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2000 DHS
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15 Posts
Discussion Starter #1
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
 

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-Administrator-
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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66,891 Posts
Welcome to the Funny Farm !!!

Have the car scanned at a parts store - their systems will give you the number of the cylinder(s) misfiring - P 0304, P 0307, whatever. That makes it easier to home in on the problem.

Using the butt of a long screwdriver jammed against an ear or using a mechanic's stethoscope, listen to each fuel injector - each should produce a steady ticking sound.

Run a 20 oz. jug of Chevron TECHRON in a tank of Top Tier (Google it) gasoline. That should rule out a sticky injector.

Is the engine losing coolant ? Any excessive tailpipe vapor on startup ? (There will be some, normally.) Proper coolant level is about half full in the surge tank, cold. Note the FULL COLD legend and flat arrow molded into the surge tank top and side. (As an aside, is the purge line flowing properly ?)
 

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2000 DHS
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15 Posts
Discussion Starter #3
I’ve had the car scanned at a shop with snap on computer multiple times. Always gives random misfire code. When I go to look at which ones are misfiring is all the front cylinders misfiring. The other day it did give me fuel injector codes for 2,6,8 and 3. No coolant is being lost at all. Minor small drip at the thermostat and that’s from a rip in the gasket. Gotta love Oreilly parts. I’m leaning towards it being a fuel problem. I’m no sure. Fuel pump was replaced when I first got the car a year ago Becusse fuel gauge was wrong.
 

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2000 DHS
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15 Posts
Discussion Starter #4
I just now went out and started the car, dead cold start sitting for a few hours and it’s 32 degrees outside and it didn’t do it at all once. It’s actually running better then the other days. No idea what’s going on but I’m sure it’s gonna come back today
 

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-Administrator-
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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66,891 Posts
Just saw your most recent post. You say new MAF - the IAT uses two pins on that 5-pin connector.

Purge line should flow a small steady stream into the surge tank at idle. It's the system that removes air/gases from the coolant and prevents water pump cavitation = overheating.

_ _ ____ __

You know that the car has its own built-in scanner, right? But that won't ID the cylinder(s) misfiring, only that there IS one or more (misfires).

Try the TECHRON trick - and check the injector electrical connectors (double safety locks on each) as well as the coil cassette electrical connectors. The ICM in each cassette is removable - maybe some moisture in the inner connector pins.
coil-boot-plug 1.JPG
 

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-Administrator-
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
Joined
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66,891 Posts
Your MAF - make very sure there are NO air leaks in the intake ducting at or after the MAF

MAF end view.jpg
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,242 Posts
The other day it did give me fuel injector codes for 2,6,8 and 3.
There are 2 injector fuses labeled IGN1 & IGN2. Pull and reinsert them a couple of times to scrape the contacts clean on the odd chance that they are oxidized and not making a good contact when cold. Long shot, but nothing to loose and it's free.

Can't hurt to also check your fuel pressure while you're at it.
 

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2000 DHS
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15 Posts
Discussion Starter #9
Checked the fuel pressure and scanned the car again to see where the misfire is. Fuel pressure stays steady at 37 psi. The misfires are all on 2,4,6,8. Cylinder 8 is getting the most misfire. I’m going to replace fuel filter first and check fuses and relays. Thanks for the help again if you have anymore info to help out please lmk
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
Joined
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86,242 Posts
Fuel pressure is just a tad below factory spec's, but should be of no concern.

Seeing as all the misfires are on the same bank, another possibility is the ignition cassette on that bank.
 

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2000 DHS
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15 Posts
Discussion Starter #11
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
 

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-Administrator-
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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66,891 Posts
Regardless, something is wrong with the left (front) bank coil cassette or the ICM.

P 0420 will always set now with no cat. There's no "before and after" exhaust gas comparison possible now.
 

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Registered
92 Fleetwood 2dr cpe - FWD, 96 Seville SLS, 02 Seville
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763 Posts
WAG , smooths out after a minute or so on cold start? Maybe it's dropping into closed loop too soon , starving the engine for air and fuel when cold.
 

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2000 DHS
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15 Posts
Discussion Starter #15
Does the same thing cold or at operating temp. Misfires then smooths right out like nothing happened would that happen also when the vehicle is already at operating temp when I start it ?
 

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2004 Deville base
'04 Deville, '05 SRX N*/AWD, Vetts/Birds/Trucks
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340 Posts
Cam or crankshaft position sensors? IDK, never had trouble on one of these models...yet.
Now if it had VVT I would be a little freaky, those things gave me the runaround in the past. :(

edit-maybe the connections/grounds of this stuff?







;
 

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-Administrator-
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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66,891 Posts
2-4-6-8 says there's something wrong with either the ICM, its electrical connections (on both ends of the ICM), the harness OR the left bank fuel injector harness. Did you check the IGN fuses for each bank ? Fuse ID is on the sticker inside each fuse box top.

Both cassettes (and their ICMs) are identical except for color.

DSCN0192.jpg
 

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2000 DHS
Joined
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15 Posts
Discussion Starter #19
Actually got them from oreillys so I wouldn’t be surprised lol when it misfires it’s only 2468 and then it feels like something almost moves out the way or finally goes into place and the misfire disappears completely. I got a whole bunch of fuses and relays I’ll replace the ignition ones and I have an old cassette that i knew worked on the back and put that in the front. It’s crazy even my mechanic is stumped on it it doesn’t make any sense why it would just go back to normal after 30 seconds or so of misfiring. The initial start is fine then 20 seconds in it misses then after that it’s perfect.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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18,864 Posts
did you replace the ICM with the new coils - or use the original ICM?

also - what spark plugs did you install?
 
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