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Northstar Engines and System Technical Discussion Discussion, 2001 Northstar - Head Gaskets blown or not?? I'm stumped!! in Cadillac Engine Technical Discussion; Originally Posted by Submariner409 Any junkyards in the area ?? Northstar coil cassettes are a dime a dozen at a ...
  1. #151
    hms200 is offline Cadillac Owners Member
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    Re: 2001 Northstar - Head Gaskets blown or not?? I'm stumped!!

    Quote Originally Posted by Submariner409 View Post
    Any junkyards in the area ?? Northstar coil cassettes are a dime a dozen at a DIY pick-a-part.
    Nice idea! I may take that route - drawback is chance of getting a bad one, but if price is right then I may risk having to do a warranty swap (which I'm sure they would give me a short warranty...maybe).

  2. #152
    jimsbox is offline Cadillac Owners Enthusiast
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    Re: 2001 Northstar - Head Gaskets blown or not?? I'm stumped!!

    Because the rear valve cover is black and the front one is aluminum colored so it makes as much sense for the packs to color coordinate

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    Re: 2001 Northstar - Head Gaskets blown or not?? I'm stumped!!

    Generally speaking, the ignition cassettes are pretty reliable. Probably more so than an AutoZone Don'tLast part. I would not hesitate to use a junkyard cassette. I would NOT use an AZ cassette.

  4. #154
    hms200 is offline Cadillac Owners Member
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    Re: 2001 Northstar - Head Gaskets blown or not?? I'm stumped!!

    Replaced both coil packs and boots with new Rock Auto OEM units - no change.

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  6. #156
    hms200 is offline Cadillac Owners Member
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    Re: 2001 Northstar - Head Gaskets blown or not?? I'm stumped!!

    Standard OEM plugs. I just recently replaced them as well in attempt to eliminate as suspect. The old ones were also OEM.

    AC Delco 41-987

    Howard

  7. #157
    Manic Mechanic is offline Cadillac Owners Fanatic
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    Re: 2001 Northstar - Head Gaskets blown or not?? I'm stumped!!

    Quote Originally Posted by hms200 View Post
    Gentlemen - I'm sure glad this is a hobby project for me!! LOL

    Ok, so I got past the A/C issue - she is ice cold!!

    BUT....

    Q1 - She STILL overheats!! No clue if original owner ever used any snake oil (stop leak or other mystery/magic substance) by chance in an attempt to stop the overheating issue - I've sent that question to him and still awaiting reply. I'm trying to troubleshoot what may now be causing the overheating. Radiator might be stopped up or restricted if any substance was used to try and fix the issue before?

    Q2 - She still has the Check Engine Light condition, even after resetting all the codes multiple times. I'm getting a code P0300, random misfiring. Symptom is low idle, idle a little unsteady, a little bit of slight lurching/jerking when put in gear at idle. She will even throw a new 0300 code by simply sitting at idle for maybe 5-10 minutes. All the performance symtoms disappear though if not at idle. There is a long list of possible causes, so hoping maybe you folks can help me here...hopefully not the symptom of failed head gaskets.

    •Already installed new crank sensors before installing engine - so that suspect is ruled out (I hope)
    •Just replaced spark plugs (though others looked near new) - so that's ruled out
    •Just replaced cam position sensor, with no change - so that's ruled out
    •No vacuum leaks that I can detect
    •Fuel pump (weak pressure) isn't suspect I think because she runs fine at higher speed
    •O2 sensors are commonly misdiagnosed as culprit - but seldom are the root cause, as I understand it?

    So I'm stumped...aside from leaking head gaskets (I SURE hope not!!), it could still be a number of other things not yet replaced or checked...
    •Spark Plug Coil Pack (either/both)
    •O2 Sensor (either/both)
    •Defective EGR
    •Defective Throttle Position Sensor

    I can't hardly imagine the check engine or overheating are still directly associated with head gasket issue/repairs. Repairs were done carefully and exactly to spec, plus reassembly and torque of head bolts also done exactly to spec. This is a true head scratcher.

    Any insight you gents may have with any of this will be greatly appreciated.

    Howard
    Hello Howard I just noticed your post was so long and had some recent activity so started at the back and read to here. I think I know where you're at right now. Here's some advice.

    On question 1, it still overheats. I would suspect the radiator for reasons you stated. But how and or when does it overheat? It would seem from your posts that it overheats gradually on long trips, is that the case? Does it cool back down if you slow or stop? Basically I understand it overheats but it would help to know under what conditions and how severe.

