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Engine shakes when turned on sometimes causing check engine light to turn on (P0300) sometimes causing it to flash

Tiny
C.HERRERA
  • MEMBER
  • 2005 DODGE CARAVAN
  • 3.3L
  • V6
  • AUTOMATIC
  • 171,000 MILES
Let me start by what I have fixed; A new coil, spark plugs, wires, fuel injectors all six evap purge valve, EGR valve, fuel injector flush, intake air sensor, oil change, new belt and belt tension-er. Now I have had P0300 code since Jan 2017 and since then have had these things done to it. When I start the van the engine shakes I was told this is the misfiring). Some times hard for fifteen to twenty seconds and causes the engine light to come on. If I wait a few seconds it will stop shaking and it drives just fine. Good gas mileage not a lot of get up and go when I need it though. Sometimes when I start it the check engine light comes and flashes engine shaking. So I will turn off the van wait start the van again and it purrs like a kitten. No shaking and drives good. This has been going on for months. I have taken it to two different shops no body can tell me what is wrong with it. Maybe my MAP? If it was my fuel pump would it not have gone out by now? I am a single mother of four and really need to fix this please help.
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Sunday, July 23rd, 2017 AT 6:06 PM

10 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,465 POSTS
It could be low pressure from a failing fuel pump, you would need to get it tested for both pressure and amp draw when it is acting up. Lack of power and the misfires also suggest a possibility of a bad catalytic converter or muffler that has parts broken and floating around and sometimes blocking the exhaust. Hard to say without testing the back pressure and tapping the catalytic converter and muffler to see if something is broken loose inside.
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Sunday, July 23rd, 2017 AT 6:59 PM
Tiny
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Thank you I will get those checked this week. Is there a pressure thing I can buy to check the fuel pressure myself?
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Sunday, July 23rd, 2017 AT 7:16 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,465 POSTS
Many of the chain stores like Advance and Autozone have them as "loaners" you basically buy them, then when you return them you get the money back. Just be sure that you open the kit in the store and verify what is in there. Do not want to end up buying the thing if someone else lost/forgot to return a piece.

Here is a guide that will give you an idea on how to do it.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Please let us know what happens.
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Sunday, July 23rd, 2017 AT 8:46 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,643 POSTS
Hello,

We will be able to tell what is going on better if you pull all of the spark plugs out and keep them in order to see if one looks different than the rest.

https://www.2carpros.com/articles/how-to-change-spark-plugs

Please run this test and get back to us we are interested to see what it is.

Cheers, Ken

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Monday, July 24th, 2017 AT 7:18 PM
Tiny
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  • MEMBER
  • 8 POSTS
Good idea I will do this today when I get off work and let you know if they look the same or not this evening.
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Tuesday, July 25th, 2017 AT 6:59 AM
Tiny
C.HERRERA
  • MEMBER
  • 8 POSTS
Hey I only had time to check the front three spark plugs (the other 3 are on the back side have to move some stuff to get to them will do that sat on my day off) two of the spark plugs still looked new the other one was really ugly all the gaps were correct. I changed the ugly one van/engine still shakes a little not as much as before when I would turn it on I forgot to tell you the day before I changed the spark plug the engine light turned off on its own changed the spark plug it stayed off for two days now today it turned back on it says the same thing p0300 so anyways I will check the other 3 spark plugs this weekend might have another bad spark plug tried to get a fuel pressure check kit since it hesitates to turn on some times but nobody had one available ( I live in a small town)will also check catalytic converter this weekend. Not alot of people know this but if you have dodge you can check your own codes just switch your ignition on three times ( not all the way on just to where the lights come on ) so kinda fast on off on off on and in a few seconds your code will pop up where your mileage is when it's through with all your codes it will say done
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Thursday, July 27th, 2017 AT 6:28 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,643 POSTS
Lets check the compression of the cylinder with the ugly plug. here is a guide to show you how.

https://www.2carpros.com/articles/how-to-test-engine-compression

Please let us know what you find.

Cheers, Ken
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Friday, July 28th, 2017 AT 11:09 AM
Tiny
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  • MEMBER
  • 8 POSTS
I finally got to check the back spark plugs one of them looks new the other one is ugly and black the other one is wet and black with oil or something. Not sure what that means.I finally I got a compression tester will do the test tomorrow when I get off
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Saturday, August 5th, 2017 AT 8:25 PM
Tiny
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Did the compression test not sure what to think the spark plug that was wet and the one next to it that was half black had the highest pressure the other four (even the first ugly one I took off) were the same some things notice when I was messing with the van. The evap purge valve. The hose that goes to the manifold when it's off the manifold ( unhooked) the van starts just fine. It idles a little high but it drives like it's new. Sped off good. No shaking when I start the van hooked the hose back to the manifold and the van would shake when I start it.
Just wondering if that meant anything
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Monday, August 7th, 2017 AT 7:43 PM
Tiny
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Can a bad catalytic converter cause this.I also smell gas sometimes when I turn the van on that's when the engine light flaahes
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Monday, August 7th, 2017 AT 7:51 PM

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