Has anyone changed their spark plugs on their Z? Can improvements be had?

 

See little to be gained unless there is misfiring.

 

I think I am having an ignition problem from what I can tell. Seems my wires are all snug so I am thinking I may have a bad plug. I am not showing a code and I know my gas is good. The dealer was not able to diagnose anything which is not surprising given what little they know about the car.

 

Current OBD2 misfire monitoring is so sensitive that if you had a bad or even marginal plug you'd know about it. They don't need to know anything about the car, as it will say

PID2476: MISFIRE! Call The EPA! MISFIRE! AEEEIIIIEEE!!!!!

(or something similar)

Am I exaggerating? Only on the text. The cam/crank position sensor package actually can monitor the acceleration and deceleration of the engine through its rotation and know when one cylinder didn't help as much as the others. Pretty simple and elegant if you think about it.

By the time YOU think there might be a miss, the computer knew about it long ago. If the computer doesn't think there's a miss, there's no miss.

 

absolutely no doubt

 

This may be correct. But I am still getting a very noticeable chugging
(Power loss) at WOT at somewhere between 80-100 mph. However there are no codes or check engine lights. Going to another dealer on Wednesday.

 

While this is supposed to be the way it works in my experience it doesn't always set a code.

The PCM does exactly as you stated but a misfire code may or may not be set with a misfiring plug. While I am fairly certain if the plug or wire is totally bad the PCM will probably set a code. But one that is marginal that "blows out" under high boost or high rpm (under load) and then subsequently returns to normal under light load, low boost and/or low rpm may not be not set a misfire code.

I chased a stumble on my LS3 for weeks because I put to much stock in not having a misfire code. Had the same issue on a friends super charged LS2 and several LS1's over the years.

I found the issue by reading the plugs the first few times this happened. But was curious as to why no code was set or if the PCM saw the misfire at all. I read the PCM data log. The PCM algorithm was catching the misfires on each individual cylinder so I compared them all and learned that (on my LS3) my good plugs where firing at 92ish %. The bad plug was firing at 76%. Firing normal at idle and cruise but missing at high RPM WOT. And no code. The cylinder balance test didn't catch it either.

I know the E92 PCM has GM's most advance technology and should be better at misfire than the older PCM's but my past experience tells me that under boost, high rpm or any other time cylinder resistance is high, you may not be able to depend on the a code being set. As with so many intermittent issues you may need to dig a little deeper.

Regardless reading or changing the plugs and checking the resistance of the wires is a cheap first step to resolving a miss or stumble. With a boosted car marginal plugs can misfire under boost and not set a misfire code.

 

Assuming this is an A8? Curious if this is happening at a speed (80-100) or an engine rpm? I mention this because a misfire will show at a given RPM not necessarily a speed. Although in the lower gears you may not be at the boost and rpm range for long enough for the miss to occur. However in the higher gears the engine spends more time under load and the misfire may show.

Point is if its a misfire you can duplicate it in any of the higher gears. A8 or M7 hold the engine at WOT in a gear 1, 2 or even 3 gears above the one you are normally seeing the suspected misfire (4th,5th or 6th gear). The goal is to load the engine under boost but not sweep through the rpm range to fast. This creates high cylinder resistance and high torque with a slow sweep through the rpm. This can be done safer and at slower speeds and a misfire will show up. If it shows in other gears its likely a misfire. If not and it happens at 80-100 mph regardless of what gear then it is not.

 

This only occurs at WOT at higher speeds after I have been on the throttle for a while. So you may be correct. I think the simplest thing to do is to change the plugs and make sure the wires are all secure and go from there. Thanks for your feedback.

 

Thanks for your suggestion. I am planning to changing the plugs and checking the wire resistance as an initial first step.

 

I usually change plugs b4 when I arrive at the strip. Not sure it makes any difference, but it is easy and cheap to do compared with all the other costs of drag racing.

With current ignition systems this is less important. For me, it is mostly an old habit that made a couple of tenths difference years ago.

 

I had a plug wire off and did not see any lights or codes? kept hearing what I thought was an exhaust leak, Tick noise. Found plug wire off reinstalled noise went away. What plugs are suggested for the Z? Anyone change the wires yet?

 

Ever figure out the misfire issue? I have a similar problem- a8- put it in 4th about 80-100 and it sputters and misfires and has a noticeable bucking and loss of power. Not like throw you around studder but it's definitely there-brand new ngk iridium 6510 plugs, gapped to .028, lower pulley intake and exhaust..... had it tuned by d3, ran great for months after- raced it plenty, ran great..... 02 sensor went bad, had misfire , had 02 sensor code, plus bank 3 misfire. I'm pretty convinced it's a coil pack. I've had two termis, played with plug gaps and boost for a long time. The little boost I make, 12-13psi tops, should NOT be blowing the spark out set at .028..... Got good fuel, fresh, I just don't get it. Anyone ever had an intermittent coil pack causing an issue such as this? '15 c7z intake exhaust and tune..... wanna go change back to a decent base tune and see if that fixes it, data log and then see what I can figure out