At a loss...Need input
Thread Starter
Instructor
Joined: Dec 2010
Posts: 134
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At a loss...Need input
I have a stock 98 C5 with an AT and just installed an AandA V2 with 3.6 pulley. I also installed Kooks 1 3/4 in header with catted X pipe and Magna Flow axle back. I had in dynoed today at a very reputable tuner here in the Northwest. On the first pull it made 470 RWHP and 427 ftlbs at 10.2 lbs of boost, but it missed very bad and stopped pulling at 5800 RPM. Redline is 6000 and cutout is 6200. My tuner checked all the plugs and ground wires and everything was good. Only thing he could think of was weak valve springs causing valve chatter typical with 97 and 98 C5 cars. He has also tuned two other 98 C5's and had similar problems getting the the car to 6000 RPM. Has anyone out there heard of a similar situation. The car runs very good and the air/fuel ratio was spot on. My tuner also bumped the 1,2 shift point down 5 MPH to keep it from hitting 5800 RPM. Thanks
Le Mans Master
Joined: Jan 2006
Posts: 6,831
Likes: 4
From: Vacaville Ca
St. Jude Donor '13
I have a stock 98 C5 with an AT and just installed an AandA V2 with 3.6 pulley. I also installed Kooks 1 3/4 in header with catted X pipe and Magna Flow axle back. I had in dynoed today at a very reputable tuner here in the Northwest. On the first pull it made 470 RWHP and 427 ftlbs at 10.2 lbs of boost, but it missed very bad and stopped pulling at 5800 RPM. Redline is 6000 and cutout is 6200. My tuner checked all the plugs and ground wires and everything was good. Only thing he could think of was weak valve springs causing valve chatter typical with 97 and 98 C5 cars. He has also tuned two other 98 C5's and had similar problems getting the the car to 6000 RPM. Has anyone out there heard of a similar situation. The car runs very good and the air/fuel ratio was spot on. My tuner also bumped the 1,2 shift point down 5 MPH to keep it from hitting 5800 RPM. Thanks
Good Luck
Steve@RSD
jobberone
Joined: Aug 2003
Posts: 2,062
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From: Kailua Kona HI
I agree. Check plug gaps and for fouling, wires, coils. Other problem is springs not able to keep the valves open. Don't hesitate to replace wires if old. Shops often have a set of coil packs lying around if it gets that far.
If that doesn't work douse car with holy water.
If that doesn't work douse car with holy water.
Thread Starter
Instructor
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Brand new NKG plugs were also checked for cracks and gaps. Also installed new MSD wire set. I plan on replacing valve springs in a few weeks because I would hate to drop a valve. Didn't try Holy Water yet but I threw a few beer cans at it. I try it though!
Thread Starter
Instructor
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Any other thoughts, who has an AandA charged early C5??? The car ran very well all the way to 5800 RPM and then just fell off. Could coil packs cause this?? Car only has 42K original miles!
Last edited by dc491; Feb 25, 2011 at 01:40 AM.
Thread Starter
Instructor
Joined: Dec 2010
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One thing I just remembered. When reinstalling my battery, I noticed that my positive battery terminal was slightly stripped out and would not tighten all the way. The car starts fine but positive terminal moves around pretty easy. Could this cause this type of problem at high RPM???
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Racer
Joined: Feb 2009
Posts: 482
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From: waldorf md
How many miles are on the car? Springs are fairly likely, a friend ruth an sts gto had to change his springs too.as fast as dyno results on a dyno jet is expect around 550rwhp on 10 psi if your a stock c5 with bolt on's ... Also check fuel filter mine did something similar at race proven motorsports I think
Racer
Joined: Jan 2011
Posts: 371
Likes: 1
From: Windsor Ontario
Have any pics of the dyno graph? It may help some people see what it is. I would deffinitly put a dual spring on the car tho! I just got my FRC and on the way home from buying the car I stopped at summit and picked up some patriot golds and trick flow hardened pushrods hahaha
Jay
Jay
Melting Slicks
Joined: Apr 2007
Posts: 2,787
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From: Lititz PA
Have any pics of the dyno graph? It may help some people see what it is. I would deffinitly put a dual spring on the car tho! I just got my FRC and on the way home from buying the car I stopped at summit and picked up some patriot golds and trick flow hardened pushrods hahaha
Jay
Jay
A dyno graph might give up the ghost if it's a valvetrain instability.
