: Misfire 1998 STS

12-12-09, 05:19 PM
Well I picked up my first caddy today. Its a 1998 STS with the 4.6 Northstar. I am getting a P0302 Cylinder #2 misfire. I pulled the #2 plug and it was covered in oil. I replaced it and the new plug fouled with oil immediately. I am very unfamiliar with these motors so any help is appreciated. What I have done so far:
Compression test, 130PSI and held until I released it
Spark test, good
Replaced Plug
Swapped coil with known good

The previous owner had some overheating issues when he got it. He replaced the thermostat and life was good. I am open to any and all suggestions. I have done a few searches but I am not finding any threads with this particular problem. Thanks in advance!

12-15-09, 10:22 PM
No ideas? I am starting to suspect the HG's but I would like to be sure. Has noone else had this problem?

12-15-09, 10:38 PM
An oil fouled spark plug is usually NOT an indicator of Northstar head gasket problems. (Assuming the plug electrodes in the cylinder are fouling, NOT oil on the shell or insulator, which indicates a weeping cam cover plug well O-ring.)

If the plug tip is oil fouled, then you have either grossly worn valve stem seals or a bad set of piston rings.

12-15-09, 10:42 PM
Thanks for the reply! I will check the cam cover o ring. The electrode is actually soaked with oil. Is there anything special about pulling the valve covers?

12-15-09, 11:18 PM
Yeah they are a PITA. Front one has the water pump drive pulley driven off of the intake cam, so the shaft extends through the cam cover. The rear is too close to the firewall. You'll have to lower the cradle or rock the engine forward. Go to the Technical Archives at the top left of the forum page and read up on oil consumption.

12-16-09, 09:03 AM
Valve seal replacement on a Northstar, particularly if the engine is in the car, is NOT for the faint of heart.................Incredible amount of very tricky disassembly involving the entire valve train. You'll absolutely need a GM/Helm shop manual or subscribe your car to www.alldatadiy.com.

The cam cover O-rings have nothing to do with oil on the plug electrodes - only on the insulator or shell hex flats.......unless there is so much oil in the plug well(s) that it runs all the way down the plug as a liquid when you pull it out of the well.

12-16-09, 06:58 PM
There is zero oil in the plug well. Only on the electrode. Do vale stem seals in these fail this catastrophically? I have had other motors with bad valve stem seals that blow blue smoke but are not soaked with oil when pulled.

12-16-09, 07:10 PM
Jake has better data on Northstar valve seals, but the subject has come up twice in here in 4 years that I know of - statistically insignificant. The compression looks a tad low. Again, Jake would know the warm pressures to expect from a late 90's Northstar. I'll guess 150 - 160 psi. But no leakdown??? Now you're in the realm of a head gasket failure that has also compromised the valve train oil feed passages.

If you got this car from a dealer or used car lot, you're on borrowed warranty time......and I do NOT like the reference to previous overheating issues. A simple thermostat change does not usually solve Northstar overheating problems, particularly in a 1998, the center of the most failure-prone 3 years. Go up to the sticky thread on head gasket failure polling - click on the lower right corner - view results - to see where this unscientific tally places your car............

12-16-09, 08:29 PM
I understand why you would be wary of the overheating I am too. But this thing does not over heat now. Is there a definitive process for testing for a bad HG? I don't want to fix the wrong problem. I have been searching this site and I dont seem to be experiencing a HG failure in the same manner. I have no water in the oil and the coolant doesnt smell like exhaust as of yet. My only symptom is #2 cylinder with a oil covered plug. If you have or know of a how to on diagnosing the motor I would love to try it to know one way or the other. Thanks!!

12-16-09, 10:25 PM
I have no water in the oil
The Northstar doesn't do that.

Is there a definitive process for testing for a bad HG?
Yes, either buy or rent a block test kit and test the air above the coolant for exhaust gases or do a cylinder leak down test on each cylinder (much more involved).

12-16-09, 11:18 PM
You should contact Jake at northstar performance, He's done a lot of these engines and can give you an idea whats going on, it sounds to me like you have a cylinder that has oil rings that are baked with carbon from the engine being babied its whole life. The recommendation to do WOT weekly helps keep this from developing.:bouncy: I doubt you have that much oil coming down from the valve train.

12-19-09, 03:33 PM
Well afetr talking to Jake I tried some more tests and I found that the injector was completely clogged. After a little cleaning it runs perfect. But now I found I am indeed in the failed head gasket club. While troubleshooting I found some sparkly gold flakes in the coolant reservoir. I wonder if it will hold till the weather warms back up. I am just going to find another long block and put jakes studs in that one then swap out the long block.

12-19-09, 04:35 PM
If its not overheating, blowing coolant out of the reservoir cap and losing coolant at a great rate, you're not in the head gasket club. A failed head gasket won't put sparkly gold flakes in the reservoir. It's entirely possible that the previous owner dumped some sort of magic sealant in the reservoir - some of that stuff has copper and aluminum dust in it.

