Thanks in advance - really need some diagnosis process advice.

About a week back I was driving on the highway with my '06 TL and I got a flashing check engine light for about 5-10 seconds, then a big clunk and the engine wouldn't run. Maybe a single cylinder would fire occasionally when I tried to restart, but wouldn't run. Because I wasn't sure what happened, I only tried to restart once in case it was timing belt etc. Coasted to the side of the interstate and called a tow to the nearest Honda dealer. Diagnosed as misfire cylinder 6, and upon further inspection, the plug had apparently come loose and launched out of the plug hole taking the coil pack with it. The plug was still there, but it was coated in carbon and the metal top of the plug was bent, and the coil pack was obviously shattered. The dealer wouldn't contemplate doing a Timesert or a Helicoil, they only were willing to pull the head and send it to a machine shop, or recommend a new used engine. I suspect they were more interested in having me trade the car and sign a loan for a $50k new one. Which I wasn't.

At this point I felt like I was getting taken for a ride and opted to pay their diagnosis bill and go get a dolly and tow the car 40 miles home. After doing some research, I saw a bunch of links showing that these plugs do sometimes get loose and launch, and that Timesert appears to be one of the better repair paths. Long story short, I picked up the right timesert kit, carefully executed the thread, seat, insert + red loctite, and got what apears to me to be a pretty good looking Timesert thread repair in place. Spent a long time blowing out the cylinders and used lithium grease to catch the shavings... verified with a camera... looked nice and clean to me. After that, 6 new coil packs and 6 new NGK plugs to spec. 4 of the other 5 plugs were, I'll just say, not very tight. These plugs have likely been in the vehicle since dealer service at the timing belt interval, perhaps 115kmi maybe a decade ago. Plugs looked worn enough that they could be that old.

Turn the key, no spark / ignition in any cylinder, just normal crank sounds in 5 cylinders. 1 cylinder sounded like no resistance to the starter. I then did a compression test on cylinder 5... came out like 110 pounds or so. I then compression tested cylinder 6... Nothing. 0. I put the camera close with the spark plug out, and I can see the piston moving up and down.

A couple questions:

1. What's the next, upstream, electrical part in the ignition system that I should be looking at? Assuming timing is OK (which I'm in the process of digging down to get the covers off so I can see the marks), I would have thought that 5 of the 6 cylinders would at least fire. There's definitely raw fuel in the cylinders when I pull the plug. Could the coil back blowing have taken out something else upstream which would now kill spark for all cylinders?

2. How would you go about diagnosing the no compression on cylinder 6 issue? What pull the timing belt and valve cover? Start digging where? Assuming I just blew out a plug, I'm frankly kind of disappointed that there could be a valve or something else mechanical broken etc. What's the smartest pathway to diagnose here?

My current gameplan is to verify the timing and do some research. I'm just not sure what else could have happened here.

Below are the finished views of my Timesert repair today. I feel like they look right, but if you see something off that would result in no compression, let me know.

Thanks so much for your advice.










So I guess my question is: what would you guys take apart / look at next?

 

For no spark: does car show rpm? Either live data on the scan tool or tach. If it sprays fuel then most likely it has crank signal. Maybe blown out coil made a short and burned up the fuse?




Each coil should have three wires, one is ground (black), second 12V power (black and white), third should be pulsed signal to fire from the ECM. Check ground and power circuits. No idea if power wire gets power only when cranking or if it also powers when key in on position. Check fuses mentioned on the diagram with the test light.

For no compression - if timing is bad it would affect more than one cylinder. I've seen couple hondas with burned up exhaust valves (as they get tight over time, then don't seal properly) but that happens over longer periods of time. You are going to check the timing to let us know if that's fine.

You could attach your compression tester (maybe via the pressure regulator) to the compressed air and see where the air is coming from (after removing the schrader valve). That would require making sure that this cylinder has all valves closed. If pulling valve cover is hard I usually try putting some air, and if it's coming out from somewhere (for example from the exhaust) I rotate the engine and see if it changes. If no matter engine position air is always coming from the exhaust then something is wrong with exhaust valves. The only problem is that it doesn't give you much info. Maybe something (like a very big shaving) got stuck under the valve and is keeping it open? But then whatever the reason, if it's in the intake or exhaust (air is not coming through the dip stick / oil filler cap) you most likely will need to pull head.

I tried using the endoscope with a mirror couple times and never could clearly see the valves.

 

Thanks so much for the great advice. I'm getting started now and will report back on most -- but, to your first suggestion - you were right on. The #2 15A fuse under the dash for the ignition system was blown. I haven't replaced and verified 5/6 cylinders are firing, yet, but the blown fuse fits the symptom.

On the no compression cylinder - obviously this will take a bunch more diagnosis. Will report back.

Other ideas welcome as well!

