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So ive got a 2005 (pre dpf) Mazda 6 2l turbo diesel and occasionally get a weird power loss issue. Ive had a mechanic plug diagnostics in but its showing no codes, he drove around for a while with diagnostics running but typically it wouldnt do the fault then and everything looked normal. He suggested maybe fuel filter and replaced it but fault is still happening.
It has happened when the engine is fairly cold still and also once the engine has warmed up, slow and high speeds. Speed basically just stays the same despite pushing harder on the accelerator, revs stay about the same too. Only lasts for a minute or so, or drop a gear and it seems to go back to normal.
Anyone else experienced this and solved it? Weird its not bringing up any codes.
Egr sticking or a Mad sensor failing but they're just guesses...
That sounds like limp mode, a get you home function when the turbo stops giving the engine a blow-job. It happens on my old Octavia, it’s something to do with the wastegate sticking on mine.
Sounds similar to something on my Astra cdti. Lived with it for a couple of years with 2 garages failing to fix it. Solved in the end by running on top notch jungle and thrashing, and I really do mean thrashing, the arse off it at every opportunity. Looking back I think (a) I didn't drive it hard or long enough and (b) I wasn't really doing the miles a diesel warranted, probably about 15k a year.
YMMV
Intermittent problems are a nightmare. It isn't throwing a code because typically the ecu is programmed to store the first occurrence and then only trigger the fault when it happens again under similar or preset circumstances. Or a component fails a test cycke (that's usually how egr faults happen)
Does it lose power (as in you are driving constant speed and car slows down in its own, doesn't respond when you press accelerator) or does it not respond by going faster when you press the accelerator?
You could buy a cheapy obdii plug in of Amazon and use e.g. Torque to do real time logging. Note when the fault occurs and look back through the logs to see what is iutside parameters.
If, however, it is a sticky TPS, for instance it won't throw a code (probably) because unless something else tells it something, the ecu just doesn't think you are pressing the accelerator.
Possible MAF
Mass Air Flow sensor fault.
But fit a new air filter first.
Turbo boost sensor (as above) would be where I would look first as cheapest to replace. Don't know how you find out without simply replacing it though.
I'd clean the inlet manifold and the egr if it were me and it hadn't been done yet -im assuming it's 14 years old so on 120-140k
If this is chocked up you'll see an egr fault when the failure occurs on live data obd
A possible cause could be.
Fuel tank vent breather hose blockage.
If you have ever opened the fuel filler cap and heard a rush of air then that is a sign that the vent breather hose is blocked.
Can't edit .... But I meant to say you'll see a maf fault on one live data not an egr fault.
People see the code and fire a new maf on blindly and wonder why it doesn't help.
The cars done 78,000 and has all its stamps so had regular oil changes at least.
It's had a new air filter fitter within the last month.
Fuel vent thing maybe as I've had a little rush of air sometimes when opening the filler cap.
Mechanic says looks like egr has been deleted as it didn't move at all whilst driving.
Someone messaged and suggested upstream o2 sensor?
Sometimes happens every few days, sometimes doesn't happen for a week or two.
Car doesn't slow down just doesn't gain any more speed/revs.
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has all its stamps so had regular oil changes at least.
It's had regular stamps anyway that's the only thing I'd take from that.
Mechanic says looks like egr has been deleted as it didn’t move at all whilst driving.
How did he accertain this?
That points even more to it being funked up rather than "deleted"
How can you delete the egr and prevent it from constantly setting codes?
I would expect that if the egr was dirty it would definitely set a code.
Not that familiar with Mazdas but in general there are so few sensors that can fail without setting a code, or so few that have a long enough period between out of spec readings that won't set a code that it should be possible to figure out.
I would start with the throttle system given your description. A tps can fail without setting a code and produces symptoms like that. That would also show up on a logger, in fact you could put that sensor on the phone screen so you would see if it failed to register a change when you move the pedal. The butterfly valve in the throttle body could be sticky. That wouldn't show up on a log.
It's a stir it yourself, I'm assuming, not an auto box? Next time it happens, if you can safely, I would dip the clutch and try feathering the throttle without lifting all the way off, see if the engine matches what you do immediately, or with a lag, or not at all. Then try lifting all the way off then back on and see what the engine does.
Talk about assumptions. Have you owned it since new? I just realised probably not, since you weren't aware if the egr blanking. Have any other sensors been blanked off? O2 and the like?
The mechanic says it looks like egr is blanked/deleted as it didn't move at all whilst driving and everything else was normal. All live data from his diagnostics was showing everything normal, annoyingly fault wouldn't show whilst we had his diagnostics plugged in.
Complete guess work here, but next time it does it, if you have cruise control turn it on and see if you can accelerate using the buttons/stalk or however its controlled in the Mazda, if it does accelerate then its much more likely to be a throttle issue rather than engine/sensor.
I have exactly this on a 1.9tdi.
I reckon its the car telling me its too cold to be outside.
My Mondeo diesel experienced the same symptoms your Mazada is getting. Turned out to be a fuel pressure regulator. It was intermittent and would not regulate the fuel correctly.