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2000 Cadillac Deville DHS 131,xxx

been dealing with this misfire problem for a few weeks now, it happens every time the car starts up even if it’s cold or warm doesn’t matter. The car will misfire heavy engine shakes for about a minute or less if I’m lucky then it smooths right out after and drives fine and normal. I’m really stumped on this problem and I’m looking for a solution. The SES light is on for a p0300 random misfire. The light will flash from time to time when it first starts and doesn’t after. I have changed plugs boots both coil packs FPR purge valve on throttle bottle MAP Sensor, intake gasket and boot, MAF sensor.
Any advice will be helpful thanks again
Follow link. Unlikely but p0300 can be cam shaft.

 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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When you become familiar with the 2000 - 2003 Northstar and its various specific ignition/injector gremlins you'll understand why the P 0300 and CMP correlation is the most remote, last problem to ever worry about.

When a CKP or CMP suffers total failure (the code sets with a C suffix) the ignition system sets sensor-specific trouble codes AND defaults to a fixed "limp home" mode of operation and stays there until the specific DTC is repaired. The miss will not come and go with either emissions monitoring loop changes (about 160 degrees coolant temp) or coolant temp changes (warmup sequencing). Once again, the single CMP monitors Bank 1 exhaust cam position - Cylinder 1 TDC. It has NOTHING to do with Bank 2 (2-4-6-8) injectors or ignition signals.

FWIW, the single CMP - in the engine in question - sends a cylinder TDC signal to the PCM and that's used with a slew of other inputs to adjust timing for instantaneous power demands. IF the CMP fails, or if one of the two CKPs fail, the system defaults to a pseudo-TDC input from the crankshaft reluctor wheel AND goes into "limp home" mode.
 

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NONE (learning about them)
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10 Posts
I replaced all that within a month or less. Spark plugs boots and the cassette for the front. The cassette as recent within 2 weeks forsure. It’s just mind boggling and been bothering me. I Have a new code today p0420 but I have no cat on the car removed it 4-5 months ago due to old cat being clogged
Removing the cat without PCM/ECU reprogramming is contributing to your headache.
 

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'93 SedanDeville 60 Special
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197 Posts
If one bank is showing current and history misfire counters try swapping right to left as to coils and see if then misfire goes to the odd numbered left head.
Possible a wiring connector pin crimp like to coils has gone worse and temp changes make it worse by increasing resistance. At idle wiggle all wiring close to connectors for all coils, sensors, etc and see if problem comes and goes

Not knowing your car 37 PSI fuel rail pressure sounds too low, early GM used 43 PSI and by late 1990s when to 58 PSI
Put a fuel pressure gauge on fuel rail let PSI build up and then key off and see how long it takes to pressure bleed down
How many miles on engine and can the fuel injectors too old and leaking ?
See if the fuel regulator is flaky or a vacuum hose leaking

Just a thought, is this all with the same tank of gas ?, IE bad tank or most people are not aware the damn feds allowed E15 gas to be sold and people are not looking or asking stations if your pumping in E10 or E15 which is crap for older engines :(
 

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2000 DTS, White Diamond, 150K
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64 Posts
@Noheartfiremen4418 - I've been meaning to get to this post for a while now. Just kept falling off my list. I haven't posted on the forum in a while but saw this one and had to respond. I have not read all the posts on this thread to date so if redundant my apologies. I'm hoping this will help though. It's certainly at least worth a try. I have a 2000 DTS that had a VERY similar issue a while back that this forum helped me sort out. @Submariner and @Ranger are excellent resources. I posted an old thread called 2000 DTS Mystery Miss. I bought a 2000 DTS (beautiful) with 150K . Shortly after started having a random miss, coded always as #4. Would miss when cold then smooth out, or sometimes come back briefly, was making me nuts. Came to this forum for help. Swapped coil packs, still #4, replaced all plugs & boots, still happened, etc. FInally one of these guys (Sub or Ranger) mentioned that they couldn't explain it but occasionally a good throttle body cleaning had cleared up a miss. Best advice ever. This in my opinion is critical to anyone with this vintage Northstar. Simply loosen the air intake (2 wing nuts), remove the air filter, unplug the MAF censor. Loosen 1 hose clamp - Remove the rubber attachment assembly and expose the throttle body. Total time about 1 minute. Open it all the way so flap is completely horizontal and you can see in. Prop a small piece of wood or whatever on the side to hold it open. Use at least two full cans of carb cleaner to spray inside (with red tube) in short bursts . Spray EVERYWHERE in there, you'll see a lot of black junk running out . Again do 2 full cans to start. . Slide the rubber back over the throttle body intake, tighten the one hose clamp, replace air filter, tighten two wingnuts on the airbox, plug in MAF sensor (total - another 60 seconds ). Will be hard to start for about 20 seconds but will fire, let it run for 10 mins. go drive it. Another 2 key steps are a bottle of Techron monthly, and regular WOT romps. These three steps are in my experience essential to keeping this engine running miss free. I recommend the throttle body cleaning about every 10,000 miles. I just started having a repeat of the same symptoms. Ran Techron, another deep throttle body cleaning, and weekly red line romps and it runs great. Smooth as can be. You MUST be able to run the car to redline occasionally to keep it cleaned out.

