87-Rocket

I guess it is time to start a new thread with my latest problem. I have a 2005 Z51 with a basically stock LS2 short block. A while back, I added a set of Billy Boat Headers, Billy Boat X pipe with cats, and Billy Boat Bullet exhaust. Recently, I added a ATI balancer that I double pinned to the crank when the stock balancer developed the "death wobble." The latest additions are a Magnuson MP112 Supercharger, LPE mass air flow tube/sensor, LPE ported throttle body, and Calloway Honker cold air. The car has the Magnuson Magnavolt boost-a-pump.

I had the car professionally tuned at XXX Porformance in Pensacola, Florida. Ever since then, the car has been a nightmare. It developed a strange squealing sound on the last dyno run of the day, which, I finally narrowed down to the PCV system that was leaking air. However, the car drove like a dream regardless of the sqeal. A clamp on the PCV line at the valve cover appears to have solved this problem. However, as soon as I got this problem solved I developed a new and worse problem.

Following resolution of the squealing problem, I drove the car all day and it drove like a great, pulling hard and not making any stange sounds. I stopped that evening for some ice cream and when I started the car back up to go home, it ran real rough with the CEL flashing intermittently. I scanned for codes when I got the car home and got a PO306 - missfire on cylinder 6. I took a quick look in the engine bay and did not see anything that immediately appeared to be a problem. The engine has Taylor wires that are about 1 year old and brand new NGK colder range plugs gapped at .030. The 42 lb Bosch injectors were rebuilt prior to installing the supercharger.

I did a search on the forum for "misfire" and it looks like the most common causes are fouled plug(s), bad coil pack, bad plug wire, or clogged injector. So the day following discovery of the misfire, I pulled the plug at the number 6 cylinder and did not see any damage or plug fouling. Following that, I switched the number 6 coil and plug wire with the number 4 coil and plug wire and still got a CEL for a miss at the number 6 cylinder after I drove it around the block (so it apparently isn't the coil or wire). I pulled the plug back out and it was absolutely clean and did not appear to be getting any fuel. I went ahead and tore everything back apart including removal of the passenger side valve cover. I found no broken valve spring(s), no slop in the valve train, and no metal or debris that would indicate an internal engine problem. I pulled the number 6 injector and did not see any indications that the injector has trash in it, however, I removed the basket filter, flushed the injector out and replaced the basket in it anyway.

When I re-installed the injector, I switched it with the #4 injector, again, to see if the problem would move. The car had about 1/8 tank of fuel or less when the misfire problem came up so I put 5 gallons of fresh 93 octane in it with some fuel treatment to see if that might solve the problem. Once I got everything buttoned up, I drove the car around the block to see what it would do. As expected, the check engine light popped up immediately. When I got it back to my shop and ran the codes, I GOT A PO300 THIS TIME. The car will idle almost pefectly. Light throttle results in rough running and the CEL blinking at around 1500 rpm. No other codes have been thrown by the EMC.

Tonight, I re-tourqued the blower manifold to make sure things haven't loosened up and resulted in a intake leak. Everything looked good. The only think that I can think of that could be causing this problem is bad fuel. The car set up for about 6 or 8 weeks as I worked on getting everything put together with the supercharger. I put some Startron gas enzyme, which is supposed to eliminate water, in the gas tank tonight. If this doesn't help, the I am at a loss.

I know that I can't be the only person that has had issues with this. Any help or suggestions would be greatly appreciated.

87-Rocket

Latest update............After letting the Startron do its thing for about 24 hours, I started the car and it is still misfiring. I put a test guage on the check valve located at the driverside fuel rail. I got a reading of about 52 - 55 psi at idle. Also checked the coolant level in the engine cooling system and the suprecharger intercooler system. There does not appear to be any drop in the coolant levels. No oily smoke or heavy water vapor in the exhaust. I am running out of things to check.

speedraider

Call Matt @ FSP. He comes to Panama City all the time and would have it running like a top in no time.

87-Rocket

speedraider - I am in Mobile, Alabama so Panama City is a fairly long haul for me.

Anyway.....talked on the phone with my tuner today about the problem I have been experiencing and he indicated that since the car is not mis-firing at idle, isn't throwing addition CEL codes, and primarily exhibits the problem under load, he thinks it is ignition related. He has suggested replacing all the plugs and wires. If that doesn't work then I guess it is back to the tuner.

John Wong

Last week,I met the same problem as you.Fortunately,a passenger helped me.He gave me a gas spring for truck and car,then deal with it.After that ,I search this gas spring online to find it's function,only to find it's a helpful tool.You can see it and click http://www.meet-at-fair.com/company/companyweb/377654/

87-Rocket

What the heck........I wish a gas spring would fix this problem!

speedraider

Sorry, I thought you were in Pensacola.

87-Rocket

Shoot, I thought you were going to tell me that a gas spring would fix my mis

Yep, I can make Pensacola in about an hour. Panama City is about 4 hours. That trip wouldn't be out of the question if I can't get this resolved.

old motorhead

Just because the plug looks good doesn't mean it's good. I've had a bad TR6 that was brand new and looked perfect. That would be cheap and easy to check.

87-Rocket

I had already replaced the plug at cylinder 6 but all the others are what I installed prior to the tune. I am betting that, if the issue is ignition related, it is going to be a plug wire. The wires are fairly new Taylor brand (less than 2 years old) but they have been taken off and on the engine so many times I could have damaged one or more.

