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1996 460 7.5L misfire

 
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Old 02-16-2016, 11:25 AM
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1996 460 7.5L misfire

Truck has misfire while driving, idle is decent. Truck jerks and feels like it died for about a half second.
Had an experienced mechanic look at it with me. checked for codes, none. Checked map or maf sensor, whatever that is, said it was fine. Checked two sensors on top of engine block under air intake, said they look fine. Checked timing with his gun, said it was good. Checked for shorting wires with water in the dark, checked for vacuum leak with starter fluid sprayed on lines.

I replaced: Plugs, wires, cap/ rotor button, ign. Coil, (all with MSD and ford racing)
Fuel injectors, 30lb/hr ford racing. Fuel filter. Iac sensor.
I'm considering hollowing out the cat converter, just cause it couldn't hurt.
Truck runs like a beast with ample power...... in between misfires. 😐Lol

My father said his '88 460 did a similar thing (back in the 90's) and it ended up being the "oil pressure cutoff switch".
I'd like to know where this switch is, or more importantly where it's wires are? So I can bypass it.
 
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Old 02-16-2016, 12:36 PM
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Those injectors are too large for a 460 with stock programming. That might be part of your issue there.
 
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Old 02-16-2016, 03:33 PM
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There is no oil pressure cutoff switch on a fuel injected 7.5L engine.
 
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Old 02-16-2016, 04:39 PM
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Originally Posted by rla2005 View Post
There is no oil pressure cutoff switch on a fuel injected 7.5L engine.
Oh, that makes sense because my dads '88 was carborated.
Any other ideas then? If it were your truck what would you look at next?

It was missing long before I replaced the injectors, they were the last thing I tried. The 30lb injectors seem fine to me, doesn't seem too rich. Idles great once warm.
Cut the air horn tubes out of the intake duct and have a Banks air box.
 
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Old 02-16-2016, 05:36 PM
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Never trust a mechanic who does not work on these every day. Anytime someone states no codes, that's a red flag. At the very least you should get the System Pass Code 111 for KOEO, CM and KOER if everything passed.

How did the "mechanic" determine the timing was good? Did they remove the SPOUT plug to verify the base timing is 10 BTDC?

Make sure the plug wires are routed so there is no crossfire. Cylinders 4&2 and 7&8 need to be moved away from each other as much as possible since they fire in consecutive order. Even good quality wires are susceptible.

The spray method to find vacuum leaks on a fuel injected engine is meaningless IMHO. Test each vacuum circuit with a handheld vacuum pump/gauge. Too many feet of brittle plastic lines and vacuum reservoirs to mask a vacuum leak(s).

Ensure the connector to the coil is making good contact. A frequent cause of issues.
 
 
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