revivo73

Hello

2006 RX-8 has 123.000 km (~77k miles) on it. Engine was replaced as brand new at 88.000 km (~55k miles)

Battery, coils, spark plugs and cables are all replaced at 121-122.000 km (~76k miles) The catalytic convertor was removed at 101.000 km (~63k miles) and since then it's been running without it.

So the engine runs perfectly on every rpm in its normal operating temperature. No misfires or missing fires even at 8500-9000 rpm range and the car can go uphill roads steadily at idle (750) rpm.

But there's only a cold-start problem: When I leave the car for about a day (i.e. completely cold engine) and then turn the ignition on, the engine begins to run after 1-2 seconds of revolution but it gets stuck at 1250-1500 rpm for a while. I think that low rpm causes one or two explosion sounds and then several moderate bump sounds at the exhaust. Please note that it never refuses to start when cold, it always starts albeit with these disturbing sounds at the exhaust.

In hot starts, there's no problem whatsoever. In a typical hot start, the engine revs to ~1250 rpm then drops to normal 750 idle rpm.

The car wasn't making any cold-start problems until the last spring time. It used to start at 2000-2250rpm and then gradually falls back to below 1000rpm, which I think is the normal cold-start values.

I suspect that problem might be caused by the starter failing. I guess it finally started to fail after 7 years of operation and is no longer able to rev the engine to 2000-2250 rpm range.

The question is, could this starter be failing? How to make sure that it's really failing? Is this cold-start problem I talked about be a symptom of a failing starter?

godesshunter

Not likely the starter. The starter motor only spins the engine at about 300 rpm. From then its up the the engine to take over and run on its own. As soon as the engine fires and is running, the starter motor's job is done. How the engine runs after 300 rpm is up the the engine.

The moment you let go of the key, the starter bendix drive retracts and is no longer doing anything.

revivo73

Alright.

But I wonder what else could be causing this problem. When I turn the engine on late at night and when "bang bang" sounds come from the car, the neighbors are distracted. I must prevent it from happening somehow.

Before the summer, it never made such a problem. I suspect the spark plugs too. They are used for about 3000 kms or ~2000 miles but the car rested too long (1-2 months) without being driven before that cold-start problem began.

godesshunter

Did the problem start after you did the coils, plugs, and wires? Do you have the correct parts in the correct position?

revivo73

It basically started after I replaced the spark plugs and engine oil in April 2013. Because of a problem in the clutch it rested for about 1,5 month and after I started to drive it in June, I noticed this problem for the first time. Even on hot June days, it started to make the explosion sounds at the exhaust. At that time, the coils were factory fitted (7 years old) and the wires were old too. But even after I replaced the coils (Mazda OEM) and wires (NGK blue coloured) that problem is still there.

I have a workaround for this problem: If I press the gas pedal a bit while turning the ignition on, it helps the engine rev to 2000 rpm and it operates totally normally afterwards. Simply because it has past the 2000 rpm level. No explosion sounds at the exhaust and the rpm. gradually and steadily lowers to below 1000 rpm, in that workaround solution.

That seems to show that engine needs more revolution at the cold-start. That's why I 'm suspicious of the starter. Is there a way of knowing if the starter is failing?

godesshunter

You may need to reset the ECU after all those parts were changed at once. https://www.rx8club.com/series-i-tec...r-reset-27548/

A bad or weak starter will typically give you problems during hot starts. The only way I can think of how to test one is to plug in a OBD2 scan tool that displays engine live data, disable the fuel and crank the engine. You can then read what the engine RPM is while cranking.

revivo73

Thank you for the suggestion.

I didn't know the ECU must be resetted after all ignition parts are changed. I haven'y done any ECU reset so far. I will try resetting it. The engine has been waiting for 36 hours and the outside temp is 13 C, it's completely cold engine now.

Edit: There are 2 different ECU resets. NVRAM and KAM. Which one should I do for my case?

godesshunter

Do them both. Then make sure to allow time for the computer to "relearn" it wont be immediate.

revivo73

I did both NVRAM and KAM reset. First NVRAM then KAM. And here is how the engine started as cold (video) It started quite fine without getting stuck at 1000-1100 rpm range causing unburnt fuel and explosion at the exhaust. But still, you might notice that the engine revs up to ~2250 rpm a bit cautiously, I mean it doesn't go there very quickly. I wonder if it's alright. Then there are one or two rev changes between 1750-2000 rpm. I wonder if they are alright. I also wonder if it's ok if the engine idles at 750rpm at normal operating temperature (see picture below) It usually idles at 750 rpm.

Note on the video towards the last 1-2 minutes I press on the gas a bit.

godesshunter

Everything seems fine... I think I heard a few of the pops when the engine was cold. Mine does that also while warming up on cold days but goes away after a minute or so.

revivo73

Yeah I agree, the engine is much better at cold starts now. Here is my 4th test: