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Low compression in 2 cylinders

 
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Old 16 Mar 2016, 01:18 am
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Default Low compression in 2 cylinders

2004 PT Cruiser w/ 2.4L DOHC; 110k miles. Out of the blue my engine light started flashing and power was drastically reduced. I had just started out after being parked for a couple of hours. Had no signs of trouble before this happened other than occasionally rough idle (plugs and wires are about 7 yrs old).

Thanks to a forum post I used the key trick to get the trouble codes (initially just P2302, then also P0300). While these indicate engine misfire and ignition coil issue, I had it diagnosed at Pep Boys where they checked the compression and found it low in cylinders 1 & 4 (around 120 psi when they said normal was 170-225). They said it probably needs a new engine or rebuild (suggested a 'long block'?) Just had the transmission rebuilt 3 months ago so was hoping to get a couple more years out of the car. I also replaced the camshaft position sensor 4 months ago. Timing belt was replaced at 65k miles (about 5 yrs ago).

I'm wondering if there's a chance it may not need a complete rebuild. Any ideas of what it might be and what I should expect to pay to repair/replace? I've got a pretty good local independent mechanic but don't think he does major engine work. Currently the engine is turning over but won't start so I'm probably going to have it towed for a second opinion.

I'd appreciate any advice or suggestions. Thanks.
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Old 16 Mar 2016, 05:39 am
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Default Re: Low compression in 2 cylinders

Does it have spark?



Read about putting some oil down the spark plug hole. Then trying a compression test again. It the numbers go up it may be the rings. If not maybe the valves are not sealing. I read about these engines sometimes "burning" a valve.

I hope it's just your coil.
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Old 16 Mar 2016, 08:30 am
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Default Re: Low compression in 2 cylinders

Did the engine overheat?

What is the compression in cylinder #2 & #3?

Is your engine light on? If so what is the engine trouble codes?

I would suggest checking to see if the spark is weak. Was the coil replaced?
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Last edited by ptcruisersteve; 16 Mar 2016 at 05:49 pm. Reason: Added more suggestions
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Old 16 Mar 2016, 08:30 am
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Default Re: Low compression in 2 cylinders

I'm sorry, but I just don't trust any shop to properly diagnose a problem like that. Especially NOT one that's attached to a parts store. Did the car start like normal when you first got in? If it did, then YOU should try to do a compression test for yourself. If not, then your engine light could be the result of nothing more than a weak battery that's about to crap out. I'd definitely at least take it somewhere else for a second opinion. And Pep Boys is about the last place I'd let do any work on it. They're kind of like AAMCO, if you've read the stories about them.
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Old 16 Mar 2016, 09:38 am
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Default Re: Low compression in 2 cylinders

Steve; the engine did not overheat. Not sure what the exact readings were for cylinders but they said it was normal. Also, the trouble codes I got were P2302 and P0300 the the engine light came on and was flashing. The coil has never been replaced...could a bad coil cause compression variations?
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Old 16 Mar 2016, 10:30 am
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Default Re: Low compression in 2 cylinders

Don't you have to pull the intake on those to check 2&3? I don't think 140 is low. Most of the people have been posting readings like that. 2302 a problem with the coil circuit and 0300 is a random misfire or misfire on more than one cylinder. If the car was running fine, it is unlikely that it suddenly needs a complete rebuild. Sounds like an ignition problem.

Quote:
P2302 Chrysler Ignition Coil Secondary Number 1 Circuit Condition

Possible causes

- Faulty spark plug or coil boot
- Faulty Ignition Coil 1
- Ignition Coil 1 harness is open or shorted
- Ignition Coil 1 circuit poor electrical connection

Symptoms

- Engine Light ON (or Service Engine Soon Warning Light)
- Engine may be running rough
In the old days we used to start the car in the dark and look to see if we saw any arcing or light. If you did, that was what was bad. When I heard low compression on 2 cylinders, my first thought was head gasket, but that would only be if they were adjoining - not 1 & 4, which are the only two you can access without pulling the upper intake IIRC.
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Old 16 Mar 2016, 11:28 am
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Default Re: Low compression in 2 cylinders

Quote:
Originally Posted by Fk5 View Post
Don't you have to pull the intake on those to check 2&3? I don't think 140 is low. Most of the people have been posting readings like that. 2302 a problem with the coil circuit and 0300 is a random misfire or misfire on more than one cylinder. If the car was running fine, it is unlikely that it suddenly needs a complete rebuild. Sounds like an ignition problem...

