Big6John Posted March 20 Share Posted March 20 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. Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 20 Share Posted March 20 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. Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 20 Share Posted March 20 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 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. Link to comment Share on other sites More sharing options...
Big6John Posted March 20 Author Share Posted March 20 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. The tach was an A team ford 240/300 inline 6 hei. I’ll double check my wiring too. Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 20 Share Posted March 20 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. 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? Link to comment Share on other sites More sharing options...
Big6John Posted March 20 Author Share Posted March 20 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? 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. Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 20 Share Posted March 20 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. 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. Link to comment Share on other sites More sharing options...
viven44 Posted March 20 Share Posted March 20 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. 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 Link to comment Share on other sites More sharing options...
Big6John Posted March 20 Author Share Posted March 20 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. I’ll have to check it. I’ll let you guys know what I find. Thanks Link to comment Share on other sites More sharing options...
1986F150Six Posted March 20 Share Posted March 20 I’ll have to check it. I’ll let you guys know what I find. Thanks 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 Link to comment Share on other sites More sharing options...
Recommended Posts