Thread: Random Misfire and P0171

Hello everyone, I need a little help with a random misfire and what you guys think it might be.

Okay, I have already changed the plugs to NGK Iridium gapped at .060, new plug wires, new fuel filter, new air filter and I am pretty sure I have fixed all the vacuum leaks it had. I have a problem with the engine setting off a P0300 code which is for a random misfire. It only misfires though when it is on boost. When it is off boost it runs good. I checked the fuel pressure and it seemed good if i remember correctly it was around 55PSI. I put some injector cleaner thinking it was a clogged injector but that still didn't help at all.

Also I'm thinking that maybe the P0171 would set off the random misfire? I hear a ticking noise in the engine bay that flutters or gets louder when you give it gas, so I am guessing the lean condition is happening from that exhaust leak.

The car is completely stock, so is it being gapped at .060 bad? That was how it came out of the box. And also, what could cause the misfire only under boost, if off boost it runs good? I fixed almost everything but now this misfire is just getting too me....

first thing is did this happen to start after you were hard on it? Second, do you use 91-93 octane? Third, do you have a scanner to check KR?
I've had first hand experience with this same problem but the odds of having the luck I did are miniscule..

second question answered BTW, I just read your other post

Subd as I have what sounds to be the same problem. 91 octane used, less than blips of 1* knock exist. I don't think I've been hard on it, just tuning but I do get into boost slowly.

TIA,
Slim

Whats your LTFTs look like both of you?

if the exhaust leak is before the O2 then yes that would cause all of the symptoms you posted. -ie misfire and lean scenarios. I just replaced my exhaust and mine went away. Before I found my 2 piece front manifold I never could find the reason for the problem. so essentially I'm saying fix the exhaust leak and come back and report in as for "Slimguns" you can post in my thread linked here> READ THROUGH MY STUPIDITY AND see if you think this helps http://www.grandprixforums.net/threa...ll-be-THAT-guy

Fix your exhaust leak first, then diagnose from there

Are NGKs recommended for your car? In my experience it is always best to run what your car was designed to work with (plug type, gap etc.). I never trust the gap that comes out of the box. You say it only happens when your car is making boost, so it's a high rpm miss. Try misting your plug wires with water at night while the engine is running and see if you are getting any arcing from them, try this at different engine speeds

I really don't know how to check the knock retard on it but it is not throwing any codes for that or I don't hear any pinging. I really don't drive it hard at all, and well I have not been driving it that much cause of the misfire. I bought NGK's since I read that the car needs iridium plugs to run smoothly. And sorry for sounding like a noob with the terminology but what are LTFTs? Ill look for the exhaust leak a bit more closer this morning and try to pin-point it. Hopefully fixing that exhaust leak will cure this misfire because I just want to drive the car already lol.

you need a scanner that reads live data to see all that kr and ltft's

iirc the torque app does all that for about 20 bucks. if you have a droid phone. some of the blue tooth obd2 scanners things also come with a disk to hook up to a pc.

Yes I do have a droid phone. Ill check out that app, thank you. So I have to have the scanner and the app then? By the way, going back to the exhaust leak I think i discovered where it is at. Its the pipe that is directly below the throttle body. It is leaking exhaust at about a foot wide crack in the pipe I am guessing. Going to take that pipe off and take it to the exhaust shop.

go to the Junk yard and get one there cheap. no reason to pay the shop +$100 to fix something that is easily replaced
LTFTs = long term fuel trims. its based on a percentage when you get it scanned after the exhaust is fixed post up the results.

Originally Posted by Mbueno19

Yes I do have a droid phone. Ill check out that app, thank you. So I have to have the scanner and the app then? By the way, going back to the exhaust leak I think i discovered where it is at. Its the pipe that is directly below the throttle body. It is leaking exhaust at about a foot wide crack in the pipe I am guessing. Going to take that pipe off and take it to the exhaust shop.

you need your droid phone with the app installed to it, then a bluetooth obd2 port thing. http://www.ebay.com/bhp/bluetooth-obd2-adapter-android

a you tube review, i have not watched the whole vid, but it should give you some sort of over view http://www.youtube.com/watch?v=vQSsUPrGLHs

Wow okay thank you. I never knew there was something like this in the market lol. That is pretty cool what it could do at such a good price. Ill be ordering it and then i can check what is going on with the car.

its not the "best scanner" but for what it is, its great. shows a lot of live data.

reads cel codes, and can clear the codes as well.

Can it read air to fuel ratio's? If it can, I will love this app forever lol. Just bought both of them.

Here is the pipe that was cracked not as bad as i said it was but still really bad.
20140207_114356.jpg

it should show all that.

get that crack welded up, cheap repair. as long as the pipes not 1/2 rusted through. i welded 2 large holes shut on my last exhaust pipe, the hangers ripped off. big holes and thin pipe dont weld well. i finally conceded and put a new pipe in.

A very small crack gave me issues galore. I would figure fixng this would be a great start lol

Well with the pipe back in place and the crack sealed good, it still misfires under boost... :/ I'm thinking of doing a compression test on the cylinders. The usual gap in the plugs is for these cars is .055 to .06 isn't it?

What cylinders though, we need to know that.

Could be as simple as a bad coil pack or maybe the ICM is bad.

It is a random misfire, code is P0300.