I'm troubleshooting a high load misfire and could use some advice. Car is an '04 MT with 56k miles, engine was replaced by 1st owner at ~25k miles. Bought the car in October and have put about 2k on since (2nd car, planned to use for track/DE events once in good condition).

Main symptom is a CEL flash with pending P0301 code stored, no freeze frame data available. Originally the problem occurred at moderate load, high RPM in all gears. After replacing all plugs/wires/coils with BHR kit situation greatly improved, but I can still generate the code at full throttle, 3rd gear or higher, >7000 RPM; basically any case which generates more than 200 g/sec airflow.

Planning to check all connections, swap plugs to see if the problem moves with the plug to the rear rotor, and do a compression check next. Are there any other diagnostics I should be considering?

 

Seafoam

 

Devilboi probably has a good suggestion, especially if the previous owner babied the car too much and allowed carbon buildup to occur.

You sound like you are no stranger to shadetree mechanics so assume you've also already checked out your cat for any signs of plugging or failure.

 

Yeah, I was gonna respond last night in a similar fashion. Sounds like he knows enough and is on the trail.

I guess one could clean the MAF and see if that helps as well?

Maybe for the hell of it, double check that a plug wire isn't loose at one end.
Since it's a "new" BHR ignition system, shouldn't be any problem there.

I will also assume..............although it shouldn't matter...........have you done the 20 brake pedal stomp reset?

Have you clean the ESS?

Just some food for thought..........not sure how many of the above would even apply?

 

I haven't pulled the cat yet to check condition, but agree it is suspect. I've ordered a BHR midpipe with cat to replace it regardless. Just waiting for delivery from BHR (or more accurately, their suppliers).

Is there any way to check the cat without physical removal? I can see a thermocouple value for the cat with my OBD2 scanner, any particular values which indicate danger?

 

Thanks for the suggestions. I've reset the ESS profile with the brake stomp method but it made no difference. MAF, ESS cleaning, and ignition check are all on the to-do list.

 

Without actually dropping the cat to look inside, the next best visual clue is to warm the car up and then go out and run as hard as the car will let you for a little while when it is dark outside. Then pull over, get on the ground on the passengers side, and look at the cat. If your getting any reddish glow you probably have a problem.

Here are a few other sites to hit with better technical data to use if you have the test equipment to go along with same:

http://www.finishlineperformance.com...4-08-1924g.pdf

Read the first & second page thoroughly to see how Mazda techs check the cat converter using Mode 6 data. Here's a wiki link to Mode 6 data:
http://en.wikipedia.org/wiki/On-boar...e_of_Operation

Here is a link to an online manual for Series 1 RX8:
http://foxed.ca/rx7manual/2003mazdarx8/

 

Not really on the ODB scanner, unless it's throwing a code. I monitor my CAT temps full time and generally see 1500--1650F during the course of a drive. At idle, it will drop to about 1340F over time.

You can take off just the front of the CAT, pull it to the side and then peer in with a flashlight and see if the honeycomb is intact.

Another way, but not sure the overall validity is to go for a good hard drive in the evening, then when stopped, take a look underneath and see if the CAT or area around either o2 sensor is glowing.

Damn it VooDoo.........we was typing at the same time!

 

Quick update, was able to check a few more things with my OBD2 scanner. Cat appears to be ok based on the scan tool data.

Rear to front switch ratio = 0.684 (range 0 to 8 expected, replace if >4.6)
Idle cat temp = ~1100F/600C (>531C expected per manual)
Driving cat temps = 700C to 920C (~1300F to ~1685F)

Plan to compression test this weekend. Since I plan to keep this car for a while I've sourced my own tester. Won't be too upset if it is the motor, as I calculated cost of a replacement into the purchase price when I was shopping last fall.

 

Well id help but you seem to be on the right track.

 

Engine is covered under warranty still. They are just going to say you need new plugs and coils.

 

Long overdue update.

