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Misfiring.

Old 01-19-2019, 04:57 PM
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Unhappy Misfiring.

ISSUE:
Rough idle, Reduced power, Fluctuating RPM when holding accelerator still when cruising.
All sparks other than number 1 leading are misfiring, confirmed with spark tester.

Testing/Problem finding:
Cleaned MAF: Unchanged
Checked electrical grounds: All fine
Reset ECU by stamping on brake 20 times: Unchanged
Checked vacuum lines: All were fine
Replaced stock coils with D858 coils: No change
Replaced ignition leads: No change
Replaced spark plugs: No change

Could it be a dodgy crank position sensor? I've heard they sometimes go bad on the RX8.
It's the last resort really.... I'm selling my car within the next 2 months so i'd like to fix this otherwise i'll have to sell it cheaper.

Also weirdly enough the CEL does not flash showing a misfire, but I think thats because the previous owner fucked with the ECU.
Reason I think this is because when I bought the car it had a gutted CAT... the CEL never came on.
And even now with my Decat pipe... no CEL.

- Thanks

Last edited by Surasonac; 01-19-2019 at 05:02 PM.
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Old 01-19-2019, 08:14 PM
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Have you found this thread?

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

Not every combination of ECU and O2 sensor will turn on a CEL for a gutted cat. Most do, but not all. Of course, it is possible a previous owner turned that code off in the ECU.
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Old 01-19-2019, 08:17 PM
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Originally Posted by Steve Dallas View Post
Have you found this thread?

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

Not every combination of ECU and O2 sensor will turn on a CEL for a gutted cat. Most do, but not all. Of course, it is possible a previous owner turned that code off in the ECU.
Yeah already been though that. Checked it all. Only thing thats plausible is a fuel pump issue, but i'm certain i'd be having far worse problems if that were the case.

Really wondering if anyone has had a crank position sensor go bad?

Last edited by Surasonac; 01-19-2019 at 08:19 PM.
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Old 01-21-2019, 07:37 AM
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bump
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Old 01-22-2019, 12:06 PM
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Once everything else has been ruled out, whatever remains, however improbable, must be the cause.

My money is on early fuel pump failure. Think it through logically. If the fuel pump is not providing enough fuel to match the available air, the engine will run lean, and detonation will be the result. Codes are not always 100% accurate. Can you post your LTFT and STFT values?
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Old 01-22-2019, 02:26 PM
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I'm going to put my nickel on vacuum leak.
What are your fuel trims and warm idle MAF rate?
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Old 01-22-2019, 06:07 PM
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Brilliant

Thanks for the replies. I also had a feeling it might be the fuel pump. Already looking for a new one, quite an easy job since its right under the rear seat.

Vacuum lines were one of the first things I checked, in don't hear or feel any leaks.

I'll get all those values tomorrow for both of you. I'll take it on a little drive and log some data. Thanks again
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Old 01-23-2019, 08:11 AM
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Originally Posted by Surasonac View Post
Thanks for the replies. I also had a feeling it might be the fuel pump. Already looking for a new one, quite an easy job since its right under the rear seat.

Vacuum lines were one of the first things I checked, in don't hear or feel any leaks.

I'll get all those values tomorrow for both of you. I'll take it on a little drive and log some data. Thanks again
You won't usually see or hear vacuum leaks until the hose or fitting is literally falling apart. Vacuum leaks start well before then.

MAF rate and fuel trims at idle after the engine has warmed up will help rule this out.
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Old 01-23-2019, 09:16 AM
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Results



LTFT is always 8.59%. The time shown at the bottom of the graph is mm:ss. This is quite mild, its usually fluctuating even more.

Last edited by Surasonac; 01-23-2019 at 09:50 AM. Reason: Update
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Old 01-23-2019, 09:34 AM
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Your MAF rate is a little low and LTFT a little high but not enough that I'd expect it would cause a misfire. You might have a vacuum leak but, if so, it's really small so I'd bark up other trees for now.

Next step will be to get a fuel pressure test.
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Old 02-23-2019, 07:34 AM
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P0302 Press gas pedal to start

I have a P0302 code and have issues starting my car cold or hot
Ive replaced Coils,Plugs,Starter,Wires,Fuel Pump, Cleaned MAF, Cleaned throttle body.
I have no idea what is wrong with my car it seems fine when i drive it only the starting issue.
Ive noticed that if im at a dead crank were the engine dosnt start if I press on the gas pedal a
little bit the car will turn on.
BUT I HAVE TO PRESS THE GAS PEDAL WHEN YOUR NOT SUPPOSED TO
Anyone know what could cause this and misfiring
---Thank you
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