Northstar stumbles, brown goo around plug

[hjb981]

My '97 DeVille has been acting up lately. It started last spring, when it stumbled slightly at light gas (around 20 mph, 1200-1300 rpm). Then, nothing much happened for a few months, but in late summer it came more often, and also at idle. It got better for a few weeks, but now it got worse again. If I stand at a red light, I can feel it stumble as much at once per second. It does it irregularly, so that the time between two "stumbles" varies. Warm of cold engine makes no difference. The service engine light came on (after weeks of symptoms with no light or codes) together with the P0300 unspecified misfire code. The stumble can be heard also when listening to the exhaust pipes at idle. It can be noticed at idle and under light load up to 1600-1700 rpm. Over that or at intermediate to heavy loads I cannot hear it or feel it while driving, but I don't know if it is because it goes away or if I just don't notice it.

I figured that I could start by checking the resistance of my ignition wires, and they were all good. I did see some scuff marks, but only very shallow ones at the surface of the insulation. But I found something else that made me worried:

Around the plug of cylinder 5, there was some kind of brown goo , that looked much like thickened engine oil. It almost covered the area around the plug, and the boot that goes over the plug was sprayed with it. It looked like there had been something similar around other plugs, but not as much and it looked dry. The boots on those plugs were not sprayed with it. At least one plug was completely clean, with no dirt around it at all.

The plugs were changed at a Cadillac dealership in California three and a half years ago (they put in the platinum plugs). Since then, the car has been driven in Sweden without any other problems than some carbon knock or valve noise or whatever it is (yes, I WOT every now and then, and yes, I have tried the 2nd gear WOT procedure without more than temporary improvement).

Can anyone tell me what the brown goo around plug 5 is? I suspect gas/air/exhaust is being pushed passed the plug and leaves some kind of residue behind. Could it cause the stumbling ? The upper part of the plug is clean, as is the contact within the boot, so the connection should not be the problem. I was thinking of pulling the plugs to have a look at them, but I am afraid to take them out because of the dirt around them. I am worried about getting it into the cylinders through the plug holes. Btw, is it OK to pull a plug and then put it back (the press-fit gasket will obviously already be compressed)?

What should I do ?

Best regards,

Jonas

[MAC]

Check for trouble codes--it may give you a definitive answer. The brown goo is most likely oil and carbon. If the plug electrode isn't fouled then I don't see it causing stumbling. But if the electrode is fouled indicating it's not firing then it would cause lack of full power and stumbling. But the first thing you should do is check for trouble codes.

[hjb981]

Check for trouble codes--it may give you a definitive answer. The brown goo is most likely oil and carbon. If the plug electrode isn't fouled then I don't see it causing stumbling. But if the electrode is fouled indicating it's not firing then it would cause lack of full power and stumbling. But the first thing you should do is check for trouble codes.

The only code present is P0300. And the car has had this stumbling without any codes up till now.

[joeb]

brown goo is probably oil residue from leaky o-ring seals on valve cover. usually not a big deal. a p0300 misfire can be due to fouled plugs, worn plug wires or even a balky coil. i put in new plugs and got a misfire soon after that was probably due to misfiring plugs. it can happen. a set of new plugs/wires could fix your problem. plus, pulling your plugs will let you inspect them for signs of misfiring.

[hjb981]

brown goo is probably oil residue from leaky o-ring seals on valve cover. usually not a big deal. a p0300 misfire can be due to fouled plugs, worn plug wires or even a balky coil. i put in new plugs and got a misfire soon after that was probably due to misfiring plugs. it can happen. a set of new plugs/wires could fix your problem. plus, pulling your plugs will let you inspect them for signs of misfiring.

Thanks, since I happened to have a spare coil pack + another set of ignition cables, I tried changing those today. No difference . I have also got some of the goo out, and it looks and smells like engine oil. How do I change the valve cover o-ring seal?

The next step is pulling the plugs and inspecting them, but I am not sure how to get the oil + dirt out of the holes (around the plugs). Any tips? I don't have easy access to shop air for blowing.

-Jonas

[Ranger]

Forget the O rings. You have to pull the cam covers. Too much work. Remember that it took 12 years to get that build up. Just clean it out with a rag and a long screwdriver every few years or so. You are probably overdue for plug wires. I'd replace them and stick with A/C Delco.

