I've got a 1994 f-150 e4od and a 351W it started running a little rough and the speedo would bounce back and forth above 40 mph the check engine light comes on for about 10 mins then turns back off the only codes i got were 173 could anyone shed some light on this please.

 

I have a similar problem with my 94 f150 5.8 e40d 4x4 new edelbrock heads, headers, e-3 plugs, msd coil, ALL new sensors, ICM, AND 24 lb accel injectors, would these injectors cause a 173 code? motor runs perfectly, MUCH more power, just throws mil's oh and complete new fuel system-tanks, pumps, lines, fp reg.

 

The definition of a 173 OBD1 code
Oxygen sensor not switching – system is or was rich – Single, Right or Rear HO2S – Fuel control

Obviously using the heavier injectors will cause a 173 code as it will run rich unless you have a custom programmer on it to bring the a/f down. To the OP, the bouncing speedo has nothing to do with this. More than likely the speedo cable needs to be regreased. If you drive it long enough it will break.

 

Sounds like a Vehicle Speed Sensor in the differential, which will cause a bouncing speedo and driveability issues. The Motorcraft part should still be available.