...When I heard low compression on 2 cylinders, my first thought was head gasket, but that would only be if they were adjoining - not 1 & 4, which are the only two you can access without pulling the upper intake IIRC.
+1

You can almost be assured that the tech did not remove the upper intake since only numbers for cylinders 1 and 4 were given. Chances are only cylinders 1 and 4 were checked and it appears they were about the same. And 140 psi may well be within the margin of error for this tech and whatever compression tester he was using. As rule of thumb, you want to check all cylinders and look for the ones that are different from the rest. There are very good procedures in this forum in the how to section that are likely better than what the tech did.

This could actually be many things including just water in the gas from a service station that may have fouled a plug. Or it could be a bad plug wire.
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Old 16 Mar 2016, 11:49 am
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Default Re: Low compression in 2 cylinders

Quote:
Originally Posted by Fk5 View Post
Don't you have to pull the intake on those to check 2&3? I don't think 140 is low. Most of the people have been posting readings like that. 2302 a problem with the coil circuit and 0300 is a random misfire or misfire on more than one cylinder. If the car was running fine, it is unlikely that it suddenly needs a complete rebuild. Sounds like an ignition problem.

In the old days we used to start the car in the dark and look to see if we saw any arcing or light. If you did, that was what was bad. When I heard low compression on 2 cylinders, my first thought was head gasket, but that would only be if they were adjoining - not 1 & 4, which are the only two you can access without pulling the upper intake IIRC.
+2

That was my exact thought when first reading this thread. If they only gave you the readings on #1 & #4, and they only tell you that #2 & #3 are "normal" then chances are they didn't remove the upper manifold. IMO, find another mechanic.
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Old 16 Mar 2016, 12:05 pm
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Default Re: Low compression in 2 cylinders

i can tell your not very mechanically savvy. That's fine, but this is my subjection. Get it home. Go to a parts store, rent compressing testing tool. Buy a new coil and wire set, should be around hundered bucks.

First check for spark.
Next, pull off intake to get at plugs.
Do compression test. Is the engine turning over fast like it should?
Find the numbers.
I'd put the new coil and wires on it at this time? Spark? Better spark?

Will it start?

No? Get it to a GOOD and honest mechanic. Not a dealer, not pep boys

Or trade in for new car or sell it as is.
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Old 16 Mar 2016, 01:10 pm
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Default Re: Low compression in 2 cylinders

If it was me, I would do the following

1. Copy down all trouble codes. Then I would clear the codes. I would also inspect under the hood really good for worn or loose wires going to the coil. And I would also unplug the wire lead from the coil, clean it and plug it back in. After this I would drive the car until the light comes back on, if it does. Then I would read the codes. These are likely the primary codes.

2. If a spark problem is indicated by the codes, I would change the plugs and plug wires. If they haven't been done in 7 years, they likely need it anyway.

3. While at the parts store, I would also get a bottle of regular STP fuel cleaner and fuel dryer such as HEAT. I would add the bottle of fuel cleaner and just keep the HEAT for later. Drive the car and see what happens. If no better, move to next step.

4. Remove upper intake and change plugs and wires. Since I got the bad compression report, I might do a compression test. But if pressed for time, I likely would not. I have a high tolerance for risk so I'd likely just go with my gut that it's bad gas with fouled plug or the wires have broken down.

5. Next I'd clear the codes, say a sincere prayer in the name of Jesus, and drive the PT. If I still had issues, I'd add the bottle of HEAT. And recheck the codes. But I suspect the issue will be gone.

Again, this is just what I would do. And remember, I haven't seen your car and I'm only going off what you have told us.
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