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Tach problems

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Big6John

Tach problems

I recently did an emissions delete on my 1986 f150. I got rid of the computer and installed split exhaust manifolds, hei , and a 2 barrel carb. I taped in to a fused power that originally ran some emissions and wired the tach wire up. Now the factory tach only works when it’s cranking over. It worked all the time before I changed everything over. I also checked the wiring and it’s good all the way up to the dash. If anybody has any ideas or knows how to fix it please let me know.
Thanks

It a 1986 ford f150 with a 300 inline 6 4spd manual.

1986 f150 std cab long bed, 4.9L 300 inline 6, 4spd, 53k miles, 2 barrel carb, EFI split exhaust manifolds, HEI distributor, and much more to come!
Pack Rat a 1985 f150 inline 6 4spd, a/c,cruise, rusty parts truck

Gary Lewis

Re: Tach problems

Administrator

If you look at Pg 95 from the 1986 EVTM, below, you'll see the power for the tach comes from a R/Y wire that is Ckt 640. If you then look at Pg 16 you'll see that circuit comes from Fuse 18 which is hot in both Start & Run.

Since that fuse also supplied the EEC, which you've deleted, my guess is that you somehow changed the wiring so it isn't hot in Run. Or you only tapped into a circuit that is only hot in Start.

I'd go back and make sure you are connected to Fuse 18.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

85lebaront2

Re: Tach problems

Administrator

Gary the other issue might be the HEI. I believe on the GM ones there is a tach terminal, whether it will work a Ford tach is unknown.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

Big6John

Re: Tach problems

The tach was an A team ford 240/300 inline 6 hei. I’ll double check my wiring too.

Gary Lewis

Re: Tach problems

Administrator

In reply to this post by 85lebaront2

But if it works when cranking doesn’t that prove the tach works with the HEI? Or might it just be that it is getting hit with some voltage that causes it to wiggle, looking like it is working?

Gary, AKA "Gary fellow": Profile

Big6John

Re: Tach problems

Thats what I would think. When it’s cranking the tach will show the rpm just like it did before. Once it fires up the tach quits working. I can’t seem to figure it out. I’m kicking around the idea of throwing a Dakota digitals dash in there.

Gary Lewis

Re: Tach problems

Administrator

Check the R/Y wire where it goes into the instrument cluster. I’ll bet it’s voltage goes to zero when the key is in Run.

Gary, AKA "Gary fellow": Profile

viven44

Re: Tach problems

This post was updated on .

Was thinking the same... If that is the case i.e. R/Y not getting power when in Run, I would suspect the ignition switch has developed high resistance in some of its contacts.

Edit:

Check output of fuse 18
- If fuse 18 is good but is not outputting any voltage, then suspect ignition switch
- if you are getting voltage there, the ignition switch is OK... but if no voltage at cluster R/Y, then you have found the problem to be in-between in one of the connections

Vivek

- 'Big Blue 2WD' - 1984 F350 RWD 460/C6
- 1978 Bronco with the heart of a 1986 F250 Bullnose - under restoration
- "Bonded Bronco" -1985 Bronco - 302 4-speed fuel injected, Hibernating future project

Big6John

Re: Tach problems

In reply to this post by Gary Lewis

I’ll have to check it. I’ll let you guys know what I find.
Thanks

1986F150Six

Re: Tach problems

Administrator

Is this a missing component?

https://swperformanceparts.com/products/a-team-performance-hei-distributor-wire-harness-pigtail-dual-12v-power-amp-tach-connectors-170072?pr_prod_strat=e5_desc&pr_rec_id=a3a75a3e3&pr_rec_pid=8044005032237&pr_ref_pid=8044062048557&pr_seq=uniform

Big6John

Re: Tach problems

Nope, I got the correct connector.

Big6John

Re: Tach problems

One thing I forgot to mention is when I did get the tach to work for a bit when I did the swap it was about 500 rpm off. That was when I was testing it with jumper wires. I’ll still check the wires and fuse.

85lebaront2

Re: Tach problems

Administrator

Was it reading low or high?

Bill AKA "LOBO" Profile

mat in tn

Re: Tach problems

use the green wire terminal off the dist.

Big6John

Re: Tach problems

In reply to this post by 85lebaront2

500 rpm to high

Big6John

Re: Tach problems

In reply to this post by mat in tn

I hooked the green on the HEI to the green and black wire on the harness.

85lebaront2

Re: Tach problems

Administrator

In reply to this post by Big6John

An always 500 RPM or does it get worse as the engine is revved up? Does the tach have a cylinder selector switch, ie 4, 6, 8, 10 etc. If it does, is it set for 6 cyl.

Bill AKA "LOBO" Profile

Big6John

Re: Tach problems

It was a consistent 500 rpm high. All I know about the factory tachs is it depends on the wire it’s hooked up to. I traced the circuit on the back of the cluster and for 6 cylinder you wire up the green and black wire and for 8 cylinder you wire in the green and yellow wire as a second ground. I have it wired in to the green and black now.

mat in tn

Re: Tach problems

a set 500 high is odd. if it were 35 percent high across a scale then I would think it were reading an incorrect signal. but if you are getting 500 regardless of what rpm then it seems odd. I feel as if I had this on a truck many years ago. but what I did to solve it escapes me. I do know that I went through three tach's on that truck though. I prefer the factory tach but really there are better ones available.