jobberone
Joined: Aug 2003
Posts: 2,062
Likes: 8
From: Kailua Kona HI
One thing I just remembered. When reinstalling my battery, I noticed that my positive battery terminal was slightly stripped out and would not tighten all the way. The car starts fine but positive terminal moves around pretty easy. Could this cause this type of problem at high RPM???
YES! But I doubt it is the problem. If persists change your plugs. If still persists try another battery. If that solves problem then replace your battery. I use yellow top or red top. You need a good set of double springs anyway. Watch your seat pressures. While there change lifters to LS7 and use hardened push rods.
Last edited by jobberone; Feb 25, 2011 at 08:26 AM.
Tech Contributor
Joined: Apr 2007
Posts: 10,924
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From: Forney Texas
Post the dyno graph. Valve spring issues typically have a signature dip and show a recovery, where clogged cats will fall down and never get back up.
The missing isn't a valve spring issue and probably not a cat issue. Make sure you put a good meter across each wire while wiggling the ends to make sure they're good. I've had brand new MSD wires cause problems and show bad.
The missing isn't a valve spring issue and probably not a cat issue. Make sure you put a good meter across each wire while wiggling the ends to make sure they're good. I've had brand new MSD wires cause problems and show bad.
Last edited by BLOWNBLUEZ06; Feb 25, 2011 at 09:06 AM.
Melting Slicks
Joined: Nov 2007
Posts: 2,197
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From: Niagara Falls NY
St. Jude Donor '08-'09
I would do the battery and springs even if there was no problem.Did you check the balancer?It wouldn't hurt to flow the injectors.Sometimes stuff like this turns out to be something totally unrelated to the problem.Did you call A&A?I doubt it has anything to do with it being an early model.How do the plugs look?Are they all the same?Good luck and welcome to the FI world.
Race Director
Joined: Nov 2000
Posts: 11,221
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From: CA
2017 C5 of the Year Finalist
St. Jude Donor '08
Post the dyno graph. Valve spring issues typically have a signature dip and show a recovery, where clogged cats will fall down and never get back up.
The missing isn't a valve spring issue and probably not a cat issue. Make sure you put a good meter across each wire while wiggling the ends to make sure they're good. I've had brand new MSD wires cause problems and show bad.
The missing isn't a valve spring issue and probably not a cat issue. Make sure you put a good meter across each wire while wiggling the ends to make sure they're good. I've had brand new MSD wires cause problems and show bad.
I've got a 98 with a supercharger on it. Please post the gragh, it may help. I've also seen spotty performance out of MSD wires...
Melting Slicks
Joined: Dec 2003
Posts: 3,315
Likes: 17
From: Near Jacksonville Fl.
Like everyone else said "post a dyno graph" but in the meantime change the springs.
I have a 98 and back when I first put my Procharger on it pulled to redline great but after a couple of years it started to lay down.
I changed the stock spring to the Z06 yellow and added 1.8 rockers and picked up ~25 rwhp.
I have a 98 and back when I first put my Procharger on it pulled to redline great but after a couple of years it started to lay down.
I changed the stock spring to the Z06 yellow and added 1.8 rockers and picked up ~25 rwhp.
Le Mans Master
Joined: Jan 2006
Posts: 6,831
Likes: 4
From: Vacaville Ca
St. Jude Donor '13
I still bet on the cats. It is not anything in the entire fuel system if he really has Good AFR like he stated in the beginning. It is not likely springs unless you can hear valve float or it is backfiring from the intake holding open too long (the compression will help them close)
CATS, I don't care if they are new......
CATS, I don't care if they are new......