Misfire on startup

Been having an occasional misfire code over the past few months (09' GT 135k miles). Only happens maybe every other week and only on initial startup when the car has been sitting for the day. When it happens, its as soon as the car starts up you can feel it running rough and the code pops up pretty quick. Its never once thrown a code while driving, either under load or coming to stops. If I reset the code and start the car back up it runs fine. Probably more than half the time its throwing the code for all 4 cylinders, the other times it will throw for cylinder 2 and 4. I had done some searching already but most of what I found, people were having codes thrown while driving or under load.

 

If its usually all 4 cylinders or at least one side (never a single cylinder) I figure spark plugs and coils aren't the problem.

 

I didn't see any hoses unattached under the hood from a quick look, didn't pull the intercooler to check underneath yet (just moved and don't have tools on hand at the moment). Probably going to dig around this weekend some more

 

Any ideas of anything that would cause the problem only on startup? Could an O2 sensor or OCV do it, or would those cause issues beyond just on start up?

I would start by making sure the MAF sensor is clean and you don't have any vacuum leaks. Both are easy to do.

 

Does the car get a driven for long distances or just short around town driving ?

 

I gather the plugs were replaced at 120,000 miles ?

Thanks for pointing out the MAF, I'll get some cleaner and go through the vacuum lines again. Plugs I did around 110k. It's usually driven 45 miles round trip on the weekdays (highway) and more than that on the weekends.

Just look everything over and make sure you have good connections at the coils and all electrical connectors.

 

Do the free stuff first.

I've been slacking, house work took priority. But the car is misfiring a lot more now. I had previously put in new plugs and tried swapping coils. Didn't clear up the cylinder 4 misfire.

 

So fast forward to this weekend. I tried swapping injectors, ocv's, checked as many hoses as I could find and did a compression test on bank two. Cylinder 2 was 135psi and cylinder 4 130psi which I thought was good news. Also checked as many grounds and connectors as I could find. Engine ground on the injector bracket was nasty. Cleaned it up. Another weird thing. When we finished swapping everything one at a time, the passenger ocv threw a code that it was open (before I swapped it to the passenger side). Tried clearing and restarting the car a few times and it kept coming back. Never had the code before. Anyway tried cleaning all the junk out and it still threw a code. So we swapped the ocv's from driver to passenger and the code went away. Maybe a coincidence? Gonna order a new set anyway (135k miles on the car).

 

None of the changes above fixed anything. Car has a very rough idle and almost sounds like an exhaust leak, that putt putt putt sound. My uncle said an old mechanic trick was to put your hand over the exhaust, it was sucking my hand back in pretty good, which he said is usually a symptom of a leaky exhaust valve.

 

Any other thoughts on what it could be before the car is tied up for a week to pull the heads (only have limited time each night to work on it)?

 

Primarily the misfires occur at idle and when coming to a stop. It's the worst when the car is cold. Gets better once it's warmed up but still misfires enough to throw a code. No cylinder roughness is logged while cruising. I do however get occasional feedback knock while cruising (not under load) up to -8degrees.

 

Just trying to rule out anything else before digging in.

The only other thing I could think of is the O-rings between the intake and TGV's.

 

I know the earlier years, we recommend replacing those with the new larger orange seals.

 

I thinking you have burnt valves somewhere.

 

Has the car always been on the stock engine MAP ? The stock MAP has been known to burn valves.

Thanks again for your help. Forgot to mention but I did the intake orings as well. Also the spark plug for cylinder 4 had a bit of carbon buildup on the outer rim and the porcelain was pretty brown (only a few thousand miles on the plugs). The cylinder 2 plug was white and clean. I was on the stock map until probably 40k-50k miles when I went stage one Cobb OTS. Then I went stage 2 Cobb OTS around 60k miles (just a Cobb catted downpipe and an Intercooler).

 

I guess while the motor is out, anything I should do while I'm there?

 

Was figuring at least cam seals, crank seal, both head gaskets, head studs (size and length?). Probably check all the valve clearances. Anything I'm forgetting? Car has 135k miles on it.

Belts and hoses.

 

do you have coolant, oil and filters for the first few oil changes ?

 

New ground wires to both heads.

 

Let us know what the top of #4 piston looks like.

