7.3 Tach (Problem???)

Reply Subscribe

Thread Tools

Search this Thread

Oct 4, 2005 | 01:58 AM

LongArmSuperDuty

Thread Starter

Freshman User

Joined: Sep 2005

Posts: 27

Likes: 0

7.3 Tach (Problem???)

Hello,
I have a 90 F-450 Superduty 7.3, just noticed that when im in idle the tach is at zero. when i rev it or drive it moves normally......is this normal for these or is there a potential problem??
any suggestions?

Thanks,
Mike

Oct 4, 2005 | 12:25 PM

PLC7.3

Post Fiend

Joined: Nov 2004

Posts: 5,638

Likes: 1

From: Manitoba

The tach should work from start to finish with no down time.........check where the wires exit the sender quite often they are bare and short out until fan wind velocity move them. Check the connector too.

The dead tach should send the automatic trans into a "failure management mode" (limp mode) with harsh engagements and firm shift feel, and an abnormal shift schedule.

Replace the tach sender on the oil fill housing a big 1" nut with 2 wires. Ford only part Engine RPM sensor E5TZ-17B384-A about $50. You can remove and clean it but usually changed later too. You can test it too, hold it in the air away from ferrous metal, using an ohm meter lead on each wire you need DC resistance between 2000-3000 ohms.

Last edited by PLC7.3; Oct 4, 2005 at 12:28 PM.

Oct 4, 2005 | 01:20 PM

goodie350

Senior User

Joined: Dec 2004

Posts: 172

Likes: 0

My tach does the exact same thing. As soon as the motor is reved it's reads fine. I haven't done anything with it since I have a 5 speed tranny and hasn't affected how it runs. Is it going to damage something if left alone?

Clint

Oct 4, 2005 | 11:14 PM

PLC7.3

Post Fiend

Joined: Nov 2004

Posts: 5,638

Likes: 1

From: Manitoba

Nope.......Just a pretty nifty guage on a standard, no effect on the trans ops other than you know when to shift it..........

Oct 5, 2005 | 12:21 AM

tdford

Senior User

Joined: Nov 2004

Posts: 305

Likes: 0

From: Bothell, WA

I don't understand how the tack on these diesels works. If the tack is reading 0 at 600 rpm can it be trusted to read correct when it comes on at higher rpm or could it just be reading 600 rpm low?

Oct 5, 2005 | 06:12 AM

jboard

Elder User

Joined: Feb 2005

Posts: 712

Likes: 0

From: Marietta, OH/Weirton, WV

Well i had the same problem and it turned out to be my idle was too low. Try to adjust your idle up a little until you get it around 675rpm according to the gauge. Mine works just fine.
Jeremy

Oct 5, 2005 | 09:20 AM

goodie350

Senior User

Joined: Dec 2004

Posts: 172

Likes: 0

I'm glad it isn't hurting anything. I actually think the problem with mine is a bad ground I haven't been able to locate. The tach will jump with the turn signals when they are on. When the truck gets warm most times it comes off of zero and is around 300 to 400 and doesn't jump as bad when the turn lights are flashing.