MustangNicky

Hi everyone. I have just gone through a heck of a time trying to solve what has been causing my misfires on multiple cylinders, and could really use a hand if anyone can help. At the moment I have cylinders 5 and 6 misfiring after adding new spark plugs, wires, and a new coil once I did a compression test to see all cylinders are good, but just to go through all the details, I'll try to explain everything from the beginning as best I can.

A few months ago, my diagnostic tool showed me codes for a cylinder #2 misfire plus a bad O2 sensor (I believe it was a low O2 sensor reading but can't remember), but I kept driving it until I got another code for a cylinder 5 misfire as well. I first changed the spark plugs, then noticed the O2 sensor error code disappeared in exchange for a misfire on first 1000 rpm on startup plus the #2 and 5 misfire codes. From here I bought new wires and made the stupid mistake of accidentally swicthing wires for cylinders #4 and 6 and tried cranking the engine a few times. From here I now had three misfires for cylinders #2,5, and 6 plus the first 1000 rpm on startup codes, so I bought a compression gauge and did a compression test. I removed all six spark plugs and pushed the gas pedal to the floor while allowing a good 3-4 revolutions or counting out 8 "one onethousands" for all 6 cylinders, and they all showed in between 150-165 psi, so I knew they were good. Not able to fix the problem at that moment, I drove the car, and believe I smelled gas burning as I struggled to go up a hill (I'm only saying this because I read someone saying this might be important for these issues before right before coming here, and I have no idea what this means), and bought a new coil just a few days ago. After installing it, cylinder #2 misfire was fixed, but the startup,#5, and #6 misfire codes remain.


Hopefully that's all the info you guys need in order to offer any advice, but I'm not more than an intermediate mechanic and don't wan't to lose any of you on unnecessary info, so I apologize if I came off as a little bit of a stooge on what I just wrote. Anyway, thank you very much in advance, and nice to meet you all.

daddyo4363

So you say you did in fact install a New Ignition Coil then?? Because I was getting misfire codes and misfires at start up and random misfires and my Ignition Coil was fried..

Derf00

Do a leak down test, misfires can be caused by valves not seating correctly as well. No, it won't necessary show up on a regular compression test. A leak down will test all the strokes in a combustion engine (Intake, compression, power, and exhaust).

MustangNicky

Yes I did. New coil and all six plugs and wires, and still cylinders 5 and 6 are misfiring and are not losing power when I remove their plug wires from the coil with the engine running, so I was hoping it was the injectors next.

MustangNicky

A leak down test? I do not know what that is yet, or maybe I forgot, but I'll check it out. In the meantime though, if it is bad fuel injectors since my gut is telling me that's what is is for whatever reason (smell of burning fuel mentioned earlier along with the other misfire blogs I read before coming here suggesting this as the cause), what would you reccomend since I'm not looking to spend too much? I'm seeing single fuel injectors going for $40 while a complete 6 pack of injectors are going for about $70. And thanks alot, also.

imp

I don't believe several injectors "go bad" simultaneously, unless dirt finds it's way past the fuel filter. Injectors additionally have a finer mesh screen on their inlet passage. However, clogged screen, or partially clogged nos inject LESS gas, not too much. Deposits on the injector pintle can also reduce fuel flow. OTOH, sometimes injectors do not seat properly between cycling, and bleed fuel in between firing pulses. That causes rich mixture, possible visible smoke, and stink, and possibly detected misfire.


Regarding valve leakage, a leakdown test would be nice, but I fail to understand the reference to checking leakdown during all four operating cycles. Leakdown on compression, power, yes, but during open-valve events, what leakdown are we talking about? Burnt or bent valves if sufficiently out of whack, should be revealed by the compression test, unless the engine has one or more cylinders with badly worn or broken piston rings. Misfiire caused by a badly burnt exhaust valve, for example, results in a most discernible "lope" during idling.


