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peterpete190, Auto Technician
Category: Mazda
Satisfied Customers: 24143
Experience:  Auto repair Technician with 17 years experience.Past ASE and other certifications.
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OK. I have a good one. This has puzzled me and my Mazda

Customer Question

OK. I have a good one for you. This has puzzled me and my Mazda tech. So.... 2008 cx7 my buddy bought running rough drove it to my place to be fixed. Performed a cylinder leak down on all the cylinders which wasn't especially cyl4. Pulled the found 1/4 of exhaust valve missing. Replaced both valves for that cylinder and had a new seat installed. While that was at the machine shop we pulled the pistons and rods. The kit he got had new pistons and rings so sized then and honed the cylinder walls and installed. Bore specs were ok. Got the head back reseated all the valves, and installed on the vehicle. Used the timing tools set it spun it over twice tools went right in. Lined up crank sensor and installed everything back together took 2-3 weeks with work schedule. Went to start it and it started started went to 2g as it came back to idle died. Immobilizer is not flashing. Not that if your wondering.
So here we go. If you start and keep you foot into the gas it will stay running longer but will die out. Pulled the plugs they are carboned up so its running rich. New maf sensor no change. Checked my square wave on my crap sensor it is fine even a few teeth got dinged up on removal by the guy who owns the car helping me take it all apart. Straighten them out cause at first that's what I thought it was but there is no inconsistency in square wave on my vantage pro while cranking. Borrowed a Mazda speed 3 manual cause buddy has a built one. Figured it wasn't to far off here checking can wave wiring in manual was wrong thought I had it figured out but was just on the wrong wire. Square wave for it is ok. Checked vvt notches they are lined up and triple checked timing. All still ok. Cleaned grounds and volt drop tested them they are ok. Check valve for pressure relief from fuel rail is ok.
Resistance test on all injectors are ok. However it still seems to be dumping way to much fuel. PCM has been reset and not throwing any fault codes. No vacuum leaks nothing disconnected. No aftermarket parts on this vehicle. Just starts and stalls going back to idle or will eventually... I used a Solaris pro to get fuel pressure but I think it only shows me low at around 70psi. It sis go up to 100psi maybe a bit more but I believe that was when I had my foot in it to keep it alive. I don't believe it can read high pressure as I looked for it.
Something tells me it has to be something we did but everything we did it panning out ok. Any ideas would be awesome. Want this thing out my garage so I can work on my toy. I'm not to Mazda / ford of person as I'm at fixing VW's. However will never own one as I stick with Toyota's.
Submitted: 2 months ago.
Category: Mazda
Expert:  peterpete190 replied 2 months ago.

My name is ***** ***** I am a professional here at Just Answer. I noticed that your question had not received a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

Even though you did not visually see any vacuum leaks on the engine in some cases this can be caused by a vacuum leak from a leaking gasket like an intake or throttle body gasket.You may have to have a smoke test done on the intake to locate any hard to see leaks like this here if this has not been done.This can cause the computer readings to be thrown off causing an over fuel,high rpm and rough running.If this has already been checked and found to be o.k. let me know.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,a rating of 4 or 5 is appreciated.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 2 months ago.
I did get a chance to hook up a vacuum gauge here yesterday. For the brief few secs it does run vacuum is at 10inhg around the 2g on first start then down to about 5inhg as it starts to come down idle then dies at that vacuum level. So unfortunately I don't own a smoke machine and average engine makes around 20inhg. The hunt is on, thinking that is was a gasket that much vacuum leak I would hear it. So everything into the intake got blocked off. Egr pipe removed and blocked with plastic cap (like red ones on hoses from like a junkyard engine found one that fit perfect) no change. Evap blocked no changed, brake booster no change, pcv hose blocked no change, vacuum tank on top of the intake removed and blocked no change, waste gate blocked no change. So now onto intake valves rechecked all clearances on .010 .009 , .010 .011, . 009 .009, .011 .010. 1-4 in that from the gear to fuel pump. All in spec unless a piece of carbon fell on them but I cleaned the intake ports before I ground them in and installed them. And I don't have compression gauge and leak down at home which I forgot at work because we were swamped. So either A its carbon on a valve. B I know I'm going to get yelled at for this one but isn't my car blow by on fuel injector seals. Idk to much about these engines as its the second of these ford motors I have rebuilt. As the first one melted a hole in cyl 4 and we decided to beef it which it made 423 on the dyno and is still kicking strong. Anyways or C the person my buddy ordered is parts for some odd reason even though we checked and measured the new pistons that they might be for na motor cause an head bolts were in the kit. However diameter, skirt length, over all piston length, dish and cut out for the intake valves were all the same. Didn't do weight though wasn't getting that technical with this build. That is all I can think off. If you can think of anything else that would be great. This was so nice to get someone else's thoughts as you get wrapped up into something you can't think outside the box or just thing of the simple things. moment know new intake and throttle body gaskets. Cleaned off all black paint head, intake manifold and throttle body plus TB was cleaned, cleaner on rag and wiped down not sprayed into and cleaned.That's all I got at this moment. Let me know. Like bouncing ideas helps fix things
Expert:  peterpete190 replied 2 months ago.

This is a difficult one for me to answer myself here.

I will open your question up for others here to see if someone else can assist further on this as there may be others here that may have more info on what to check or do with this issue.I hope you can get this resolved with ease.No need to reply to my last post here unless it is a last resort as it will keep your question locked to me and others will not be able to view it.If you feel you want to continue to work with me on this feel free to reply at any time but keep in mind in some cases it can be difficult to fully diagnose or help repair this without seeing your vehicle.

Thanks Pete

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