Mysterious Engine Trouble...knocking and power loss.
Jul 14, 2009, 06:43 AM
#32
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If compression is the same across all 4 and air entering the engine is even, fuel delivery seems to be the only other variable that could cause knock. You might be 10.3 AFR's in 3 cylinders and 12.5 AFR in another for a combined 10.8 on your wide band which is reading the average from all 4 cylinders downstream of the turbo. I know if all the plugs seem evenly colored with no signs of detonation that possibility seems remote but you literally have to do a WOT run and turn off the engine within 30 seconds in order to read the plugs accurately.
...
If compression is the same across all 4 and air entering the engine is even, fuel delivery seems to be the only other variable that could cause knock. You might be 10.3 AFR's in 3 cylinders and 12.5 AFR in another for a combined 10.8 on your wide band which is reading the average from all 4 cylinders downstream of the turbo. I know if all the plugs seem evenly colored with no signs of detonation that possibility seems remote but you literally have to do a WOT run and turn off the engine within 30 seconds in order to read the plugs accurately.
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Symptoms were random knock all over the place under wot, varied from run to run. Would not take the same timing as other VIII's and required richer over all afr. After replacing the injectors and then retune I was able to pickup about 30hp or so across the board.
I would think though that you guys were able to get a look at the pistons when you scoped it so this may not be the issue, or it may only show up under wot at high duty cycle so the hot plug test might be the way to go.
Edit... Just saw you guys already swapped the injectors. And to SiC's point about the exhaust, deffinetly check that, or for that matter just drop the catback off the car for a quick dyno pull and see if there is any improvement. I've seen plenty of cars not reach their power potential due to catbacks that neck down.
Last edited by Mad_SB; Jul 14, 2009 at 06:52 AM.
Jul 14, 2009, 03:47 PM
#33
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Thanks for the input guys...I'll check out the exhaust, that will be a bummer if that is the issue because I love this exhaust.
Sic...where would I look to see if it has the stamp?
Sic...where would I look to see if it has the stamp?
Jul 14, 2009, 03:55 PM
#34
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It'll be a metal plate about 1inch by 2 inches or so on the muffler and center pipe but I saw pics of your exhaust and it may not have it for the US export model. Can you look into your tail pipe and see how large the inner diameter of the muffler is? Is it narrow like 2 inches? Or is it a straight 80mm?
Jul 14, 2009, 06:03 PM
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^The Greddy exhaust starts off with a 2.5" pipe for about an inch or so, so it would mate up with stock cat. Could this little sliver of taper bottle neck the whole system?
Jul 15, 2009, 06:01 AM
#37
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If it has the 2.5 inch taper for the stock cat, I'm really thinking this IS the JASMA exhaust with the 2 inch restrictors in the mid pipe resonator & muffler.
Jul 15, 2009, 11:06 PM
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Did you check yours out? I also have the Greddy and my exhaust does not have the JASMA plate. The muffler seems to have a straight 3" hole, but I do have the taper for the stock cat.
I noticed my car (w/ blouch dom2.) does not like to hold boost above 6500rpm's even with a forge wg acuator (25 psi tapering to 20psi). I'm wondering if the bottle neck exhaust is the cause of this.
Jul 15, 2009, 11:44 PM
#41
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Did you check yours out? I also have the Greddy and my exhaust does not have the JASMA plate. The muffler seems to have a straight 3" hole, but I do have the taper for the stock cat.
I noticed my car (w/ blouch dom2.) does not like to hold boost above 6500rpm's even with a forge wg acuator (25 psi tapering to 20psi). I'm wondering if the bottle neck exhaust is the cause of this.
I noticed my car (w/ blouch dom2.) does not like to hold boost above 6500rpm's even with a forge wg acuator (25 psi tapering to 20psi). I'm wondering if the bottle neck exhaust is the cause of this.
Jul 21, 2009, 10:22 AM
#42
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If you're running the stock cat it shouldn't cause much of a restriction there. But if you're running a 3 inch straight pipe then reducing to a 2.5 inch piping afterwards will cause some restriction in the exhaust flow.
If it has the 2.5 inch taper for the stock cat, I'm really thinking this IS the JASMA exhaust with the 2 inch restrictors in the mid pipe resonator & muffler.
If it has the 2.5 inch taper for the stock cat, I'm really thinking this IS the JASMA exhaust with the 2 inch restrictors in the mid pipe resonator & muffler.
I can't see into the resonator...but I have a feeling that it is not restricted. I'm hoping to get some time at the shop soon to test out a few theories. Still considering the coil pack thing and the MAF...but I'm sure we'll take off the exhaust as another test.
Jul 21, 2009, 01:07 PM
#43
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Good luck in your trouble shooting. I just started experiencing some random knock on a FP Red w/ 1000cc injectors. We are pulling 2* out of it up top to see what happens. My knock is not audible, but you CAN feel it on the street on an ultra hot muggy day.
What amount of Knock Retard are you seeing? I'm only seeing random 0.35's and some 0.7's.
- Louis
What amount of Knock Retard are you seeing? I'm only seeing random 0.35's and some 0.7's.
- Louis
Aug 6, 2009, 10:42 AM
#44
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Good luck in your trouble shooting. I just started experiencing some random knock on a FP Red w/ 1000cc injectors. We are pulling 2* out of it up top to see what happens. My knock is not audible, but you CAN feel it on the street on an ultra hot muggy day.
What amount of Knock Retard are you seeing? I'm only seeing random 0.35's and some 0.7's.
- Louis
What amount of Knock Retard are you seeing? I'm only seeing random 0.35's and some 0.7's.
- Louis