    Question 2, Code P0300 : Random misfire. Sets at idle. Idle is notably low and rough. Runs fine under load and at higher engine speeds (With full power on tap right? A clogged cat will cause misfires and overheating but would also severely limit power).

    Ok here's some clarification, a misfire that ONLY occurs at idle or very light throttle loads is almost never ever related to the secondary ignition. The secondary ignition is the business or working end of the ignition i.e. plugs, boots, coils. When those components fail the misfire will always get worse under higher compression loads (under more throttle). At idle the engine is burning the amount of air trapped by the cylinders in a vacuum, very little air and fuel. Air is what an ignition must fight or overcome to produce a good spark at the plug gap, it is actually a very good electrical insulator. So at idle it has very little work to do as it's actually easier for the spark to jump the gap under vacuum than it would be with the plug exposed to the open air at it's barometric pressure. On a running engine when you open the throttle and pack 200 PSI into that plug gap the ignition is put to the test, the spark voltage will follow the path of less resistance. If there are carbon tracks leading it to ground it would rather go there than jump across the plug gap filled with high pressure air. Same goes for a hole in a wire or boot, the voltage will find it easier to travel down the ceramic insulator and out of the hole in a boot or jump out of a wire at a point where the insulation is weak than jump that little gap full of air. So all of this being said, you're getting a misfire at idle that is apparently scattered about two or more cylinders but goes away when you make the ignition work harder. Stop spending money and time on the secondary ignition, that's not where you'll find a solution to this.

    Sensors that are bad enough to cause a misfire almost always set a code for the problem before the code for a misfire, esp. if you're driving it around without a miss under load. So for now don't start swapping out O2 sensors, cam and the like.

    What an engine does have at idle is a very small amount of air needing a even smaller puff of fuel. The ratio of air to fuel is very important because at idle there's so little to light off that if it's not correct it probably won't even burn (this is a misfire). You said you have already checked for vacuum leaks and found none, and I don't doubt this due to the fact that the idle is low. If you had leaks the idle would be too high if anything, esp. in open loop (cold start). If anything you may not be getting enough air to idle properly and cause a random miss. I would like you to check your throttle body and make sure the throat and blade are clean and there's no excesive coking in the area where they meet. If so clean it out. This engine is still a cable throttle so you have an Idle Air Control valve on the side of the throttle body, this is the plug that's on the top of the throttle, not on the side which the position sensor (reading from the shaft). Remove the Idle Air Control solenoid valve itself and clean it with throttle cleaner spray and a old tooth-brush or similar. Clean both and see if the idle comes up and clears.

    Since the amount of air trapped in a cylinder at idle is very small (vacuum) the mechanical compression building ability of the cylinder it's in must be very good. A cylinder that bleeds down even 30% of it's compression will miss at idle because too much of the small charge leaks away before it can be lit, but under throttle the 200 may be 140 or even higher because the engine is running faster and there's less leak time, but the point is a weak cylinder will start firing when you feed it enough air. That doesn't mean that the air/fuel ratio will be spot on, but that it will com-bust and not be a miss. If the throttle assembly is supplying enough air but the miss is still evident and low rough idle then pull all the plugs, block the throttle open, and measure the compression on all cylinders. They should all be over 175 and relatively even. If not that's where the problem is and you will have to go further to find out why. It could be pressure sealing problems or pressure building problems (valve timing).

    If compression is good and you're getting enough air to idle that narrows it down to fuel and spark timing.

    Lets start with fuel. Random miss, low rough idle. No air/fuel codes. No injector circuit codes. Runs good under load. This leaves partially clogged injectors as an most likely fuel delivery issue possibility. Since the car sat up, likely with fuel standing on the injectors for a while, when you put your project on the back-burner and took care of more important things it's very possible that the fuel varnished or evaporated leaving petroleum residue in the injectors. When this happens they have a hard time making those small little puffs of fuel needed to provide the proper amount of fuel at idle. What ends up happening is that they may not spray at all unless they are open a longer time like under load. Or they do flow but it just bleeds through around the muck. It make collect a few pulses of fuel that drip off in a bunch causing a few lean misses followed by a rich miss and then repeat. If this is suspected you could have a good shop do an injector flush on the engine. One that plumbs into the fuel rail and runs the engine on a flammable detergent designed to remove these residues and carbon deposits etc. It takes about a hour and usually cost about $150-200. The chemical kit itself has more than doubled in price in the last ten years. It will usually renew a set of old clogged up injectors.

