Ford 351 has me stumped...

[Bubba1235]

Newly rebuilt long block.

New FlameThrower distributor and Coil.

New plug wires and spark plugs.

New carb. all dialed in. (Fuel flow is good)

New starter.

New raw water pump.

New intake and exhaust manifolds. (No leaks.)


Problem: Engine starts at the touch of the key and idles great (650 RPM) but as soon as I come off idle I have a miss. At 2000 RPM it misses so bad engine looks like its doing the shimy dance.

Tested each plug, all firing as they should. Put back in engine and confirmed each is firing with a timing light.

Double, Triple and Quadruple checked firing order and plug wires, they are right.

Timing is at 10 degrees BTDC and it advances with RPM as it should.

Pulled valve covers off and re-torqued rocker arms to spec. (They were correct but did it anyhow.) Cranked engine and checked that all valves are opening/closing and measured travel, all the same and in spec.

Did a compression (155 to 165) and leak down test. Nothing wrong there.

So it's got fuel, it has ignition and valves are working as they should. What in the heck can cause this miss? Color me baffled...

 

[slydog75]

Re: Ford 351 has me stumped...

Certainly sounds like a timing advance issue to me. You said that the timing is advancing as it should but have you actually double checked what it should be at higher RPMs and verified it for accuracy?

 

[mkast]

Re: Ford 351 has me stumped...

At 2000 RPM it misses so bad engine looks like its doing the shimy dance.

My thinking takes me to, if you pull a plug wire off, rev the engine to 2,000 RPM, the engine won't shimmy, it just misses on that one cylinder.
I guess I'd start by shorting out each cylinder to isolate the cylinder or cylinders.

 

[JustJason]

Re: Ford 351 has me stumped...

Does the miss go away after 2k rpm?

Just a couple of thoughts....

Incorrect firing order... did ya happen to cross a pair of wires?
Is the miss acc pump related.... to little or to much fuel?

I guess the only way your going to figure it out is to float it and see if this baby makes power or not. GL and keep us posted.

 

[Bt Doctur]

Re: Ford 351 has me stumped...

And the firing order your using?

 

[fuzzybob]

Re: Ford 351 has me stumped...

Have you tried pulling the tack wire off the coil?

 

[fuzzybob]

Re: Ford 351 has me stumped...

Would it be possible to get cross firing between your new wires.... numbers 6-5 or 5-4?

 

[searay3]

Re: Ford 351 has me stumped...

Sounds like you have the electrical well checked. My bet is it's in the valvetrain. Bad lifter or broken or weak valve spring. Have seen bad assemblies straight of the crate....my 2 cents..

 

[MikDee]

Re: Ford 351 has me stumped...

I bet you got a bad, or damaged spark plug.

 

[Maclin]

Re: Ford 351 has me stumped...

Cross fire between plugs was my first thought also. Didn't the 351's have a tech bulletin on that? It had to do with a particular firing order being very susceptible to cross firing between a certain pair of plugs.

 

[sjdoo2]

Re: Ford 351 has me stumped...

More of a truck mechanic than a marine, but I would double check vacuum lines.

 

[J. Mark]

Re: Ford 351 has me stumped...

a Ford 302 cam will fit in a 351 motor. If you have the valve covers off and hand turn the engine over, you should be able to tell which valves are open and closed and whether your engine has a 302 cam. If so just shift to a 302 firing order (or just shift it and try for ****s and giggles)

How is your oil pressure?

Did you change the oil and filter after the cam break in (which is only about 20 minutes? Assembly lube can clog an oil filter and cause oil to bypass the filter, a chunk of loose grime that the hot tank missed in the oil passages can damage a pump or bearing in a heartbeat.

Watch the pressure and if isn't perfect, figure out the problem before you crank the engine excessively.

Check the electric choke set up and spray the carb base to check for vacuum leaks.

And here is weird and unusual check to perform Are the heads grounded to the block? With some head gaskets and sealers and such it is possible that the head is not acting as a good ground for the plugs. In this case a ground wire from the head to the block will cure problems.

Good luck

 

[wejaz28]

Re: Ford 351 has me stumped...

In another direction. Wrong Harmonic balancer? Got the wrong one once, about vibrated engine apart. Kinda felt like a miss at first.

 

[mkast]

Re: Ford 351 has me stumped...

And here is weird and unusual check to perform Are the heads grounded to the block? With some head gaskets and sealers and such it is possible that the head is not acting as a good ground for the plugs. In this case a ground wire from the head to the block will cure problems.

I never thought of composite head bolts.