Newbie - Week #2 Modding Results
05-22-2011, 11:54 AM
#41
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Just a quick update: I've talked to three tuners, and they all think that the engine is sporadically misfiring under low RPM, torque demanding situations because the fuel/air mixture is being driven extremely lean due to the lack of cats (the ECU is trying to compensate).
But *if* they are looking at datalogs, a misfire will show as lean, when in fact it is fuel rich (as none of it burned). O2 sensors, as the name implies, sense oxygen. In a misfire condition, it will sense a shitload of oxygen, and report an extremely lean condition.
Also, cats are downstream of all the control inputs. Other than possibly increasing the exhaust flow, they should have no effect (as others mentioned). Plus you are talking about low RPM events, where exhaust flow is not huge.
05-22-2011, 12:08 PM
#42
Yeah, to reiterate: you (OP) really need to start by eliminating the more obvious things that cause misfiring, such as possibly the dropped plug and making sure your filters, injectors and ignition is in proper order before you start throwing a bunch of random ideas on it. If, after you are sure the car is running right, THEN you start getting into things like the tune and so on. However, if you're not running cats and no O2 eliminator or something (compensate in the tune) and/or doing things the ECU was not designed to do (stock), then IMO you're asking for mystery issues. Still, regardless, start with the more obvious areas...
In troubleshooting, you always start with the obvious and easier items and generally speaking, most of the time you'll find your problem there. I see too many people (and I've ben guilty myself) of thinking the more complicated, expensive items must be the culprit, when it's something simple and a 'duh' type thing, lol.
btw - I just replaced my ignition wires yesterday (they are like $30 if you look around) and it was literally a 15 minute job and man I was surprised at the difference in idle quality and smoothness driving around...Even sounds better.
Why people don't run cats, I don't understand, but ask yourself is it worth the headaches if you don't do it properly, like compensating to the ECU somehow.
In troubleshooting, you always start with the obvious and easier items and generally speaking, most of the time you'll find your problem there. I see too many people (and I've ben guilty myself) of thinking the more complicated, expensive items must be the culprit, when it's something simple and a 'duh' type thing, lol.
btw - I just replaced my ignition wires yesterday (they are like $30 if you look around) and it was literally a 15 minute job and man I was surprised at the difference in idle quality and smoothness driving around...Even sounds better.
Why people don't run cats, I don't understand, but ask yourself is it worth the headaches if you don't do it properly, like compensating to the ECU somehow.
05-22-2011, 08:24 PM
#44
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Plugs, and wires, it was like a completely different car. Next we did was wheels/tires, and it felt like it was brand new.
It's amazing how just the "small" things can make a huge difference.
-meaty
05-26-2011, 12:02 PM
#45
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Not to thread jack but... My car back fires like crazy between gears while under load. I have the P0420 code, no cats. I've been told that a tune along with a "turn off rear O2s" tune will fix my problem, but from what ya'll are saying, it won't? I have replaced all wires & plugs.
05-26-2011, 11:53 PM
#46
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Not to thread jack but... My car back fires like crazy between gears while under load. I have the P0420 code, no cats. I've been told that a tune along with a "turn off rear O2s" tune will fix my problem, but from what ya'll are saying, it won't? I have replaced all wires & plugs.
You can't knock the badassedness that comes with an angry V8 and explosions...
Any idea if you get flames out the back?
-meaty
05-27-2011, 05:10 AM
#47
You really haven't posted much in the way of findings (vs opinions). So I've no idea what your tuners are going on.
But *if* they are looking at datalogs, a misfire will show as lean, when in fact it is fuel rich (as none of it burned). O2 sensors, as the name implies, sense oxygen. In a misfire condition, it will sense a shitload of oxygen, and report an extremely lean condition.
Also, cats are downstream of all the control inputs. Other than possibly increasing the exhaust flow, they should have no effect (as others mentioned). Plus you are talking about low RPM events, where exhaust flow is not huge.
