MP5 Loss of Power at Higher RPM

Paddywiggle

Member
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2003 Mazda Protege5
Greetings,

Recently I ran into some trouble with my 2003 MP5.

Car seems to run normal at lower RPMs (500-4000), although it may not be running perfectly. I simply can't tell. The real problem hits when I start to rise in RPM. Since this car is only a 4 speed automatic, it makes my car really slow. Once I hit 4500 or 5000 RPM it loses all of its power and will stop accelerating, but still climb RPMs slowly. The car also sounds kind of stressed and under more of a load. Basically, as a 4 speed auto that means I have no potential for passing people since it requires a downshift into that RPM range in order to get any acceleration. Hills are impossible as I can't stay high in RPM to go up it, therefore losing speed gradually and pissing people off.

I checked the oil, the level is fine. Transmission fluid is fine. I use 89 octane fuel.

The car also sometimes makes a high pitched and fast rattling/ticking at these higher RPMs, and especially when going up hills. Not sure whether these problems stem from the same part.

I have been looking up this problem, obviously, and have concluded it may be a bad fuel filter? Since it has enough flow to operate at low RPM, but may not get enough fuel at the higher RPMs?

Any thoughts? thanks
 
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Keno1542

Yellow Jacket
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Mazda MP3
Our fuel filters are integrated with the pump and are supposed to be 'lifetime' filters. Have you checked operating fuel pressures? Or are you just guessing that it is fuel? I would check your spark plugs. You are on the right track though, check that you have enough air, fuel, and spark before moving on to other possibilities. Might be worth changing the air filter, spark plugs, wires, and coils if they havent been done in a while. Use quality parts if you do. NGK plugs and wires are OEM and are the best replacements for a decent price.
 

Paddywiggle

Member
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2003 Mazda Protege5
After all this time we've come to find my engine has been sending oil through the cats and the cats are all clogged up. I know straight piping the cats in california is illegal, but does anyone have any idea how loud it will becomes if I do this? Also, what kind of performance problems will I have with the engine and ECU when considering back pressure? Straight piping might be the only option I have for the long run of this car, since replacing the cats will just lead into them clogging again. Obviously, I replace the cats when smog comes up, but for now, I don't have the money and need a daily transporter.
 
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Protege5
After all this time we've come to find my engine has been sending oil through the cats and the cats are all clogged up. I know straight piping the cats in california is illegal, but does anyone have any idea how loud it will becomes if I do this? Also, what kind of performance problems will I have with the engine and ECU when considering back pressure? Straight piping might be the only option I have for the long run of this car, since replacing the cats will just lead into them clogging again. Obviously, I replace the cats when smog comes up, but for now, I don't have the money and need a daily transporter.

You will probably not notice a huge difference in sound if the factory muffler is still in place.

If it were mine I would just remove the manifold and punch out the pre-cat, see if it runs better. If not, do the same for the mid-pipe and primary cat.

As for the PCM, it does not care what kind of exhaust you have. You will likely get a PO421 (pre-cat non-functional) code, but I'm guessing that you already have that.
 
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protege5
Some seafoam at high RPM may help to clean up the cats. Sometimes they may be salvageable if you get them red hot and burn off all the crap that is clogging them up, but most of the time you'll just have to replace them. Worth a shot, don't have anything to lose. Worst case I would just take them off, hollow them out with a screwdriver and then replace them when it comes time for smog testing. Wouldn't waste the time/money on a straight pipe when you can take 'em off and ram a pry bar or screwdriver down in them for free.

But you will still need to address the bigger issue... the valve seals or rings that are causing your cats to clog to begin with. Otherwise you're just going to foul out the new ones when you replace them. Also, if it's burning enough oil to clog the cats then when removing or hollowing out your current cats so the car runs better, the car will probably smoke a lot more than before. You may not have even noticed the smoke before but i'd bet you will now. That may draw attention if the smog police see you driving down the road and ask what kind of diesel you swapped into that little car.
 

GJ-Molestor

Banned
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2011 BMW 528i, 2015 Mazda 6, 1995 Nissan Maxima Manual
I strongly agree. you are certainly burning oil or running rich if the cats have gotten clogged out. you can gut the cats (your best bet is to replace them with a straight pipe) but I would recommend tuning the ECU if you do this.

have you scanned the car for codes? CEL is on?
 
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protege5
I strongly agree. you are certainly burning oil or running rich if the cats have gotten clogged out. you can gut the cats (your best bet is to replace them with a straight pipe) but I would recommend tuning the ECU if you do this.

have you scanned the car for codes? CEL is on?

I think he lives in CA, which does regular smog inspections so he can't permanently delete the cats/tune the ECU for deleted cats. Think he's just looking for a band-aid to make the car run better until next emission inspection.

At least that's how i read it.