Engine stmbles under even moderate load

RABID_MP5

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2002 Protege5
New problem started in last couple days. Starts and idles down OK. Runs fine under very light load in all 5 gears. But get on it even a little, or go WOT, and it bucks constantly. Stock engine with 250K miles. No codes in ECU (yet). Much worse will be undrivable. Running Injen intake and the MAF to throttle body hose looks good.
 
Have you checked for air leaks? Not just air intake, hoses on the IM as well, if EVERY hose is fine try seafoam. In oil gas and in the brake booster.
 
I didn't see or hear any leaks. I'm leaning towards fuel pump. Any easy way to check the rail pressure, etc.?
 
I would put money on intake leaks. My car had those issues when I was experimenting with CAI's and honestly they aren't worth it. Just go back to the stock intake. Check your intake filter. You won't see or even hear leaks. The engine noise will cover up miniscule air leaks and it doesn't take much of a leak to totally mess up the idle.

EDIT: https://www.mazdas247.com/forum/sho...ty-air-filter-dead-MAF-learn-from-my-mistakes!
Make sure this isn't your problem. Especially if you live up north.
 
Injens been on there 150K miles. Again, the idle is fine. At WOT there's practically no intake manifold vacuum too, so that pretty much covers vacuum leaks. Autozone has the pump in stock for 35 bucks. I may do the filter body too since I'm due. It's one of my less favorite things to do. So I'm still wondering if I can take the pressure first. I wanna say there's a schraeder valve somewhere? Not sure.
 
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Did you spray around the hoses on the IM or intake? If the idle changes at all it's a leak. When giving it WOT it wants to suck in more air. If you get more air then fuel it'll bog down, if your not getting enough fuel it'll eventually die.
Check for a vacuum leak. ALL THE HOSES, if not use seafoam. Use most of your fuel then put it in before filling up, then put some in the brake booster. That will help clean everything out.
 
When did you last replace the coils and spark plugs? Sounds like a failing coilpack or dirty MAF, could try cleaning that first.
 
I'd like to test the fuel pressure. I don't know the spec and I don't see where to hook one up. Somewhere I have a spare coil I can try too. MAF cleaned but wasn't it.
 
100% coils. Put on 2 new coils and fresh spark plugs and your problem is solved. Had the exact same symptoms. When driving normal and idle all is ok, but when you want to accelerate and in particular like driving beneath 2500rpm and you press the pedal all power is gone and runs on 3 cilinders.
 
just did this yesterday (converted to 1.8 liter coils though)... solved all acceleration issues! was having my car stumble like crazy until 2000rpms. usually ignition is the first thing you wanna check. new plugs + coils/wires are cheap... start there for sure!
 
Well thanks guys. You were right again. I just got one coil to test it. First swap - no difference. Second one bingo. I'll order a second new one and carry the old good one as a spare and for testing. Check out the plugs too. Only 50K miles on the coils too. I even noticed the bad one had a slight electrical burning smell to it.
 
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Always buy the OEM spec coils, not the cheap copies. The copy coils will give you nothing but headaches.

The OEM spec coils have the following markings on them. These are the "Hitachi/Mazda" coils, but are available through other retailers cheaper than Mazda spares.

coilpack.jpg
 
isn't there a way to test if a coil is bad? i have a spare and wouldn't mind learning how to.

(awaits instructions from pcb)
 
That's what sucks about coils for our car ... They can bench test fine and still fail when they're on the car.

Temperature, humidity, engine load, whatever, they just fail when they feel like it.... And not necessarily enough to throw an engine mis-fire code.

And,.. an engine misfire is the only code that flashes the MIL on our car... You can fry your pre-cat in a couple of minutes if raw gas is dumped on it... A $1,200-1,4000 job if OEM parts are used.

In California, OEM parts must be used for any emission related repair.

So Yea... There's a test for our coils, and if they test bad then they're definitely bad, BUT they may be crap even if they test fine.

They can even be crap brand new outta the box... But still test fine...

So here's the bench test... (make sure your bench is hot, humid and shaking a lot)



 
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