Ill ask this here since i didnt want to hijack the compression post.
Have a 1994 f150 with 4x4 and 5.8 automatic. I had a miss not real bad but noticeable so i changed the plugs, new ford wires and cap and rotor an the thing runs 100% better and just once in a while sitting stopped i have a tiny miss. is there some other source for a miss other than above mentioned that im not seeing?? It is not a regular or steady miss.
Thanks

 

I would check fuel pressure which should be 30-45 psi. Check for vacuum leaks. Replace any faulty vacuum lines.A lean miss might be possible.

 

Thanks raski: one question the fuel pumps on the 1994 f 150 has two tanks are there two pumps? have to check both? thats something i never looked at I just assume they use in tank pumps like everyone. I have checked for vac leaks til i was blue in the face and the vac gauge an all tests say not one.
Thanks for any info.

 

Each tank has a low pressure pump in them and there is a high pressure pump common to both tanks along the left side frame rail, about under where the door is.
Hopefully your vacuum gauge is steady between 18-22 inches.

 

if i remember correctly the vac gauge is steady at 15 we are at about 4700 ft elevation i understand that is good???
Thanks

 

Do you have a timing light to use ?
We are not looking to use to check timing .

 

I dont think i do hanky, I think my kid took off with that years ago. Do i need to find one?

 

No, not really. I was going to suggest you check each individual plug wire with the light and if it was something aside from the plug, you would be able to see it.

 

Did you check fuel pressure as suggested in # 2?Low pressure can cause a lean miss.If you have a tach. a miss will cause a fluctuating engine idle. I even seen a few engine mounts which were not in very good condition caused the engine to move excessively making it look like an engine idle issue. If everything checks, a compression test of all cylinders may be needed. If the highest and lowest cylinders are more than 20% apart, you will never get an engine to run perfectly smooth.

 

yes raski i did comp test ran 136 to 131 over 8 cyl i was quite happy. Did however eliminate the miss. Seems changing everything and running it down the road a few miles it has disappeared an i dont miss it a bit. pun intended. Thanks everyone for the help evidently it was a flakey wire on a plug.