300 6 Missing
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300 6 Missing
I have a 1990 150 with a 4.9 5 speed. i have had this truck for about two years and i have always noticed that whenever the motor gets wet it will start missing. any other time it will run great with no problems at all but if i drive through water fast and water gets splashed on the motor then it will start missing but it never happens right away its always a few minutes after i went through the water and if i put my foot to the floor for a few seconds then it runs fine but as soon as i let off the gas it will miss again. i have went through everything but i cant seem to figure out what is causing the problem.. any suggestions??
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Joined: Feb 2012
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From: north carolina
check your distributor cap for cracks. check your boots for proper seal would be my very first instinctive self diagnostic. have you already done this? i know i sprayed my engine down and didn't cover the distributor cap up properly and it did this until i took the cap off and let everything dry pretty good.. (one of the two screws to my distributor cap that go into the distributor doesn't seat because the flange is snapped in half) so i used zip ties to make sure it is seated.. fixed my miss fire and i am betting mine would have done that too if i would have driven through puddles
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i replaced the cap wires and all that about a year ago and i just went out this morning and checked it and it all seems ok. so i dont think the problem is there. but i was searching around under the hood and i found a few places water might get in. there is an air pump on the passengers side of the motor ( i think it has something to do with the fuel injection) there is a hose that leads up to a plastic filter housing behind the battery and it is cracked up pretty bad. i was wondering if water where able to get through the system to the injectors would that cause it to miss im thinking it would if there was enough water.
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Joined: Feb 2012
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From: north carolina
water would cause a miss.. and alot of other things if left un treated.. you can't ignite water.. you can compress it all you want but if the water is overpowering what fuel is getting squirted in the cylinder that things not going to spark and you will have a miss also a bad o2 sensor reading more than likely.. i believe thats right.. have someone else verify me.. shade tree mechanic not 100% sure
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Joined: Apr 2011
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From: Hartland, WI
With the truck running take a spray bottle and start spraying the ignition system, sensors, etc. When it begins to miss, you've found your problem. Did you use dielectric grease when you changed the plugs and wires?
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I repaired the filter and i still had the problem so i sprayed water around the engine thats when i found a small canister with a missing cap and when i sprayed water in there it did start missing. so i ordered a cap but for now i just put duct tape over it. ill let you know if this solves the problem. and no i did not use dielectric grease when i changed the plugs and wires.
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Joined: Sep 2010
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From: Monmouth County, NJ
Maybe the vacuum leak is sucking up the steam from the water hitting the exhaust manifolds. I assume the canister with the missing cap is either the steel one that looks like a coffee can, or the square plastic one? Both of these get sucked on when the engine is running.
The round plastic one and the air pump do not feed into the intake. Getting water on them would not cause a miss.
Make sure you use grease with the exposed ignition components. They cause a miss very easily when they get the slightest amount of water on them.
The round plastic one and the air pump do not feed into the intake. Getting water on them would not cause a miss.
Make sure you use grease with the exposed ignition components. They cause a miss very easily when they get the slightest amount of water on them.
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Fleet Mechanic
Joined: Oct 2010
Posts: 1,690
Likes: 32
From: Delhi, Iowa
I miss my 300 straight six too ... it was an awesome engine ...
Oh, i guess i read the thread wrong ...
Anyways, change your cap and rotor. Make sure to get a cap and rotor set that has SOLID BRASS TERMINALS. the cap and rotor fix the problem 97.84% of the time when you get this issue ...
Oh, i guess i read the thread wrong ...
Anyways, change your cap and rotor. Make sure to get a cap and rotor set that has SOLID BRASS TERMINALS. the cap and rotor fix the problem 97.84% of the time when you get this issue ...
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sorry for not posting in a while i havent had the time to work on my truck till this week. and i finally found the problem. i had pulled my truck around back to replace the power steering pump and to run a new exhaust. and when i was crawling around under there i found that my o2 sensor was snapped off and hanging down so i sprayed some water on it and it started missing. so im going to replace that this weekend. i think when it was getting wet it would send confused messages to the brain and mess with the fuel mixture. Thanks to everyone for your help i was able to learn a few new tricks about my truck. 
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