[joeb]

ditto on valve covers. very difficult on northstar. i just got a P0302 code on my grandprix last week. got it 1 year ago too. pulled #2 plug. looked fine. car ran fine after that. anyway, code popped up this week and after 10 min or so, the engine ran ok. i changed out coil for #2 cylinder since i had a spare and car is running ok now. is it plug, wire or coil? who knows.

[caddypete]

The oil around that plug may be causing it to ground out and giving it no spark on occasion

[hjb981]

The oil around that plug may be causing it to ground out and giving it no spark on occasion

Interesting idea, but there is only a little bit of oil (it does not cover the entire circumference of the plug). The inside of the boot and the white (insulating) part of the plug were also clean, so I don't think that is the problem in this case. I will clean it out though - I will try sucking it out with a thin pipette and then clean with a screwdriver + rag. I also went and bought a compressor today, so that I can get the dirt out of the plug holes (I do have som small particles of sand and other dirt in some of them - hard to avoid during Swedish winter driving). I will go easy on the pressure though, not to hurt those O-rings I have just learned about (thanks joeb).

I am considering ordering new wires (Delco) together with a bunch of other stuff (regular maintenance items).

After pulling the plugs, inspecting them and documenting with my camera, I will see were to go next. I am a bit sceptical about the problem being a fouled plug, because I have read that fouled plugs usually cause misfires at harder load, which is the opposite to what I am experiencing. Has anyone had misfires at light loads due to fouled plugs?

Thanks all for your tips and ideas. I will let you know what happens and what the solution turns out to be.

-Jonas

[hjb981]

I have found the cause of the misfire! The plug in cylinder 5 had lots of deposits on it and missed the platinum tip on the ground electrode (the one that bends like an L). I don't know what is the cause and what is the effect here - did the platinum tip go off, leading to bad sparks and thereby deposits, or did deposits build up for some other reason, causing the electrode to overheat (I am not sure if that would happen) and thereby the tip to go off, or something else...

After putting in some old plugs that I had, the engine ran smoothly again. (they had been used only a little and ha no real deposits, only a light tan - looked much less used than some other plugs taken out at a little less than 100k miles). I will anyways add new plugs to my list of things to get.

Can fuel injector cleaners like Redline SI-1 or STP complete fuel system cleaner cause deposits on the plugs? Unfortunately there is no techron available in Sweden (to my knowledge), so I have tried using those two (the second only once, after last winter). All plugs had deposits, and on all but plug 5 the deposits looked like normal aging (but too much for only 3000 miles). The plugs I got out were supposed to have been put in new about 3000 miles ago or so. Now I am starting to wonder if the shop missed it, or if the plugs have aged prematurely for some reason.

Should I worry about the lost platinum tip? My guess is that if it were to damage the engine, it would already have done it by now. Probably it was just blown out right after it came loose (the engine was of course running) without casing any harm. At least the engine runs fine know with the "new" plugs.

Regards and thanks for the help,

Jonas

[KHE]

The platinum pad most likely was blown out the exhaust - it didn't harm the engine.

[BodybyFisher]

We have seen lost platinum tips before, the loss of the tip accelerates anode wear and the gap increases.

I am not sure why the plugs loose their pads

[Texas Jim]

I am not sure why the plugs loose their pads

Maybe a little detonation if you got some bad gas?

I don't know the reason they come off either.

[Cadillac Jim]

The plugs come gapped from the factory for multip0le reasons, not the least of which is to prevent damage to the electrodes, such as cracking the bond between the platinum and the steel support for the ground electrode -- and the center electrode. Detonation is a possibility, but with the knock sensor working (no codes, no MIL), that seems remote to me because plug damage doesn't happen with the first ping. And, plug damage usually amounts to whanging the ground electrode until the whole thing comes off at the weld to the rim of the plug -- and I've never heard of that happening with an engine that has a knock sensor.

This kind of thing, among others, is why I recommend that you never put a used plug back into a Northstar or any other engine with an aluminum head.

