2001 Deville DTS PO300 Random Misfires
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Northstar Engines and System Technical Discussion Discussion, 2001 Deville DTS PO300 Random Misfires in Cadillac Engine Technical Discussion; Got a flashing SES last night on an 80,000 mile engine. Pulled codes and got PCM0300. Taking off the front ...
  1. #1
    Bberger is offline Cadillac Owners Member
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    2001 Deville DTS PO300 Random Misfires

    Got a flashing SES last night on an 80,000 mile engine. Pulled codes and got PCM0300. Taking off the front coil pack I noticed a good amount of corrosion on the tips of each coil. A little scotch brite got rid of it but there is some pitting. Plugs are OE and look like they have seen 80K. I have new AC Delcos on the way.

    Will new plugs and cleaning the coils be sufficient?

    Is there no mechanical connection between the plug and coil?

    Thanks in advance.

    -Brian

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: 2001 Deville DTS PO300 Random Misfires

    Inside each of those plug boots is a s/s coil spring. That should supply the coil-plug connection. A new set of 8 boots is $40 or so from www.rockauto.com (look at your car, ignition, and look at boots, wires whatever: they're sort of willy-nilly in their listings on plug boots.)

    A new set of ACDelco #41-987 plugs and boots should do it. Have fun on the rear coil pack and that darn A.I.R. valve.

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    Bberger is offline Cadillac Owners Member
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    Re: 2001 Deville DTS PO300 Random Misfires

    Sub... you are the best, thanks for the quick reply.

    Ah... so there are springs in the boots... I hadn't looked yet. Took two springs out and they look like new.

    Funny you mention the A.I.R. valve as that was my next question. Does it have to be removed or is there a way to work around it? I have the three mounting studs removed from the bracket but the valve is still attached to that bracket. I can move it a bit but not enough to get at some of the bolts and surely not enought to remove the coils...

    What's the best way and again... thank you.

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    Ranger's Avatar
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    Re: 2001 Deville DTS PO300 Random Misfires

    A little scotch brite got rid of it
    I know you used this on an external part of a closed engine, but read this. http://www.cadillacforums.com/forums...ite-never.html

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    Mark C's Avatar
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    Re: 2001 Deville DTS PO300 Random Misfires

    Yes, you have to remove the AIR valve completely to get at the rear coil. There are two 10mm nuts (studs in the AIR valve) that hold the valve to the bracket and the lower pipe that have to come off, and another 10mm nut that holds the pipe that wraps around the back of the valve and connects to the side with the piece of tubing that has to come off so you can move the pipe out of the way. Fun times, a racheting flex box end wrench works great, takes about 10 minutes to get the bolts off.

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    Bberger is offline Cadillac Owners Member
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    Re: 2001 Deville DTS PO300 Random Misfires

    Quote Originally Posted by Mark C View Post
    Yes, you have to remove the AIR valve completely to get at the rear coil. There are two 10mm nuts (studs in the AIR valve) that hold the valve to the bracket and the lower pipe that have to come off, and another 10mm nut that holds the pipe that wraps around the back of the valve and connects to the side with the piece of tubing that has to come off so you can move the pipe out of the way. Fun times, a racheting flex box end wrench works great, takes about 10 minutes to get the bolts off.
    Thanks Mark, that did the trick. I was trying to remove the pipe from the valve... much easier to go a bit deeper and remove the pipe and valve.

    The rear (cowl side) plugs are all white while the near side plugs seem more normal in color though one does have some white tint to it.

    Off to pick up the plugs and reassemble... hope this solves the PO300.

    Our of curiosity, how many hours would a dealer charge for this job?

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    Bberger is offline Cadillac Owners Member
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    Re: 2001 Deville DTS PO300 Random Misfires

    Argh... got it all back together and still have the miss.

    Codes:

    134 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)

    135 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)

    300 Random/Multiple Cylinder Misfire Detected

    Thoughts?

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    Submariner409's Avatar
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    Re: 2001 Deville DTS PO300 Random Misfires

    Take the beauty cover off, start the engine, and spray a tad of choke cleaner at the base of the rubber plenum which connects the intake manifold to the throttlebody - down in there by the s/s clamp screw head (#2 in the diagram). Idle speed change ??? Cracked plenum - common.

    Intake manifold bolt torque in your car is 5.5 ft/lb/ Not much. Plenum, dealer only, $40. #12555840

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    Bberger is offline Cadillac Owners Member
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    Re: 2001 Deville DTS PO300 Random Misfires

    Quote Originally Posted by submariner409 View Post
    Take the beauty cover off, start the engine, and spray a tad of choke cleaner at the base of the rubber plenum which connects the intake manifold to the throttlebody - down in there by the s/s clamp screw head (#2 in the diagram). Idle speed change ??? Cracked plenum - common.

    Intake manifold bolt torque in your car is 5.5 ft/lb/ Not much. Plenum, dealer only, $40. #12555840
    I replaced that last May I think. Not a bad job... car was running okay then but it did throw a code. The carb cleaner test did indicated a leak and once off there was a small hole. Replaced it with a new one and new gaskets and it has been fine since... until now that is.

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    Bberger is offline Cadillac Owners Member
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    Re: 2001 Deville DTS PO300 Random Misfires

    Disregard the 134 and 135 codes... the mechanic forgot to reconnect the rear O2 wire!

    I still have the 300 code though. Just to be sure I sprayed carb cleaner around the plenum and intake and did not get any change in idle.

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    Bberger is offline Cadillac Owners Member
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    Re: 2001 Deville DTS PO300 Random Misfires

    Just to close out this thread, I took the car to the local dealer to get a diagnosis. Turns out it was the coil cartridge on bank 2, the easy one. They quoted me ~$450 for the part and $200 ish to install. I paid the $90 inspection fee and called Rock Auto. The part plus next day air was $230. Installed it and no more miss, thankfully!

    Thanks again to the forum.

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    Re: 2001 Deville DTS PO300 Random Misfires

    They quoted me ~$450 for the part and $200 ish to install.
    Yikes!

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    Mark C's Avatar
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    Re: 2001 Deville DTS PO300 Random Misfires

    That must be about a $600 an hour labor rate.

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    babyjabs is offline Cadillac Owners Member
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    Re: 2001 Deville DTS PO171 174 and bank 2/4 Misfires

    I have a DTS 2001 that the codes are reading that bank 2 is misfiring and code po0171 and 174. What do I look for than? Would it be the ingnition coil or sparkplugs?

    Thank You
    Joe

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    Submariner409's Avatar
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    Re: 2001 Deville DTS PO171 174 and bank 2/4 Misfires

    Quote Originally Posted by babyjabs View Post
    I have a DTS 2001 that the codes are reading that bank 2 is misfiring and code po0171 and 174. What do I look for than? Would it be the ingnition coil or sparkplugs? Thank You Joe
    DTC P0171/0174 are vacuum leaks common to both cylinder banks. In here, Seville, and down in Northstar Performance and Cadillac Tech Tips search for "plenum" replacement.

    Click on my username, open my profile. 2 albums in there, 6 pages of Northstar diagrams and parts - most for your engine. Look at the intake manifold, fuel rail, and ignition cassette stuff.

    While you're in the engine you might as well replace the spark plugs, too - AC Delco #41-987 ONLY. Do more searchibg as to why. Study my picture of the ignition cassettes.

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