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996 Baseline Dyno OK Power..Ugly dips

Old Mar 28, 2008 | 02:11 PM
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Did some work today. The plugs were changed 10K ago , and look great. The MAF is the 986XXX01, which is the latest w/ the air ramp...it looks clean. It was due for an oil change..though it was clean, there was evidence of a decent amount of fuel. Maybe that was hurting my cause. Drove it on the scanner and the sensors are acting fine. I think I will put it back on the dyno tomorrow to see if the oil change changes anything, and then start adding parts one at a time and see what happens.
For those who are familiar with tuning these cars I have a question..if I start adding parts and the A/F continues to be fat, can it be trimmed up with a tune ?
 
Old Mar 28, 2008 | 03:23 PM
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Originally Posted by Rush996
Did some work today. The plugs were changed 10K ago , and look great. The MAF is the 986XXX01, which is the latest w/ the air ramp...it looks clean. It was due for an oil change..though it was clean, there was evidence of a decent amount of fuel. Maybe that was hurting my cause. Drove it on the scanner and the sensors are acting fine. I think I will put it back on the dyno tomorrow to see if the oil change changes anything, and then start adding parts one at a time and see what happens.
For those who are familiar with tuning these cars I have a question..if I start adding parts and the A/F continues to be fat, can it be trimmed up with a tune ?

If you are running an 11.4:1 fuel/air ratio, your sensors CANNOT be reporting correctly. What is the MAF reading at WOT near redline? What are the readings of both after cat O2 sensors at WOT near redline? What does your LTFT read - both banks?
 
Old Mar 28, 2008 | 07:06 PM
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I don't know..I was driving. I've got a 2 min print out after the car was warmed to temp and everything is good. The tech said he didn't see anything out of spec at WOT. The only concern is the camshaft deviation, which is slightly out of spec. I may go back Monday and record what it's doing. According to the dyno printout, it's below 12:1 from 5750 up. (below 12.5 from 4900 up). I'm doubting the accuracy of the dynojet sniffer...the plugs look perfect, no CEL's and the car is not down on power the way you'd think at that ratio. The exhaust on the dyno was colorless..never puffed or seemed rich exiting the mufflers. I only made 2 baseline passes b/c I was in a hurry..it picked up 2.5hp and 4 ft lbs from the first to second pull. Maybe it would have gotten better.
 

Last edited by Rush996; Mar 28, 2008 at 07:07 PM. Reason: typo
Old Mar 29, 2008 | 06:32 AM
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Originally Posted by Rush996
I don't know..I was driving. I've got a 2 min print out after the car was warmed to temp and everything is good. The tech said he didn't see anything out of spec at WOT. The only concern is the camshaft deviation, which is slightly out of spec. I may go back Monday and record what it's doing. According to the dyno printout, it's below 12:1 from 5750 up. (below 12.5 from 4900 up). I'm doubting the accuracy of the dynojet sniffer...the plugs look perfect, no CEL's and the car is not down on power the way you'd think at that ratio. The exhaust on the dyno was colorless..never puffed or seemed rich exiting the mufflers. I only made 2 baseline passes b/c I was in a hurry..it picked up 2.5hp and 4 ft lbs from the first to second pull. Maybe it would have gotten better.

Like I said - IF you are running an 11.4:1 fuel/air ratio....

Take a look at your after cat O2 readings at WOT above 5500 rpm. That will tell you if you are truely running that rich or not. Should read between .87 and .90.
 
Old Apr 11, 2008 | 12:54 PM
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Dead on...87 and .89. I think this puts the nail in the coffin of my A/F issue. we've now checked all the sensors, plugs, and the power it made is actually above average. I decide to go ahead with the plenum install yesterday and I'll hit the dyno tomoroow afternoon.
 
Old Apr 11, 2008 | 01:28 PM
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What model of dyno are you using?
 
Old Apr 11, 2008 | 03:43 PM
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Old Apr 15, 2008 | 04:10 PM
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Will do. Re-scheduled dyno session last weekend due to a hail storm! Thurs is the day. Plenum definitely did some good..can't wait to see it on paper. Dynojet..
 
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