The Northstar V8 stigma spooked a true fan...

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14Accent

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This past weekend I took the Cadillac on a relatively small road trip to Stillwater, MN for a Sunday Fun-day. It was a gorgeous spring day here in Minnesota so a group of us met for drinks on the river.

Anyhow, as soon as I pulled in to town the car developed a hard misfire. It felt like a single cylinder, but the only code being thrown was a P0300. I limped it to my dad's place and left it to be towed to the shop. Keep in mind, up until pulling into town the car ran flawlessly.

I finally got a chance to dig into it today. A quick scan showed that cylinder #2 was the culprit. I went about the usual tests: removed the ignition cassette and plug, plug was wet with (what smelled like) fuel but looked good so I assume coil died, no spark. I swapped coil packs, still #2. Hm. Alright, the coil boots look good but they may be arcing, so swap those around. Still #2. Alright... swap injectors quick. STILL #2.

At this point I'm already jumping to conclusions. The Northstar "stigma". I ran a quick compression test, had 160 psi. Ok, so nothing is hanging up. I put it back together and fired her up, letting it idle with the misfire while I set up my hydrocarbon tester. Within 3 sniffs of the overflow tank the fluid turned yellow. Great! She's blown up...

I took a few minutes to think about things, thinking there's no way the head gasket is bad when I have NO coolant in the oil, NO over-pressurization of the cooling system, and NO overheating. Then it hit me: I never swapped the actual spark plug around. I inspected it, it looked perfectly fine, so I moved on. Low and behold, swap the plug to #4 and the misfire follows. Threw in a set of OE's and she runs better than ever.

Definitely a case of me getting ahead of myself, all because I assumed the worst. Plugs were actually on my list of to-do's with this car, I just haven't gotten to it yet. I did just the front bank tonight, the rear requires removal of A.I.R. valves and other crap so I'll get to it soon, when I have time.

The lesson? Be logical! Sometimes just taking a step back and slowing down does wonders. I still can't explain why the hydrocarbon test failed, however. Since I replaced the radiator, thermostat, overflow tank and flushed the system the temps have been absolutely rock solid. I'm happy to call it a false positive, for now.
 
Originally Posted by Snagglefoot
Thanks for the post. I wonder what that plug looked like. Were they Iridiums?


I wish I would have taken pictures, I was in a bit of a rush. The "failed" plug came out clean, but wet. That's all I can say. They were Denso's, fine-tip on the electrode so I would imagine they were iridium. The gap was fine, however the other 3 plugs from that bank all had some white deposits as is expected with a used plug. I saw no cracked insulation or any visual defect on the failed plug. I guess it just didn't feel like zapping anymore!
 
Good practice though and a pretty thorough job nonetheless. At times, all of us get ahead of ourselves and focus on something that is the "normal" failure mode.

I almost bought one of these Northstars last year.....but got spooked by all the negative press. 47K miles Caddy.
 
Other than the issues with head bolt pull out on the early versions these were a good engine IMO, I never had any real problems with the ones I owned.
 
Originally Posted by 14Accent


At this point I'm already jumping to conclusions. The Northstar "stigma". I ran a quick compression test, had 160 psi. Ok, so nothing is hanging up. I put it back together and fired her up, letting it idle with the misfire while I set up my hydrocarbon tester. Within 3 sniffs of the overflow tank the fluid turned yellow. Great! She's blown up...


You may have fixed the misfire with a new plug, but you still have a combustion leak. The Hydrocarbon tester is pretty conclusive. Sometimes you can get a false negative, but never a false positive.

These open deck engines almost never leak coolant into the oil. It's always into the combustion chamber and gets burned off.

Northstar's performance was impressive when it came out back in '93, but I loved my old 4.5/4.9 Cadillacs for their reliability and simplistic nature (relative to other offerings in the luxury arena). The Northstar cars - not so much.
 
Originally Posted by emmett442
Originally Posted by 14Accent


At this point I'm already jumping to conclusions. The Northstar "stigma". I ran a quick compression test, had 160 psi. Ok, so nothing is hanging up. I put it back together and fired her up, letting it idle with the misfire while I set up my hydrocarbon tester. Within 3 sniffs of the overflow tank the fluid turned yellow. Great! She's blown up...


You may have fixed the misfire with a new plug, but you still have a combustion leak. The Hydrocarbon tester is pretty conclusive. Sometimes you can get a false negative, but never a false positive.

These open deck engines almost never leak coolant into the oil. It's always into the combustion chamber and gets burned off.

Northstar's performance was impressive when it came out back in '93, but I loved my old 4.5/4.9 Cadillacs for their reliability and simplistic nature (relative to other offerings in the luxury arena). The Northstar cars - not so much.

Interesting that you mentioned the 4.5,4.9 engines.IMO those and the 4.1 were less reliable than the northstar. The shop I worked at in the 90's always had one or 2 there to work on.

