Cold starting trouble
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Senior User
Joined: Jun 2007
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From: Milwaukee, WI
Cold starting trouble
Heres a head scratcher! I have a 85 F150, 300/6. I have replaced: Cap/rotor, plugs, wires, distrib mounted ECC, distrib stator asseb/pick-up coil. Checked and reset timing. The truck starts and runs fine when warm. Even after sitting long enough to have the choke close. However, after sitting over night, I have to crank the engine for a long time to get it to start. I have had the carb rebuilt and the choke works fine. I can smell gas so I dont think it is lack of gas. I have found lack of spark several times on the number one cylinder during these episodes. Sometimes even having only one spark show then no more, or one spark at the coil then nothing for the duration of the cranking. I am out of ideas other than replacing the computer but I have heard that has nothing to do with starting only running and emisions control.
Any thoughts or ideas are welcome!!
Thanks, DEAN
Any thoughts or ideas are welcome!!
Thanks, DEAN
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Joined: Jan 2001
Posts: 56,999
Likes: 2,746
From: Virginia
Hook a testlight or voltmeter to the coil + when it won't start. You should have voltage there during starting and when the key is in the run position. If you don't, then wiggle the key back and forth and see if you can get voltage on the coil +.
Thread Starter
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Senior User
Joined: Jun 2007
Posts: 140
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From: Milwaukee, WI
Yeah, I tried all that already. I ran all the diagnostic tests that the repair manuel outlined and every thing checks out okay. I have the proper amount of voltage at both the coil and the distributer in both the start and run key position. My next thought might be an intermitent coil failure because when checking the coil spark, I only see one brief spark at the moment the key is turned then gone until the next time the key is turned. Very weird! The coil does pass the primary and secondary ohm checks. Again this only happens after the truck has sat overnight. The only way I have found the truck to start in the morning is frequent short bursts on the key rather than a long crank which has only shown to kill the battery!
Thanks for your ideas and keep them coming, I am desperate for a solution!
Thanks for your ideas and keep them coming, I am desperate for a solution!
Moderator
Joined: Jan 2001
Posts: 56,999
Likes: 2,746
From: Virginia
Hook a testlight or voltmeter up to the neg of the coil.
Hook the + testlead or testlight to the negative of the coil, and hook the negative lead of the testlight or voltmeter to the engine block. Have someone crank the engine while you watch the testlight or voltmeter. When the engine is cranking, the testlight should blink, or the voltmeter needle should jump up and down.
Hook the + testlead or testlight to the negative of the coil, and hook the negative lead of the testlight or voltmeter to the engine block. Have someone crank the engine while you watch the testlight or voltmeter. When the engine is cranking, the testlight should blink, or the voltmeter needle should jump up and down.
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Senior User
Joined: Jun 2007
Posts: 140
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From: Milwaukee, WI
I have run that test also. I get some mixed results. Sometimes the test light blinks and sometimes the light stays on without blinking. I belive a "pass" result for this test would be the light blinking. The shop manuel is sort of vague on possible causes of the test light staying on other than: "clean and tighten electical conections" which I have already done.
Thanks for your replys and thoughts!
Thanks for your replys and thoughts!
Moderator
Joined: Jan 2001
Posts: 56,999
Likes: 2,746
From: Virginia
The blinking is the module turning the coil on and off which makes the spark. If it's not blinking, then the module is not turning the coil on and off.
You have found the problem area, you just need to find the exact problem. I would take a hairdryer and heat one area at a time(module, connectors, etc.) and see if it makes a difference.
You have found the problem area, you just need to find the exact problem. I would take a hairdryer and heat one area at a time(module, connectors, etc.) and see if it makes a difference.
