I've got an 89 f150 300 fuel injected. I've replaced the plugs, rotor, cap, and fuel filter and it still misses during acceleration. Any suggestions as to what I should try next?

 

There is another link a bit further down the list on the 300-6 miss problem. You will however find that there is no answer to this problem there either. We all seem to have the same problem with the miss, although, some owners seem to experience a more pronounced effect than others. I recently called the Ford garage where I purchased my truck and inquired about the problem. He told me that they have not experienced any trucks doing this....... right.... this must be all of our imaginations. Of a truth, I believe they know full well that the trucks are doing this, but, have no idea what to do for them. As I stated in my other posting, I believe the problem is the software of the EEC. Others have changed everything on their engine except the color, only to have the same results. I have never been able to poll a error code either KOEO or KOER. (By the way.... do clean the idle air bypass valve, they carbon up quickly) I am trying to get in touch with an aftermarket firmware supplier to see what they have to offer in this regard. When (if) I hear back from them I will let you know. My investigation was sidelined when the slave cylinder on my clutch blew out, requiring me to remove the xfer case, transmission, etc to replace, however, now that it is behind me I intend to pick up working on this again. If you get anything, please post it.

Fordrulz

 

Let your engine warm up to operating temperature and using a can of starting fluid spray all around the intake system and all vacuum hoses. If the engine speeds up at an idle while you spray then there is a vacuum leak somewhere. This problem will give symtoms like you're describing.
This is the was I found the problem with my engine. I found that the intake manifold where it bolt to the head is a bit warped and gets worse when the engine warms up.

 

Well, it is worth a shot. I would dip the engine in maple syrup if I thought it would point me to a cure. It is rainy here today, I had a hard time with it running, more than usual amount of misses. I've been through the ignition ritual already, and it is not that. I will try this and post the results.

Fordrulz

 

 

Look at the timing advance, mine is doing the same thing only quite a bit worse. I think its related to the timing advance, on an 89 you have the hall effect advance system which is all electronic, I would also test the TPS sensor and the ignition mudule on the side of the distributor. Might even want to test the coil.