can you believe it??? I've got a 79 351W in my '55 F-100. all wiring and powertrain is 79 12V. Pull out of the driveway; I have a slight miss on mild acceleration. It straightens out when i put my foot in it. Engine at operating temp. (good and hot) approaching a stop sign, stop at sign, idle gets increasingly rough, motor dies, hard to re-start till allowed to cool 3-5 minutes, then re-fires and runs ok, except for that darn miss under mild accellaration. Runs fine at [font=verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif][font=verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif]cruise[/font][/font] speed. I changed the module, (new) got a new coil, got a new re-built distributor (electronic). BTW, ran back to look at tailpipes when idling rough at stop sign, no black smoke. Ran to hood and pulled breather, squirts plenty of fuel thru venturis. Changed carb. From [font=verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif][font=verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif]Edelbrock[/font][/font] 1406 Performer to Carter AFB Competition, performed better, same problems. Next I'm going to check the power supply to the module. Iwas wondering if there is supposed to be a resistor, or resistor wire somewhere in that line?? I don't think so. BTW, plugs look good, almost too tan-white, like too lean. no comp test yet. I pulled the [font=verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif][font=verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif]ignition [/font][font=verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif]switch[/font][/font], looking for loose conn. or something, looked fine. i checked for body-chassis-engine ground. all good. I just feel like it's electrical, not fuel. OPINIONS??

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Sorry bout that fellas. Kindly bleep over the blue text.. Copying and pasting from the engines forum did not produce the desired results... Please note the part about the resistor wire and/or resistor. I asked for and got a coil for a 79 351W with the lugs and not threaded posts as i have a 2 wire harness with the indexed U-shaped factory connector that snaps onto the coil. i'm the type that obssesses ovar a problem like this, so plz help me regain my sanity..Acleaned up version of this post is in the SB engine forum under "another flippin 351W question". Thanks, Jim

 

Oh, 1 more thing. It was suggested to me that the voltage on the red wire going to the coil should be 8.5-9V. A book I consulted said "battery voltage". BTW the last part of that pasted post is sposed to say that I pulled the switch assembly out and checked it.. (it was fine)

 

If you are running the 1979 Ford duraspark II ignition, then yes you are supposed to have a resistor inline with the coil power wire. The resistor is made into the original harness you have laying there(special resistance wire) and should read 1.05 to 1.15 ohms from the keyswitch connector to the coil + connector. The resistor drops the voltage to 8.5-9v when the engine is running. This keeps the module and the coil cooler.

 

Dave, is there an ignition system in 79's other than the DurasparkII? and how can I tell if thats what I have (recognize resistor wire) Thanx very much

 

No. If you have the large aluminum module that mounted on the fenderwell, and you have a vacuum line going to the distributor, then you have a duraspark II system. Just to make sure, take the dist cap off, and underneath the rotor there should be a little star wheel instead of points.

Of course someone could have put something else on the vehicle you got the parts from.

You said you have fuel, but when I got my 53 f100 on the road, I had the same problems. It would drive fine down the road, but once I got in town it would run rough and then quit and would not restart till it cooled off. I had a clear fuel filter and could see I did not have much fuel in it. I also noticed when it was starting to quit, I would see large bubbles in the fuel filter.

What fixed my problem was moving the fuel line. I was using the original six cylinder fuel line that runs down the driver's side inside frame rail. When I put duals and headers on the v8, I was 3 to 4 inches away from the line, but still the radiated heat made it vapor lock.

I made a new line and ran it on the outside of the frame rail, sneaking it under the pitman arm(I had the original steering box setup). I then ran it over the top of the rail to the fuel pump(I had a 351c). Problem went away after that.

 

Thanks again Dave. V-lock possible, but truck misses when cold. Poor idle when hot. If I can't find an elec. problem, will re-route and go with electric fuel pump. Again, how do I fecognize resistor wire, in case it was changed to non-res at some point?

 

The wire is red/green I believe. It should be running to the horseshoe connector for the coil in the harness. The other end goes to the ignition switch plug. It may be red/green and then turn to pink over there.

If you find both of these ends, take an ohmmeter and measure from one end to the other and it should be 1.05 to 1.15 ohms.

If you are curious if you have a resistor on the truck now, measure the voltage on the coil + when it's running and it should be something less than 12 volts.

I can assure you, if you have a duraspark II system, it had a resistor in it from the factory, and requires a resistor to run correctly. If you don't have a resistor, feel the coil after you run the engine awhile, and it will probably be pretty warm.

 

Thanx, Dave. I'll let you know.

 

Dave, pulled her out yesterday after checking the coil voltage as specified. Voltage=8.5V Pulled her out of the garage and down the road we went. Moderate throttle, no miss. Showered down on it. Smooooth. Rode by a buddys house 2 miles away, and let her idle for 5 minutes. Jumped in, took off slowly, missing badly... missed all the way home, where it died in the driveway. No black smoke out the pipes. Squirting fuel out the squirters. Failed to check the voltage again b4 she passed away.. I am going to pull the wiring out from the coil and distributor to the firewall tommorrow, and look for damaged or broken wire. IT MUST BE ELCTRICAL!!!! AAAARRRRRRGGGGGGHHHHHH!!!!!!!!!

 

I am a big fan of MSD ignitions sence I swaped my DS2 in my 79 to a 6 offroad. Also look at the coil, they can get hot and not charge properly leading to a random miss. While your at it, check your grounds (alt to block and batt to block).

 

Dave, another shot please?

 

Get it in the state where it will not start. Make sure again you do not have spark. After verifying that, take your meter and put the positive lead on the negative wire of the coil, and put the negative lead of the meter on a good ground on the engine block.

Get someone to crank the engine. If you have a meter with a needle, you should see the meter jump back and forth. If you have a testlight, you can use it the same way, and you should see the light flicker. If you have a digital meter, it may be hard to see if the voltage is going up and down. If you want to compare, do the same thing when it will run, and you will see the voltage going up and down on the negative coil lead(take the high voltage wire off the coil so it will not start-the voltage flickers too fast when it's running and you would have to have a scope to read it).

If the voltage is going up and down on the coil, that means the ignition box is turning the coil on and off, and you must have a problem with the coil. If you are not getting anything on the negative of the coil, move the meter lead to the + of the coil just to verify again you have 12 volts there.