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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

1994 460/ 7.5 bad spark & miss

 
  #1  
Old 05-17-2019, 10:31 PM
dungeonwarlock
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1994 460/ 7.5 bad spark & miss

Hello, I'm having trouble with a 460 and hoping it's something that might be recognizable to someone willing to share their knowledge.



#4 cylinder is not firing or at least not firing well. The truck misses and I've pulled the plug wires one at a time and there's no difference in idle when #4 is pulled.

Here's what I've done- the truck has been sitting for quite a while and had been run hot- water in oil. A salvage yard engine- which had also been sitting a long time was swapped into the truck. It's suppose to be a 70,000 mile engine that was running good. From the looks of it I think the hood was either left up or off. None the less- it fired up easy enough. New plugs, wires, cap and rotor button were installed.


Using a inductive spark tester number 4 might occasionally flash it- but mostly it stays dead. The others light it well. Plug and wire for #4 replaced- no change.

The cap was a new Accel but was changed back to the original Motorcraft for trouble shooting- the inductive spark tester lit up noticeably brighter on the 7 firing cylinders so the Motorcraft was left in place. No change in #4.

. Laying the plug on the engine block does show a spark but it's tiny and weak. Changed the coil- maybe improved the spark color but no change in 4/miss.

Compression checked and is good. Plug wire routing checked and separated in case of cross induction firing- no change. Firing order checked.

Originally it had a Cylinder 1 missfire code but it changed to #4 in the original trouble shooting attempts- last couple of codes checks came up with none at all.

My thoughts are to check or replace the inductive pick up in the distributor next- but I've never known of one failing for one cylinder???

Anyone ever have anything like this? Any help is appreciated- Thanks!
 
  #2  
Old 05-18-2019, 12:00 AM
88n94
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With all the testing you've done it would seem like the problem is in the distributor. Will the distributor from your old motor work or did you trade the engine in?
 
  #3  
Old 05-18-2019, 12:32 AM
dungeonwarlock
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Still have it- or at least I hope so. Left it a friends place way longer than I should. It's suppose to still be there though. I did start it before removing so I know it's not dead- that makes more sense to try than purchasing new parts so hopefully can try it over the weekend.
 
  #4  
Old 05-18-2019, 12:48 AM
88n94
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Make sure everything is compatible. For instance on the 351 they changed the material of the distributor drive gear to match the material of the camshaft drive gear at a certain time. What year is your replacement engine out of? I don't know anything specific about the 460. I will let someone else reply if you know what year your replacement engine came out of.
 
  #5  
Old 05-18-2019, 10:44 PM
dungeonwarlock
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My good news- Changed the distributor today and #4 is now firing as it should. Both distributors gave me a ton of resistance getting them out- but finally got both out without breaking anything. Before tackling this problem I would have never thought it possible for the ignition to lose a single cylinder!


I hope there are no issues with drive gear material- the one removed from the engine currently in the truck (95 model) looked to be steel. The one from the original engine (94) which is now installed in the truck looked more like bronze. In the past I've replaced steel with bronze as supposedly a better gear- hope this works the same way.

My bad news- though it's greatly improved I still have issues to tackle. Anyone ever have injectors that have sat for a long time to cause a problem?
 
 


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