I've posted several times about MY04 experiencing random misfires in all 4 cylinders. Dreaded P1399 code. I've replaced everything suggested in all the misfires threads, from injectors to valve adjustment...my other posts have a list of everything I've done. With that said, Billman has suggested leak down, so leak down it is.

I purchased an 8 gallon 150psi air compressor & am ready to do a leak down test (compression test was fine). I know to do each cylinder at top dead center, but I've also read about running the test with the cylinder at it's lowest point to see if there are any issues on the cylinder wall itself. Do you suggest this?

Now let's say I have a bent or burnt valve, or multiple (I didn't know one bad valve on one cylinder could cause misfire in all cylinders). Let's say it's one valve what would your suggestions be? Replace the entire valve train while I'm in there? I want to do it myself, but this may be beyond my skill level, any idea average cost for a shop to do it?

One of my many questions...the car has 155k miles.... Is there a possibility the timing change is so stretched or skipped a tooth (if possible), I would guess that could cause misfires & also make the leak down test poor in all cylinders. Has anyone had this happen?

 

Its easy enough to check for chain stretch (or tooth jump) issues. Just check timing marks crank and cam gear. If they align, chain is fine. Chain issues on this car are super rare. Ballade does make a special cam gear to correct chain 'stretch' issues. If you find an issue, you could use that instead of tearing apart motor to replace chain and gears.

What to do about leakdown from valves of you find that, it depends on how bad it is. If its not bad, you can just pull head, and lap those valves. Its something you can diy. Google it.

But really if they aren't that bad, its unlikely it would be causing a lot of misfire issues. So if there are serious valve leak issues, you'll probably need to send head off to have valve seats machined, or possible even replaced.

The machine shop is going to insist on planning the head surface. Don't let them. It'll mess up chain geometry and cause lots of problems. If there is a serious issue with the head not being flat, check back in with the experts here on what to do.

 

Your car doesn't have enough mileage for chain stretch to be an issue. Let me ask you, does your soft top have any tears? Any way for water to seep through? How many mysterious misfires are caused by water leaking through the top that somehow find their way into the fuel tank? What is keeping water out of the fuel tank? A lid with some bolts, what about the junction of the filler neck and the lid of the pump housing? If water were getting into the fuel tank it would absolutely cause a misfire. Valve leakdown numbers have to be over 20% for it to throw misfire codes.

The real debate is whether it's worth working on the cylinder head, or buying a good used one?

 

I actually had the typical 4 corner rips, water definitely got in the car. I replaced the top 2 years ago tho. I have a Walbro 255 sitting in a box (planning on going boost once I fix this). Despite the fact that I replaced the top 2 years prior to the issue, do you think I should install the new FP before doing leak down?

I'm 30yo now & I enjoy a a great tire & ripping corners now more than ripping redline everywhere. I probably have hit vtec 20 times in the last 5 year, no lie. It was my DD until I got my other car. I just don't understand how I destroy a valve(s) driving like a grandma (except in the corners.) I'd like to fix this motor & boost it because it probably doesn't have much life left boosted, then by a new motor.

 

The only way would be if the car never had a valve adjustment, and the valve clearance got too small as the valve wears into the valve seat. That leads to valves not fully closing, which leads to the valves only transmitting heat to the head via the valve guides instead of both the guides and seats. This is especially harmful on the exhaust valves due to the exhaust heat they have to deal with. Since the guides are bronze, and are now tasked with dealing with all the heat, they tend to become soft and wear out. Once that happens the valves no longer open in a linear fashion, the increased lateral play reduces valve contact on the valve seat, as well as wearing the valve seat in an oval manner.

That's how worn valve guides lead to low compression and high leak down, the valves are no longer sealing the head because the valve seats are not concentric to the valve face.

For this reason, I personally will live with a little more valve train noise and adjust the exhaust valves on the looser end of the spec, because I don't want worn valve guides.

 

I did a valve adjustment a few months ago, thinking that it may be causing the issue. All of them were so close to spec. I've done so many things & the car runs like absolute trash, it's undriveable. Reason I was thinking fuel pressure was because I've done 4 sets of injectors, two of them untrasonically cleaned. Got a new PFR, & while during terrible idle I pulled the vacuum hose off of the FPR & the idle went back to normal. Just at wits end & every answer I've read online has fixed the issue for someone...not mine.

 

Pulling the FPR hose boosts fuel pressure a bit.