    Now the spark timing. This engine's spark timing is completely controlled by the programming in the PCM. This programming references all the engine's sensors and determines when to fire the spark. There's nothing you yourself can do to change, adjust, or effect timing other than drive it. But The PCM needs good information to generate proper timing. If the PCM is getting some bad information or is referencing it incorrectly you can have incorrect timing. Usually timing type sensors work better at lower speeds because they have more time to switch, if they are starting to malfunction it starts to show up at higher speeds where they loose precision. So I don't think you have a bad sensor. What I wonder is if the PCM is referencing the crankshaft sensors correctly because you have replaced both of them and had the timing components at least off (I don't know what you did or did not replace in this area). When you do those things you change the input signal's profile. Sometimes it's enough to confuse the PCM. When initialized on the new running engine the PCM stores a sample of the crankshaft sensors signals and uses this as a reference to ever changing input signals to determine exactly what the crank is doing. Knowing what the crank is doing tells the PCM things like where it currently is, whether it is slowing, speeding up, or steady. Then it knows when to send the next spark and other cool stuff like if that cylinder just misfired. Even compression changes like new pistons and rings will change the rate of crankshaft travel after each firing event and skew the calculations if it's basing them on a now incorrect or outdated reference. Even old sensors change the signals up enough to cause ghost misfires that aren't actually misfires in the physical world. In order to account for these changes the PCM has a function called a "Crankshaft Variation Relearn" which is a scan tool initiated PCM process that has strict conditions, not hard but must be followed to the letter and the engine must at least start and run long enough to reach 160* before it can begin. The process will have one rev the engine up to a level high enough in park/nuetral for a long crank coast down without fuel. During this time the PCM re-samples all the crankshaft signals and stores the new profile to start referencing running condition signals against. So I could be that you have made enough changes in this area at one time to make the current reference sample cause problems with spark timing at idle. The same as before, a good shop and or technician should be able to perform this function for you for a reasonable fee. I have over $10,000 of my own money invested in my scan tool and my boss has supplied two other brands for us to use also that have similar costs. The amount of time it takes a tech to do this, about 15 minutes, is not the only consideration in how much you should pay. Also with a good shop/tech you pay for knowledge and experience. We see stuff overlooked or unknown to DIY'ers all the time. We charge up front for this, not tell you later that you need to pay me before I tell you something I noticed yesterday, that would be dumb. But that all being said this should still be at $50 to $120 charge. Get one done in any case, I've seen that alone clear up a rough idle on brand new vehicles that the dealer has told the customer "Was within specs" and that there was nothing that could be done about it. Yeah well most of the best techs don't work at dealers. Some do but it seems like a bunch of dummies love it there.

    Go through this methodically and see if it gets your misfire squared away. I think the two problems are separate but as stated I would need some more information on the overheating to advise any further there.

    Vernon

  8. #158
    hms200 is offline Cadillac Owners Member
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    Re: 2001 Northstar - Head Gaskets blown or not?? I'm stumped!!

    Wow!! Great detailed info Vernon...thx much!

    As for radiator, prior owner did reply to my question and said he never used any snake oil. I do still have new radiator all boxed up though that I bought way back before when I wasn't yet convienced of the head bolts problem...never installed it. So...maybe I just go ahead and swap it out? It will overheat slightly with just idle on a hot day. On highway it will can get to two o'clock, but never into the red. Driving around parking lot easy to test for normal performance (not driven hard) it goes to slightly beyond TDC...
    Maybe 10 minutes past 12 o'clock.

    On misfire issue...you touched on one point that was to be my next suspect...crank sensor relearn process. I actually printed out both methods...shop procedure using diagnostic tester AND the highway DIY procedure. I replaced both crank sensors while engine was out and I had simple access as just a PM replacement...but then I forgot all about the relearn step.

    Your suggestion on injectors and the sensor both make total sense as suspects. I did clean the throttle body completely during reassembly so that is ruled out...it's very clean. I also cleaned both the sensors, but maybe not well enough? I also replaced the intake plenium during reassembly as it was torn. So the top sensor might be a suspect target...and the injectors. Also tested intake manifold the other day for leaks by spraying brake cleaner (as good as starter fluid?) along intake manifold base with engine running to test for leaks. No results...engine idle didn't respond...so no gasket leaks there I think.

    Howard

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