Searched - 2006 LGT Engine "Breaking Up"

I've searched to no avail so I'm posting here hoping someone can help. My LGT 5MT has started "breaking up"at 5,000 RPM at full throttle, popping & banging despite running Shell 93 octane. It sounds kind of like detonation & fuel starvation, or maybe plug shorting? It threw a P304 "cylinder 4 misfire" code. I immediately stopped running it above that RPM, and it's normal below there. At lower RPM (even WOT) it runs normally, doesn't misfire or anything, although there is slight detonation at certain mid-throttle & mid-RPM conditions I attributed to crappy gasohol. Fuel economy is unchanged. She has 160,000miles on her, oil consumption is under a quart/1,000 miles. All original besides maintenance parts. Autolite platinum plugs, The Bosch +4 plugs I wanted were the wrong length(?) & that's all they had in stock.

 

I changed plugs, swapped #2 & #4 injectors, cleaned the MAF, changed the oil while I was i there, no change.

 

Any ideas? Maybe clean the OCS valves? Could my converters be plugged? I would think the oxygen sensors (all original, still get 27-28 mpg at a constant 70 mph) are not part of the equation at full throttle? Help!

Air, fuel, spark, compression. Could possibly be a malfunctioning OCV. Could be a leaking manifold o-ring on that cylinder.

 

Ditch the autolites for NGK iridiums. Gap at 0.28".

Thanks for the quick reply. I'll try the plugs.

 

Can the OCV be cleaned?

 

Wouldn't a leaking o-ring cause a rough idle? She's about the same as ever....

Little bit of carb cleaner sprayed around that cylinder should tell you if theres an intake leak anywhere.. boost leak test would help too, theres a few guys on here that have built good testers for it..

Should I use the one step colder NGK iridium plugs, or stay w/OEM heat range?

dont need to change heat range unless your running some high boost numbers

Thanks. Did some searching, looks like LFR6AIX-11 is the readily available part #, needs to be re-gapped then good to go?

Definately check the gap but they usually come close

Stock heat range. -11 will be a 0.41" gap. Carefully close the gap to 0.28".

Picked up the plugs last night, O'Reilys had them for $7.48 each (before tax).

Got the plugs in this weekend. Acceleration is much brisker, idle steadier.

 

After warming up the first WOT blast thru first gear felt much stronger, it was still breaking up a bit near redline. Second gear still stronger up to 4000 RPM, then it started breaking up & popping a bit, got bad at around 5000 and it threw a CEL, which stopped blinking after a minute or so. After getting fresh 93 octane unleaded I repeated the test, same results, only now the CEL is blinking constantly along with the cruise light. I'll get the code pulled tonight, but suspect it'll be the same P0304 #4 misfire; it feels & sounds the same.

 

BTW all 4 old plugs were gapped at about .044"; all had the same whitish coloration, on the lean side. Curiously, my exhaust tips are a bit carboned up, with a very thin sooty film. Normal after 160,000 miles?

 

I'm thinking the exhaust is getting plugged up. Is there a simple, safe way to test, like unbolting the exhaust just downstream of the turbo?

 

I've also noticed my IC is leaking (oil seepage) on the turbo side, but don't a small leak would cause such drastic behavior. Less air would equal a richer mixture, and the plugs would have reflected this?

At 160k if still misfiring in 1 cylinder (after changeing plugs) quick check is to move coil packs around. Then move injector. Then time for a compression check.

 

Remember the black coil connectors go on 3 and 4. The two coils closest to the firewall.

Follow up - I finally had time to switch #2 & #4 coilpacks; at first the problem persisted, this time throwing a #2 cylinder misfire. Called in a coilpack, wasn't in stock but would be available early the next morning.

 

I went ahead & removed the coilpack, & decided to test it while it was out. The electrical connector on #2 cylinder had a broken tang, so I had secured it to the coilpack w/a zipty. This was cut off to remove the coilpack, & I put a new zipty on to test. To my surprise, the plug fired nicely at idle, even creating a really long spark when I purposefully moved it away from ground! Thinking the coil must be failing when hot/had a flaky electrical connector pin I reinstalled it, using multiple zipties.

 

The engine ran great!:):) Full, clean revving out to the fuel cutoff in first and second gears. I drove it a good bit this weekend & so far so good!

 

Thanks to all for their help, maybe this post will help someone else.

I have replacement coil pack electrical connectors.

Will a standard connector crimping tool (for butt connectors) do or is a special tool needed?

The connectors come with new pins and seals. So, if you want to complete replace the pins/o-rings and connector all parts are supplied. It is usually easier to push the pins out of the old connector and insert into the new. But if you want to replace or clean up the wiring you can. For new pins I would recommend a pin tool.