Massive backfire

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R1DSO
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Massive backfire

Post by R1DSO » Mon May 11, 2020 11:42 pm

I replaced my (presumably) OEM filter that came with my RX-8 today. It was a bit grubby and I couldn’t find proof of a recent replacement in the service records.
F34B5B0B-1EAE-4F5F-8AE2-F42DBF452F82.jpeg


So, a good excuse to get a K&N panel filter in there:
0651B5A1-6367-4006-9E6C-6427DFAB4B05.jpeg
After a few minutes of taking the car out for a test drive, it threw a check engine light. This is something I’ve been expecting since temporarily running a ghetto decat. I’ve yet to invest in an OBD scanner, so don’t know for sure, but the timing straight after the filter change felt like more than a coincidence:-k.

On another drive later that day, changing at the beep under hard acceleration from 2nd to 3rd, the car gave out a massive backfire. Nothing like the usual rotary pops – this almost sounded comparable to someone firing a gun from my back seat :shock:!

I’m pretty sure the backfire is due to unburnt fuel as a result of my ageing coils. Fingers crossed, the RRP mkIII replacements will arrive this week.

The car continued to drive as well as ever after the backfire, but I’m wondering if/how the new filter may have influenced the engine light and backfire. Could a bit more air flow have exacerbated the issues with the cat and coils?

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Re: Massive backfire

Post by warpc0il » Mon May 11, 2020 11:47 pm

It could just be that you disturbed something while moving stuff around replacing the air filter.

Prime candidates would the wiring to the MAF/IAT or the vacuum pipe for the VFAD
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R1DSO (Tue May 12, 2020 8:13 pm)
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Re: Massive backfire

Post by 350matt » Tue May 12, 2020 10:28 am

Might also be worth cleaning the MAF sensor while you're there
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Re: Massive backfire

Post by R1DSO » Tue May 12, 2020 8:20 pm

Thanks for the steer. I haven’t had the car out today, but will check the MAF and VFAD tomorrow.

Based on one of Dave’s guides, I’ve also ordered a can of CRC Air Sensor Clean to give my MAF and its housing a good clean. I wiped some light black grime off the filtered inside of the air box and first air flow straightening grill thing when slotting in the K&N. I expect the spray will be able to get out some more where that came from.

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Re: Massive backfire

Post by New Duke » Wed May 13, 2020 10:02 pm

While you're doing the MAF and poking around where Warc0il said, if you haven't already done it it's worth taking off everything there up to and including the throttle body and cleaning it all out. While you're there you can check the throttle body is opening smoothly.

Good call on getting the CRC Sensor cleaner, it's great stuff.
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Re: Massive backfire

Post by R1DSO » Thu May 14, 2020 9:15 am

New Duke wrote:
Wed May 13, 2020 10:02 pm
While you're doing the MAF and poking around where Warc0il said, if you haven't already done it it's worth taking off everything there up to and including the throttle body and cleaning it all out. While you're there you can check the throttle body is opening smoothly.

Good call on getting the CRC Sensor cleaner, it's great stuff.
Nice, OK. My can of CRC Sensor Cleaner is turning up today, but I don’t have any specific throttle body cleaner. Do you think the latter will be necessary on a 55k miles car?

It looks like many people clean the throttle body with it still bolted to the engine so that the throttle can be opened via the drive by wire system with an assistant pressing the accelerator pedal. Any drawback to that approach?

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Re: Massive backfire

Post by R1DSO » Fri May 15, 2020 11:21 pm

My MAF sense looked pretty clean when I took it out. I gave it three decent blasts of CRC with 10 min intervals + left it drying overnight before screwing it back in and checking the VFAD.

The car’s still showing a CEL after an hour-and-a-half of trouble-free driving, so I’m thinking it might be the cat (or lack of) after all. I guess I’ll need to buy an OBD II reader to find out for sure.

I’ll clean out everything up to the throttle body when the intake is out next for installing the car’s incoming new ignition system.

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Re: Massive backfire

Post by warpc0il » Fri May 15, 2020 11:41 pm

There's no point in second guessing the cause of the CEL
viewtopic.php?f=25&t=43997
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R1DSO (Sat May 16, 2020 11:52 pm)
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Re: Massive backfire

Post by R1DSO » Sat May 16, 2020 11:53 pm

warpc0il wrote:
Fri May 15, 2020 11:41 pm
There's no point in second guessing the cause of the CEL
viewtopic.php?f=25&t=43997
Thanks for the link. I hadn’t found and read that one. It looks like I’m in the market for an OBD 2 scanner now, then :).