[KHE]

When my '96 Seville had 95,000 miles on it, it began to misfire - not bad enough to set the check engine light/code. It acted like there was water in the gas - it would stumble and misfire on acceleration. I removed the plugs and 4 of the 8 plugs were missing the pad on the ground electrode. GMPartsdirect took almost three weeks to ship me plugs (I don't use GMPartsdirect anymore...) so I reset the gap on the four plugs and reinstalled them. The misfire was gone and the engine ran fine until I installed new plugs. I forgot all about it until this thread jogged my memory.

[hjb981]

The plugs come gapped from the factory for multip0le reasons, not the least of which is to prevent damage to the electrodes, such as cracking the bond between the platinum and the steel support for the ground electrode -- and the center electrode. Detonation is a possibility, but with the knock sensor working (no codes, no MIL), that seems remote to me because plug damage doesn't happen with the first ping. And, plug damage usually amounts to whanging the ground electrode until the whole thing comes off at the weld to the rim of the plug -- and I've never heard of that happening with an engine that has a knock sensor.

This kind of thing, among others, is why I recommend that you never put a used plug back into a Northstar or any other engine with an aluminum head.

What does it have to do with having aluminum heads? Is it because they would be damaged more easily by debris (like spark plug electrodes) flying around in them?

And would it be bad to use an old plug that had not run its entire useful life for a while? The ones that I put back in still had service life left when they were taken out before. My plan was to use them until the new ones arrive.

[BodybyFisher]

The threads are coated with an anti-seize compound at the factory that works for the first installation. It is NOT recommended that your remove them to clean them, inspect them or regap them, once they are removed they must be discarded. The danger of them bonding to the aluminum and wiping out the threads is greater if they have been pulled and reinstalled

[Cadillac Jim]

Me, I would change the plugs at 80,000 miles, whether they needed it or not.

[hjb981]

The threads are coated with an anti-seize compound at the factory that works for the first installation. It is NOT recommended that your remove them to clean them, inspect them or regap them, once they are removed they must be discarded. The danger of them bonding to the aluminum and wiping out the threads is greater if they have been pulled and reinstalled

Thanks, I did not know that! I guess I'll be fine though, since I have only driven very little with the re-installed ones, and I also tightened them very little.

When I was taking the plugs out, they all came easily, except for number 2. At first I could not get it out at all. I solved that one by starting the engine and letting it get to 122 F (50 C). Then I let it rest a little while I went and got some stuff from the store room. Then the plug came out easily, since aluminum expands more than steel with heat. I would normally do everything on a cold engine, but I think a slight warming up is better than running to get your biggest handle for the socket wrench, and then ripping it loose with brute force. The plug could be comfortably held in my hand right after coming out, which means it could not have been hotter than 113 F (45 C).

So, when the plugs I ordered from RockAuto arrives, are there any other precautions or procedures for putting them in? How hard are they supposed to be tightened, for example? Do you use your fingertip feel, or a torque wrench? I would have to buy one for the appropriate interval, since the one I use for wheel nuts is for higher torques (and it is to big, anyway).

[KHE]

The plug threads are plated to reduce corrosion between the plug and the cylinder head. It is not an anti-sieze compound. Using your old plugs until the new ones arrive is perfectly fine to do. Do not use any anti-sieze compounds on the new plugs as that will result in over-torquing them.

Torque the plugs to the factory specification with a torque wrench. Someone will post the spec - as I recall, it is below 20 ft-lbs so the spec needs to be converted to inch-pounds since most ft-lb. torque wrenches have a low limit of 20 ft-lbs.

[BodybyFisher]

The plug threads are plated to reduce corrosion between the plug and the cylinder head. It is not an anti-sieze compound. Using your old plugs until the new ones arrive is perfectly fine to do. Do not use any anti-sieze compounds on the new plugs as that will result in over-torquing them.

Torque the plugs to the factory specification with a torque wrench. Someone will post the spec - as I recall, it is below 20 ft-lbs so the spec needs to be converted to inch-pounds since most ft-lb. torque wrenches have a low limit of 20 ft-lbs.

Thanks for cleaning up my post Kevin. I said anti-seize, they are nickel plated to stop corrosion. The factory service manual states not to clear or regap plugs as this plating is disturbed and to replace the plugs

See page 7 in this PDF

http://www.acdelco.com.au/PDFs/Catalogue_A...ark%20Plugs.pdf