cylinder #2 missfire

**Trett93** · 06-09-2014

Hey guys, i have a 2001 sunfire gt with a 5 speed swap and an l67 lol, anyways im having a missfire on cylinder #2, ive tried plugs wires and coil, and still getting my missfire code, the plugs are about 2 weeks old and #2 is already carboned up again, im not really looking forward to a tear down but looking for maybe a general direction, any help appreciated thanks!

**ericspecullaas** · 06-09-2014

this soulds like gasp a chiped pistion time for new motor

**ericspecullaas** · 06-09-2014

also double threads arent cool

**BillBoost37** · 06-09-2014

Did you have a mangled plug?

**Trett93** · 06-09-2014

no plug was fine, just black like a dry foul, compression is at 30psi in that cylinder and sorry didnt mean to double post considering my issues arent the same and im new i didnt think it would be a huge deal...

**Trett93** · 06-09-2014

also ive never ran anything but 91 octane (hardly find 93) and there are no mods really besides a flashed and tuned pcm and 2.5in full exhaust with hi flow cat and ss series welded muffler, supercharger pulley is still stock aswell, how would a chipped piston happen?

**Trett93** · 06-09-2014

just some more info now that i have free time, the car doesnt seem to missfire unless its warmed up, also anywhere below 4,000rpm it is really boggy but after 4,000 it runs like a dream, any info would help, has a CAI and 180 degree thermostat aswell, no other mods

**FordMan77** · 06-09-2014

Chipped pistons come from predetonation (spark knock). Usually happens if someone pulley drops w/o supporting mods, but these engines are known to knock even being factory.

Maybe try a new (or known working) ICM (the part under the coil packs). Sounds like something is failing when the system enters closed loop after it warms up.

Are you sure you don't mean 130psi on that cylinder?

**Trett93** · 06-10-2014

pulley is stock as far as i know, and nope it has 30psi, all the rest are 160-170psi, when i give it gas to pass if im under 4,000rpm the car boggs and my boost guage flutters around 10vac to 5 boost, like i have a vaccum leak, only way i can see a chipped piston dropping the compression that low is if an edge of the piston snapped off or the valves are burnt on the head

**REDCRAPGP** · 06-10-2014

30psi ? Yup I'm betting that pistons is toast. Time to get a inspection camera down there and have a look

**tomtom123** · 06-10-2014

This was my pistons 1 and 3. 3 was creating 0psi. It is definitely possible. And this was a completely stock engine. I bought the car and replaced the downpipe. I was even getting 0° of knock except a 5 - 6° spike around shifting under WOT for about 0.6 seconds =/
I hope this isn't your situation though

Sent from my SM-N900P using Tapatalk

**FordMan77** · 06-10-2014

The only other thought I have is a broken valve spring. But it's usually that or a chipped piston.

**Trett93** · 06-11-2014

yeah i just dont get why id only have the issue on one cylinder for pre detonation, wouldnt that be a timing issue? could be a broken valvespring or possibly rings, havent gotten a chance to actually tear down the head, but im hoping its not chipped, if it is, is it possible to just replace that piston with a new/used one? aslont as the cylinder isnt worn down?

**FordMan77** · 06-11-2014

If the piston is bad, then find yourself a used motor and swap over your top end parts if need be. Cheaper and faster. You "could" replace just that one piston, but the amount of money/time/machine shop work needed to ensure it lasts more than 20 miles after rebuilding isn't worth it. We just had someone on here install new crank and rod bearings in one because their Dad told them to, against all of our advice. Guess where he's at now, lol... Yup- another new motor. These aren't like the old 350's unfortunately.

**Trett93** · 06-12-2014

yeah i could get a used motor for $500 but who knows if that motor isnt chipped either, atleast if i buy it and look at it find a good piston i can swap the good one into cylinder #2, i have a feeling its rings but havent done a wet test yet, motor has 100,000 miles

**FordMan77** · 06-12-2014

You can get a used motor from more than just a GP. Get one that comes w/ a warranty. Heck, find someone parting one out where you can still hear it run.

Here are some threads I dug up via search that should help you make a better informed decision on replacing the piston vs. a used motor:

http://www.grandprixforums.net/threa...ons-HELP/page3

http://www.grandprixforums.net/threa...uilding+engine

http://www.grandprixforums.net/threa...uilding+engine

**Trett93** · 06-12-2014

yeah this one was from something lol idk what it was out of, but yeah mines a 2004 impala l67, all i need is one good used piston out of the 6 haha

**Scottydoggs** · 06-12-2014

changing a piston on these engines never seems to work out. just find a use engine.

if you cant find a l67 or l32 buy a n/a engine and top swap it with your parts. add a set of headers and a canned tune and your all set.

**Trett93** · 06-12-2014

id rather my l67 sc than a stock n/a, headers would sound nice with the 2.5in exhaust and standard, might go dual exhaust

**Scottydoggs** · 06-12-2014

little secret we all know and you dont yet.......a stock ran top swapped block is faster then a stock l67. chew on that a bit.

you need the headers to let the high compression block exhale. its automatically added mod when you top swap, or pulley up to a 4.0 pulley.