I have a 510 flywheel horsepower ls6 in my 99 z28. I had what I believe to be a piston slap (possibly due to bad gas) about a week ago (loud bang.. car immediately died) and since then I've been having problems. I have a chug at low RPMs that seems to come and go.. my mechanic thinks it's becuase my stock coils aren't putting out enough voltage along with a misfire or two.

My plan as it is is to change my plugs and wires and see what happens and then look to upgrading all of my coils whether or not they're bad. The MSD coils are all I've been able to find and not only do they seem unreasonably priced at 75 bucks a pop but they only put out 40,000 volts. Apparently I need somewhere around 60,000.

If anybody knows of a higher output coil for a relatively affordable price, let me know. I'd think they're somewhere out there considering there are LT1 55,000 volt coils running for 50 bucks each.

Feel free to advise me on what you think any other issues I may have are.

 

I'd venture to say your mechanic's diagnosis should be investigated. There are plenty of cars more powerful than this that are still getting by on their factory coils.

MSD is the only company that makes replacement performance coils.

Why would your coils have suddenly stopped providing enought spark after the episode you described? If they were fine for the power level you had previously, I'd say continue looking, they're probably still fine.

Ben T.

 

The car always lurked at low RPM. It would go up and down in power under 3,000 RPMs and then rip open all at once. This wasn't constant, but it would happen consistently. Do you think it's an airflow problem? I just know it started doing this to a much higher degree after the episode. A lot of vibration and noise and not a lot of power at low RPMs.

On top of that there is black sludge coming out of one of the cylinders and the car puffs black smoke at WOT shifts. This is the first time my mechanic's worked on a performance LS6 so his diagnosis isn't that of a "specialist."

But I consider that good news. I didn't/couldn't drop 600 dollars on a silly thing like aftermarket coils.

 

Can you tell us a little about your combination and who tuned it?

Ben T.

 

piston slap doesn't just appear....it would have been there from the beginning.

and bad gas causes knock...not piston slap.

definately check your plugs and wires.

 

LS6 block, barely bored for aftermarket Diamond forged dome pistons. Eagle 6.125 forged rods. Stock ls1 crankshaft.

Comp cams cam: 222/224 @ .50; 566-568 lift; 112 lsa

LS1 stage II heads, titanium valves, aftermarket springs, chromoly pushrods. Roller rockers (not sure on specs I think 1.7:1?). When the bottom end was ready the pistons stuck out above it about half an inch, that required a lot of head work and ended when over 11:1 compression.

Flowtech longtube headers/y-pipe. Stock intake manifold.

Computer was programmed by madz28 and I've yet to have a dyno tune, waiting on my LS6 intake manifold for that. All in a 1LE style silver z28 (no t-tops, pw, pl, ps, cloth interior, aluminum driveshaft).

 

You aren't making enough power to over power your coils.
1. Do what you are and change plugs and check wires, and check all underhood sensor connections. Also run fuel from a different station if you use the same one.
2. Check for a dead or dying coil & check for codes. I'm still not convinced its ignition related.
3. Check tune
4. Change mechanics for him trying to get you to spend $ on crap you don't need. I wouldn't be suprised if the cam was a tooth off and he is covering for it.

Ya, the LTI coil has more volts but it also has to fire 8 times/cycle and pump the power through longer wires.

 

I changed the spark plugs and wires and the problem is not solved.

Cylinders 3 and 4 had very black plugs--displaying rich cylinders. Obviously there's not enough spark to burn the fuel and that makes sense with the strong scent of gas and the black smoke that comes out the exhaust.

Although the engine only has 10,000 miles on it the coils have 81,000 miles and that could explain why they've crapped out. Does anybody else agree that coils are the best bet to solve this problem?

 

Did you scan pcm for code?








2002 Z28 6m
Hot cam, headers and PCM for less tune

 

There's no check-engine light and my scanner doesn't get a signal. I'm gonna use a friends sometime this weekend.

 

We swapped the two bad coils and nothing is improved. I've dropped 240 dollars on this "misfire" and nothing is different.

I scanned the computer and it said there was a misfire but the only codes were related to the O2 sensors not working.

Now my mechanic thinks it's the fuel filter, which hasn't been changed in over 20,000 miles (as long as I've owned it at least). Can I get a second opinion? Maybe some other things it could be?

 

So if it's running rich you're getting plenty of fuel.
Because you're having a fuel delivery problem? I thought it was running rich....
Which codes? There is a misfire but no misfire codes? If you list the codes somebody may be able to help you out. If you haven't changed the fuel filter in 20,000+ miles it's not going to hurt to do it, they're not even expensive. But if you have misfires and cylinders running rich, and O2 codes, you're probably not going to fix your driveability problem by throwing a fuel filter at the problem. Figure out what's broken, fix that, then play catch-up with your preventive maintenance.

Here's my second opinion: you should give us more information. If your oxygen sensors (pre-cat) are original with 81,000 miles, then you've gotten lucky because they rarely last that long on these cars. Bad O2 sensor(s) could cause the problems you're having. I've got 40,000 miles on my car and I'm pretty sure one (if not both) of mine are starting to crap out on me. You may also have some other problems going on. What exhaust setup do you have? 11:1 compression? You need to be using some good gas. I'm really interested though in this:
Where is there black sludge coming out of? Let us know some more info, we'll get the problem solved because it doesn't sound like your mechanic is doing a very good job of it.

Abe

 

Not tryin to be Mr. Driveability man or nuthin but back to the coil questioning; (and im assuming) u can check them by testing their resistence with a fluke/multimeter. Best of luck man!!!

 

DTC P1153 HO2S Insufficient Switching Bank 2 Sensor 1
DTC P1154 HO2S Transition Time Ratio Bank 2 Sensor 1

The only argument I have against the O2 sensor causing the problem is the fact that they've been out since I bought the car and it only recently developed this problem.

It could be the fuel filter because it could have been running rich and the fuel filter clogged up and caused my problem and now we see both problems. If it's passed due replacement I might as well change it and see what happens. The fuel is coming out of the cylinder 3 side, a cylinder that was running noticeably rich.

 

One fuel filter for all 8 cylinders. So my reasoning is that if this was the cause of your problems you would have different driveability symptoms. O2 sensor malfunction will cause the "chug" at low RPM's you first described. It may go away or just seem to go away as the engine builds RPM's or as you open the throttle more. I'm just trying to steer you away from things that don't really seem as if they're going to fix your problem. By all means replace your fuel filter. It seems like you have your mind set on spending an assload of money on coils, even though I doubt that this is your problem. On to actually fixing your problem: you say that "they've been out since I bought the car", but I'm not really sure exactly what that means. Have they been replaced? Anyway:

http://www.gearchatter.com/viewtopic9334.php
http://www.gearchatter.com/viewtopic9335.php

there ya go.

Abe