Need help tuning! Mysterious knock problem has me flustered.
Thread Starter
Racer
Joined: Apr 2003
Posts: 328
Likes: 0
From: Miami FL
Need help tuning! Mysterious knock problem has me flustered.
Had my car on the dyno today after install of FLP headers for some LS1 edit tuning. After countless pulls on the dyno and tweaking the a/f ratio to be about as close to perfect as possible the car was only putting out 360 rwhp and about 345 rwtq. The car seems to be sensing knock at around 4000rpm on up and begins to pull out timing which is preventing me from hitting the 380 rwhp numbers I am seeking. I can't begin to fathom why their is knock retard with a perfectly stoich a/f ration measure with a wideband 02. The plugs and wires are brand new so I don't know where else to look, other than maybe the cats from the FLP setup are restrictive and causing some knock. Any suggestions on what might be causing my horsepower dillemna? I will try to post pictures of the graph shortly.
Melting Slicks
Joined: Mar 1999
Posts: 2,499
Likes: 0
Re: Need help tuning! Mysterious knock problem has me flustered. (Z06TheKid)
Check for something rattling on the exhaust. I could be a false knock. Are you using a scan tool like AutoTap or anything else to measure the knock?
Thread Starter
Racer
Joined: Apr 2003
Posts: 328
Likes: 0
From: Miami FL
Re: Need help tuning! Mysterious knock problem has me flustered. (MMarquez)
Ruled out any false knock by pulling back a lot of timing and adding fuel around 4k rpm and on up just to make sure that this was not occuring. Unfortunately I wish it would be that simple :cry
Pro
Joined: Mar 2001
Posts: 568
Likes: 1
From: South Florida
Re: Need help tuning! Mysterious knock problem has me flustered. (Z06TheKid)
Up.......
Someone must have some ideas :nopity
Someone must have some ideas :nopity
There will be a hell of a lot of smoke but it will clear up after driving it for several miles and is perfectly normal. This is the best way IMO to get rid of any carbon deposits that might be causing the knock we are getting on the dyno.
Former Vendor
Joined: Jul 1999
Posts: 2,103
Likes: 0
From: Indianapolis Indiana
St. Jude Donor '11
Re: Need help tuning! Mysterious knock problem has me flustered. (Z06TheKid)
Z06TheKid,
A couple of questions for ya. You mentioned a perfectly stoich A/F ratio with the wideband. This generally means a 14.7-1 A/F ratio and if this is the case, it is way to lean at wide open throttle. The A/F should be in the 13.0-1 ball park to be right. If is at 14.7 or so at WOT and maybe added fuel to get to 14.0-1 as a guess, it wouild still suffer. This just a guess since you did not give a specific number.
Also, what are the fuel trims at idle and cruising? How much timing? How was the A/F adjusted, with PE or IFR? I would doubt that it is false knock and can be tuned out. Heat on a hot day can also raise heck after a bunch of back to back runs, but can be cured easily.
Let us know and we will go from there :cheers:
Mike
A couple of questions for ya. You mentioned a perfectly stoich A/F ratio with the wideband. This generally means a 14.7-1 A/F ratio and if this is the case, it is way to lean at wide open throttle. The A/F should be in the 13.0-1 ball park to be right. If is at 14.7 or so at WOT and maybe added fuel to get to 14.0-1 as a guess, it wouild still suffer. This just a guess since you did not give a specific number.
Also, what are the fuel trims at idle and cruising? How much timing? How was the A/F adjusted, with PE or IFR? I would doubt that it is false knock and can be tuned out. Heat on a hot day can also raise heck after a bunch of back to back runs, but can be cured easily.
Let us know and we will go from there :cheers:
Mike
Racer
Joined: Oct 2001
Posts: 483
Likes: 0
From: Downingtown PA
Re: Need help tuning! Mysterious knock problem has me flustered. (Z06TheKid)
You might want to try a bottle of octane boost and see if that helps. I know you shouldn't need it, but it might be interesting to see if that cures the problem.
Intermediate
Joined: Jan 2003
Posts: 41
Likes: 0
From: Paradise Valley AZ
Re: Need help tuning! Mysterious knock problem has me flustered. (01C5fan)
01 C5 Fan has the right idea,however it would take 2 cans of Turbo 108 to add up to 1.6 octane(UP TO!!!!)I would get some Union 76 100 or What we use at Xtreme which is Sunnoco 109(which is really 104) add 5 gallons to a full tank or to save $$$$$$$ and get the same results,when your at less than 1/4 tank add 1 gallon of race fuel,if it goes away IMHO your PCM is not tuned correctly.
If you cared to and if Mike Witkopf has time we can do a mini Dyno tune VIA mail for 495.00 max,my best guess is 150-250,and it should alleviate your pinging and we can add more timing.
Autos are much more prone to the pinging problem but its not really damaging in most casses.
I wouldnt do the De Carb until at least 50K on the car.
Good Luck and if we can help call 480-517-4969,Ask For Mike not only IMHO the best tuner in the Chev world but an engineering genius as well,Dave
If you cared to and if Mike Witkopf has time we can do a mini Dyno tune VIA mail for 495.00 max,my best guess is 150-250,and it should alleviate your pinging and we can add more timing.
Autos are much more prone to the pinging problem but its not really damaging in most casses.
I wouldnt do the De Carb until at least 50K on the car.
Good Luck and if we can help call 480-517-4969,Ask For Mike not only IMHO the best tuner in the Chev world but an engineering genius as well,Dave
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Thread Starter
Racer
Joined: Apr 2003
Posts: 328
Likes: 0
From: Miami FL
Re: Need help tuning! Mysterious knock problem has me flustered. (Iggy Pop)
Going to try replacing the cats with the straight pipes included with the FLP kit and also going to give the motor the full decarb treatment recommended by Brian. I will let everyone know how it goes.