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Mazda CX-7 Smoke



  • wwestwwest Posts: 10,706
    edited August 2010
    Turbocharged engines MUST be designed to run in detuned/derated mode, "off-boost", 99% of the time. Intercooled turbo boost on a DFI engine must NOT cause the effective compression ratio to rise to the point of detonation. There are two reasons why a turbocharged engine is handicapped for use during idle or constant speed cruising, resulting in HORRID FE in comparison to a N/A engine.

    1) You cannot take advantage of intercooled boost pressure if the base/native compression ratio is already near the point of the onset of detonation, knock/ping due to dieseling. A normally aspirated DFI engine can easily accommodate a base/native CR or ~12:1. Throw in a turbo and you'll consider yourself lucky to have a base/native CR of 8:1, maybe even as high as 9.8:1 if you're really lucky.

    2) In order to reduce turbo lag the CR is lowered even moreso in order to put more of the energy of A/F mixture combustion into the exhaust manifold where it can be, is used, to spin the turbine up most quickly.

    An Atkinson cycle DFI engine can have a base/native CR as high as 15:1, but can NEVER be turboed due to the unusually high efficiency compared to the standard "Otto" mode engine. With an Atkinson cycle engine virtually ALL of the energy of the A/F mixture combustion is used to push the piston downward. Typically only enough energy left in the exhaust to keep the catalyst heated to operational temperature, >800F.
  • fonefixerfonefixer Posts: 247
    Does this mean that 4 cylinder DISI direct injection spark ignition engines with single turbos like the cx-7 are inherently weaker engines with noticeably less of a service life than naturally aspirated engines even with regular oil changes?

    Driving the turbo 4 cx-7 com pared to a naturally aspirated 4 cylinder competitor is amazing. Manually shifting through the 6 speeds really blows the others away, but of course the mpg is probably less. Achieving about 21.5 mpg in town using premium fuel.
  • wwestwwest Posts: 10,706
    "..inherently weaker engines.."

    In the sense that it needs the turbo to produce a reasonable level of HP/torque, then yes. But in the sense of reliability the turbo engine is likely to be a bit more robust mechanically. Remove the turbo or wire the wastegate fully open, and this engine's reliability would probably be extended substantially over an equal displacement engine that wasn't turbo "prepped".
  • My parents currently have a 2007 Mazda CX-7 with a little over 40K miles on it. They just received a letter about the recall on their A/C compressor. The letter aparently stated that it was safe to drive the vehicle as long as you don't use the A/C. Less than a week later, my folks were driving back to Visalia, CA from Pismo Beach, CA and my mom said that she heard a loud knocking noise under the hood, so they pulled over, popped the hood and didn't notice anything... Then they got back in the car, started it up and heard a loud whining noise. The car also lacked acceleration.. (sounds like the turbo.) Now let me add that my father also complained about seeing black smoke come out of the tailpipes on more than one occassion. At this point they decided the car was undrivable and had it towed to the Mazda dealership in Selma, CA.
    Selma had the car for 3 days and aparently couldn't figure out what was wrong with it. They just called my folks back and said that the Turbo is shot and possibly the entire engine. They also mentioned that it was out of warranty, since it has 40K miles on it. When my parents told me this, I asked, "what about the Powertrain Warranty?" I looked it up again and realized that it's 5yr/60K miles.. We should be covered. I even called Mazda Corp in Irvine and spoke to a rep. He said that it would be covered, but the dealership is going to want to see the Service Records for it. If they are not all available, they might want to do an inspection on the vehicle and make sure it's not full of "sludge" or anything. Welp.. My parents had some of their records, but not for all the oil changes.. and guess what? "They aparently found sludge in the engine and will not honor the Powertrain Warrnanty. Now my parents are stuck with some ungodly Service Bill, that I'm afraid to hear about... This is where we're at.. They haven't okay'd the work to be done yet and I'm just trying to help them out.. IF ANYONE HAS ANY ADVICE FOR US.. PLEASE LET ME KNOW.
  • epoagepoag Posts: 1
    I have a 2007 CX-7 with 70,000 miles. I have had the compressor replaced before the warranty situation but did respond for reimbursement. Anyway, recently the vehicle started making a loud tapping noise and vehicle will not accelerate as it did before. After taking the vehicle to Precision Tune (BBB rating is high and have used them since the dealer ship in my city has closed) they determined that there was slack in the timing chain and two of the engine modules were giving bad codes. I took to a friend who is a Mazda certified tech and he told me the same plus there is ludge in the engine. I feel dooped on a vehicle that I thought would be a quality vehicle not to mention previous issues when we first bought like sensors etc. Please someone guide me through this ordeal.
  • My CX-7 just started smoking yesterday I had driven to supermarket, came home, started somewhere else. I had idled it a short time, then started down the the street. Huge amount of smoke! Does it hurt to drive it (this is weekend)?
    Thanks for any info.
  • fonefixerfonefixer Posts: 247
    First--I would check all fluid levels--oil or coolant levels low? If your critical fluids are normal it sounds like the turbo has /or is going out. Wouldn't drive the vehilcle until consulting with a shop/mechanic familiar with the cx-7 engine.
  • Thanks, Will consult with a mechanic.
  • aviboy97aviboy97 Posts: 3,159
    If your critical fluids are normal it sounds like the turbo has /or is going out

    It most likley is not the turbo. If the smoke is white, it's due to the PCV system, in which there is no fix for. Initially, Mazda was replacing turbos and testing them only to see they were fine, and Mazda discovered an issue with the PCV system. I believe the white smoke is built up carbon of some sort, according to my Mazda techs. When they take off the intake manifold, they have noticed a heavy build up on the valves, which is not common with non-DI engines.

    If you are blowing blue smoke, than it could be the turbo, but, I'm betting it's white smoke, since I have seen many blow white smoke.
  • wwestwwest Posts: 10,706
    And then again the A/C compressor could be stalled/locked and it is the compressor drive belt generating all the smoke.
  • aviboy97aviboy97 Posts: 3,159
    And then again the A/C compressor could be stalled/locked and it is the compressor drive belt generating all the smoke.

    That's a possibility. Im not a tech, but, either way, these CX-7's have had issues. No other Mazda in the last 20 years, outside the RX-8, have been plagued by such issues.
  • pc57pc57 Posts: 1
    Yesterday I waited 45 minutes in line to get my emissions test and was rejected due to excessive smoke. The smoke is grayish and has a smell. This problem started about a year ago - I've taken it to Mazda twice for this reason. The first time synthetic oil was recommended which helped for awhile. Just recently they told me there doesn't seem to be a problem - all cars smoke from time to time. So what do I do now if I need this problem resolved to pass my emissions test? My car is a 2007 CX 7 with 62,000 miles. It drives fine with the exception of it hesitates from time to time when I turn on the ignition. I plan to call Mazda first thing tomorrow- I have a 9 hr car trip planned this weekend, so am a little concerned about getting this problem taken care of. Any advice is appreciated!
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