My '90 Q began running rough several weeks ago. Missing cylinder, and it was intermittent. Happened rarely at first, but progressively got more and more frequent. Apparently the missing wasn't affected by the engine temp...sometimes it would miss cold, sometimes hot, and recently it was missing all the timeI figured it was a bad coil based on the symptoms. I got some used ones this past week and tore into the car today. The #2 and #4 plugs looked horrible!
http://home.socal.rr.com/robverna/DSC01 ... C01239.jpg
These plugs are almost brand new! They were installed on 2/21/03, and have less than 1000 miles on them. The other six plugs looked fine. The #2 coil contact looked a bit rusted too. The #4 coil boot looked OK. The plug ports did have moisture in them, but I thought that was normal. All the other ports have moisture too.
Could this have been caused by some wierd arcing from a bad coil? That black stripe down the #2 plug isn't oil...looks like carbon deposits and it doesn't wipe off easily. I pulled out the old plugs that I removed in February, and all 4 from this head look fine. Nothing at all like these 2. I'm not all that up on corrosion priciples, but I'm hoping that swapping the coils will fix my problem. I ordered new wire harnesses for both heads when the problem first appeared, and they will be swapped when they arrive. Any thoughts? Anyone seen anything like this before? Thanks a bunch for your insights!
Cause for concern
I figured it was just some kind of condensation on the walls. Not like the plugs were swimming or anything. I think I've seen condensation in there most if not all the times I've opened up the plugs. I haven't washed the engine in at least a year. I wouldn't be quite as puzzled if all plugs were the same, but these 2 are pretty far along, almost like they were made of the wrong material or something. The other 6 plugs have abslolutely no visible corrosion. Corrosion is an electrochemical process, so I'm thinking that something is going on that is actually driving it, in the same way that gold is forced into an ion solution by electricity (electroplating). The plug boots appear to be just fine on both, just the metal contact point is rusted on #2. But I think that's more a symptom than a cause. I'll keep an eye on it and maybe take the plugs out in another 3 months for an inspection. I'm pretty stumped.
MAYBE it has something to do with the wire harness. What does the 2.2 k-ohm resistor do? I wasn't able to find it with my multimeter on this head's harness, but I could find it on the other head's harness. Seemed odd, but I'm not sure what it's there for. The car runs just fine now, but I don't want a repeat of the problem.
MAYBE it has something to do with the wire harness. What does the 2.2 k-ohm resistor do? I wasn't able to find it with my multimeter on this head's harness, but I could find it on the other head's harness. Seemed odd, but I'm not sure what it's there for. The car runs just fine now, but I don't want a repeat of the problem.
It sure looks like arcing on the plugs. Hard to believe that the wire harness would cause such a problem, as it's low voltage before the coils kick it up. I've never seen moisture in the plug wells, but I've been in pretty low humidity locations. I'd guess the resistor is to avoid radio interference, but am right past the limit of my electronic knowledge now. If plugs and harness replacement fix it, you're a genius. If it reoccurs, I guess you'll have to play the random parts replacement game like the rest of us. It just occured to me that those plugs could possibly have been loose and leaking combustion gases could have caused the corrosion and black marks. That would explain a lot of your symptoms. perhaps a chunk of goo got between the plug gasket and the head surface preventing a good seal on those two plugs.
Took the plugs to my shop instructor...he just laughed and jokingly asked why I traded my Infiniti for a domestic car! Obviously he wasn't sure what the actual cause was...said they (dealership) just replace everything (coils, plugs, harness). That's the philosophy tht gets 8 coils replaced at once when one cylinder's missing! (recent thread). Actually I guess I'm doing the same thing--coils, harness, plugs, but not without some troubleshooting and educated guessing.My mind keeps going back to the 2.2kohm resistor and what it does. Probably either a spike cutter or a low-current bleed. I think it's too high a resistance for any sort of RF ground, but who knows? My guess is that I do have a bad harness because I couldn't find that resistor at the terminals...it may or may not have damaged the coil. Someday I'll delve into the schematics and figure it out. For now I'll be happy just to keep hearing the old girl purr.