But *if* they are looking at datalogs, a misfire will show as lean, when in fact it is fuel rich (as none of it burned). O2 sensors, as the name implies, sense oxygen. In a misfire condition, it will sense a shitload of oxygen, and report an extremely lean condition.
Also, cats are downstream of all the control inputs. Other than possibly increasing the exhaust flow, they should have no effect (as others mentioned). Plus you are talking about low RPM events, where exhaust flow is not huge.
The cats (both the OEM ones and the aftermarket ones) are right in the middle of the two sets of O2 sensors. Unless I'm misunderstanding you here, you're wrong on this count.
05-27-2011, 08:35 AM
#49
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Thats how the "low catalyst activity", and related codes pop up
05-27-2011, 02:58 PM
#50
I think your brain needs a tune. A lot of the advice provided is complete and utter BS (especially some of the electrical stuff regarding spark plugs). I won't say any more than that, given my job and my aversion to starting flame wars.
05-27-2011, 05:56 PM
#51
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Sounds like you are living up to your screen name. Sometimes what you see on paper isn't what it is in real life. If you have all the answers already, go get the damn thing tuned and then let us know what really fixed the car when the tune doesn't.
Last edited by raven154; 05-27-2011 at 06:01 PM.
05-28-2011, 08:01 AM
#53
I didn't mean you need a tune or to turn it nasty. You are ignoring the advice of most likely years of experience with cars. It was already mentioned you should start with the simple items first. Checking resistance on the plug wires means nothing. Let me repeat that. Nothing. You already admitted to dropping a spark plug on the ground. So my point was go get a tune if thats what your heart is set on.
05-28-2011, 11:23 AM
#54
If the tuners think it's running lean, do your own test. Unplug both front o2 sensors and see if that makes a difference, drive it around shortly and listen for any missfires/roughness etc. If it makes no difference then you can eliminate the "too lean/needs a tune" issue and move on.
05-28-2011, 11:32 AM
#55
I didn't mean you need a tune or to turn it nasty. You are ignoring the advice of most likely years of experience with cars. It was already mentioned you should start with the simple items first. Checking resistance on the plug wires means nothing. Let me repeat that. Nothing. You already admitted to dropping a spark plug on the ground. So my point was go get a tune if thats what your heart is set on.
2. You're talking to an electrical engineer specializing in power, freshly graduated from the #2 EE graduate program in the country. You're wrong, and it's obviously not worth my time to educate you. Rant all you want about how it doesn't matter--I don't care.
3. Dropping a spark plug on the ground is not a big deal. There's nothing magical or complicated about them. As long as the fall didn't crack the porcelain insulation, chip the insulator tip, change the gap, or introduce foreign material into the center electrode area, you're good.
The amusing thing about the incessant discussion about the spark plug is that I had sporadic misfires on all eight cylinders after the header installation, not just a misfire on one cylinder. On a related note, if I needed new spark plug wires, either because I damaged the wires when removing them, or because the stainless steel headers did not block EMI as well as the cast iron manifold, the problem would have been continuous and gotten more pronounced as RPM increased. In this case, the exact opposite was/is true.
As far as I'm concerned, I'm wasting my time on this forum. Once I'm done with my V, I'll do a summary post for the benefit of new members and then stay away.
05-28-2011, 04:10 PM
#57
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+1 No offence but you came on here claiming to be a "newbie" and looking for help, and told everyone you asked help from they were wrong. And even got upset from the people who wrote 'how to's'. Having a bad attitude is not a good way to get any help around here.
12-01-2012, 03:31 AM
#60
Installed new spark plugs (NGK TR55IX) and wires (MSD 8.5mm) to no avail. Got the car tuned, and the problem went away instantly. Never came back.
The problem with the Internet is that bad ideas come premixed with the good--you're in for a world of pain if you can't or won't exercise critical thinking when reading forum posts.