You may have cured your wet, fouled plug problem with the injector cleaning.

Drive it for a while and see what happens.............and have your local radiator shop do a test for gasses in the airspace over the coolant in the reservoir after you have driven it and not messed with it for a week or so.

12-19-09, 07:26 PM
Will do. I am hopefully getting plates for it this week so I will put some miles on her and see how quick the coolant goes. I am certain the previous owner put stop leak in the coolant. That is what I was implying. Thank you very much for all the help so far!

12-19-09, 10:48 PM
It's possible he did that to stop an external leak.

12-20-09, 11:10 AM
Anything is possible with a used car lol. I am working with Jake to nail this problem down. I am going to send him a video of the white smoke after the snow stops lol.

01-03-10, 05:34 PM
Ok, if anyone wants to check out this video I made of the white smoke I am getting.

YouTube- 00081.MTS

The car was fully warmed up and the air temp was 41 degrees. Revved to 3500ish

What do you think? I sent the link to jake but he has not responded yet. I am borrowing a cooling system pressure tester from work so I will post back with that.

As a side note once I got #2 cylinder running I now have a light knock that follows the RPMs cold or hot. Seems to get a little more quiet with higher RPM's. As a refresher here is the history as best as I can piece it together:

Car was sold to the guy I bought it from in good running condition.

Previous owner let it sit for a month and then ran it about 1400-1500 miles during which it began to over heat but not to redline.

PO noticed Check engine light for cylinder misfire

PO replaced thermostat and overheating stopped but misfire remained

I purchased the car and drove it 90 miles with the misfire

I found and cleaned a clogged fuel injrctor. motor ran smooth as silk but now had a knock.

01-03-10, 09:17 PM
The cylinder knock may be carbon buildup from the faulty injector - the Northstar has a very thin quench area and tends to develop carbon raps if not driven aggressively once in a while.

When you made the video, was the entire exhaust system HOT, as in coming off the highway, or was it cool with just an around the block run........I ask because, given the snow in the background and your observed air temperature, the amount of exhaust vapor is not excessive for a cool, humid day, particularly if the muffler(s) are full of condensate from plugged weep holes. Each muffler should have a small hole in the bottom at the low point in order to drain off condensate - all cars piddle a bit nowadays, and your weep drains may be plugged.

Have you lost any coolant, or is it still at the level of your pre-Christmas posts ???

01-03-10, 09:57 PM
The car was idled up to temp. I have not had it on the road as I am waiting for the title to arrive. I have run the car about 2 hours total since before christmas and I believe the coolant is still where it was when I filled it. I will double check tomorrow. If the weep holes are plugged I will check. As you saw the smoke isnt as thick as most motors I have seen with blown head gaskets. So I am hoping to get at least the temp tag this week so I can try to put some miles on it.

Would that carbon knock continue when the car is warm? Thank you so much.

01-04-10, 09:09 AM
If you have only idled the car and fooled with it in the driveway, dollars to doughnuts the exhaust system is full of condensate. Do you see any water dripping out of both mufflers when the car sits, idling ? If not, those weep holes are plugged - run a 3/32" drill into each one. There will be a discolored, rusty-looking patch around each hole.

Each gallon of gas you burn, you exhaust up to about a gallon of water - that's the exhaust pipe vapor on cool mornings, smokestack vapors, and jet contrails.............made up of ambient humidity re-condensing and water created by fossil fuel combustion.

Yes, the "cold carbon rap" can continue in a warm engine - you need to get out and run the thing. When you do get it on the road, first thing, dump in a 20 oz. jug of Chevron TECHRON, fill up with 92-93 octane and head for a highway. Run it. Idling is the worst possible thing you can do to an engine. You get more engine wear in two weeks of city driving than you do on a 2,000 mile Interstate run to Florida and back. Google "top tier gasoline" and "chevron techron" to get some insight.......

01-04-10, 11:54 AM
From my experience cold carbon rap generally only lasts for 30 -60 seconds after start up. As Sub said, a good WOT run will usually cure it.

01-06-10, 07:06 PM
UPDATE!!!! I finally got my tags on the car and took her for a shake down cruise. Everything was going great until I got to the highway. I floored it from 30ish on the ramp to 70ish in the passing lane and about 30 seconds later the temp rose and the heater lost heat. I got off the highway at the next exit and the car was 1 line from redline. I pulled in to wally world and let it cool down for about a half hour. Before I started it I slowly opened the overflow bottle cap and holy cow was there pressure in there. I was also down a full gallon of coolant from when I filled it in my driveway. So The car is head for Nemesis Mustang in Wakefield Mass for a HG job with Jakes stud kit.

On the bright side the WOT run cleared up the knock I had.

One last thing when I was filling the coolant the drivers rear and passenger front windows rolled themselves down and the rear would not go back up until I got home. I have a code for the drivers door module. Any clue where that SOB is located?

01-06-10, 09:01 PM
I think it is inside the door.

01-06-10, 10:00 PM
Awesome. Thanks man.