Final update I think. The new harnesses came in the other day (thanks Joe!). I began measuring the right harness, and I couldn't find the resistor on this one either. So I take another look and realize this one doesn't even have a resistor on it. I had only assumed it did cause the left side does. Aha... So with some more testing I find out that all the pins on the harness have the same continuities as the old harness. So I'm pretty certain it was the coil that was bad on #2, and perhaps #4 as well. Problem should be solved, but I'll pull the plugs at the end of the summer to verify.
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Q451990
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Back to the moisture issue... I don't think that's normal either. As hot as it gets in there - wouldn't it cook off? You're right - the old plugs looked aweful! The carbon fouling looks abnormal for that age of plug too - maybe a bad fuel mixture from dirty injectors?
Just remember, the coil boots are available separately from Joe... even if they are green instead of black
Heath
Just remember, the coil boots are available separately from Joe... even if they are green instead of black
Heath
dare I say it --- cracked head?
I agree about the mosture. That area should never be cool enough to condense, no matter the humidity (unless a sudden spike in ambient temp and humidity occurs AND you haven't the car in more than 24 hours.
Rember that the plugs sit deep in the head, the hottest place in the engine besides the exhuast system.
I changed my plugs Friday morning - 86 degrees with 80% humidity - car had sat all night long bone dry plugs and coils.
What was the nature of the water - any possibility it was coolant?
dan
Rember that the plugs sit deep in the head, the hottest place in the engine besides the exhuast system.
I changed my plugs Friday morning - 86 degrees with 80% humidity - car had sat all night long bone dry plugs and coils.
What was the nature of the water - any possibility it was coolant?
dan
Since we're on the subject....
How long does it take to replace the plugs and how difficult is it? I've got the service manual and it looks somewhat simple but, since I'm not much of a mechanic, I'm not sure if I should venture there. I could take it to the local garage but wouldn't want to pay for four hours labor either...
It's a '91Q and I just got a set of Denso double-platinums for it.
It's a '91Q and I just got a set of Denso double-platinums for it.
change plugs in 4 hours with a short nap.
Since the Q45 has a number of layers to peel off before you get to the plugs, the time required is longer than one might think.
You need to pull:
I guessed some times for the newbie who's read the manual and knows how to run a wrench.
the air duct - 10 minmove harness, including disconnting some connectors - 15 minornamental covers - 20 min eachcoil harnesses - 1 min eacheach of the 8 coils (2 min each for the front six, 5 min each for the back two)
Pull the plugs - 1.5 min each (average)
total time: 101 min
and reverse. Give yourself a 20% penalty on the backstrech for each task. - 120 min - Oi! that's almost 4 hours! Take a nap in the middle and you are done in 4 hours.
Suddenly $70 for a set of factory NGK's that will last 60,000 miles (4 years for the EPA's mytical average driver) doesn't seem so bad.
Anyone who's done it in the last 90 days can do it in about 1/2 - 1/3 that time.
On my Mitsubishi Gallant I can change the four plugs in under 12 mins, but there is neither romance nor mystery there.
Dan
You need to pull:
I guessed some times for the newbie who's read the manual and knows how to run a wrench.
the air duct - 10 minmove harness, including disconnting some connectors - 15 minornamental covers - 20 min eachcoil harnesses - 1 min eacheach of the 8 coils (2 min each for the front six, 5 min each for the back two)
Pull the plugs - 1.5 min each (average)
total time: 101 min
and reverse. Give yourself a 20% penalty on the backstrech for each task. - 120 min - Oi! that's almost 4 hours! Take a nap in the middle and you are done in 4 hours.
Suddenly $70 for a set of factory NGK's that will last 60,000 miles (4 years for the EPA's mytical average driver) doesn't seem so bad.
Anyone who's done it in the last 90 days can do it in about 1/2 - 1/3 that time.
On my Mitsubishi Gallant I can change the four plugs in under 12 mins, but there is neither romance nor mystery there.
Dan
I've pulled the plugs 6 times total on 2 Qs, and I still can't do it in less than 3-4 hours. Those damn little screws holding the coils down are friggin tedious. And that's with what I consider to be the best tools for that particular job--locking extensions with a 8mm jointed socket. Both cars have had moisture in the plug wells. I can't explain it, but I'm pretty sure I don't have a cracked head. No other symptoms. Not losing coolant. No coolant in oil, no oil in coolant. Exhaust looks/smells fine.