Rebuilt motor won't start - Fires every 3rd compression cycle.

Question: Rebuilt motor won't start - Fires every 3rd compression cycle.

Question

Rene LeBlanc, 2.4L 4 Cylinder, Farmington, ME, September 19, 2010, 17:01

Rookie

Hi,

I lost a rod bearing in my 2.4L Jeep Wrangler. Manual transmission. 2004.

I replaced the crank and one connecting rod. All bearings and seals. New Rings. New timing belt. New plugs.

It sputters every so often, but isn't consistent. I tore the whole front end apart and rechecked the valve timing and it is as described in my Haynes manual.

It is only throwing one diagnostic code, 1489, which is a High speed radiator fan error.

The plugs are getting wet and the compression feels good in all 4 cylinders, although my compression tester isn't long enough to reach the plug holes.

I also used a ratchet to manually turn the motor over and ensured that it had a compression cycle then an exhaust cycle because I was still worried about the valve timing.

I've tested the plugs for fire, and found that the coil fires the plug every 3rd time the engine goes over compression.

With the lack of diagnostic codes, I'm thinking that the coil pack is the problem, but don't want to buy a new one without anything to back up my suspicion. The engine was running when I stopped, it hadn't seized. The coil pack was covered in oily crap, so I cleaned it with gasoline and a brush. Could that have killed it?

Thanks

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devilscap4 September 19, 2010, 18:05

Journeyman

I am concerned about that replacement crank. If the tone ring is improperly installed, damaged, or an incorrect application, the crank sensor will receive incorrect information about the crank's actual position. This condition might not set a code, as there is no actual electrical fault. The sensor itself can also be damaged, and sometimes faulty camshaft sensors can cause the same condition. Chryslers are notorious for crank/camshaft sensor sync problems. A lab scope should be used to check the pattern of the crank and camshaft sensor to verify this. It is not possible to check compression pressure by hand. Even 20p.s.i. will feel, and sound, like alot coming out of a spark plug hole.

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ZeeTech, September 19, 2010, 20:57

Master

Great answer, I absolutely agree to the last world.

Zee

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Visitor, September 20, 2010, 05:16

Fair enough about the compression.

As for the tone ring, even if it was off, wouldn't it still spark every other cycle? I thought the crank sensor determined when #1 cylinder was on Top, and the camshaft sensor determined whether it was on compression or exhaust. So every other time the piston is on Top Dead Center, you should get a spark. Right? So even, if it was off, shouldn't I get a spark every other revolution, it just might be way off? If the valve timing was off enough for the camshaft sensor to not jive with the crank, shouldn't it never get a spark, not just an intermittent one?

This sparks every 6 cycles (every 3rd compression), and seems to fire about the right spot.

I'm glad (or worried) that the Crank position and camshaft position sensors may not throw a code. I'm going to try a new coil pack and if that still does the same thing, I'll have to have it towed somewhere where they can diagnose it.

Thanks

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Answer #2

Visitor, September 23, 2010, 06:01

Here's an update.

You got me concerned about the tone ring, because I couldn't remember there being one, so I pulled the oil pan and checked. There is no tone ring on this crank. There is a lan machined on the crank itself that passes by the CPS. I had laid the 2 cranks side by side before installing this one to make sure they were the same.

So, I've tried a new coil and it still sparks every 3rd compression (6 revolutions). I've got a factory service manual, and it says that it should spark 1 & 4 every revolution and 2 & 3 every revolution. So that is way off. BUT, when it does spark, it sparks on #1 compression.

I also found a schematic for the Ignition System and it shows a coil capacitor. Is that the same as a condensor in a points ignition? If so, and it is bad, it could explain why the firing is so sporadic. Right? Any insight on this would be appreciated.

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Answer #3

rc parts February 02, 2011, 20:14

Technician

follow that code already showing fan error without running sounds fishy so check real good sounds to me like some has a loose ground. if u panted engine to make pretty ugly it up some be sure no paint between grounds and block thick paint will cause a poor ground.

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