Thanks

 

Following up on this thread; maybe made some progress. First off, replacing the 15A fuse for the electronic ignition in the driver seat fuse box successfully got the engine to start and run a bit rough. I assumed that there was still something going on with cylinder 6. I ran it for a few minutes, not quite up to temperature but for a bit. I revved it up to maybe 2500 a couple times.

Timing check:
I pulled off the timing belt upper cover for the front 3 cylinders. I rotated the crank to line up the serpentine belt pulley mark with the lower timing belt cover mark. The front camshaft was lined up pretty much on the mark at #1 TDC, as expected. I didn't see any evidence of skipped teeth or anything, and everything seemed tight / normal, no debris or anything. While the engine was running, timing belt action appeared normal / smooth.

Further investigation on cylinder #6:
Re-ran the compression test, and got 40 psi instead of the 0 that I had previously I modified the compression tester to hook up to my air line and put 120 psi air pressure into the cylinder at TDC. Pulled the oil cap and listened closely. I couldn't hear any air flow. Cylinder 5 compression tested at 140PSI at that time, when I re-ran it for a direct comparison.

Put the plugs back in, re-ran the car for a bit longer, let it get up to temperature, revved it to 3000 and held it for 5-10 secs maybe 3 times.

Re-ran compression test. Compression test now showing 140PSI like cylinder 5.

Put plugs back in, car started and ran fairly well. Still a little rough, but the car always ran a little rough on first start before it warmed up.

My next steps are going to be to get the upper timing cover and serpentine belt back on and take it for a test drive, and see what happens. I don't see much I can do at this point other than drive it and hope for the best.

I've attached below a couple pictures from inside cylinder 6. Pistons look a little carbon-y to me, but I couldn't see any obvious cylinder wall scoring or anything. There were some telltale scratches on top of the cylinder (shiny), but admittedly, those could have been from putting a wire and a screwdriver in the hole to see where the piston was for clearance when I was doing the timesert. I didn't use force, but maybe some carbon flaked off easily or something (doubt it, but i can hope I guess).

Let me know what you think, and / or what else you'd do. Best current guess: plastic debris from the original blow-out got sucked in and kept the valve from closing; Could also have been aluminum + heavy grease that got on the valve seat somehow during tapping for the Timesert?

Also - what kind of compression pressure would you expect to see, on average in this '06 3.2 V6? 140 seems a little low, right? 180+ would be clearly OK. This car has 182,000 miles on it.



Piston top scratches?

 

A few comments:

• I'm wondering if possibly some debris got caught in one of the valve seats when the plug blew out and by running the engine you've mostly cleared the fragment.
• The marks on the piston are a non issue, don't give those a second thought.
• If you want to try and figure out whether the leakage is past the piston, or through the valves, you can play that game in a number of ways:
  • The old squirt some in the cylinder method; perform an old-fashioned compression test before and after squirting some oil into the cylinder, if the "after" number is appreciably higher, you're leaking past the piston.
  • Cylinder leak down test; rotate the engine so all intake and valves are closed on the suspect cylinder and secure the engine from further rotation. Then feed pressurized air into the cylinder; if you're leaking past and intake valve you'll hear a tell-tale hiss coming from the intake, if you're leaking past an exhaust valve, you'll hear the hiss coming from the exhaust pipe.

 

Wanted to provide a final update... Took the car out for a 30 minute mid speed test drive today. The car started and made good power; I didn't hear anything that sounded or felt like a dropped cylinder at mid-high RPMs. At least - the questionable cylinder #6 seemed like it has sorted itself out. BUT - I was watching dash command on my phone while on the drive...

Pending code P0404 came up, and the car started to stumble / quit at idle with the clutch in etc. Had to feather the throttle to keep it running when stopped. This behavior seemed to correlate correctly with the P0404 EGR valve code. Luckily, the EGR is an easy pull in this car... 2 12mm nuts later I found what I think is some small plastic debris in the EGR circuit, and enough had melted to the EGR valve piston that it was jammed. I cleaned out the EGR valve, scraped off some carbon, vacuumed out what I could and reassembled.

Started a bit hard, but after 5-6 seconds cranking, the engine started up and ran super smooth. I'll do another test drive this afternoon, and check tightness of the plugs in about a week after they temperature cycle a couple times. I'll also use the camera to double check that the Timesert is still fully in place.

Hoping to call this one done. I'll feel pretty lucky if it is running well in a month and I've escaped having to pull the head.

Thanks everyone for your advice. I do still have one question, though: for a 180kmi 3G TL (06 MT, non A Spec), what would you expect for a realistic cylinder compression test reading? is the 140psi I got crazy low and it should be 200psi? Or is 140psi not uncommon for a high mileage motor? Would the 115kmi valve adjustment you do with the timing belt help the compression in any way?

 

FWIW, there is no 105,000 mile valve adjustment called for; just "Inspect and adjust if noisy" (or some such language). If the valves aren't leaking, then an adjustment will not help. As for your 140 reading, I would take that with a grain of salt given the other readings you had immediately prior; I'd recommend driving for a few thousand miles and then retest.