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It is recommended to prefill the oil filter during an oil change to reduce the amount of time needed for the oil pump to fill a new oil filter. In cars with vertical oil filters it is easy to fill the new filter before installing it on the car but this solution is not effective for other cars.

In cars with non-vertical oil filters, one solution is to fill the engine with fresh oil and then to disconnect the coil pack connector and start the engine for a few seconds with only the starter turning the engine slowly to fill the new oil filer. After that you can reconnect the coil connector and start the engine normally.

This is the method I use after each oil change but there is a problem. Whenever I disconnect the coil pack, turn the engine by starter and reconnect it the engine fires up rather violently. In a normal cold start-up, my car revs up to around 1600 RPM then goes back to 1000 - 1100 RPM but when I disconnect and reconnect the coil pack, it suddenly jumps to 2000 RPM violently and then everything goes back to normal. I think this aggressive behavior is not good for a stone cold engine to fire up like that. How can I solve the issue and start the engine normally after my oil change? I think the reason of this aggressive behavior is the presence of unburned fuel inside combustion chambers during the time I start the engine with the coil disconnected. I tried to disconnect all 4 fuel injectors too but that didn't solve the problem.

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    No clue why your engine starts up violently, but understand why you're doing what you're attempting to do. A MUCH BETTER way of accomplishing what you're trying to do is to remove either the fuse for the fuel injector circuit if there is one or the relay which covers this. If the spark plugs fire in a dry cylinder (without fuel), nothing happens. As you pointed out, with the fuel injectors firing, you get excess fuel in the combustion chamber. This can cause other issues such as washing down your cylinder walls, which causes extra wear and negating any benefits from what you're trying to do. Apr 20, 2022 at 14:48
  • As I said, I also disconnected all 4 fuel injectors and started the engine with injectors and coil disconnected but when I reconnected all of them (coil and injectors) and started the engine normally, it started up violently again. Maybe I have to disconnect and reconnect the battery to erase the ECU completely before starting the car normally.
    – LFY MP7.3
    Apr 20, 2022 at 15:12
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    There are other benefits to following my suggestion of ONLY pulling the fuel injection fuse. It accomplishes EXACTLY what you are trying to do without the downsides. Also, repeatedly taking the connectors off of whatever you're taking them off of will wear them out. It's really easy to break a connector. If you break a fuse, you're only out a few cents and can be bought at most any parts store. Apr 20, 2022 at 15:20
  • I checked my fuse box and it seems there is no injector fuse in it.
    – LFY MP7.3
    Apr 20, 2022 at 15:33
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    It would be in the underhood fuse box. Apr 20, 2022 at 16:29

2 Answers 2

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I believe your guess is correct as far as the fuel in the cylinders that hasn't been fired. I believe another contributing factor is the cylinders have generated heat from the compression and are warmer than they would be if the engine hadn't been cranked.

You don't say how long you wait between the cranking with the disconnected coil pack and the startup, but I'd suggest waiting 10 minutes to let the cylinders get back to ambient temperature.

As another solution for not being able to prefill the oil filter, an oil filter will absorb about the first full quick fill if you rotate it. I've done this on my engines that had upside-down oil filters. As quickly as I could fill it up without filling, then stop, rotate it around until I get it completely sideways and let the oil filter soak up the oil in there. So far it's worked with everything from the tiny oil filters to the larger ones.

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  • Regarding the waiting time between cranking and startup, I have to say I even waited for 3 days but it started up violently again! I didn't understand your last paragraph about how to fill the oil filter by rotating it.
    – LFY MP7.3
    Apr 20, 2022 at 16:15
  • So the heat buildup theory is out! With the oil filter pointed up so you can fill it, put enough oil in to come to the top, then stop. As the filter is absorbing the oil, slowly begin to rotate it around to let the oil go to the top of the filter without spilling. You will start vertical and as you rotate, you will end up horizontal or a bit more until all the oil is absorbed by the filter mat. Does that make sense? It's a bit hard to explain, but once you see it done it makes perfect sense. Apr 20, 2022 at 16:18
  • Does your method of filling apply to horizontal filters too?
    – LFY MP7.3
    Apr 20, 2022 at 18:40
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    Yes, I've used this method for every orientation of filters. Although with horizontal I can keep a bit more in as long as it's not spilling out the hole. Completely upside-down filters have to absorb all of the oil. I've noticed that just getting this first bit of filter mat absorbing the oil speeds up the time until the engine reaches full oil pressure. Apr 22, 2022 at 13:22
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I don't agree with your method because the wear is miniscule when installing a dry horizontal filter. But, if you want to do this you may want to first remove the fuel pump fuse then relieve the fuel pressure preferably with a fuel pressure gage before you start the oil change. Then disconnect the primary connector to the coil pack. Now you have no fuel and no spark. After oil change crank the engine to fill the filter. Then plug in the coil replace pump fuse. Turn the key to the run position and let it stay there for about 4 seconds to pressurize the fuel rail. Then start the engine.

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  • This really doesn't answer the OPs question of "why does it rev violently" when he does what he does. Apr 20, 2022 at 15:23
  • @Paulster2 - Yes, I want to know the cause of this violent behavior which still happens with no fuel and no spark (cranking with both injectors and coil disconnected). I want it to start up nicely and smoothly like when I start it normally.
    – LFY MP7.3
    Apr 20, 2022 at 15:32
  • Suggest you try relieving fuel pressure. I'm thinking if there is a little weepage from a slightly leaking fuel injector it might be in the combustion chamber when trying to restart. One problem with this theory is it would start violently at other times also. Especially after sitting for shorter than an hour or two. But if it doesn't start violently after fuel pressure has been released, then you could check for injector leaks.
    – Jupiter
    Apr 20, 2022 at 17:55
  • If it had leaky injectors, it would never start smoothly and nicely all the time. My car starts up smoothly even when you have just turned off the engine and it is still hot. Cars with leaky injectors usually have problem starting up when hot.
    – LFY MP7.3
    Apr 20, 2022 at 18:38

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