2005 6MT, 111k miles
105psi compression (low, but even).
New plugs, wires, and coils, all checked out good. Coils are after market, but i swapped rotor 1 with rotor 2 and did not change misfire.
Cleaned & performed E-shaft sensor NVRAM reset.
SSV, APV, VFAD, VDI confirmed working correctly, no other vacuum leaks found. Seeing healthy 210+ grams/sec MAF rate.

Getting flashing CEL and P0302. I have attached freeze frame data (2 files). The freeze frame indicates the issue always happens at around 7500 rpms. I can't FEEL the misfire.

Does the freeze frame data appear to indicate anything to those who are RX8 savvy? That rpm point in particular?

Also, second post shows my ESS tip has a dark spot. Not sure if this could result in errant misfires...


I've been following the troubleshooting suggested in the Mazda repair manual:
http://foxed.ca/rx7manual/2003mazdar...html#wp1025486

Here's a surprisingly good write-up on $06 diagnostics data accessible with OBD2 software, and how to interpret misfire data:
http://www.taurusclub.com/forum/82-m...-advanced.html


UPDATE 1: The misfire occurs at high rpm (>7,500), regardless of the load - I get misfire at part and full throttle. However, it DOESN'T appear to misfire even at full load below 7,500, so it seems like an RPM dependent issue and not necessarily a load issue.

UPDATE 2:
- MAF readings clearly show the APV and VDI dips. MAF is reaching 212 grams/sec, which is healthy.
- I'm seeing rich AFRs (close to 11:1) as RPMs exceed 5,500; log attached. This would not suggest fuel pump, but i'm not sure if it rules out a rotor 2 injector issue?
- I swapped rotor 1 and rotor 2 coils and plugs for the heck of it - no difference. Wires are almost new NGK.


UPDATE 3:
Issue solved. Sometimes the stupid easy things are the culprits. I couldn't tell you how many times I inspected the wires visually and with a multimeter and reinstalled as carefully as possible. Nonetheless, I believe one of the spark plug ends was exceedingly stubborn and would not make a good seat on the plug tip. This led to continuous misfires above 7000 rpms.


In addition, at the track on sunday, I fuel starved hard in a left bend, so I suspect the fuel pump was also getting weak (Thanks Charles Hill @ BHR for the well-founded recommendation to replace the fuel pump, especially after 100k miles). I've replaced the fuel pump using autozone special loan-a-tool 27160. Took maybe 45 minutes.


The combination of addressing the stubborn wire end and the fuel pump should keep my misfire issues at bay (for now!). I'll stay on top of the plugs/coils every 15/30k.


Thanks to everyone's recommendations and to the valuable misfire thread(s).


https://www.rx8club.com/series-i-tec...t-here-222280/

 

Here is a picture of my ESS after i pulled it and cleaned it. Is that dark spot normal?

 

UPDATE: Generated a second freeze frame data. Issue very consistently happens just after 7500 rpms.

 

The secondary injectors should open by 3750 RPM under heavy load (as should the SSV).

The VDI should open around 7250-7500. Have you checked that yet?

Here's good info on how to check your SSV and VDI:
https://www.rx8club.com/series-i-do-...valves-174009/

 

Yes. I used a hand held vacuum pump and checked all of the lines, solenoids, chamber, and valves. All function nominally.


From Eric Meyer in a post linked below,


Perhaps my engine is borderline lean (a single injector, or fuel pump, etc) as the VDI point is passed...?
EDIT, logged AFRs. Does not appear lean; appears quite rich after 5,500 rpms.


https://www.rx8club.com/series-i-tro...500rpm-201522/

 

I read that thread, as well.

It's possible. Do you have a way of logging the injector duty cycle or fuel flow rate? IF not, short term fuel trims and AFR might give you useful information.

 

I guess if injector duty cycle was near max, that could suggest low fuel pressure and the ECU trying to compensate by holding the injector open for longer?


I do have an OBD2 cable and laptop with which to record data. I posted one such log in the OP, but not with the data you mentioned. I will try to log AFR and STFT.


If I am seeing healthy MAF readings (210+ grams/sec), would that rule out a clogged cat?

 

If the cat is clogged enough that it's providing enough back pressure to reduce flow, the engine should just refuse to rev beyond a speed that would overwhelm the flow restriction.

Your data shows your revs topping out at 8500-ish. Is that the fastest the engine will spin (or just the fastest you're brave enough to go with it misfiring)?

 

The latter; it's still pulling strongly at 8500+, but I'm choosing to lift out of it.

 

UPDATE: I am getting the misfire flashing even at light/part throttle loads, only at high rpm. There is no misfire at high loads (WOT) under 7000 rpms. So this doesn't seem load sensitive, but is RPM dependent...

i have an OEM fuel pump laying around i will install, but i figured a weak fuel pump would only show up at high loads?

 

if I log fuel flow rate, do you know what value I should be looking for at WOT and high RPM?

 

Not a clue, sorry. If it were me troubleshooting, I'd look to see if it's plateauing around 7500 RPM.

 

UPDATE 2:

- MAF readings clearly show the APV and VDI dips. MAF is reaching 212 grams/sec, which is healthy.
- I'm seeing rich AFRs (close to 11:1) as RPMs exceed 5,500; log attached. This would not suggest fuel pump, but i'm not sure if it rules out a rotor 2 injector issue? Is this too rich potentially causing rich misfire?
- I swapped rotor 1 and rotor 2 coils and plugs for the heck of it - no difference. Wires are almost new NGK.

At this point:
- disconnect / cap off VDI and eliminate the extra airflow as a source of potential stressors (DONE, VDI is working)
- could be carbon build-up? could seafoam the engine. could just be low compression / poor engine health.
- check spark strength / wiring to coils
- wiring to injectors
- have injectors cleaned & inspected professionally
- replace the ESS (it has that funny spot, but otherwise checks out...)
- replace the ECU (not sure how i'd diagnose this, but it's the last component on Mazda's list of culprits).

 

Does anyone know when the secondary injectors come on? If they happen to be coming on at 5,500, and they (or the ECU?) have an issue, that would be an indicator. I pretty much peg the lambda sensor rich above 5,500 rpms.

 

Years probably? Cars aren't getting any better - the RX8 is a great platform for autocross and HPDE.

 

UPDATE 3:
Issue solved. Sometimes the stupid easy things are the culprits. I couldn't tell you how many times I inspected the wires visually and with a multimeter and reinstalled as carefully as possible. Nonetheless, I believe one of the spark plug ends was exceedingly stubborn and would not make a good seat on the plug tip. This led to continuous misfires above 7000 rpms.


In addition, at the track on sunday, I fuel starved hard in a left bend, so I suspect the fuel pump was also getting weak (Thanks Charles Hill @ BHR for the well-founded recommendation to replace the fuel pump, especially after 100k miles). I've replaced the fuel pump using autozone special loan-a-tool 27160. Took maybe 45 minutes.


The combination of addressing the stubborn wire end and the fuel pump should keep my misfire issues at bay (for now!). I'll stay on top of the plugs/coils every 15/30k.


Thanks to everyone's recommendations and to the valuable misfire thread(s).


https://www.rx8club.com/series-i-tec...t-here-222280/

 

Good to hear you got it fixed.