1990 Bronco 5.8 Tach runs Backwards

[bigwave65]

I tried searching threads and could find nothing. My 90 Bronco's Tach was working fine until yesterday. I started the vehicle up tach should Idle just fine but when I started driving it started running backwards. Any help would be appreciated.

[Steve83]

What do you mean? The needle can't move the wrong direction unless it comes off the shaft. Click this, read the caption, then go to the NEXT few:

[bigwave65]

Thats what I thought also that it cant run backwards. However, It started again yesterday I started it up it registered the idle fine. When we took off it was working okay then it swung all the way around it still registered idle then when I took off it ran backwards and went above the six grand mark. I have not pulled cluster yet to see if anyone had any thoughts of a wiring issue.

[Steve83]

There is no wiring fault that could cause the needle to do that. But what you're describing isn't "running backward" - it's "wrapping around". I'd snag a JY '87-91 tach and swap it in.

BTW
Put your truck's details in your profile AND signature so they appear with each post, and we don't have to scroll back through your posts to see what truck you're talking about. Click this & read the caption:

[sackman9975]

If the tack is registering higher or bouncing around other than what the engine RPM's are, then you could have faulty wires. This is because the spark that the coil is generating is not grounding properly (to the plugs) and back feeds into the tach. I have had this happen before.

Not saying this is your problem, but wanted to add it into this thread.

[67BlackCat]

I did the required amount of searching and found this thread... but my tach is actually running backward...

my truck is an '83 XLT, 5.0, 2bbl, c-6, only mod is an HEI distributor.

ignition off: the needle is at 0

as soon as I start the motor the tach needle jumps to 6000 then uses 6000 as the zero point... cold idle reads about 5000 (actual ~1000), warm idle about 5500 (actual ~500)...

the truck has some obvious wiring "fixes" so Im not surprised at finding an electrical issue... i looked through Steve83s page and did not see a wiring diagram for the 83.

[McNine]

My 91 5.0 is doing something similar. All stock parts. No mods. Sometimes it will rotate counterclockwise on accelleration then go back to normal when I let off. Other times it will be stationary @ 3000RPM. Then sometimes it works OK. Could it be the PIP going bad?

[67BlackCat]

I should actually put the question there... does anyone have a wiring diagram for the '83?

[Steve83]

If the engine runs, the PIP works. If the tach is operating wrong, the tach is bad. Replace, delete, or ignore it. Haynes has the wiring diagrams, but there is no wiring fault that can make the tach do that.

[67BlackCat]

This is where Im supposed to tell you that Ive already changed the spring diode and the shock fuse and im still having the same issues, right?


a lot of Steves answers seem to be followed by some type of argument and I dont want to buck the trend

[inxy]

Spend $10-15 on a Haynes manual. The manual has all kinds of wiring diagrams. To find out exactly how your Bronc is wired you will has to look at 2-3 different diagrams. Besides wiring the manual will tell you are kinds of goodies about your Bronc. I have one. It is generally considered a pos but better than no manual.

[89broncodove]

Check grounds. Continuity between connections.

[67BlackCat]

found an 80-86 haynes on ebay for 13 bucks... might as well eliminate 10 years of info not relevant to my truck...

[Steve83]

Actually, you'd have been better off with one that goes to '91 in case you ever want to upgrade the truck with newer parts. It wasn't until the edition with '96 on the cover that it started losing older content. But what you got is certainly better than nothing.

[miesk5]

yo BC,
Wiring Diagram in an 83 Duraspark II
(diagram 4)
Source: by Seabronc (Rosie, Fred W) at Ford Bronco Zone Forums http://broncozone.com/topic/13341-wiring/
See #3 for Ign Module diagram showing Circuit 11, DG/Y to Tach
and Circuit 60, BK/LG from Tach to Ign Module
etc.

and in case you pull a yard queen's tach;
Installation in an 83
Source: by Michael C (collinsperformance, The Money Monster) at http://www.fullsizebronco.com/registry/6364/52813

[67BlackCat]

Just an update to let Steve know about the wiring fault that can cause the tach to run backward in an 83...

the bad ground caused the tach to run high... I did not use an external tach, but I can earball the difference between idle (engine) and ~2k (tach reading)... tach needle was also bouncing while engine RPMs did not change... indicative of a bad contact

The backward running tach was actually caused by an incomplete installation of the HEI distributor... or incomplete removal of the stock ignition.. however you want to look at it. HEI dizzy went in using the 12V and tach wires from the stock coil (removed). The ignition module was left in even though all wires to dizzy were cut. power, ground and tach were still running to the ignition module... as soon as ign mod was completely removed from the system (and the described above ground issue was resolved) tach started working perfectly.