87-Rocket

New plugs and wires arrived yesterday and were installed last night. The old plugs didn't look bad but they didn't look good either. It looks like the blower may be pulling some oil into the intake tract from somewhere. The oil in the crankcase appeared to be at normal levels (per a dip-stick check) and their isn't any blue smoke in the exhaust so it can't be excessive. The engine idled fine and ran a little better with less stumble when I brought the rpms up. I didn't get a chance to drive it as it was raining cats and dogs. I will drive it tonight and see if I get a CEL with the engine under load.

87-Rocket

Well......I drove the car tonight. The bad news is the car still has a mis. The good news is I have pretty much narrowed it down to a bad injector.

After talking with my tuner the other day, I learned a few things. First, it is very unusual for a LS2 coil pack to go bad. My tuner indicated that he could count on one hand the LS coil packs that he has seen go bad. Second, even though you reset CEL codes with a code scanner, the egine management computer will still store them. You have to disconnect the battery to eliminate stored codes. For this reason, my PO306 misfire on cylinder # 6 went to a PO300 random misfire after I started switching parts around. The computer was now comparing stored codes with what happened after parts were moved from cylinder to cylinder.

I had disconnected the battery prior to the installation of the new plugs/wires last night, so all the stored codes were deleted. When I drove the car tonight, I got a PO304. Cylinder # 4 is where I had moved the injector that was previously at # 6. So, I am about 99% sure that it has to be a bad injector.

Anyone think my logic is flawed?

87-Rocket

I ordered a new injector, which shipped in yesterday. I installed the new injector tonight at the #4 cylinder. I was right it, it was a bad injector causing the mis.

5 Liter Eater

Awesome! I wish my P0300 problem was that simple but I'm getting misfires on virtually all cylinders.

87-Rocket

If you haven't already, you may want to clear the CEL memory by disconnecting the battery. Maybe then you will get a more specific code.

kazoo794

My injector, plug, wire and push rods were changed, I still have a misfire in #5 cylinder. I had it at a Vette specialist then to a Chevy Dealership with suposedly a good reputation. After about a week and a half they were still in the dark. They wanted to pull my cam because they think i may have what they called a cam wipe. They were still searching. I brought my car home after the service rep told me to clean my car up sell it and run as fast as possible. Because it was going to cost me $5k to pull the cam and a new engine would cost me around $18k, DID I JUST FALL OFF A TURNIP TRUCK, has any one experienced this before?

87-Rocket

kazoo794 - From your post, it sounds like you might not be very mechanically inclined and are having to farm out your repair work. If I am correct in this, it will make it tough for you to try to diagnose or understand the problem yourself. With that said, lets talk about your problem.

A bad ignition coil could also possibly be the source of your misfire. The LS engines have a coil on plug system with 8 separate coils that sit on top of the valve covers. An easy way to diagnose this is to remove the coil from the #5 cylinder (2 bolts), switch it with the coil next to it. Disconnect the battery so the computer will reset. Start the engine and see if the misfire has now moved to the other cylinder.

A "wiped cam lobe" is something that I would classify as fairly significant damage. It is where the lobe of the cam has been worn off to the point where the it no longer controls the valve train properly. The LS engines have what is called a hydraulic roller lifter which actually has a small wheel on the bottom of it that follows or rolls along the profile of the cam as the cam turn inside the engine. This style of lifter actually reduces the chances of having a wiped lobe and is very reliable.

Generally, a wiped lobe is going to show up in other ways. For example, debris in the oil at oil change or excessive valve train noise. If you haven't been seeing other problems besides the misfire, I would be willing to bet it isn't the cam. Another possibility is a bad lifter. If the hydraulics in the lifter have gone bad and it isn't opening the valve properly, you could end up with a misfire. Same thing with a broken valve spring.

If you like the car and don't want to sell, I would suggest that you have someone pull the intake manifold and valve covers off of the engine and have it checked for valve train damage. This shouldn't be to expensive and then you would know for sure.

kazoo794

I am pretty mechanically savvy however I don't really have the time or location to perform many task. I haven't spent extensive time under the hood in years but I do understand the basic principles of an internal combustion engine, like I said, I didn't just fall off a turnip truck. My coil pack was removed and another one tried with no effect however I haven't reset the battery, i will try that. A little history but no history on the car. I purchased the car from a dealer who took it in on a trade and I am the fourth owner with no past service or maintenance records. I didn't say but the car has had some mods done to it. Hall Tech Intake, Cam, long tube headers free flow cats and Corsa exhaust.

87-Rocket

That history helps a bit. Do you know if new lifters and/or valve springs were installed at the time of the cam change? Often, if these components are not matched to and changed out with the new cam it can result in valve train problems. An aggressive cam may need stiffer valve springs and heavy duty lifters.

Do you know if this car was raced or abused in any way? Is this a high mileage car? If the answer is no, I would just have to doubt that you have any serious mechanical damage. The LS platform is pretty durable with many enthusiasts making huge power with basically stock components.

kazoo794

My Vette currently has 47k on it, I have been trying to get the Dealer whom I purchased it from to contact the previous owner to find out what or if they were the one who modified the car, I am the fourth owner. The dealer is not being to cooperative so I am purely going in the blind. It is not a high mileage car but not sure if it was raced. When I purchased the car this year in June, on June 22nd I had it on the dyno and its runs were like:
Max Pwr=395.9)HP)@6150(RPM), Max Torque=376.4(ft.lbs.)@4900(RPM)
Min A/F_1=13.5(A/F (Petrol)), Max None
Max HP=395.9HP, Eng HP=455.3HP, Max Torque=376.4ft.lbs., Eng Torque 432.9ft.lbs.
It also has been tuned, I had East Coast Super Charger to tweak it a bit and they sent me the file copies but I don't have the software to read it.