help understanding what plugs are telling me

[Tom]

I have a 1994 Honda Accord LX F22B2 (4 cylinder non Vtec single cam). The engine has 242k miles on it, good compression across all four cylinders, and a new head gasket done about a year ago. When the head gasket was done, the head was machined, and new plugs were installed.

It has had leaking lower plug tube seals for pretty much the entire 4 years I have owned it. I finally decided to replace them. When I was buying parts for the job, I went ahead and got a new set of NGK plugs, knowing that I would be removing the old ones to drain the oil out, I figured that even though they only had about 15k miles on them, I might as well put in new ones.

After watching the ETCG video on this a couple of times, and writing down the correct torques and the proper sequence, I had at it. When I pulled the plugs out, I took the opportunity to check them out. The first three plugs looked perfect. Actually much better than I was expecting. The engine uses a fair amount of oil, so I was expecting to see it on the plugs, but they had no signs of oil on them, nearly a perfect light tan color, no unusual wear.

The fourth plug was a bit different though, the ceramic was much lighter in color, nearly white.

The engine has had a slight ping every once in a while under load, which I have been blaming on the timing being a bit too advanced. At some point, someone butchered the timing cover, so there is no pointer, which makes timing the engine properly impossible.

Now that I am seeing that one plug looking nearly white, and certainly much lighter in color than the rest, it makes me wonder if perhaps that one cylinder is running a bit lean, maybe due to a dirty injector. That could potentially be the cause of my slight ping.

Does this sound reasonable?

Topic

[richiepearce]

As it is lean on one cylinder and the compression is good I would say chances of injector fault are high. You could put some injector cleaner through it, move the injector to another cylinder then check results after running for a period, get injector cleaned and tested.

A word of caution you also need to discount the electrical side, check wiring, and pulse test, I use noid testers, but you could rig up an led and connect it to the injector supply multiplug for that cylinder.

[Dustin Hicks]

[quote=”Tomh” post=68705]I have a 1994 Honda Accord LX F22B2 (4 cylinder non Vtec single cam)….. At some point, someone butchered the timing cover, so there is no pointer, which makes timing the engine properly impossible.

Now that I am seeing that one plug looking nearly white, and certainly much lighter in color than the rest, it makes me wonder if perhaps that one cylinder is running a bit lean, maybe due to a dirty injector. That could potentially be the cause of my slight ping.

Does this sound reasonable?[/quote]

Yes it does. Two of the symptoms of preignition are ‘pinging’ under load and ‘white’ plug insulators. That can be caused by several things, including over-advanced timing and lean fuel mix. As richiepearce said check the injector for that cylinder. I’d also try to replace the timing cover if at all feasible.

As for the oil use, check for external leaks. Since this is a 242k mile engine, the compression is good and the plugs don’t seem to show poor oil control, that’s what I’d look for first.

[Tom]

I have been through external oil leaks . . changed oil pressure switch, rear main (wasn’t leaking, but I was there doing the clutch already) seals inside, and outside the distributor, oil pan gasket, valve cover gasket. I think the only thing left that could be leaking are perhaps the cam seals.

I suppose an electrical issue is possible. The engine runs quite well though, which kind of makes me lean toward thinking that one injector might just be crudded up a bit. I will send some injector cleaner through the system and see if that makes a difference. If not, I will swap 2 injectors around and see what the plugs look like a while down the road.

I have every intention of replacing the timing cover. I had the timing belt replaced a few years back, shortly after I got the car. Unfortunately, the mechanic who did the work for me didn’t tell me about the problem with the timing cover until he had already rigged it back together. Had I known about it when he took it apart, I would have ordered up a new one then. I’ll be due for a timing belt again in the not too distant future (I put a lot of miles on it) and at that point will replace both the lower and upper covers, as well as the cam seals.

I don’t think that the timing is the cause of the pinging. Of course, I can’t know this for certain, but I believe by the way the engine runs, it’s fuel economy, and the read on the other 3 plugs, that the timing is set reasonably close to where it belongs. With just that one plug looking a bit too white, I am leaning towards an issue just in that one cylinder.

In the meantime, I suppose I could search around and see if any of the old school mechanics around here have a degree wheel I could borrow, then find TDC on the number one, and make my own pointer for the time being just so I can verify correct ignition timing.

[Bluesnut]

Too much advance can lead to a plug turning white and this can also affect one plug only. It’s complicated to try and explain but I will say that I’ve torn several engines down that were destroyed by too much timing advance. The damage would show that one piston was wiped out, the next in line not as bad, the next very mildly damaged, and the last no harm at all.

Sucking excess air into a cylinder can bleach a plug and so can engine coolant seepage into a cylinder.

If you have pinging that is usually caused by too much timing advance or a fault with the EGR system.

[college man]

You may want to check ignition timing with a timing light.

http://www.justanswer.com/car/01fhk-91-honda-accord-lx-recently-changed-distributor-the-specs-adjust.html

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp

[Tom]

Yeah, I thought of that quite a while back, then discovered that the timing pointer was missing from the timing belt cover . . . kinda makes it useless to hook up the timing light, unless I either replace the cover, or use a degree wheel to find TDC of the number one, and make my own pointer.

EGR is a possibility that I haven’t looked into. I checked over the engine pretty well for vacuum leaks a while back, though I could do that again, the way the engine runs hasn’t changed noticeably since the last time I checked for vacuum leaks, but one never knows for sure.

Lots of great suggestions here though, will go through some additional trouble shooting, including looking for vac leaks, and going through the EGR. I believe that the EGR valve on this engine is NOT OEM Honda, so that is on the “to be replaced” list.

[Author]

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