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Question:

why does my car not start unless i add an additive to the gas tank?

i‘ve been having problems with my car not starting for almost a year.i‘ve taken it to a mechanic and he kept it for about 3 days and said he couldn‘t find anything wrong with it.he did replace a module that he said might be the problem.that didn‘ t fix it.one day at the gas station i decided that i would try some fuel additive when i got gas.i repeated the gas treatment about 2 to 3 more times and while i was doing that i never had a problem with the car starting.i then refueled without an additive.i drove it a few days and then it wouldn‘t crank again.i went over 3 weeks without having a problem.i went to the store and bought some sea foam cleaner/ additive and in a few hours the car startedall of this is a mystery to me.someone please help me figure out what might be the problem.i have done numerous searches online for this problem uld it be something in my gas tank? a blockage? fuel pump?

Answer:

This is really strange. Fuel additives don't really do all that much. They have some detergents that help clean injectors and valves but that is about it. You need to start eliminating possibilities. You only need 3 things for the car to run. Air, fuel and spark Air is not an issue. the engine can pretty much always get enough air unless there is a squirrel in your throttle body. Air going out may be an issue if your catalytic converter has melted down and won't let exhaust pass through. aside from that not likely anything wrong there. Start with fuel. When the car isn't starting, spray some ether ( starting fluid) into the intake. If it starts up you probably have a fuel delivery problem. Start by checking your fuel filter. Cheap and basic maintenance anyway. Then check the fuel pump if you can access it. Sometimes it's inside the tank and you are up the creek. Whatever you put in the tank may have lubricated a bad pump to the extent where it will still work but not very well. Just a guess. If that seems OK, move up to the injectors. Either replace them outright or try and clean them. Just be careful with these. It's easy to mess them up. If you can remove the intake manifold ( pain in the butt) look at the valves for excessive carbon build up that might prevent the car from running. It would have to be really really bad, and it would be obvious. If it still doesn't start you have an ignition problem. Check each plug for spark. remove one at a time, connect it back to the wire and crank the engine. Have someone check for spark. Do for all plugs. If your car has a distributor, replace the cap. It's cheap and easy. Just replace it. If it has coil packs for each plug, you might need to replace one or more of them. They do go bad over time. I hope this is enough to get you started.
Well, if you car flat out won't crank, then it has pretty much nothing to do with the fuel system. The fact that it starts with additives sometimes can't be anything other than coincidence. Check the battery is good, no wires are loose, and the terminals are in relatively good condition. When it doesn't crank, do you get it going by jumping it?
Well a gas treatment simply adds octane and a cleaning additive. Is your car a high performance car like a Trans Am or Mustang GT? If so you must use High Test gas or you'll get those results. Could be stale gas as someone else suggested. Have you tuned the car lately? Worn plugs and old plug wires would cause that condition as well. Have you made any modifications to the engine like headers, high performance injectors etc? You'll need to tweek the computer settings to accomodate the new equipment.

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