1005 ext. 1. Thank you.

Cameron

 

[Glacier991]

Stay tuned all, we are gonna do a tester diagnosis on his trannie, I'll photo the diagnosis procedure.... might be fun for us all. Probably next weekend....