As I said earlier whoever noted it to me (Ranger or Sub) said they couldn't explain it and I can't either other than it works, or at least has for me. I'd seriously consider trying it. Certainly no downside, and just might be surprised. Rule out all the other obvious items first such as coil packs, boots, and no head gasket signs at all, but when all those show no results give this a try. Costs a few bucks and less than 10 minutes. Add Techron and WOT runs and you may be all set. I am . Hope this helps. I'm a believer
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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The OP is driving a 2000 DHS.

Run a TopTier gasoline - it uses a powerful proprietary* fuel system cleaner as one of its additives.

Chevron TECHRON* is not recommended any more frequently than 5,000 mile intervals. Using a bottle a month grossly inflates your fuel costs.

It is not wise to get any quantity of TB cleaner past the throttlebody/intake manifold inlet area. Pooled TB cleaner in the manifold log can cause an explosion that would destroy the manifold itself. Scrub the TB bore and blade with an old toothbrush, using TB cleaner judiciously - maybe a half can total.
 

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2000 DTS, White Diamond, 150K
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64 Posts
I would never argue with the experts that know 100X more about this than I do, only offering what has repeatedly worked for me. Get it cleaned out and do it regularly. I've used toothbrushes, zip tie a rag on a small stick, anything to get in there and clean it, and then spray it with more carb / TB cleaner. Personally I'm fine with a bottle of Techron a month as it's about the cost of 2 gallons of gas. The WOT runs are the best part.. These cars need regular exercise.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Not arguing with you - just trying to prevent an over-zealous new gearhead from breaking stuff.

Read the white papers on TECHRON. The recommended use spacing is partly because it IS a powerful system cleaner and when over-used, tends to eat the insulation varnish off the (submerged) fuel pump armature windings. BUT it is good for the fuel level sender resistance strip cleaning - sulfur deposits.

Top Tier gasolines give you the same benefits as TECHRON already mixed into the gasoline at the fill depot.

 

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White Diamond '03 DHS (with DTS floor shift)
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86,315 Posts
Yeah, I am hard pressed to explain how a dirty TB can cause a misfire, but I've seen it several times here. The TB bore is out of sight and out of mind so it is more often than not, neglected. If it has never been done, the first time can be a lot of spraying and scrubbing, but if you do it once a year as a spring cleanup kind of thing it becomes a simple spray and wipe, with no scrubbing required.
 

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2000 DTS, White Diamond, 150K
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@Submariner409 and @Ranger - thanks gentlemen. You guys are the best. Great forum and more advice to be gained here I know the longer I keep my car. Definitely agree with last comment that if never been done before a lot of spraying and scrubbing is needed to get it clean, and yes a regular spring event is great maintenance advice.
 

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'93 SedanDeville 60 Special
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197 Posts
On the subject of the P0300 DTC

That is supposed to identify that there was multi misfires within a very short period, like in uSecs
This is the maximum time in microseconds between misfire events for the PCM to declare a misfire in cylinder mode as a function of RPM and percent volumetric efficiency.

Units: usec
Edit Step Size: 1
Minimum Allowable Value: -0
Maximum Allowable Value: 32767

The problem is the PCM is looking at the crank position sensor and is looking for ANY uneven motion on the crank
True misfire can cause that but other things also can cause that

As example I had a tuning customer that PCM was reporting lots of misfires but the AFR looked great and the only DTCs tripping was misfire ones.
In short, there was a warped rear brake rotor causing a studder that traveled right back via driveshaft to flex plate for auto tranny

Another case turned out a real cause was U-joints off the driveshaft and another case was faulty torque convertor
As mentioned the PCM is looking at a very short time-frame and in many cases the GM calibration has set the trigger point of tripping a misfire DTC way too short of a window

As I show below you can see in one misfire table where the time in uS is way to short and you see in another misfire table they set it to maximum amount of time before triggering for the same DTC
Problem is one of the DTC EPA required as to OBD-I and II

The older the vehicle is the less PCM functions were designed to handle when to trigger for misfires or not
where older OBD-1 vehicles had very little control and newer vehicles, esp with DOD/AFM have to have several misfire tables and countless values as to issues when DOD comes on and off and also the effects to auto tranny

Using a good OBD scanner that includes GM enhanced PIDs will help see all of their PIDs they feel are needed to the far less supported PIDs a EPA/SAE generic scanner supports.
Tracking all current and history misfire DTCs and counters can help sway the tech if there is true misfires or are false of something causing uneven rotation of crank

So my point is do not take for granted if P0300 trips that in fact it was really a true misfire and may require to simply degrade when the DTC window is met to trip the misfire DTCs

Here is example of two misfire tables, notice one gives almost no window and trips misfire DTCs real easy and another misfire table of the same 2012 CTS-V with 6.2 liter engine


575075
 
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