408 running rough headache for 2mo!!
01-09-2007, 10:37 PM
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408 running rough headache for 2mo!! Yeah I've had some damn missfire or whatever it is that I cant trace.
It happened after a highspeed run where I maxed-out the car in 5th@7k... afterwards the car has always been running rough and SUPER rich. It runs fine and stoich for a while then goes back to running rough, I cant duplicate the problem nor can I resolve it. It seems that it runs better at higher rpms and under load.
I've checked so far:
Could it be a burnt head gasket??? (no water in the oil, nor oil in the water, and motor doesnt smoke) Exhaust leak maybe??? Fast Intake leak???
I have EFILive I'm just not good enough to diagnose something like this with it.
Also I just bought a lazer pointer thermometer so that I can check the temp on the exhast primaries in the hopes of figuring something out.
Anyone have any ideas what this could be? Experiences etc... Mods are in sig for reference.
It happened after a highspeed run where I maxed-out the car in 5th@7k... afterwards the car has always been running rough and SUPER rich. It runs fine and stoich for a while then goes back to running rough, I cant duplicate the problem nor can I resolve it. It seems that it runs better at higher rpms and under load.
I've checked so far:
Could it be a burnt head gasket??? (no water in the oil, nor oil in the water, and motor doesnt smoke) Exhaust leak maybe??? Fast Intake leak???
I have EFILive I'm just not good enough to diagnose something like this with it.
Also I just bought a lazer pointer thermometer so that I can check the temp on the exhast primaries in the hopes of figuring something out.
Anyone have any ideas what this could be? Experiences etc... Mods are in sig for reference.
01-10-2007, 04:09 PM
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O2 sensor could still do it while in closed loop and causing it to go into OL. If it goes into OL and the VE is off it could still have poor performance at idle and midrange and seem to be ok under load or WOT. You can check for 14.63 in CL and see what happens when it runs rough. Have you done a complete autove in OL to set the VE table to match your setup? You can also do the cylinder balance check with Efilive to see if one cyl or more is down in power at idle? Any Codes? I had an intermittant O2 problem that acted like that and didn't set a code.
01-10-2007, 04:31 PM
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I've done the cylinder balance test and the results are all over the place. There are no codes that I'm aware of, but then again, a lot of them are commanded off.
What was the problem with your O2?
Is there a way to check if its a bent pushrod without taking them off?
What was the problem with your O2?
Is there a way to check if its a bent pushrod without taking them off?
01-10-2007, 04:40 PM
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A bent pushrod is easy to check. Just remove the coilpacks, remove the valve covers, remove the rockers and pull them out. Put them on a very flat surface and roll. If this is not the problem I would say a lifter or two. And that is a bad day....I am having that day right now.
01-10-2007, 04:50 PM
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The sensor was fouling similar to a plug after being way too rich before I got the VE setup. I replaced it and it was fine. How does your VE look comparing commanded AFR to actual AFR in CL and OL? It sounds like a fuel problem instead of spark.
I would think you would be able to rotate the pushrods when the cyl was at TDC with both valves closed and check for wobble. It would have to be noticeable to be causing your problem wouldn't it?
I would think you would be able to rotate the pushrods when the cyl was at TDC with both valves closed and check for wobble. It would have to be noticeable to be causing your problem wouldn't it?
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01-10-2007, 09:41 PM
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Originally Posted by TARyan21
A bent pushrod is easy to check. Just remove the coilpacks, remove the valve covers, remove the rockers and pull them out. Put them on a very flat surface and roll. If this is not the problem I would say a lifter or two. And that is a bad day....I am having that day right now.
As for my commanded AFR vs actual its going to be a little off as I was still doing the AutoVE.
The weirdest thing is that everynow and then it runs super smooth for a few minutes then goes back to running rough jerky and super rich 10-10.5 AFR and when it runs smooth it shows ~15 average at cruise.
01-10-2007, 11:01 PM
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I don't think it is valvetrain. You might log the O2 voltages, CL-OL status, Commanded AFR vs Actual AFR and other related items to see what else changes when it acts up. When the O2s are working right you should be in CL and commanding 14.7 and if not it will go into OL and rely on the VE table. If the VE is off it will do as you describe. I would suggest you put it in OL and tune it for SD mode until you get the VE dialed in. I would almost bet it will run the same when you put it in OL as it does when it is messing up. A very rich condition could ruin a O2 sensor.
01-11-2007, 03:03 PM
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It wasn't running rich before, it was in fact running very well. I'll have to buy 2 used sensors just to check if its the O2's or not. going to do a compression test now just to check something.
01-11-2007, 03:27 PM
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I don't necessarly think the sensor caused the rich problem but that the "rich" problem caused the "sensor" problem. A new sensor could become just like the ones you have if you dont fix the "rich" problem. Efilive has a great scanner that should be able to allow you to see what is going on when it acts up. What did you find when you logged it?
01-11-2007, 04:16 PM
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Originally Posted by RWC
I don't necessarly think the sensor caused the rich problem but that the "rich" problem caused the "sensor" problem. A new sensor could become just like the ones you have if you dont fix the "rich" problem. Efilive has a great scanner that should be able to allow you to see what is going on when it acts up. What did you find when you logged it?
01-16-2007, 11:11 AM
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01-16-2007, 01:18 PM
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Ain't that a bitch? God doesn't sleep when you **** people over.
http://forums.corvetteforum.com/show....php?t=1359230
http://forums.corvetteforum.com/show....php?t=1359230