They ate camshafts and head gaskets often.
 
Originally Posted by Chris142
Originally Posted by emmett442
Originally Posted by 14Accent


At this point I'm already jumping to conclusions. The Northstar "stigma". I ran a quick compression test, had 160 psi. Ok, so nothing is hanging up. I put it back together and fired her up, letting it idle with the misfire while I set up my hydrocarbon tester. Within 3 sniffs of the overflow tank the fluid turned yellow. Great! She's blown up...


You may have fixed the misfire with a new plug, but you still have a combustion leak. The Hydrocarbon tester is pretty conclusive. Sometimes you can get a false negative, but never a false positive.

These open deck engines almost never leak coolant into the oil. It's always into the combustion chamber and gets burned off.

Northstar's performance was impressive when it came out back in '93, but I loved my old 4.5/4.9 Cadillacs for their reliability and simplistic nature (relative to other offerings in the luxury arena). The Northstar cars - not so much.

Interesting that you mentioned the 4.5,4.9 engines.IMO those and the 4.1 were less reliable than the northstar. The shop I worked at in the 90's always had one or 2 there to work on.

They ate camshafts and head gaskets often.


The 4.1 was it's own problematic animal. There were numerous significant updates to the 4.5 and 4.9. Extra block ribbing to resolve head gasket and bearing problems. They went roller cam when the 4.5 came out in '88.

The 4.9 ('91-'95) is considered by many to be the best Cadillac-exclusive engine the company used. GM's early port fuel injection systems with their Multec injectors weren't the best, but at it's core the 4.9 was great engine.

Cadillac's sales (especially Deville) were through the roof during this generation. Zillions of them on the road. Not surprised to hear you saw a number of them.
 
Yes , just step back , go back into the house and get another cup of coffee , drink it and relax .

Even come back to the car the next day .

Several years ago , I was shopping for used cars ( probably a Ford or Chevy ) . Ran across an add for a used Caddy at what sounded like a decent price . I seemed to remember reading the Northstar engines had some problems .

Did some internet reading & decided to shy away from the Caddy . Ended up buying a 2006 Buick Lacrosse 3.8l .

Is there any way to check a spark plug , with an ohm meter to see if it is shorted / grounded ? A megger ?

Good to hear you solved the problem ! :)
 
Originally Posted by 69GTX
Good practice though and a pretty thorough job nonetheless. At times, all of us get ahead of ourselves and focus on something that is the "normal" failure mode.

Originally Posted by demarpaint
A lot of people tend to think the worst. I'm glad it wasn't in your case.

Guilty of this myself, about a month ago I replaced the timing chain tensioner in my Camry and when that didn't work I almost replaced the timing chain... all because of noisy bearings in the alternator which is right next to the timing cover...
 
I was able to figure it out by listening through a long screwdriver... after I had already replaced the tensioner
frown.gif


At least it was an easy fix, and I replaced the valve cover gasket that was starting to leak into the spark plug tubes while I was at it.
 
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Before I purchased a stethoscope I also used a long screwdriver . You can hear better if you bite down on the plastic handle . The sound is transmitted directly through the jaw bone to the ear . Very loud and very clearly .

Just be careful !
 
Originally Posted by Chris142
It takes a lot of lost coolant to make the oil milky. Why did the chemical test come up positive?


I didn't want to go there, cradle drop and head stud kit. 19hrs IIRC.
 
Last edited:
Originally Posted by emmett442
Originally Posted by 14Accent


At this point I'm already jumping to conclusions. The Northstar "stigma". I ran a quick compression test, had 160 psi. Ok, so nothing is hanging up. I put it back together and fired her up, letting it idle with the misfire while I set up my hydrocarbon tester. Within 3 sniffs of the overflow tank the fluid turned yellow. Great! She's blown up...


You may have fixed the misfire with a new plug, but you still have a combustion leak. The Hydrocarbon tester is pretty conclusive. Sometimes you can get a false negative, but never a false positive.

.


Well, I guess if that's the case, you might foul a wet plug again. We'll stay tuned!.
smile.gif
The internet is filled with info on how to bullet proof them. The all seem to start with: " drop engine from below body" .
 
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There won't be any dropping of any cradle in this car. If the head gasket lets go, so be it. Someone can make a project out of it if they want. I've got less than $2k in this thing and it's going on a year of basically flawless service, and I'm not easy on it.

I did have an interesting moment this morning on the way to work: just about a block from pulling in the temp gauge spiked to the notch past half, and quickly. I shut it off immediately and went in, didn't touch it again until lunch. Everything seems fine now, so who knows. I think I'm going to order a pack of the GM cooling system tabs and pop them in the upper radiator hose, just in case. It can't hurt, and most of the cooling system is new so I know it flows fine.
 
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