I've got an '04 with about 65k miles on it. No mods right now and normal city/highway driving.

So I got the plethora of P030X codes and then P1399 and started chasing the dragon to find the problem. I recently took a business trip that was about 160 miles each way and I averaged close to 26 mpg for my gas use, so it seemed that those may just be mystery codes. I used a few of the threads here and tried to eliminate possibilities.

Did new OEM plugs first. Set the gap at .040 and installed. Nope.

Did new OEM ignition coils. Nope.

Got a compression gauge. Went through the DIY steps from here.

Cylinder 1 (furthest out to the front of the car, right?) - 245, 247, 245. Great!
Cylinder 2 - 247, 250, 250. Super!
Cylinder 3 - 252, 252, 252. Terrific!
Cylinder 4 (one closest to the firewall) - Ummmm, hello?? Cylinder 4?? Anyone home? Thought I set up the gauge wrong. Unscrewed it, put it back in, tried again. Couldn't even hear the rhythmic thump thump thump of the car trying to turn over. More of a consistent sound. Both times I got "0" for the reading.

So it appears Cylinder 4 has a problem. And I am not equipped to go inside the head. So I've got to take it to a shop.

My question to the knowledgable ones here, what should I have them look for and try to fix? What would be the next step to diagnose things? And should I go a dealer or a local shop?

Any help would be appreciated. Driving around in our Pilot all the time sucks ......

 

Valves out of adjustment on Cyl#4? Like way-too-tight, so that they are not closing. Or burnt. Or compression rings are shot.

Do a leak-down test. See what you get on #4.

 

Okay, sounds good, thanks!

Anyone else have any other thoughts? Just want to have my ducks in a row to tell the shop the right thing.

 

You may have drained your battery too hard getting to the last cylinder. People typically do something like 3, 1, 2, 4, 3, 1, 2, 4, 3, 1, 2, 4 to get their 3 sets of numbers. looks like you did 1, 1, 1, 2, 2, 2, 3, 3, 3. three complete tests on a battery is tough on the battery if it's older. Obliviously having a code is bad, but just want to rule this out at least.

 

This and/or not holding the clutch in like a dope will cause some numbers to be off. I thought I was losing my mind a few months ago.

OP,
Although this method of performing a leak-down doesn't give you an exact number, it's free and easy!

 

After all was said and done I put everything back together and car started right up with no hesitation, so I think the battery is okay.

It's been running like total sh-t lately and definitely gas smell from exhaust. So I am positive that there is something wrong. I'm going to find someone to do the leak-down (or check out the DIY posted above).

 

Leak down or bore scope sounds like a great next step. I think cyl 4 is the first one to suffer due to oil starvation.

If it was truly 0 comp, I'd bet that you have a super burnt/stuck valve.