[kolo]

I am trouble shooting no tach rpm indication, The rpm sensor may be the culprit. Also when you place the truck in D, you really have to accelerate to get it to move, at first I thought it was a tranny issue, or slipping, Then I started to read about the tranny may be in safe or limp mode. I don't know if the light is flashing as the end or the shifter knob is broken. This truck is one I picked up from auction and had been abused but seems to run well. Does the the need to accelerate quite a bit have anything to do with the rpm sensor and or no tach operation. I am going to try another sensor as I saw one at the salvage yard on a late 80's diesel. My truck is a 93 F450 with what I believe is and E4OD. Thanks for any help, cdnsarguy already provided the specs for testing, just wondering about the tranny issue? Thanks

 

[cdnsarguy]

A dead tach sender should/would send the automatic (E4OD) trans into a "failure management mode" (limp mode) with harsh engagements and firm shift feel and an abnormal shift schedule. It has no effect on a manual trans only the Tach readings.

Check the wires where they exit the big nut on the oil filler housing , known to short out due to bare wire.....

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.

DO NOT drive it in limp mode or you will burn up the trans............

 

[kolo]

Thanks for telling me about driving in limp mode, the truck is ungegistered at this time but I take it up and down the road to keep it freed up and test it now and then. How can I tell if it is in limp mode, as I said my shifter end is broke off , is there another test. also would the limp mode also cause it to start off like the brake is on. You have to lay into the throttle some to get it to move in drive>?but it then seems to go alright.

 

[cdnsarguy]

Your starting in second gear...... don't be driving it without fixing it or a new trans is in your worst nightmares.......

 

[kolo]

Ok I tested the rpm sensor and got 2,635 ohm, within spec. I have also determined that a maxi fuse # 22 a 20 amp in the underhood power dist. box blows anytime the key is turned energizing the system. Could this have anything to do with the tach not working, What does #22 control , I don't have a schematic or service manual. Would like to get manual , any recomendations?