I just purchased a 2009 LNF, got a bit of a deal on it, it runs fine most of the time but it dumps fuel. Upon further inspection the stock downpipe is hacked up to be catless with a o2 diffuser welded in. Halfway home from buying the car it developed a slight misfire under certain load conditions (~60kpa of boost, only sometimes)

Check with the scan tool calls a cylinder 1 missfire, swapped coil packs miss stays on cylinder one. During missfire conditions the rear o2 is reading lean (assuming because of the diffuser and the catless pipe?) and the engine is dummping fuel.

Car has a k&n intake, injen charge pipes and 3bar map sensors so I am assuming some sort of a tune. I will be swapping 2.5bar map sensors back in and getting GM to flash the ecu back to stock as well as welding in a new cat and proper o2 bung. Is this the correct way to deal with this or should I be looking at a bigger problem?

 

Getting it back to stock would definitely be a good start. any codes?

 

Hopefully the o2 that has the defouler is not the primary o2 which fueling is adjusted from (in the manifold just after the turbo). The o2 in the downpipe is just emissions checking.

Whats the AFR or lambda when you go WOT?

 

Where are you located?

If it has the 3bar maps you would be better off for someone to flash GMS1 to the car.

The misfire on only 1 cylinder and doesn't move with coil pack is a couple things.

Bad spark plug
bad injector
bad cylinder
COKED VALVES

 

I'll add a little to this.

Wire harness issue to coil #1, harness issue to injector #1

My $$ is on coked valves.

You'd think a compression check would tell the tale though.......

 

OK I suppose I will do a compression check, I'm not sure a wiring issue as its not a consistent miss fire,

I was debating on a compression check but figured since sometimes it boosts to 18-20 psi with no issues that it couldn't be bad compression. I could be wrong. I suppose if it is dirty valves it will be time to send the head off.

 

Also worth adding. It did miss fire on 4 a couple times, but hasn't since I ran a intake system service through it (not fuel based, sprays directly into throttle body)

Might be a bigger sign to dirty valves and a head job.

Only code now is for cyl 1 miss fire. No rich or lean codes but it is running rich. New o2 sensor because the old one was dirty as hell and fuel rail pressure is closer to spec.

I haven't personally had time to work on it, it's been at my buddy's show while I've been at work, will spend more time on it this weekend but will be without access to a high end scan tool.

On a side note. I get to fix my biggest complaint with the lnf this weekend - the lack of Centre console. Convienently was able to rip it out of my totalled g5 before insurance took her to salvage.

 

Threw codes today for maf and cam solenoid. Replaced the solenoid, going to put a buddy's stock intake on to maybe fix the maf code. Runs ok until you try and boost it, then sometimes it misfires, sometimes it doesn't.

 

K&N is known to be a temperamental intake. Might just need to spin the filter around a bit to fix that MAF code.

 

I've head as a whole these cars dont like intakes. I'll put my buddy's stocker on and look for my own eventually if it cures the problem.

Car runs ok. Sometimes it boosts up fine sometimes it misfires and won't build boost. It seems to be dumping less fuel with the o2 and the cam sensor, I might blast another intake service through it next week to see if it helps as well as putting a cat back on in the next week or so.

I think I'll also have the gms1 tune flashed to the he ecu just to be sure, saves me buying another set of map sensors.

 

Runs great as long as im not beating on it, No misfires crusing around or lightly accelerating.

Car does not seem to want to make boost more often than not in 1st gear, Sometimes misfires under boost in 2nd, sometimes doesnt.

Threw a code last night i'll check today.

 

Can you view your LTFT and STFT? Also, if you've got a boost leak that'll cause the engine to drive funky and sometimes miss.

 

Ltft and stft what are those? Sorry I'm a bit of a newbie to these cars

I'm gonna try and borrow a buddies boost leak tester as well cause I knew that could be a possibility.

It made boost in 1st the last run I took. Hasn't really had a major misfire the last couple runs although I haven't tried to go wot since yesterday

Edit.