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Re: Massive backfire

Post by 350matt » Sun May 17, 2020 8:50 am

I've got a the little brother to one of these

http://www.obdiitool.co.uk/wholesale/fo ... gIFGvD_BwE

and it works well so this one thats now on offer looks like very good value to me as you can plot out sensor outputs which always helps
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Re: Massive backfire

Post by R1DSO » Sun May 17, 2020 10:46 am

350matt wrote:
Sun May 17, 2020 8:50 am
I've got a the little brother to one of these

http://www.obdiitool.co.uk/wholesale/fo ... gIFGvD_BwE

and it works well so this one thats now on offer looks like very good value to me as you can plot out sensor outputs which always helps
Thanks for the link :thumleft:. That looks like a good piece of kit for the price.

Ideally, I’m looking for a reader that works with iOS and that I can leave plugged in for monitoring OBD data whilst driving and for track days.

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Re: Massive backfire

Post by R1DSO » Sat May 23, 2020 11:44 pm

Sure enough, from the few mins I got to play with my new OBD scanner today, my CEL appears to be from the exhaust O2 sensor and (ghetto) cat-related.

The software my OBDLink MX+ came with showed a P0139 (O2 sensor circuit slow response) code. ForScan broke this down into two sub codes (P0139-FF and P0139-C) along with showing error codes C1093-20 (ESP lamp switch defective) and U2064-FF (warning indicator requested by another control module).

I’ve yet to fully get my head around these codes, from the limited searching I’ve had time to do so far of the service manual and online. However, I’ve now ordered a Racing Beat mid-pipe with 200 cell high flow cat which I’ll fit after installing my new coils. Hopefully the cat will make the CEL go away. If not, I’ll try resetting it :).

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Re: Massive backfire

Post by qwakers » Sun May 24, 2020 8:30 am

you will need to reset it to make it go away,

id reset it now and see if it comes back immediatly. the code caused by the decat wont come back until the car has been cruising on the motorway for a while.
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Re: Massive backfire

Post by R1DSO » Sun May 24, 2020 9:08 am

qwakers wrote:
Sun May 24, 2020 8:30 am
you will need to reset it to make it go away,

id reset it now and see if it comes back immediatly. the code caused by the decat wont come back until the car has been cruising on the motorway for a while.
Got it, OK; thanks. I’ll reset the P0139 codes before I take the car out next.

I’m hoping my RB mid pipe/cat will arrive during the week. I’ll do a motorway run after fitting it to check that the CEL doesn’t come back again :).

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Re: Massive backfire

Post by untakenname » Sun May 24, 2020 12:05 pm

If the code does come back then you can buy O2 spacers which contain a mini catalytic convter that the sensor screws into to fool the car into thinking the cat is still there, cost around a tenner.
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Re: Massive backfire

Post by R1DSO » Sun May 24, 2020 4:52 pm

Deleted the PO139 code and the CEL remained off for 40mins of driving today :).
untakenname wrote:
Sun May 24, 2020 12:05 pm
If the code does come back then you can buy O2 spacers which contain a mini catalytic convter that the sensor screws into to fool the car into thinking the cat is still there, cost around a tenner.
Never heard of these. Thanks for the tip :thumleft:. Will check one out if the O2 sensor triggers a CEL again after fitting my new cat.

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Re: Massive backfire

Post by Vj4sothername » Sun May 24, 2020 5:06 pm

R1DSO wrote:Deleted the PO139 code and the CEL remained off for 40mins of driving today :).
untakenname wrote:
Sun May 24, 2020 12:05 pm
If the code does come back then you can buy O2 spacers which contain a mini catalytic convter that the sensor screws into to fool the car into thinking the cat is still there, cost around a tenner.
Never heard of these. Thanks for the tip :thumleft:. Will check one out if the O2 sensor triggers a CEL again after fitting my new cat.
RRP's mini map map will stop it from coming back. 10/10 recommend as they can tweek a few other bits also.
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Re: Massive backfire

