P0302 Missfire and Power Low (-60BHP) - Help Please
 

Hi

I am new to the owners club and this is my first technical related post so if I miss anything please let me know and sorry it's going to be a long as a lot of diags have been done.
It is a UK 2007 Kuro with 25K Miles on the clock
I would really appreciate any help and advice you can provide.
Well after looking for a long time I recently bought a Kuro privately and love it.
I had a thorough test drive and everything seemed OK though I didn't drive it too hard. It started perfectly when hot too and still does.

However it has became apparent I may have some issues when the CEL came on.
I booked it in for a service as I had intended to anyway. The codes shown were P0302 and P0420.
The diagnosis was the CAT required replacement and this has been done.
Unfortunately this hasn't cured the problem and so after further diags the misfire code is still present and the car is 60 BHP down.
The following has been done by experienced rotary engineers to try and resolve this.
• Coils, sparks and leads have either been changed for new or known good sets.
• Exhaust (after Cat) has been checked.
• MAF and ESS have been changed with a known good one.
• Valves have been checked for correct operation.
• Operation of secondary shutter valve has been checked and OK. Loud noise at higher revs not expected sound with intake box off.
• Air filter has been replaced as existing was blocked.
• Checked pressure of fuel pump
• Compression test has been performed twice with the following results
o Front 7.10 7.15 7.60 280 RPM
o Rear 7.40 7.80 7.30 280 RPM

And possibly more
I trust the mechanics but am now at a point where I think this is such a rare issue that I wondered if anyone else might have seen this before.
The thought now is that one or more of the Apex springs under the seal is slack or similar and not holding the seal at high revs. I thought the seals would stay closed due to centrifugal force but I am not an expert, just my thoughts.
Any suggestions/advice would be appreciated before I get the engine stripped and rebuilt.
Thanks in advance

Well
1) How do you know you are down 60 BHP?

2) Assuming that those are "already" normalized compression values your engine hasn't exactly done that well, it's pass is marginal at best.

@250rpm Kg F / cm^2: 8.5 Standard - 6.9 Minimum - 1.5 diff / chamber - 1 diff / rotors

3) Check that the plug leads are on correctly

You wouldn't be the first person to lose an engine due to a failed Catalytic.

Hi WCS,

Thanks for the reply.

1) The car has been on a proffesional Dyno/Rolling Road tester

2) Take your point about the compression figures. Starts great hot or cold though

3) Plugs and leads have been checked with new.

The car is in with a pro rotary workshop.

They may have heard this noise when checking the operation of secondary shutter valve once before in a race car but as it was not a commom problem I decided to see if anyone had experienced this. They say they are 95% sure a rebuild will cure it.

Thanks

Stu

What do the LTFTs look like? AFRs? Any evidence of an exhaust leak between engine and cat? Air injection pump working properly? Condition of O2 sensor?

Fried coils didn't burn enough fuel, it burnt the cat that clogged and overheat the engine accelerating its wear. Have fun rebuilding it, looks like the "rotary specialists" you brought the car to aren't too smart.

1) Being down 60 BHP only counts if you have had a previous dyno .. even then you could argue it's not apples to apples. Understand that the RX8 never delivered (very rarely) the advertised BHP.

2) If those compression values are not normalized your engined failed .. and failed with authority

I was rolling this around as well, I've had failed O2 sensor give me issues.
Funny thing is, when I experience misfires that I can feel/sense the car never seems to pick them up.
When and if I do get some misfire events, to me the car seems to be working fine.
<shrug> I guess I just suck

A failed o2 sensor may indeed cause a lack of power or whatever but given his compression numbers i'd just throw it in with the rebuild kit order lmao.

HiFlite999,

Sorry I don't know what LTFTs and AFRs are.

I am sure the CAT/Exhaust are OK

Not sure about the air injection pump.

I will try and ask today.

bse50,

You may be correct with your diagnosos though Orginal Coils changed about 20K and new ones have about 5K on them.

Glad someones getting some amusement out of this ;-)

WCS,

I agree that it can not be said that it is specifically 60BHP down. Though it was 30BHP lower than a 192BHP one they also have in.

I'll check about the compression figures. Though no issues apparent at low revs and also starts just as good hot.

I'll ask about the o2 sensor.

Thanks Stu

Once the damage is done to the cat you can keep changing coil as much as you want unfortunately but the heat from the cat and the possibly faulty o2 sensor will keep on damaging the engine.
Low compression may result in just a loss of power without other issues, add a possibly faulty o2 sensor and you get the picture.

Long Term Fuel Trim, and Air Fuel Ratio.

They did at one stage say it was running lean at high revs. That was fairly early on in the diag.

That's not good

I am starting to think I'm just gonna run it for a bit as it is and at some point sell it and declare what I know about the problems. It will still be faster than anything else I have driven.

It's gonna cost me £3k for a rebuild and it needs some work on the brakes so I might just keep the cash towards something else when the time comes.

I did order one of the OBII devices. I used to be pretty good with cars but well out of practice and no experience with rotarys.

"lean at high revs" could be from a misfire which leaves extra oxygen in the exhaust stream; ironically the actual mixture is then too rich (a cat killer). Did you check that the spark plug wires are connected to the correct plug position and that the "T" and "L" plugs are in the correct spots?

What mods do you have?
Are you running the Stock Air Intake?

Hi HiFlite999,

I don't have the car at the moment it is with a rotary specialist. They have tried everything they can think of including plugs coils and leads.

The only reason I am pursuing this is that they say the compression is OK even though I have had a comment to say that if the compression test was performed at 280RPM then the figures would be lower when normalised.

They are pretty sure (95%) there is an issue with one or more of the apex seals and reccomend a rebuild.

I'm not sure I want to spend the money as I would be looking at double the purchase price of the car with a rebuild, new cat (purchased and installed) and some work needed on the brakes.

Hi WCS,

All stock as far as I am aware.

Stu

Hi,

Update on Compression values. These have been normalised to 250RPM even though the test was performed at 280RPM

I have also asked about the noise. It is a machine gun type noise that start at about 7000RPM

Thanks

Check your SSV if it comes from the engine bay.

Does it sound like this youtube video in this thread, post#1

https://www.rx8club.com/trouble-shoo...-rotor-238946/

They heard the noise while checking the SSV and it is working OK.

I haven't had chance to hear the noise yet but I get it back over the weekend and will take a look then.

Thanks

Exactly how many HP did they say that your car has?
Don't tell us how low it is compared to other cars, or how many it is low vs an imaginary number, just tell up how many hp they claim it currently has, and what company dyno it was tested on.

You car might be fine in that regards, or getting a bit weak.
Also, are your tires stock size, or do you have a different setup?

BC.

Hi it was tested on a Dynapack machine

I have 2 sets of figures relating to BHP

137HP 117MPH 7075 RPM
148.8 HP 118MPH 7144RPM

Some other figures are with this

Ratio 4.4
tcf 1.18
gain 11.8

Wheels are stock and I believe the tyres are but I will have to check

Update

Tyres are also stock size

Stu

Is your car a high power or low power car?
With hp values that low, I think you are either a high power car with an internal failure (low compression, etc), or a low power car that's right about where it should be.

I believe all low power 4 port engines only rev up to 7500 rpms, while all high power 6 port engines go up to 8500, unless attached to an automatic transmission.

BC.