Have you checked fuel pressure? imp

MustangNicky

I actually feel a little foolish for forgetting this part. I'm not sure if this is part of the problem, but I bottomed out pretty hard before getting the bank 2 running too lean code, P0174 I think was the error code, and this was after the P0305 and P0306 codes. The floormats under my feet are burning up after a long drive and not on the passanger side from what I can tell, I can see the heat coming off the cat specifically while looking under the car (couldn't see which end yet), and the sound of an exhaust leak has been painfully obvious since I started this thread. I just saw a video about the bank 2 too lean code being connected to this part being clogged and the symptoms he mentioned are all what I am experiencing. Low power especially on acceleration, occasional sound of something rattling around then stopping like a chunk just found it's way out the exhaust, and a very slow idle rpm. The sound of an exhaust leak seemed to be there when I had the 3 misfires, but from the time I reduced the misfires to just cylinders 5 and 6 until bottoming out, it has much louder plus the above symptoms seemed to just start.


As of two hours ago, though, I still have error codes,
-misfire detected on startup first 1000 rpms (p0317 I think)
-misfire cyl 5 and 6 p0305 & 6
-system running too lean bank 2 (p0174 I think)


I think that covers all the symptoms I'm experiencing, so If you say the passing compression test knocking out certain variables in the leak down test is correct, I hope this added info narrows down the causes even more. And again, I'm no expert mechanic but something about fuel injectors along with one or more of the cat donut rings seem to be standing out to me as root of this problem. Is that likely?

MustangNicky

Wish I knew how to edit, but I don't know what "lope" means and I haven't checked the fuel pressure yet, Imp.

Derf00

I over explained the leak down, yes the leak down is useful in the compression and power strokes only. Basically the times when the cylinder is completely sealed.

I have personally seen on two occasions where a compression test didn't really reveal much but a leak down revealed intake valves that were not properly sealing/seating.

My son's 2007 Chevy cobalt. From 2006 to 2009 2.2L ecotecs are prone to misfire codes caused from intake and/or exhaust valves not seating properly over time. It's rooted in the way they GM formed the heads for the 2.2L Ecotec motors. If you look at the polished surfaces it looks like the surface of styrofoam in the sense that you can see where the styrofoam beads expanded and glued together during the molding process. Only in this case it was beads of molten aluminum. This visual oddity rears its ugly head on surfaces where carbon can build up on the microscopic surfaces. Over time, enough build up and you get valves that don't always seal right. This will come up as an intermittent misfire while driving or Random misfire detected at start up.

In the case of my sons car the cylinders were all within the expected 10% of each other. The faulty cylinder turned out to be the one that was on the low end of the 10% but still passable by compression test alone.

I chased my **** on that one for two weeks (swapping plugs, fuel injectors, coils, combing forums) before going to the leak down test as a last resort. I had a shop verify my results (compression and leak down) same results without telling them what I found. Compression passed, leak down failed (intake valve). Replaced the head. Problem solved. The old head did not have excess carbon and by all accounts looked fine but the seats did have some discoloration and a rough feeling. Car had 65K miles. It was cheaper to buy a remaned ready to go vs having his rebuilt.

The second case was a Ford Fusion with the direct inject ecoboost motor. Direct inject motors are by design prone to carbon build up around the intake valves because they no longer have fuel constantly passing through them. Boosted motors are even worse off because the PCV system gets extra blow by from the FI system and added pressure. Anyways, same scenario. Code would only occasionally show up, in most instances the car would appear to run ok or with minor hiccups.

Owner went through the same troubleshooting steps as me and was just as frustrated. They took it to a shop. Leak down revealed intake valves not seating properly. In his case he had an Intake cleaning performed to remove excess carbon build up. Problem solved. Car had 37K miles.

imp

A lope is a repeating inconsistency in a normally smooth system, like engine idling with a slight "bump" or jerk recurring every second or two. Burnt exhaust valves may be detected by hearing that lope, confirmed by the "paper-matchbook" test in which a folded paper-matchbook is held over the tailpipe, allowed to flap in the gas stream coming out. If the flap repeatedly "sucks back" against the pipe opening, a burnt valve or valves is strongly indicated. This happens due to the bad cylinder's intake stroke drawing air momentarily backwards in the exhaust runner. imp