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sprinkles08
sprinkles08, ASE Certified Technician
Category: Mazda
Satisfied Customers: 21605
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Re: 2008 Mazda CX7 I'm a dealer and bought this car at

Customer Question

Re: 2008 Mazda CX7
I'm a dealer and bought this car at auction. It had a CEL Misfire Cylinder 3. I replaced proper plugs and switched coils around. Still had misfire in cylinder 3. I took to a Mazda dealership. They said the compression was 168 in 3rd cylinder and others were ok. Recommended a used motor. Upon starting, it idles a little uneven. After it warms up for about 5 minutes, you can clear out the code and it won't come back. It only comes on at cold starts. Once the engine warms up there is a rattling down low that sounds like it's the VVT. It has 121,000 miles and I think it's all original chain and associated parts. When it's driving, it runs perfect. Would replacing chain and associated parts help this problem. If not, what would you suggest? The only code I'm getting is the P303. I don't want to sell this card to someone if there is an underlying major problem.
Submitted: 26 days ago.
Category: Mazda
Expert:  Dan replied 26 days ago.

Welcome to JustAnswer, my name is ***** ***** I'm here to help get your problem solved.

Expert:  Dan replied 26 days ago.

The chain would effect all cylinders not 1 so I agree with dealer that you have some more serious internal engine problems such as valves not sealing or compression going past worn piston rings. Next step would be to do a leakdown test to see where pressure is being lose then make repair as needed. If valves are leaking it may be worth getting a valve job done instead of replacing engine. Let me know if you have more questions or if there is anything else I can do to help. Thanks

Customer: replied 26 days ago.
Great!
Expert:  Dan replied 26 days ago.

You are looking at around $2000 to have timing chain replaced, valve repaired, and headgasket replaced. I'd recommend getting quotes from at least 3 different places. You can also look on www.car-parts.com for used engines in your area incase that ends up being a option. Let me know if you have more questions, ,thanks.

Customer: replied 26 days ago.
I am wanting to know if that's really the solution. If I check out repairs for that code there are other possible solutions. Given the symptoms of the car I'm wondering if the problem is really that bad or if there are other things I should be checking first.
Expert:  Dan replied 26 days ago.

Only thing that would cause a specific cylinder misfire such as this is coil/wiring to coil, injector/wiring to injector, or internal engine problem such as piston rings or valves. The first 2 options wouldn't cause low compression but it wouldn't hurt to verify you have good spark and injector pulse on that cylinder. Let me know if you have questions, thanks.

Customer: replied 26 days ago.
we had that checked and the injector is fine. Another mechanic told me that that small of a variance in compression should not cause a misfire. So do you think that a new VVT, timing chain and accessories are part of the problem? What is the first thing that you would do? This car just runs too nice to try to sell it with a code.
Expert:  Dan replied 26 days ago.

The other mechanic you talked to probably doesn't realize this engine needs 180 psi to properly fire. The VVT and timing chain would effect all cylinders, not 1. If you are trying to sell it then I'd probably recommend selling as is otherwise do a leakdown test to see where compression is being lost and do repair as needed. Let me know if you have more questions, thanks.

Customer: replied 26 days ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Customer: replied 26 days ago.
The other mechanic knew it should be 180 but thought 168 was within an acceptable variance of 20. My biggest concern is that I fix the engine and it still misfires.
Expert:  Dan replied 26 days ago.

If you have good spark and good injector spray pattern then internal engine issue is only possible problem and leakdown test will tell you exactly what. I wish I could tell you exactly what problem is but without testing it is impossible. From what I'm hearing it sounds like Mazda dealer was leading you in right direction. Let me know how it turns out or if you have questions, you can reply to this answer at any time without additional fees. Thanks.

Customer: replied 26 days ago.
Can you call me?
Expert:  Dan replied 26 days ago.

I can but it will cost you a extra $26 when we can continue chatting just fine. Let me know, thanks.

Customer: replied 26 days ago.
Ok. I am relaying your answers to my husband who is driving to work and going back and forth. Sometimes I think I may be losing something in the translation! :) I guess he mainly is hoping to find a solution that's less than replacing the engine. A couple of mechanics have told him this isn't really a serious problem and the engine could easily go another 100,000 miles without problems. It's running great. But, he doesn't want to sell it to someone if it's getting ready to have a major issue.
Expert:  Dan replied 26 days ago.

I hear what you are saying but it seems like you are asking me to give you a easy solution to a major problem without any testing. I wan't to help but do not want to lie to you and give you false hope. I think mechanic that said it is something non serious is giving you false hope, I'd tell that mechanic you would like them to look at it so the optimistic solutions can be crossed off the list. I'm not trying to be negative, I'm just trying to be truthful. I can open question back up for someone else to help if you would like. From what I'm hearing it sounds like problem is definitely engine related but some tests will need to be done to exactly know what part of engine. Sorry about the bad news, let me know if you have more questions or if you would like me to open question back up to see if someone can help. Thanks.

Customer: replied 26 days ago.
I appreciate the honesty and I guess we would like open the question back up to see if there are any other possibilities. We are only getting the code at start up when the engine is cold. If we clear it it will run great and the light stays off.
Expert:  sprinkles08 replied 23 days ago.

Hello and welcome to JustAnswer!

Do you still need help?

Customer: replied 22 days ago.
I would like to hear your opinion.
Expert:  sprinkles08 replied 22 days ago.

Was the source of the lost compression not investigated?