greaseman69

To preface I should mention that I just installed 1 7/8 long tubes and true duals about a week ago, I changed all spark plugs, wires, and O2 sensors and it's been running fine until now, no tune yet. Yesterday I was racing my buddy's car and did a few hard pulls from 2nd to the top of 4th, ran fine during those pulls but was cruising at about 70 mph and noticed on any throttle my car would shake pretty badly. Parked and scanned it and its getting a random misfire code (along with all the other codes associated with deleting cats, EGR, and AIR). I know typically this is a spark plug/wire problem but I checked them and they all seem fine. What is most likely to go bad and cause this after straining the engine like that? Starts and idles fine still, only noticeable under hard acceleration.

G Atsma

Which plugs are you running?

greaseman69

Ngk tr55 and the wires are MSD. I'm not very good at interpreting DTCs so correct me if I'm wrong but wouldn't a random misfire code make it unlikely that it's the plugs since it's being detected on multiple cylinders? Unless something has simultaneously fouled multiple plugs

Xboxoff

There's probably a good chance you may have cracked a spark plug during installation. Are you able to check misfire data at all?

Darth_V8r

iTrader: (4)

Random misfires just means more than one hole is not happy. Example, you burn up #4 plug you get #4 misfire. You burn up #4 and 2, you get random misfire.

That said, may be as simple as fuel filter plugged.

greaseman69

It just seems unlikely to me that I wouldn't notice a misfire before and then suddenly two or more plugs cause misfires. But I did just double check all plugs and wires including gap, no problems there. I'm going to replace the fuel filter and see if that helps, hasnt been replaced since I got the car 10k miles ago and I have no idea if the previous owner ever replaced it.

ddnspider

iTrader: (26)

If you have access to a tuning suite you can disable the cylinders 1 by 1 and listen for the change in sound. If you have a cylinder intermittently firing this will help narrow it down. Otherwise can unplug 1 injector at a time.

greaseman69

Update:
Reset PCM, no misfire!!! For now...

Any idea why this worked? I never reset it before, not even after the lts and true duals install.

RichyB33

I had a similar issue on my LT1 car back about 7 years ago. I know it's not a LS, but it started and ran fine when cold and in open loop. Once it got into closed loop it started misfiring like crazy. After going through the plugs, opti, fuel filter, injectors etc, it wound up being something wonky in my PCM. We re-flashed my tune and the car never misfired again. I would say that it's possible that your car just didn't like having all those codes popped. The PCM is already trying to make fairly large adjustments for the new exhaust on the stock tune, and then you max performed it.

greaseman69

Well the misfire is back already. You think because resetting the PCM fixed it theres something wrong with the PCM?

RichyB33

In my situation, that was the case. Can't say for certain.

RevGTO

iTrader: (12)

No. It sounds like you have a tuning suite, so program it to log misfires and you'll be able to see which cylinders are affected and once you isolate it, go from there - wires, plugs, coils, injectors, etc.

But if the misfire is randomly skipping all over the place from cylinder to cylinder, then you may have a PCM, electrical, or grounding problem.

Darth_V8r

iTrader: (4)

No most likely resetting the Ecu reset all the trims. Likely you need a fresh tune and your current tune is fouling plugs.

greaseman69

Alright I'm gonna get a quick mail order tune with new plugs and see how it does. Was gonna get one once I got my intake but it couldn't hurt to do it now. The plugs are a little black around the rim which I thought was normal but after only a couple hundred miles maybe it shouldn't look like that. Thanks for the advice

greaseman69

By the way, is this plug normal for only a couple hundred miles? They all look like this.

RichyB33

Looks pretty normal to me. I could be wrong though.

LilJayV10

iTrader: (39)

Ahh no.

RichyB33

You ever get this thing figured out OP?