shooffnyc

Ever since I got the car, it had intermittent misfires where the car would idle roughly, have a massive power loss and obviously throw CEL for random misfire on the entire passenger side bank cyl1-cyl6.

When I warm up the car to idle temperature, turn it off, then turn it on again, the car comes alive and it idles normally and has all the power back. The CEL would stay on for another day then go away.

I came to the conclusion that the humidity in the air has been the cause of this. When there is less humidity and moisture, it doesn't do it. But when the air is humid it does it more frequently.

Two days ago, ever since the CEL went on, it isn't going away. Mind you, there is a huge heat wave in my area and it's carrying alot of humidity.

I thought since the entire passenger side bank throws misfire code, it must be either the coil-pack, spark plugs, or even the voltage transformer. I figured that somehow moisture is getting inside the spark plug holes or maybe the coil boots, etc. I spoke to Clark Rupp of v12icpack.com and he told me that humidity shouldn't have an effect on the coilpack nor the voltage transformer. He believes there is a good 10-15% chance it's the MAF sensor.

So I pulled apart the intake, inspected the vacuum lines including the ones from the power brake booster. All looked fine after a visual inspection.



Then I took a video of the cars MAF when I press the gas pedal. It def seems like it's not taking in much air at all. You can hear it barely suck air in. And if I put my hand near it, the idle almost dies off. I feel like the MAF has gone bad. I already ordered another one. Should be here in few days. What do you guys think? I always end up starting to diagnose the bigger and more expensive things and overlook the little and less expensive things.

Plutoe

My WAG is that as you have not tested the MAF you have wasted your money,however you will no doubt be overtaken by sympathetic psychosis and believe that because it's new you have solved your problem,when in actual fact the problem will persists.

And if you recall from HS physics,damp or humid air is more dense and therefore typically produces more power-----and yes if you restrict the air flow through the MAF the engine will stop---the MAF doesn't do that your hand over the entrance does that!!

I know you gotta fix everything, however you need someone with good diagnostics and knows the cars systems to provide you with solutions!!but go getem!!

Jack_88

I also appreciate the value of thorough diagnostics, but your statement about humidity is incorrect. Humid air is actually less dense than dry air. Humid air also contains less usable oxygen, so the engine typically compensates but will not produce as much power as under cool and dry conditions. The driver really won't notice, though.

ZephTheChef

I know it's kind of off-topic, but that statement is exactly the opposite of correct. Humid/moist air is less dense than dry air, and cars will produce much less power on a humid day vs a dry day of the same temperature. Now if the air is much cooler as a result of the humidity, that can change things...but then we're not talking apples to apples. The same temperature of dry air will always make more power than humid air. Water vapor is effectively inert with respect to the combustion process and it can displace a fairly large mass of oxygen in the charge air.

When injected at the proper point in a hot intake stream, the charge cooling CAN possibly outweigh the volumetric displacement, but it's very difficult to get it right. The test the EPA did on water injection showed in all but one of the injection location and quantities they used that the mass flow rate of air actually decreased. But as far as humidity in the atmospheric air which is already present and does not contribute to charge cooling, it will always hurt power and performance.

ZephTheChef

Beat me to it...by a lot, lol. I was so focused on getting that corrected that I failed to see you had already done so, lol.

ZephTheChef

Back on topic, I agree, the MAF replacement is a wild-*** guess. I very seldom see MAF sensor failures on vehicles. Much more often, the MAF is working as intended but the car has a vacuum leak. What you are describing is very typical of a car that has an intake gasket leak. It will have a cold misfire/stumble and as it warms up, things expand, and the leaky gasket seals up and everything is fine. I see it all the time on vehicles at the car lot. I can't speak as to whether or not it is common on these cars because the only one I have experience with is my own...but in general, the first thing I do when I have a car with those symptoms is replace the intake gaskets (if it's a model I know is prone to having issues there, or break out the smoke machine to see where the leak actually is if it is not).

I would really suspect you have an intake gasket or lower injector seal issue that is sealing up as things warm up/expand.

Jack_88

I do that a lot when responding to the bottom comment on a page, and don't notice there's another one.

shooffnyc

BTW, scratch all my theories out. It turns out the voltage Transformer was bad. Replacing the transformer fixed all the issues described. No more misfire and no more CEL.

So in case anyone runs into a similar issue where starting it up in the morning gives it a misfire and CEL on all 6 passenger side cylinders and then later on it goes away, there is a GOOD chance it's the voltage transformer.

ZephTheChef

How long did the misfire last? I haven't been able to evaluate my WOT issues now that the intercooler system is down for the count, but I'm still having delayed starting/misfires right at startup. Only for maybe 1-2 seconds though. It feels more like a fuel pressure bleeding down issue to me, as it only happens the first time I start it that day. I have yet to borrow the fuel pressure gauge overnight to see if that is in fact the case.

shooffnyc

When I start the car up, it would start with a misfire and last for a long time, until the engine was at operating temp. Then when I turned the car off, and restart it would go away. Misfire as in CYL 1-6 shutting down and running on 7-12, as that's what a failed(or in this case failing) voltage transformer does.

ZephTheChef

Ok that's what I thought. Definitely not a match for my situation, that's more like when my coil went out. It's amazing how smooth they still run with a whole bank off (just no power), at least it's silky smooth on the TTs, I don't know about the 5.8. This is definitely more random/multiple and for a very short time period.

tusabes

When one bank is off it's essentially a straight 6 engine which is inherently super smooth

ZephTheChef

Yeah, it wasn't unexpected so much, just impressive.

DrDoe

I have an issue with misfire on #7. If I park the car overnight and start it in the morning then I would have #7 misfire if I let the car sit idle. If I drove off immediately after I start the car then the misfire never take place.
After the engine gets hot then the car can sit idle and it won't get #7 misfire. Misfire always on #7 and not on any other cylinders.

#7 is the first cylinder on the driver side toward the front of the car. What would caused this issues?

ZephTheChef

I've found the cylinders towards the front are more prone to act up on my car from water intrusion i to the plug wells. Which causes issues whenever the firing voltage requirement gets too high. This happens at low rpm, especially on a cold engine with lean fueling (which is often the case on a cold engine even if the vehicle is commanding rich due to vaporization issues...in fact it's part of the reason why most cars have significant cold-start enrichment for 15-30 seconds). It also happens under very high load, like WOT, or even light acceleration uphill in high gear (which is another lean, high load, low rpm example).

DrDoe

Sounds like there is more than one way to fix the issue? Change idle RPM, change fuel mixture, change spark plugs, fix 02 issue?

ZephTheChef

If that is your problem, then yes. Denso has a really nice write-up on things that affect firing voltage on their website. It could be a number of other things though, an injector issue perhaps, or the coil itself getting weak. But what was happening in my case is water had gotten down in the plug wells and the spark was arcing to the plug's hex instead of jumping the gap. So if you pull that coil you could possibly do some more diagnostics.

DrDoe

Coil packs were replaced in Mar-16.
Spark Plug NGK Iridium IFR6Q-G installed in Jan-16.

The #7 misfire issue just started as the weather get to 50F in my hood. Perhaps more air (O2) related issues?

ZephTheChef

I finally found mine was caused by a bad seal to the hood at the fresh air intake for the AC. When it would rain, water was getting onto the underhood heat shield/soundproofing and running up and dripping right over the coils. Just something to check, but I believe thay was more of an issue on 1-6.