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Old 04-06-2009, 11:18 PM   #1
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Default Knock... What do I do???

My build thread: https://www.miataturbo.net/forum/t27300/
My 'other issues' threads: https://www.miataturbo.net/forum/t32703/, https://www.miataturbo.net/forum/t33106/

So, I have been having idle issues and found an air leak around one of the injectors. I removed all the injectors to find a cracked o-ring on one of them. I replaced all the o-rings and no leaks at this point, using the brake cleaner technique recommended by Braineak (thanks again).
The idle is great now, I still get CELs but that's not the main problem.. the problem is I hear knock between 4000 and 5000 rpm under load. Stephanie sent me two maps, one rich and one regular map and both still allow some knock. She recommended I change the fuel filter... so I did, still knock is present! She had suggested before that I change the fuel pump if the knock is still there, but I don't want to do that if it just a hunch or a process of elimination. With how messy the fuel filter change was, I would probably have someone do it for me and it would probably cost 5-600 dollars
I really don't think it is the fuel pump, because I don't hear any knock above 5000 rpm or below 4000 rpm and I would guess engine load is higher above 5000 rpm than in exactly that range?!
Any ideas? I have XEDE if anyone has any different maps for a 2002 Miata...
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Old 04-06-2009, 11:59 PM   #2
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Changing a fuel pump is easy. Easier than a fuel filter IMHO. Less mess anyway. You could check your fuel pressure to see if your pump is dying.
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Old 04-07-2009, 12:01 AM   #3
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Changing a fuel pump is easy. Easier than a fuel filter IMHO. Less mess anyway. You could check your fuel pressure to see if your pump is dying.
But do you think that is it? Or could it be something else, less involved?
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Old 04-07-2009, 12:04 AM   #4
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But do you think that is it? Or could it be something else, less involved?
It's impossible to tell without knowing what kind of timing you are running or knowing what your air:fuel ratio's are like. If you want to know if the knock is fuel related, buy a wideband.
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Old 04-07-2009, 12:06 AM   #5
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It's impossible to tell without knowing what kind of timing you are running or knowing what your air:fuel ratio's are like. If you want to know if the knock is fuel related, buy a wideband.
I have a wideband, but have not tried to do a log yet. I will read up on that next.
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Old 04-07-2009, 12:08 AM   #6
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I have a wideband, but have not tried to do a log yet. I will read up on that next.
Yeah, do that. Once you know if you are getting enough fuel, you can rule out your fuel pump. FWIW, my fuel pump was weak and my tune was getting leaner and leaner. I replaced it and now everything is rich. Walbro255 is what you want.
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Old 04-07-2009, 12:09 AM   #7
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Yeah, do that. Once you know if you are getting enough fuel, you can rule out your fuel pump. FWIW, my fuel pump was weak and my tune was getting leaner and leaner. I replaced it and now everything is rich. Walbro255 is what you want.
Thanks, I will do that tomorrow hopefully.
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Old 04-07-2009, 12:14 AM   #8
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on the Walbro255, does it fit a 2002? Just in case I have to get one, I searched, I can only find compatibility with 94-97 on the websites selling it so far.
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Old 04-07-2009, 12:24 AM   #9
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I have a wideband, but have not tried to do a log yet. I will read up on that next.
Don't you have a wideband gauge? If not; you should seriously consider installing one. FWIW, I had some fueling issues myself a few months back (in my particular case it was the fuel filter but I only found out about it after I had purchased a 255 Walbro fuel pump and a new O2 sensor) and it was my wideband gauge that saved my motor then. My car was going lean when going into boost and I was able to notice it just by looking at the gauge. I even took my car to a dyno to doublecheck and found that my WB sensor was working properly and my car was indeed going lean when boosting. Just a heads up.
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Old 04-07-2009, 05:54 PM   #10
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on the Walbro255, does it fit a 2002? Just in case I have to get one, I searched, I can only find compatibility with 94-97 on the websites selling it so far.
Yes, it does fit. I have one in my 2002. If I remember correctly, no install kit was needed. Just crushing some type of washer/o-ring.
Stephanie
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Old 04-07-2009, 06:51 PM   #11
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Check your timing belt. If you've jumped a tooth on your intake cam the motor will be very prone to detonation.
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Old 04-07-2009, 08:05 PM   #12
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Default Knock... What do I do?

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