Post by R1DSO » Mon May 25, 2020 8:55 am

Vj4sothername wrote:
Sun May 24, 2020 5:06 pm
R1DSO wrote:Deleted the PO139 code and the CEL remained off for 40mins of driving today :).
untakenname wrote:
Sun May 24, 2020 12:05 pm
If the code does come back then you can buy O2 spacers which contain a mini catalytic convter that the sensor screws into to fool the car into thinking the cat is still there, cost around a tenner.
Never heard of these. Thanks for the tip :thumleft:. Will check one out if the O2 sensor triggers a CEL again after fitting my new cat.
RRP's mini map map will stop it from coming back. 10/10 recommend as they can tweek a few other bits also.
Thanks for the recommendation. Had a look at this on the RRP website and it looks good. Hopefully the CEL won’t reappear, but I’ll definitely explore mapping further regardless when I‘ve installed a few more mods.

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Re: Massive backfire

Post by R1DSO » Thu May 28, 2020 12:53 pm

New Duke wrote:
Wed May 13, 2020 10:02 pm
While you're doing the MAF and poking around where Warc0il said, if you haven't already done it it's worth taking off everything there up to and including the throttle body and cleaning it all out. While you're there you can check the throttle body is opening smoothly.
I got round to giving the induction system a bit of a clean when fitting my new coil packs this week. There was evidence of a previous oil burp that hadn’t been cleaned up, with plenty of oil in the bottom of intake accordion pipe to clean out (although nothing in the air box).
71C5D4C0-DE27-4B03-9A5B-B18CE2A61E35.jpeg
53B7C96E-58BB-4C7A-AB0B-ADA5FEC03C02.jpeg


I didn’t take the throttle body off, but cleaned what I could get to with the throttle open. It was a bit sooty:
D04914B9-0173-4339-8AEC-EFBB6E172886.jpeg
A point of clarification on the optimal oil level to avoid future burps... is it best to keep the oil a notch (i.e. roughly 0.5 litres) below full when checking the oil level 5 minutes after shutting off a warm engine, as per Mazda’s guidance? I’ve noticed that the cold engine oil level is already roughly a notch below full, so don’t want to run with too little oil, especially on the track.

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Re: Massive backfire

Post by untakenname » Thu May 28, 2020 1:19 pm

I think it's dependant on the track, I've had my oil at max level at Brands and never had an oil burp but at Bedford I had it at halfway mark yet had two burps.
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Re: Massive backfire

Post by New Duke » Thu May 28, 2020 4:01 pm

Crikey, the previous owner (gonna blame it on them :) ) did well to get that much oil into the accordion pipe. The breather pipes were revised in the R3 so it's really hard to oil burp. I'm impressed and curious how they managed that. Massive overfill maybe? :-k

On the R3 'full' on the dipstick is indeed full and you should top up all the way to there. It's not the same as the S1. I'm sloppy with oil changes and overfill a bit fairly often, even in the middle of trackdays by a few hundred ml, and I've never had an oil burp.

Good on you for cleaning it up. I'd keep it topped up to full and forget about oil burps unless it ever happens again.
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Re: Massive backfire

Post by R1DSO » Thu May 28, 2020 11:19 pm

New Duke wrote:
Thu May 28, 2020 4:01 pm
Crikey, the previous owner (gonna blame it on them :) ) did well to get that much oil into the accordion pipe. The breather pipes were revised in the R3 so it's really hard to oil burp. I'm impressed and curious how they managed that. Massive overfill maybe? :-k

On the R3 'full' on the dipstick is indeed full and you should top up all the way to there. It's not the same as the S1. I'm sloppy with oil changes and overfill a bit fairly often, even in the middle of trackdays by a few hundred ml, and I've never had an oil burp.

Good on you for cleaning it up. I'd keep it topped up to full and forget about oil burps unless it ever happens again.
Yep, it definitely wasn’t me :D. I used half a blue roll cleaning the gunky oil out of the accordion pipe! My hypothesis is that a previous owner (or garage) topped up oil to the dipstick full mark when the engine and oil was cold, which would presumably equate to circa 500ml too much when warm.

Thanks for the steer on the R3 dipstick. I’ll keep the level at full (with a 5min switched off warm engine) then. I’ve got in the habit of checking the oil more than once every refill as the car seems to like to drink it a little more than average consumption amounts I’ve seen in various forum threads.

I’m putting this down to the R3’s extra oil injector and me regularly getting my beeps in :lol:. I’m sure my (now replaced) knackered coils didn’t help either.

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