I have an 1981 E-350 cutaway (motorhome) It had a 400 in it which was replaced with a 351m from a 78 bronco. Motor was a daily runner until it was put in the motorhome. Long story short it has run intermittantly. It sometimes will start and run a short distance then quits dead with no sputter - attempts to restart it sometimes work, sometimes don't (no spark) It can sit for hours or days then start again - no real rhyme or reason. It doesn't seem like a part overheating cause it will at times start and run for a day or two with multiple starts and stops. so far I have replaced the ignition switch, ignition module, ignition coil, pick up coil, pos battery cable. WHAT ELSE CAN I REPLACE?? OR CHECK?
Also could this problem be related to a low oil pressure shut off?
Should i go to a wreaker and get a used wiring harness?
Can this age of a vehicle be hooked up to a diagnostic computer to track down the problem?

 

This is what I would do. If you have a 12 volt test lite, connect it to the coil primary terminal that is fed power from the ignition switch. When the engine runs as required you should see power /test light on when ignition is on. If the engine quits what is the status of the test lite? If on, power is getting to the coil. If not , there is a break in the supply to the coil from the ign switch.

If you do have power to the coil, check for blinking test lite on the other side if the coil primary with engine cranking. This is controlled by the pick up coil in the distributor which could be opening upon getting warm/ hot.
Sometimes poor connections show up as intermittents and drive us nuts. If you don't find anything , let me know and I will offer some additional things to check.
Hank

 

Thanks for the replies. I am hoping to get to it this afternoon, of tomorrow aft. I will let you know how it works out. At this point I think it probably is a faulty wire of connector, but I will start from the start ond go from there...

 

Are you purchasing all these parts you're replacing? "It's gotta be gettin expensive!" On the other hand if you are using other used parts , I hope you know for sure they are good.

In checking your original post, I noticed you didn't mention anything about checking the ground system. If you did, then we can move on, but if you did not, THERE IS A GOOD POSSIBILITY THEREIN LIES YOUR PROBLEM. A loose ground cable or poor or intermittent ground connection for the ignition system is taking you for a ride. On changing engines , sometimes people overlook a needed ground wire or feel it isn't necessary and rely on other connections to do the job. Did you change the engine or did you have someone else do it? I'm sure you by this time know where I'm going with this.
Hang in there we, will find the answer to this problem. Please keep me posted,
Thanks, hanky

 

i did not change the motor - I had someone else do it. I did have someone check everything and they said it was ok... So how do I go about checking the ground? I finally have time to do a little poking around this thing.

 

ok, so i have tried 2 different pick up coils, 2 different ignition coils and a different cap - the seconds were all of the old running 400. The distributer seems to rotate freely in my hand when i turn it - is this normal? I made sure that the armature lined up with the pick-up coil. I have power to the ignition coil on the bat side and power out the other side, but it did not seem to blink when I cranked the motor. I traced the power on the other side of the coil (non bat side) and it went all the way to the ignition module when the key was turned on. I am thinking about going and picking up a wiring harness from a wrecker...not sure what else to do...

 

Don't go for the harness just yet ! Did you use your own distributor or did you use the one from the engine that is presently in the truck? The reason I am asking this is; You had to remove the distributor to change the pick-up coils, correct? On the bottom of the distributor is the gear that is driven by the camshaft. The best way to check this is; get the engine up to TDC for #1 cylinder. DON'T USE THE DISTRIBUTOR TO TELL YOU THE ROTOR IS POINTING TO #1 CYL. The reason for this is ; there is a roll pin that goes through the distributor gear and shaft. These roll pins sometimes shear and will drive you nuts. After you remove the distributor, see if you can push a small pin or nail through the roll pin. If you can't the pin has sheared and will require removing the broken pieces and lining up the gear with the hole in the shaft and installing a new roll pin. If I remember correctly the gear will line up only one way so you can't install it incorrectly. Let me know what you find! Thanks,

hanky

 

I'm still learning how to get around with this forum.

This is the way you can get under way.
Remove the #1 spark plug. It's the front plug on the passenger side. If you can turn the engine over by hand in its normal directation of rotation by grabbing the fan belt great. If not, have someone turn the key to start position , with the coil wire removed from the cap and contacting the engine so the spark is grounded and the engine can't start, When you hear the compression coming out of the spark plug hole you are getting near TDC. If you miss it a couple of times no big deal. The idea is to stop cranking just before the compression gets strong. You will be approaching TDC on the crankshaft pulley. Try to do the last amount of turning over by hand so you can stop it at TDC on the pulley If you pass it by a small amount you can back it up by hand and bring it so the pointer lines up with the mark on the pulley. Once you have it there, you can remove the distributor. You will notice that the rotor will turn as you remove the distributor. Take note of where the rotor is pointing if it's not at #1 the pin is sheared. If it is and you have now replaced the pin, replace the distributor so the rotor will be pointing right at #1 spark plug wire on the dist. cap It is important to do this right because if you aren't particular , the engine will start after you replace the plug and connect the coil wire ,but it won't have the power it should and you won't be able to set the timing correctly. After that and you set the timing you should be OK.
hanky

 

turns out is was the pick-up coil ground. the little screw that looks like it holds the wires in place as they come out of the distributor had broke.
Thanks for all of the help!!