04 Neon sohc cranks over but won’t start and backfired out of intake

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Yellow04stx
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04 Neon sohc cranks over but won’t start and backfired out of intake

Post by Yellow04stx » Wed May 02, 2018 10:46 pm

Randomly quit running and was throwing codes for the cam and crank sensors. Replaced both and still won’t start. It cranks over and backfires out of the intake while it’s cranking over. Any ideas?

occasional demons
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Re: 04 Neon sohc cranks over but won’t start and backfired out of intake

Post by occasional demons » Thu May 03, 2018 6:40 am

Check the cam timing. Belt may have slipped.

If it slipped too much, all/half your valves are toast. If it broke, maybe 4 of them are toast.

You will need to pull the crank pulley and timing cover to get a good view of the timing marks.

Or you could use a wooden dowel rod in #1 spark plug hole to determine TDC, and see if the cam mark is still straight up. It is difficult to see in the tiny inspection hole at the top of the timing cover. Turn the crank by hand, via a ratchet/extension and 19mm socket.

If the car has near, or over 100,000 miles, chances are very good it is a belt issue. Even at less than 80,000 miles, given the age, if all original parts, the belt can be suspect. It is 14 years old...

Edit: Depending on your knowledge of engines, If you don't see the cam mark at #1 TDC, turn the crank 360º (1 full turn) and reset TDC, and check again.

If the timing cover is off the mark will either be strait up, or straight down, depending on the cam phase, and if nothing has slipped or broken. Broken would need no explanation, it would be obvious. Slipped would require looking at the teeth/lack thereof on the belt.
- Bill

desmodromic wrote:You have to remember what's important here, while they make New humans everyday, they'll never make another Neon.
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NickKo
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Re: 04 Neon sohc cranks over but won’t start and backfired out of intake

Post by NickKo » Sat May 05, 2018 7:54 am

Have your spark plug wires and / or spark plugs been changed recently ??
It sounds like it is time to replace them.

- Nick
-1998 2-dr SOHC MTX= 52mm TB; Maddog STS
-1999 4-dr DOHC ATX= went to car heaven (junkyard)
-2000 Ply.LX with MTX = Maddog STS; CAI; R/T muffler + Header
-2001 Ddg.ES ATX = UDP, Magnum Header; + Syked PCM 'pending'

-1971 Ply.Scamp SL6cyl. ('Horse Traded' away)
-1968 Chry.300 w/440 V8 (sold)
"MoPar or No Car"

b10alia
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Re: 04 Neon sohc cranks over but won’t start and backfired out of intake

Post by b10alia » Wed May 16, 2018 3:57 pm

You'll hear broken or damaged valves as the car cranks, the cylinder with no compression will crank "faster" so it won't crank evenly, the starter will speed up as it goes over compression on the damaged cylinder. Any snapping or smashing noises when the engine stopped are a good clue that something's gone wrong. A compression test will pretty much determine if you have broken or bent valves, you won't be able to generate good pressure on the damaged cylinder.

Do the cam and crank sensor codes come back if you pull the battery cables for a while?

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