This is about an 05 RX8 m/t i've been working on for a customer at work. I've been baffled by this car and i've been fighting with for about a month. Mazda put a new engine in the car for the owner. It's got 86k miles. Now that it's been done the car has a low idle about 700 and it vibrates so bad it'll rattle your teeth and it sounds kinda like a motorcycle or outboard boat engine (smells like it too)The idle roughness goes away around 1500-2000rpm. The car has no power under 4000RPM. The customer had me put an advance auto parts cat. converter by mazda's request before they'd replace the engine. The old one was in chunks since an apex seal went through it.
I've noticed at idle no loads the readings are at O2 sensor: 0.000, with 38% load in the computer with over 6.5 ms of duration on the injectors like the ECM thinks the car is under a load. I've also noticed now that the cat glows bright red when it's running.
I'm wondering if there's a spark problem causing fuel to dump on the cat or the aftermarket cat is clogged causing the load conditions and low power under 4000.
The local mazda place tried to sell him plugs, wires, coils and an O2 sensor to fix it. I replaced the plugs since they were the old ones from the blown engine that mazda put in the new engine. It will now stay running and not stall but still has the other issues. Since the customer drove it and just one day heard the magic "bang" under the hood I can assume the coils and wires are fine.

 

Sounds like a blown apex seal.

 

But what's the possibility of that on a new engine? They put a reman motor from mazda in and tried to start it, it ran rough so it was towed to my shop where i got it started running rough and drove it into the shop and that's all it's been driven since this new motor.

 

Compression check it. Then you can focus on chasing a mistake on the re-install.

 

That's what it sounds like i said. Do a compression test first of all. If its below 80 psi it won't run very well at all

 

And there know for doing that if improperly installed

 

first, check all 4 plugs with a timing light to be sure they are firing, bad coils are VERY common on the 8. their placement on the engine was a horrible idea, they need better cooling.

next, what does your downstream O2 sensor read? a good O2 sensor will never read .000v so i'm thinking you have a burnt/shorted wire, a bad or pinched connection or they forgot to clip it on during the engine install(the upstream O2 sensor is connected right at the top of the transmission bellhousing between the engine and transmission so it's a pain to reach.

if all of that checks out i would do a compression test to verify the engine, just because it was rebuilt doesn't mean it either isn't damaged due to other issues or a faulty rebuild.

then check the fuel tank. pop up the passenger seat right behind the driver seat base. access the fuel pump access panel and remove it, see if there is fuel pushing out on top of the tank which will cause low fuel pressure and lean conditions. this is another common failure, the fuel pump outlet cracks just underneath the outlet port on the pump assembly, if yes then replace the whole pump module. Airtex is a cheap alternative and their replacement modules are made in japan, may even be a rebadged OEM for half the cost of OEM.

the motor mounts will also cause a rough vibration, teeth chattering. make sure neither side is oily indicating a ruptured gel innard.

the 8 has 6 injectors, also the clips can be put in the wrong order if the tech wasn't careful which will cause some of these symptoms.

one other thing is stuck auxiliary ports. the factory techs don't clean the intake and an 8 with 100k miles is going to have a TON of **** in there and possibly stuck port sleeves. you can check them by manually turning them by hand with the exception of the 5/6 port sleeves which are electronically controlled by a stepper motor. a zoom zoom or seafoam treatment may unstick them if they are stuck, i physically clean them while the engine is out.

last thing to consider, while cleaning the intakes i have noticed broken 5/6th port sleeves, the debris went through the engine and could be causing these possible premature failures. these are only small particles where the pins hold the sleeve locks in place for the gears and armatures, but even a small bit of aluminum floating around a renesis will cause all sort of bad **** to happen with their side exit ports. it may only be a 4mm by 4mm chunk of aluminum but it's still plenty enough to take out a side seal.

i'm mainly curious why the 8 guys have no such list, maybe something here or there but after only a few of these engines i have pinpointed numerous probable failure points. does no one actually look at things with a magnifying glass anymore?

 

Thanks for the info. When I get back to work friday I'll check those things. Im not getting paid to work on it so It sits in a corner and I tinker on it from time to time. So it looks like if compression is good i'm ripping the upper intake off to check injectors and 5/6.
Mazda told them it needed coils. We had a used 06 8 that got traded in but a salesman sold it the day before yesterday before i could snag it for inspection so I'm SOL on swapping coils. Weak spark would make sense dumping fuel on the cat causing it to get so hot.

 

What is it starting like? Is it blowing smoke when it warms up?

 

last post was a few months ago ....