Cleaning ESS and resetting memory had no effect.

Cleaning MAF had no effect.

Plugs look good, swapping plugs from front to rear rotor had no effect.

Compression test shows all rotor faces above 120 psi (corrected to 250 rpm cranking). Front rotor (124, 123, 123) is lower than rear rotor (129, 129, 131), but all in spec. Interesting that misfire to date is only front rotor - possibly related? Actually kind of surprised at the normal to high compression - could carbon build up result in too much compression?

Have BHR mid with cat in house, will be installing this weekend if luck holds. This should rule out any issue with the installed stock cat, even though it tests ok per Mazda's standards on a scan tool.

Beyond this, the main thing left I can think to check is the fuel pump starving the engine at high RPM. Anyone know what AFR should been seen at high load, high RPM with a stock calibration?

 

Damn, that's a high compression reman motor, nice.
Mazda runs these cars RICH at high load so on the stock wide band, you'll most likely peg the sensor at 11, or at least I used to all the time.

 

It would seem I'm having this issue as well, all of my ignition components were replaced at the same time the clutch and engine were, minus the wires, but I just did those, so..minus the cleaning the MAF, I'm at a loss.
I'll keep you updated.

 

Agreed, and since this is the first time I've used this compression tester (Rotary Diagnostics ReCT-MMT) I'm a little skeptical of the results - pressure transducer might be out of calibration, etc. At least the readings are consistent. If it really starts to bother me I'll find a regular compression gauge and see if the average of the faces still has the same magnitude.

 

I've had the same issue when I red line the engine at full throttle. I too have the full BHR kit, let me know what you find out.
I still need to sea foam the engine to see if that helps.

 

Sounds like you may have an issue with the plug wires seating into the coil packs. Its a pretty fragile connection if it was installed incorrectly the terminal may be shorted.

FYI its very easy to break those terminals, so if you remove them from the coil packs be patient and take your time.

Also you may have a fried coil pack, I forget what they are supposed to ohm out to but they are d585 coil packs you can Google it.

 

i get that on some track days.. in order. check wires for tight. plugs. then coils..

and i got to tell you sometimes on a track day, when everything is fine, i get it.

and it just goes away. usually in the middle of a session..

thanks denny.

beers

 

Removed stock midpipe and header today as part of BHR midpipe and RB header install. Cat has no visible issues, as expected based on scan test results. Unfortunately I can't debug further for a while - passenger motor mount was partially broken, need to get this fixed first.

Any chance extra vibration (or knock sensor activity) from a busted motor mount can result in a misfire code?

 

Some people have related a misfire to a busted motor mount. For me personally, not the case. My passenger side mount went after a few years on my 03 build MT, only indication was a small amount of vibration at idle.

 

Another one who is behind the times;
1) The BHR Ignition System has come with improverd terminals for a LONG time now and they are no longer fragile.
2) Resistance values mean little or nothing for internally-ignited coils.

If you have more than 80K miles on our car, Karl, you may have fuel pump problems.
If you suspect coil misfires, place a timing light on each coil and rev the engine to redline. Should you have problems, send me an e-mail and we will fix it.

 

It is actually somewhat difficult to get the knock sensor to do anything, even when it is supposed to.

Weakened motor mounts have indicated engine problems (not caused them), most notably shaking idle, because the engine NVHs more easily enter the passenger compartment.

 

Exhaust and motor mount are installed. Drove about 100 miles, including a few dozen runs to redline, and have not seen the blinking CEL. Not declaring victory yet, but it is certainly a good sign.

Going to take a second look at the cat I pulled off. It passed the scan tool diagnostic from Mazda, but it does seem to be the most likely culprit.

 

Which mount was it that you replaced?
Because I'm still getting the Blinking CEL after installing my mid pipe. I don't ever feel a loss in power, just the ******* light.
Lol

 

Thats not uncommon man, most people get cel's after installing a mid pipe.