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

Rebuild, now a miss. GAH!

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  #1  
Old 09-05-2020 | 12:51 PM
kevinv10's Avatar
kevinv10
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Rebuild, now a miss. GAH!

1994 F-250. 460, Auto.
Motor has been completly rebuilt. .030 over, new pistons, rings, bearing oil pump, water pump, fuel pressure regulator, etc. Complete banks exhaust, headers to tailpipe.
Air pump was removed. All vacuum lines except for line to thermactor valve, still in place, and that one capped off at the solenoid. All vacuum lines good.
Timing is dead on, have checked multiple times. Firing order is correct, checked that several times as well.
Will not idle, even after warmed up. Runs rough and seems to have a stumble. I am leaning towards a vacuum leak somewhere. But, can't find any bad lines, or missing caps.
Any ideas would be extremely appreciated!
 
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Old 09-05-2020 | 01:16 PM
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R&RFord
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From: Candy Mountain
I assume you put in new spark plugs.. did you replace the ignition coil. I could barely get a new engine to run several months ago on account of a brand new Motorcraft coil being bad out of the box. A vacuum leak will cause a stumble but it would have to be pretty bad to cause the engine to very poorly all the time. You can disconnect everything vacuum related except for the MAP sensor and FPR as a way to eliminate most of the accessory vacuum system. Checking fuel pressure wouldn't be a bad idea if you haven't already.

I would also look at the EGR. If it is open even a little at idle it will cause your problems.
 
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Old 09-05-2020 | 01:20 PM
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kevinv10
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Originally Posted by R&RFord
I assume you put in new spark plugs.. did you replace the ignition coil. I could barely get a new engine to run several months ago on account of a brand new Motorcraft coil being bad out of the box. A vacuum leak will cause a stumble but it would have to be pretty bad to cause the engine to very poorly all the time. You can disconnect everything vacuum related except for the MAP sensor and FPR as a way to eliminate most of the accessory vacuum system. Checking fuel pressure wouldn't be a bad idea if you haven't already.

I would also look at the EGR. If it is open even a little at idle it will cause your problems.
Yes on new plugs. Also new egr, and pipe to exhaust. Haven't checked fuel pressure as it was fine prior to rebuild. Same with coil.
 
  #4  
Old 09-05-2020 | 06:15 PM
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torq'ta 5 8
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From: N.W. Alabama
if you cleaned IAC, you can test it just to be safe. and your new EGR, may not be the issue, but the solenoid could be letting enough vacuum by (4in.hg) is half open, to cause issues.
How to Clean and Test your IAC - Ford Bronco Forum

Ford Fuel Injection » EGR Valve Position sensor (EVP)



 
  #5  
Old 09-05-2020 | 06:34 PM
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kevinv10
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Good info, and thank you. I have done a crude vacuum test on my egr, it seems fine. Will look into my IAC. Frustrating part is apart from exhaust leak, motor ran fine prior to rebuild.
 
  #6  
Old 09-05-2020 | 06:50 PM
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torq'ta 5 8
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exhaust leak in front of or behind O2 sensor, if in front aint helping, O2 will think lean, and PCM will add more gas, could be PITA, to remove all vacuum lines and plug, except MAP, and see if it goes away, then add one line at a time until it stumbles or you have them all back on.
 
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Old 09-05-2020 | 06:57 PM
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kevinv10
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Originally Posted by torq'ta 5 8
exhaust leak in front of or behind O2 sensor, if in front aint helping, O2 will think lean, and PCM will add more gas, could be PITA, to remove all vacuum lines and plug, except MAP, and see if it goes away, then add one line at a time until it stumbles or you have them all back on.
I'll try that....tomorrow. To frustrated right now. I did check all the vacuum lines, ones at solenoid to intake and reservoir, pcv, brake booster, charcoal canisters in frame. All were good, but, never hurts to try. Thanks.
 
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