Rough Runner
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Rough Runner
I have just bought a 1987 Ford F150 300 I6 Manual 4 on the floor
When I start it up, at idle it will jump around in RPMs going from around 1200 to 600 and back and forth like that. Another thing that just started happening is on long trips it will act as though it running out of gas. Even though it is full.I have changed the plugs and wires but to no prevail. Someone told me to check the PCV valve, could that be it. Another question, when the gas guage jumps around, that is the Sending unit starting to act up right?
When I start it up, at idle it will jump around in RPMs going from around 1200 to 600 and back and forth like that. Another thing that just started happening is on long trips it will act as though it running out of gas. Even though it is full.I have changed the plugs and wires but to no prevail. Someone told me to check the PCV valve, could that be it. Another question, when the gas guage jumps around, that is the Sending unit starting to act up right?
Last edited by Nyoonch; Apr 11, 2007 at 04:18 PM.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
How many miles are on it? Has it been sitting?
First thing I would do is a complete tuneup. You said you changed the plugs and wires, but didn't say you changed the cap and rotor. If you haven't, do that. Then pull the codes - http://broncodata.com/tech/codes.htm.
It could be the sending unit, or it could be a loose ground.
First thing I would do is a complete tuneup. You said you changed the plugs and wires, but didn't say you changed the cap and rotor. If you haven't, do that. Then pull the codes - http://broncodata.com/tech/codes.htm.
It could be the sending unit, or it could be a loose ground.
Senior User
Joined: Mar 2007
Posts: 224
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From: San Jose , ca
In addition to everything else, the distributor bushing (upper) may be worn and is causing the tach to hunt, since the dwell is also changing due to work bushing, if it is a real bad worn part, the dwell may be allowing the points to stay closed. Then "ah ha" - no spark for an instant.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
There are no points in his distributor. 
I am not all that familiar with points style ignition systems, so I don't know much about bushings and dwell, but I would imagine that the tach is hunting because the engine itself is. Idle surging is very common in EFI trucks and it can be causes by a lot of things.
I am not all that familiar with points style ignition systems, so I don't know much about bushings and dwell, but I would imagine that the tach is hunting because the engine itself is. Idle surging is very common in EFI trucks and it can be causes by a lot of things.