Engine swap, rough idle
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Engine swap, rough idle
1984 F150 4.9l. I posted a while ago about my truck overheating... ended up with a used motor out of an 81, I swapped the carb and the distributor from the 84 and got it fired up. The engine is making a knocking sound and idling very rough... I heard this motor run before I bought it and it ran fine. Is it possible that the distributor is 180 out? I also read something about newer carbs being no good for older engines... any ideas?
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From: Orlando area
Maybe you got some plug wires mixed up.
If that's not it, I would do a thorough inspection of all the wires, hoses, and connections, and if nothing turns up then do a compression check next.
Is the oil pressure good?
If distributor was 180 out, it would not start.
If that's not it, I would do a thorough inspection of all the wires, hoses, and connections, and if nothing turns up then do a compression check next.
Is the oil pressure good?
If distributor was 180 out, it would not start.
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From: Angier, NC
Mike listed some good information, I would check the firing order as a plug firing when it is not to can cause a knock.
Where did you hear this? Could they have been talking of the computer controlled (newer) carbs on a non-computer controlled motor?
Dave ----
I also read something about newer carbs being no good for older engines... any ideas?
Dave ----
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the thread said something about a "feedback " carb... this was an 86 carb on an 81 motor. The oil pressure is good, I'll double check Everything tomorrow. It sounds like it's knocking in the bottom end, I would assume bearings but it ran smooth when I bought it.
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From: Angier, NC
86 carb on a 81 motor is not the way to go.
Now a 81 carb on a 86 motor is ok.
If a plug is firing when it should not, can and I hope is the cause of the knock down low.
Also with the oil PSI good it is not a bad bearing as oil PSI goes low when that happens.
Dave ----
Now a 81 carb on a 86 motor is ok.
If a plug is firing when it should not, can and I hope is the cause of the knock down low.
Also with the oil PSI good it is not a bad bearing as oil PSI goes low when that happens.
Dave ----
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If the oil and filter was not changed, pull the filter and cut it open. Look for any metal in the filter pleats.
Did you buy this engine recently (from a stranger)? How long did it run (without the noise) before you did the swap. Long enough to know for sure the engine is good?
Did you buy this engine recently (from a stranger)? How long did it run (without the noise) before you did the swap. Long enough to know for sure the engine is good?
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From: Angier, NC
If the oil and filter was not changed, pull the filter and cut it open. Look for any metal in the filter pleats.
Did you buy this engine recently (from a stranger)? How long did it run (without the noise) before you did the swap. Long enough to know for sure the engine is good?
Did you buy this engine recently (from a stranger)? How long did it run (without the noise) before you did the swap. Long enough to know for sure the engine is good?
When the plugs are out do a compression test.
The other thing you can try is when running and making the noise to pull each plug wire 1 at a time and see if the noise stops.
If so that tells you what cly is making the noise and I think would show a bad piston pin as they make noise under load.
Also because if it was a bad rod bearing you would have the noise all the time and the oil PSI would be low.
Good luck
Dave ----
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1984 F150 4.9l. I posted a while ago about my truck overheating... ended up with a used motor out of an 81, I swapped the carb and the distributor from the 84 and got it fired up. The engine is making a knocking sound and idling very rough... I heard this motor run before I bought it and it ran fine. Is it possible that the distributor is 180 out? I also read something about newer carbs being no good for older engines... any ideas?
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The motor was purchased from a stranger but I heard it run for 10 minutes or so, in the truck it's a rattly mess immediately after starting. I'm sure there are a few vacuum leaks, not 100% on where everything goes but all the open lines are plugged... I'm going to do a compression test cuz the plugs didn't change anything. The engine is shaking violently while running and more throttle doesn't change anything.
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so I'm thoroughly pissed off now, ZERO compression in #6... you can't trust anybody nowadays. I may be crazy but does anybody think it's possible that the piston is stuck in the cylinder and the rod is just beating around in the case, causing the knocking?
I'm just about ready to give up.
I'm just about ready to give up.
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that's my next move, I had to walk away for now. I'm going to investigate more tomorrow.
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From: Angier, NC
Hope you fine a push rod out of place and once back it runs great.
I don't think the piston is not moving but could test that.
With that plug out take a stick and stick it in the plug hole. Turn the motor over by HAND and the stick should move up & down.
You might give this a try, with all the plugs out by hand rock the motor back n forth to see if you can feel & hear that knock and where it may be coming from.
You know the knock could be an exh leak. Sometimes it can sound just like a bearing knock.
This is a 300 six right? it could be when pulled it cracked the intake/exh manifold to cause a vacuum leak & exh leak to sound like a bearing knock.
Little carb cleaner between head & manifold and where the 2 bolt together under the carb.
Dave ----
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Sometimes that is the best, just walk away for a bit.
Hope you fine a push rod out of place and once back it runs great.
I don't think the piston is not moving but could test that.
With that plug out take a stick and stick it in the plug hole. Turn the motor over by HAND and the stick should move up & down.
You might give this a try, with all the plugs out by hand rock the motor back n forth to see if you can feel & hear that knock and where it may be coming from.
You know the knock could be an exh leak. Sometimes it can sound just like a bearing knock.
This is a 300 six right? it could be when pulled it cracked the intake/exh manifold to cause a vacuum leak & exh leak to sound like a bearing knock.
Little carb cleaner between head & manifold and where the 2 bolt together under the carb.
Dave ----
Hope you fine a push rod out of place and once back it runs great.
I don't think the piston is not moving but could test that.
With that plug out take a stick and stick it in the plug hole. Turn the motor over by HAND and the stick should move up & down.
You might give this a try, with all the plugs out by hand rock the motor back n forth to see if you can feel & hear that knock and where it may be coming from.
You know the knock could be an exh leak. Sometimes it can sound just like a bearing knock.
This is a 300 six right? it could be when pulled it cracked the intake/exh manifold to cause a vacuum leak & exh leak to sound like a bearing knock.
Little carb cleaner between head & manifold and where the 2 bolt together under the carb.
Dave ----