Long term fuel trim
Short term fuel trim

I have to check my scan tool I'm not sure if it can or not.

 

I was having a very similar misfire issue on cylinder #3


I replaced cylinder #3 coil pack, worked fine for a few weeks then started misfiring again.


so then i replaced the fuel injector, because the plug was covered in fuel. So I thought it was stuck open dumping fuel. Nope..


I replaced the variable timing solenoids both intake and exhaust. Didn't do anything for the misfire.


Now this is the important part!
Our wiring loom sits over the back of the head over the exhaust manifold. Needless to say its a lot of heat.
So I had the plug to the coil pack tested, it read zero volts. hmmm


We opened up the loom and the wires were very brittle(76,000mi), we singled out one of them and bent it. The wire literally ripped in half.. Brittle from the heat off the exhaust manifold.


I was getting absolutely no spark. What would happen is at higher rpm it would run great because the wire would arch across the break. When I replaced the coil pack I nugged the wire just enough to cause it to reconnect for several weeks.


Get the coil pack connector tested with a volt meter. If you have spark then you have other issues but you should start with this, its literally a 10 minute fix. Not to mention a lot cheaper than what I went through /:


Im pretty sure your having the same issue I was. Which is great because its a easy fix.


(Disclaimer: I realize I wasted money and didn't follow the best diagnosis plan. But in the process I learned some valuable diagnosing and troubleshooting techniques. So in the future, I will be better off if similar issues turn up again)

 

My mechanic checked over the wiring to the ecu, but now that is the weekend I will double check it myself (I'm an electrical engineer so it should be easy to diagnose for me)

I appreciate your help and will check back in tomorrow after I do some testing. Does anyone know what the pinout of the ecu to the coil packs are?

 

Here's the coil pinout for the LNF, specifically coil 1. All coils share the pin number assignments, wires will be different colors.

 

What about on the ecu side? Wouldnt mind checking resistance from the ECU to the coil pack as opposed to measuring voltage.

I'm also going to check the wiring at the MAF sensor as well as a boost leak test in the next couple days as i read one of the other posts about a guy having similar issues with no boost in 1st gear. etc.

I checked it out visually yesterday and the charge piping has worm gear clamps, I read on here somewhere that they arent recomended. Whats the recomended type of clamp and why not worm gear clamps? I would have thought they would be able to handle 20psi.

 

P0300
P0301
P0014
P0304

developed today. Cleared them and they haven't come back.

 

Replace the spark plugs, they're cheap and its a good maintenance idea anyways. Stick with the stockers

 

Already replaced the plugs with NGK, which makes ACdelco plugs. @100k it was worth doing. Made no difference.

 

Checked codes after my 100km commute this morning -

P0300 DTC Set
P0301/304 DTC Pending
P013E DTC Pending

Which further makes me think the car is running rich under boost. Bad MAP Sensor/Wiring or Boost leak i'm thinking more and more.

I have to figure out what size of PVC I need to buy to make a boost leak tester with the Injen charge pipe. Internet says its 2.5" DIA piping, i'll try and measure the ID of the coupling today now that i'm at work with access to tools.

I appreciate everyones help. I will try to update soon with some actual results other than just DTC codes.

 

Were the 3 bar MAP sensors saudered/crimped together? or were they the ones that came with pigtails? I remember there was many a issues with sauder cracking or bad crimps coming undone at the 3 bap MAP sensor. Check the one on the manifold and the one on the lower charge pipe.

 

P013E is the downpipe not getting the right flow. Do you have defouler or something in the downpipe?

The misfire codes can be all kinds of things as listed above.

 

Yeah theres a defouler on the downpipe. I figured that was the problem.

Im hopefully going to go the boost leak test in the next couple days, will tell me whats going on.

Im suspecting that or wiring to the lower map sensor.

 

Crimp connectors, im a bit uncomfortable with them as well, I will be soldering and heat shrinking them when i have a chance. The lower one seems like its a bit of a pain in the ass to get to but its the one i would doubt as opposed to the upper one.