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2000 deville
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58 Posts
Discussion Starter #1
I changed both coil packs a few years ago, also changed plugs and plug boots at the same time. Any other ideas on why this is coming up?
I reset the codes last night and this morning it ran fine until later in the day, then the stumble and code came back.
Thanks
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,900 Posts
P 0300 - misfire detected. Our onboard scanner won't tell the cylinder number of the miss, but a parts store scan will. Have it scanned and use this link to define and post any codes found.


Codes read out as a letter, four digits, a letter.

P = Powertrain
B = Body
C = Chassis
U = power and data
XXXX = code sequence number
C = Current - the fault exists now
H = History - the fault has not been detected for 3 start-run-drive cycles.
 

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2000 deville
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58 Posts
Discussion Starter #3 (Edited)
Thank you. I will go to Advance today and get it scanned and post results. My Car Medic scanner just showed the Random Misfire code, nothing else.
 

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2000 deville
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58 Posts
Discussion Starter #4
My Advance does not have a code reader even though thier website says they all offer the service.
When I reset the codes it runs fine until it warms up then the code comes back.

I also got this one today and I'm sure it's related: C0660 Level Control Exhaust Valve Circuit Malfunction

I will find a repair shop that can run the codes so I know which cylinder is misfiring. Last time I got the specific cylinder code and ended up replacing the coil pack, 6 months later another so both were done by me. As I said I did all plugs and boots then. (two years ago) Thanks.
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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P - Powertrain - codes are associated with engine functions.
C - Chassis - codes are associated with suspension problems.

The rear suspension ELC has nothing to do with engine function - it compensates for extra weight in the trunk or rear seat. The code says the compressor control head supply/vent control is faulty.

View A - 1, 2, 3, 4, 5, 6. Compressor assembly

ELC compressor system.png
 

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2004 Deville
2004 Deville, Silver, Gone, but not forgotten, 1972 Eldorado, 1974 eldorado, 1975 CDV
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700 Posts
The c0660 code is not related to your engine miss, it points to the air compressor for the rear ELC shocks
 

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Registered
2000 deville
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58 Posts
Discussion Starter #7
Thanks. I had shocks put on last year from a recommendation here, and since then my shocks have not adjusted like they used to. The ride is fine because of the new shocks but it does sag a bit when I load it up for a trip.
 

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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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19,867 Posts
Thanks. I had shocks put on last year from a recommendation here, and since then my shocks have not adjusted like they used to. The ride is fine because of the new shocks but it does sag a bit when I load it up for a trip.
====================
the C0660 code points to a failure of the air compressor exhaust valve -
meaning the compressor is NOT inflating the air bladders in the shocks as it should -

assuming you had the MONROE MA822 shocks installed -
the air bladders WILL BE DESTROYED - if they aren't already -
by driving around without a minimum of 15psi in the bladders -

you NEED to replace the compressor - NOW - around $200 -

OR install the MONROE AK29 - manual-fill kit - around $15 -
this will allow you to inflate/deflate the air bladders - just like inflating a tire -
 

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2000 deville
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58 Posts
Discussion Starter #9
MONROE MA822 Was what I put in on the forums recommendation. I checked the hookups and they were connected but no sound of the pump coming on since the shocks were installed. I will get the MONROE AK29 - manual-fill kit. Thanks for the info.
 

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2001 Deville base
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33 Posts
YMMV but I would first check for an air hose that is not fully connected or is broken. Then I would check fuel pressure. Then I would see if the battery is dying.
Are all air hoses connected and not cracked?
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,900 Posts
Why? No need to check fuel pressure or battery condition if the ELC compressor and system don't function as designed. Totally unrelated.

A loose or broken air line would result in constant compressor operation. His ELC compressor has an exhaust valve problem and apparently does not run at all.
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,900 Posts
The fill/vent Schrader valve either goes in a hole drilled in the bumper or the trunk floor. The lines T together and go to each shock fitting.

Please see the system diagram in Post #5.
 

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2000 deville
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58 Posts
Discussion Starter #14
Thanks for the quick reply but my t valve does not have the schrader valve in it. There is no connecting piece of hose to that valve. What are the white plungers for?
584662
 

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2000 deville
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58 Posts
Discussion Starter #15 (Edited)
Seems like an unnessecary connection, but I cut a piece or hose and had the parts and o rings to hook up the valve. Will test it tomorrow. Thanks
584663
 

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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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19,867 Posts
Seems like an unnessecary connection, but I cut a piece or hose and had the parts and o rings to hook up the valve. Will test it tomorrow. Thanks View attachment 584663
=======================
this is CORRECT -
you want to use as LITTLE hose as possible -

connect the ends to the shocks -
connect the hoses to the "T" - using the SHORTEST amount of hose as possible -
run a single line from the "T" to a convenient - protected - location -
 

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Something German S, 69 Eldorado, 68 Impala, If I tell you the rest, well
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504 Posts
As Bass stated that is the correct way the t-valve has no valve in it.

Also don't over tighten the fittings, if you do you'll crease the lines and will leak air.
 

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Registered
2000 deville
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58 Posts
Discussion Starter #18
Thanks for the advice. The kit is installed and works. I found a great spot to install the valve (using the shortest run) and the car looks much better lifted up a bit, and the ride is better as well.
 

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2003 DTS
'03 Deville DTS
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282 Posts
I changed both coil packs a few years ago, also changed plugs and plug boots at the same time. Any other ideas on why this is coming up?
I reset the codes last night and this morning it ran fine until later in the day, then the stumble and code came back.
Thanks
Any progress on what's causing the P0300? Having the same problem over here, runs fine until engine heats up then misfires galore.
 

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Registered
2000 deville
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58 Posts
Discussion Starter #20
No luck so far. Same as you, once I get three bars on the engine temp, the car runs poorly and the service engine light blinks. I reset it, let it cool down and it repeats the pattern. I have a code reader and it told me which cylinder was misfiring before. I replaced both coil packs, plugs and all plug boots two years ago or so. Now I just get P0300 No specific cylinder. It's a head scratcher.
 
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