I have put about 10,000 miles on my freshly rebuilt head with no issues (new valves, stems, seals; all installed and remanned professionally). Needless to say it has been running perfect.

All of a sudden, when I was accelerating up a hill, it began to rumble, not stall just a slight loss in power. Getting home easily, I read the codes and went from there. A misfire on #5 codes P1310 and P0305. It misfires at idle (on one cylinder) up to around 3K.

I have done some troubleshooting with no luck. Tested the plugs/wires/rotar/cap. No change.

This is what I've noticed so far. It only misifres at low rpms. Once I get above ~3K it begins to run smoothly, perfect acceleration, perfect throttle repsonse. I confirmed this by holding above 4K, clearing the codes, driving for 5 minutes or so at or above 4K. No code thrown the whole time. Then as soon as I slowed to a stop and dropped below 3K the CEL code triggered right away. So am I wrong to assume I can rule out any compression issues? No smoke out the tailpipe or anything.

My thoughts now are a leaking/bad injector or stuck valve/lifter...

 

Clear the code, then swap injectors between #5 and #4 cylinder and see if it throws a code for #4. IF so, you know it is the injector. Otherwise try new plugs and check the cap and rotor again for cracks or arcing.

 

It's possible to have a bad plug or a bad wire, but I am not too sure why it would work above 4000 rpm. I would suggest swapping plugs between 4 and 5, or stick a new plug in there. If the #5 wire will reach to #4, you could also swap wires (not at the same time as the plug) and see what that does.

 

I had the same idea yesterday to swap injectors to see if it caused a misfire on the other cylinder. I'll try it tonight after work...

As for the plugs, I pulled a good one from #1 and swapped with #5 and let it idle for a minute. No difference. But I did notice the good plug I put in #5 had either gas or oil on it. I didn't think to distinguish which it was at the time. Again, I'll retest that tonight too...

So before I started this thread, I went to the JY and pulled a decent set of Bougicords and Bosch Cap/Rotor. I have had the car for almost a year and have yet to replace the wires or cap and rotor. But when I rebuilt the head I inspected them and they had little wear; the car had also been well maintained. I WILL get a new set of plugs regardless, for piece of mind. My wireset were Napa Belden's but were in good order as well. So, I have a full set of both slightly used wires, cap, and rotor, haha...So yeah, I will try to put a good wire from my extra set in #5 to see if there is any difference...I'll report back later...

Is there ANY chance a lifter could be collapsed? Also, I am not sure the validity of this but I almost want to add oil above the max line to create more oil pressure to MAYBE free a lifter/valve, but idk, it's just a thought...I have been driving the **** out of it above 4K to try to free a valve with no luck yet...But I am really hoping it's an injector. I will pull the cam cover only as a last resort. It has been 6 months since the rebuild. I would only hope it isn't anything internal since I was extra patient and detailed about putting it all back together, but who knows, maybe I fluxed something up...

 

Not a lifter, it would be clacking really loud.

 

I highly doubt it is a lifter as it would clatter to all hell at idle and run like crap. If you are really concerned about it, do a search on Seafoam and how to use it in an 850. SOme folks call it voodoo, but I swear by it and/or Marvel Mystery Oil.

 

Yes. Never assume you have good compression, ck it. Especially if you have misfire codes!

 

Turns out compression is low on cylinder 5...Did a dry comp test on a slightly cooled down motor. PSI from 1-5

154, 148, 150, 152, 10

I am assuming this is not "0" compression because it did build up some pressure. I added a little oil to #5 but it only raised it to 15 PSI...

I am going to let some seafoam soak in the cylinder over night...Since the head has all new parts I'd like to think it isn't a burnt valve or bad seal/stem. Still need to do a leak down test to better pinpoint the issue but anyone more experienced have any thoughts?

 

No need for a leak down. Connect your compression tester on the cylinder(other end on a controlled air source), put the engine at TDC on that cylinder and pump air into it. There is so much compression loss that it should be easy to find.

Can you get a hold of a bore scope? It may be a bent valve that is hanging down causing the lifter noise and compression loss.

 

Burnt valve. A valve can burn in no time. If it wasn't seated good or was defective it can burn in a month.

Why was NEW valves installed?

 

I will try to use a video borescope to check the valves tonight, along with a leak down test. I also suspect a burnt valve...

RSPI, back in January my water pump seized (bending both intake and exhaust valves) and I had the head rebuilt by a friend who builds performance engines...Took care of a lot of other maintenance items with the head off...As for a possible reason that the valve burned this time, I suspect a bad injector. I noticed when I was checking the injectors that the tip of the #5 injector was cracked. So I will also be finding new injectors after the diagnosis...

 

Do you remember what kind of water pump is was?

Before installing a head it should be leak tested. See the end of the video here:


Maybe one of the valve seats was damaged in the head. That sucks.

As for the injectors, if one is damaged that is all you need to replace. If it is the small ring on the end of the injector, you can toss that in the trash and keep on moving. You can also have the injector in question tested, that is what I did a few months ago.

 

I couldn't get a good picture of the valves through the plughole but I was able to get a good look at the piston. This is the only oddness I saw, in the bottom right corner (hopefully it isn't camera/glare trickery)...this is at the bottom of the stroke btw...And I also still have to do a proper leakdown test...

 

So after months of running around with the misfire I finally figured it out. It IS a burnt valve...

I couldn't get a good look at the valves through the borescope so I bought a #000 (10mm) and #00 (12mm) SS dental mirror...



I stuck the mirror into the plughole and snaked the scope in after it. It took some maneuvering to get a good look at the valves but it worked! The intake valves were fine but there was a chip out of the passenger side exhaust valve on cylinder 5, pictured below...


You can see about half of the valve and a chip...

Surprisingly, the car runs relatively well with the constant misfire at lower rpms. And I commute 50 miles a day to work. I am sure it probably isn't good to keep driving like this but it hasn't gotten worse and I am only noticing low mpgs(around 20 combined when I was easily get about 26)

Time to coordinate another head teardown

 

Bummer. Great diagnostic work, though! Good job.

 

Talk about a thread revival...Thanks for all of your inputs thus far...

I'm sure I could get lightly insulted for neglecting to fix this problem more quickly, but you know, life, kids, money, time; some years are more overwhelming than others...AND it has been running rather fine, other than low mpg, and probably damaging the O2 sensor a little...

So here I am, spending two nights after work(5 hours total)the head is off and, sure enough, the scope didn't lie. A pea-sized hole in the cylinder 5 exhaust valve. Thankfully, I have everything I need to finish the job and have planned to do a full brake replacement as well...

My pressing question, WHY would a valve burn so quickly after a fresh head rebuild? Before I put everything back together I'd like to do some extra troubleshooting and cleaning to assure it doesn't happen again...

Possible pertinent info.
The head had maybe 5Kmiles on it before it burned
I haven't looked TOO closely yet, but the head gasket doesn't seem to have failed
The lifter looked okay
I always run 91-93 octane
I did not "break in" the new head after install (30 min at 1500-2500)
I have not tested my injectors, YET
I have not tested the fuel pressure, or volume

Thanks again, some pictures to follow soon

(if these should be a new thread, I will make it)

I found this to be an informative post... https://www.brickboard.com/AWD/volvo...ers_solid.html