 

Did you get in touch with Eastwoods ? I haven't stopped by Marks since summer time. I'll have to swing by some day and just say hi. Its a real cool shop to see, not much to look at from outside, but they work on so many different types of engines. Stuff most of us have never even heard of or seen.

One time Mark told me to go smell that 454, it smelled like a Yankee Candle, that's because that's where it came from. It was one of there generator engines. I've seen Chinese engine that they didn't have any spec's for but it was close to an Isuzu engine.

Thanks, I did get in touch with them. Took me a little while to break everything down. Should be bringing the heads to him as soon as my gasket kit comes in so I can give him the valve seals. Its definitely at least one leaky exhaust valve. The valve wasn't chipped and didn't look as destroyed as many of the pictures I've seen on the forums, but shining a flashlight down the exhaust port, you could see light around the entire circumference of the valve. Back side of the valve where it seats (the valve not the head) was pretty pitted as well. Not smooth, looks like a lot of dents. I'll have to try uploading a pic at some point.

 

The top of Piston #4 looked pretty good. Bit of carbon build up on all 4 cylinders, so I'm going to clean that up then get a better look at the tops.

 

Did the timing belt last year, and the accessory belts are in good shape. Have coolant and oil. Grounds looked good to the heads, going to clean them up while I'm at it.

 

The bolts on the exhaust cam pulleys were a nightmare. My uncle was even able to dig up the cam tool. Passenger side bolt popped free after using a jack handle on the end of the breaker bar for some more leverage. Sadly the drivers side head stripped. Fortunately my dad had a socket for the job, bolt extractor I think. Looked like a corkscrew inside. Hammered it on over the head of the bolt and we were able to use the breaker bar and jack handle to break it free. We tried heat on the bolt a bunch of times, so I think I'm just going to order another cam pulley to be safe. Also the back side cam cover on that side cracked as well so need to order one of those.

 

So for now, at least an exhaust valve and bucket, cleaning and re seating all the valves and I'll see what else Eastwoods says. Full gasket kit, drivers side exhaust cam pulley, back cam cover, cam bolts, cam seals, coolant crossover pipe (thing looks gross) and head studs. Also finally pulled the banjo filter under the intake hose. 135k miles and it barely had any junk on it so that was good. Turbo also didn't seem to have any shaft play. No wear against the inner housing.

 

That's pretty cool about the 454. Been to the Yankee Candle before, that place smells potent! Looing forward to seeing the machine shop. It'll be a few years but it will be nice to have a place in mind when I finally get the money and time to build the 65 Mustang I've had sitting at my house for years.

Update, shop said the heads need 8 new valve guides as well and it could have contributed to the bad valve I have.

Meant to post these before. Cylinder 4 before and after cleaning it up. Looked good. Cylinder walls still showed all the crosshatching.

 

 

 

Also had the turbo rebuilt by jmp.

 

 

Got everything back together this weekend. However, like an idiot, I barely grazed one of the radiator fins putting the fans back in and sprung a small leak. Had a bottle of subaru coolant conditioner that stopped it, for now. Pressure tested the radiator after the leak stopped just to be sure. Stayed plugged. Unfortunately low on coolant now and the dealership parts dept was closed yesterday. So I let the car sit, hopefully it'll be back on the road today after work.

 

(**EDIT** Reading forums stresses me out haha, after reading up a bit on the coolant conditioner I see everything from its fine, to it'll clog the radiator, turbo coolant lines, and head passages. Should I be draining this crap back out?)

 

Just started it up and idled a few times to check for leaks, it's never idled or started this smooth probably since I got the car with around 10k miles. Used to have a drivers side valve tick for as long as I could remember, that seems to be gone which is nice, was annoying. Will see how it runs over the next few days. Hoping the radiator leak is plugged.

 

Total parts list:

Rebuilt heads: one valve, eight guides, decked, cleaned, and all valves reseated

Gasket set

New cam bolts (destroyed two getting them off)

Drivers exhaust cam gear (didn't trust it after using heat to remove the bolt)

Coolant crossover pipe (looked like it was about to leak)

Thermostat (while I was in there)

Rebuilt turbo (billet compressor wheel)

ARP head studs

 

Going to swap out the OCV's soon as well.

 

Hoping this is it for a while.

 

 

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