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Old 12-17-2012, 09:33 AM   #1 (permalink)
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Default Mazda 6 2.0 Diesel: Power Loss

Hello all,
I have a 2007 (57 plate) Mazda 6 2.0 diesel. The problem is after approximately 30-40 miles on the motorway at 70 - 80 mph, using the cruise control or not, the power drops off. It's particularly noticeable on hills / inclines. I can drop it to 4th/5th gear and drive at 50-60mph to get home but not much happens if I try accelerating. It first happened a week before a service/MOT. They did a static DPF regeneration and oil/filter change. Oil levels weren't excessively high (below "F"), and I've always had the low ash oil put in. This didn't cure it. "Current" fuel consumption readings as I drive are good suggesting that the DPF isn't trying to regenerate as I'm driving.

I took it back to the garage and I was told the error code indicated an intermittent fault with the mass air flow sensor. I had that changed, but the problem is still there. Driving to and from work etc is a 15-20 minute drive and the car performs fine. No warning lights have been displayed. When it happens I can stop the car for a few minutes and it's ok again for a while. I've had the fuel filter changed too.

Has anyone had a similar experience and if so what was the resolution?

Many Thanks

Paul

Last edited by PaulR17; 12-17-2012 at 12:31 PM.
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Old 12-18-2012, 07:04 AM   #2 (permalink)
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Hi Paul
How many miles are on your car? does your turbo sound louder recently, maybe a loud whistly or hissing? might be worth driving with the window down to hear it better....
What sort of revs and gear are you using on the motorway?

Dave
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Old 12-18-2012, 07:56 AM   #3 (permalink)
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Hi Dave,
It has 86,000 miles on it. I've had it 2 years and average 10,000 per year. I make sure I do one decent run a week to prevent the DPF blocking significantly. When the problem occurs I'm on the motorway at 70 - 80 mph, which is just over 2000 rpm (6th gear).

I haven't noticed the turbo being louder recently, but I've only been driving with the radio off since the issue occurred. I'll listen more carefully tonight and let you know.

I drove it on Sunday until the problem occurred, stopped in a layby for 2 mins with the engine off, started up again and it was Ok for a while. I thought perhaps a sensor was over heating and when it cools its Ok.
Paul.
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Old 12-19-2012, 04:12 AM   #4 (permalink)
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Hi Paul
I think part of your problem is the use of 6th gear, yes i know it sounds daft but the revs are to low for a passive burn, your better off in 5th at around 2500rpm which is around peak torque, this generates the most heat for the burn to start.
When the power loss happens does the engine refuse to rev in lower gears?
It does sound like your DPF is partly blocked or has broken up.

Dave
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Old 12-21-2012, 11:16 AM   #5 (permalink)
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Hello again,
I know there's 3 of us on this forum with similar(ish) problems at the moment. Today I went out with an On Board Diagnostic (OBD) computer linked up, and my trusty mechanic sat next to me! The problem appeared after about 40 mins on the motorway. This time the power loss occurred but the power came back again after a few minutes (first time that's happened). However, the OBD computer logged the "mass air flow sensor" error code again as it happened, while on cruise control at 75mph, 6th gear, just over 2000rpm. As I said previously, I did have this unit changed and we assumed that it could no longer be the problem. Back at the garage we put the old one back on again (it's since been cleaned) and noted that output voltages were different with the 2 units. I've left the old one on for a bit to see what happens. I'll change it if the car runs poorly. We also noted that the OBD said the DPF isn't clogged and also there's no soot at the end of the exhaust indicating it's probably not broken down. The mechanic listened to the turbo and said it sounded fine.

Perhaps there's something else that can fail to cause the MAF error? The intermittent nature is a bit puzzling too.

I've seen you can buy a bluetooth OBD II connector from Amazon, and use your smartphone to log the data with one of the many OBD apps you can download. Has anyone tried one?
Cheers,
Paul.
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Old 01-04-2013, 04:57 AM   #6 (permalink)
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Can't say I've noticed much power loss but my MPGs are down (upper 30s, lower 40s). The situation you described in another thread sounds perfectly plausible to me, where a significant ash build up is causing the ECU to actively regenerate the DPF much more often. Mine has 107000 miles on it, and you can bet it's the original DPF unit.

Incidently, I've never seen the DPF light illuminate, except when the ignition is turned on initially. The only indication I have of something happening, is the current fuel consumption figure (approx) doubling for a period of time. I was going to take a look at the EGR also, it certainly can't do any harm to be cleaning that out.

Regards

Stuart
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Old 01-06-2013, 07:55 AM   #7 (permalink)
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I have just found the paper work, and they did and oil & filter change on the car the week before I checked and found it 3/4 to X. Its now almost touching X. Is it possible for the engine to cause this? or has it been over filled? Sorry for the dumb questions!
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Old 01-06-2013, 12:19 PM   #8 (permalink)
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I find getting a decent oil reading on that sorry excuse of a dipstick is a pain... Make sure the level you think it is is wrapped all the way around, and not some residual oil picked up on the way out (i.e. take the reading several times).

If it really is approaching the 'X' then the engine management is trying to actively regenerate the DPF, and diesel is diluting the oil. You want to change that oil ASAP, with C1 spec 5/30 before your engine runs away and dies.

How did they ascertain that the DPF wasn't blocked? If you look at my other post today there are some figures you can use if you have a scanner...

Plus, I took some MAF readings on mine also...

You can find physical testing figures here https://euroesi.mazda.co.jp/esicont/...0f1800700.html but for some reason mine always shows 0V regardless (I think it's the scanner software). Input in g/s is about 11-12 on startup, 4-8 on warm idle and more when you put the foot down. I might have to get the multimeter out to be sure.
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Old 02-02-2013, 12:15 PM   #9 (permalink)
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Well, hopefully, I think I may have finally solved this mysterious problem (fingers-crossed, touch wood etc). I bought one of the inexpensive ELM 327 OBDII bluetooth units from Amazon, and loaded "Torque Pro" app onto my smartphone (don't use Torque Lite, it doesn't seem to see all the error codes). I took the car out a few times, made the problem occur, logged all the sensor data and had a good look at it at home. I was getting the P0104 intermittent MAF error (we'd already changed that without success), and then I saw a pending error code P0402 excessive EGR flow. I noticed that when the problem occurred the air fuel ratio dropped a bit low. Perhaps the EGR valve wasn't shutting after light engine load (downhill running), then when the hills appear the EGR valve stays open hence the lack of power. We decided to clean the EGR valve and more importantly the pipe work connecting it. The pipes were seriously clogged with soot and the EGR valve had significant soot deposits. Today, after the clean up I ran the car for 50 miles, my usual motorway route that would've had the problem occurring easily. Nothing :-) The car feels more powerful, smoother, the fuel consumption has improved significantly, and I checked the OBDII data and the air fuel ratio looks good. Obviously I've only done the one run, but there's such a difference in performance it would suggest that this was the problem. If it occurs again I'll post another note.

I would advise anyone who has had this problem to check the EGR valves and pipes. It's just a case of a good clean up and no new parts. My mechanic said it took a couple of hours to do (and charged me for them of course) but it seems to have been worth it.
Cheers,
Paul.
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